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  • Articles: DFG German National Licenses  (4,788)
  • 2010-2014
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  • gene transfer
  • somaclonal variation
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  • Articles: DFG German National Licenses  (4,788)
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  • 2010-2014
  • 1995-1999  (2,774)
  • 1955-1959  (2,014)
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  • 1
    Electronic Resource
    Electronic Resource
    RAPD polymorphisms among variant and phenotypically normal rice (Oryza sativa var.indica) somaclonal progenies (1997)
    Springer
    Plant cell reports 16 (1997), S. 320-324 
    Details
    ISSN: 1432-203X
    Keywords: Oryza sativa ; rice ; somaclonal variation ; genetic integrity ; RAPD analysis ; DNA markers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary RAPD analysis was performed among eight rice somaclonal families known to vary for specific characters and four somaclonal families which were phenotypically normal. The parental cultivar,indica rice cv. FR13A, was found to be homogeneous and homozygous at all but one of the 45 RAPD loci. Polymorphisms were found at 28 of the 45 bands among the somaclonal families, including both loss of parental bands, and the appearance of novel non-parental bands. Segregation data revealed both heterozygous and homozygous mutation events, with recessive mutations more prevalent than dominant. All somaclonal families differed significantly from the parental material, indicating that genomic alterations occurred in all families regardless of phenotype. None of the variant families could be regarded as isogenic lines of FR13A at the DNA level. However, some of the DNA level variation may be in highly repeated sequences with no phenotypic effects. The implications for somaclonal breeding and genetic engineering programs are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01088289
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  • 2
    Electronic Resource
    Electronic Resource
    Use of a hammerhead ribozyme with cationic liposomes to reduce leukocyte type 12-lipoxygenase expression in vascular smooth muscle (1997)
    Springer
    Molecular and cellular biochemistry 172 (1997), S. 47-57 
    Details
    ISSN: 1573-4919
    Keywords: smooth muscle ; gene transfer ; DNA ; RNA ; ribozyme ; liposome ; lipoxygenase ; gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Chemically synthesized hammerhead-type ribozymes targeted against the porcine leukocyte-type 12-lipoxygenase (LO) have been developed and studied. One chimeric ribozyme consists of DNA in the non-enzymatic portions, and RNA in the enzymatic core as well as two phosphorothioate internucleotide linkages at 3′ terminus. The second ribozyme consists of ribonucleotide sequences generated by in vitro transcription. In this chapter we describe methodologies to first analyze the ribozyme catalytic activity in vitro by studying cleavage of target RNA in vitro. The subsequent sections will describe how to target the catalytic ribozyme and deliver it to porcine vascular smooth muscle cells (PVSMC) by a liposome-mediated method. Finally ways to evaluate its activity to inhibit expression of the 12-LO mRNA will be presented. These results demonstrate the feasibility of using ribozymes as novel candidates for therapeutic agents to block specific gene expression in vascular cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006855219018
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  • 3
    Electronic Resource
    Electronic Resource
    Transfer of macromolecules into living adult cardiomyocytes by microinjection (1997)
    Springer
    Molecular and cellular biochemistry 172 (1997), S. 103-109 
    Details
    ISSN: 1573-4919
    Keywords: adult ventricular cardiomyocytes ; microinjection ; gene transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Among techniques commonly used to deliver bioactive molecules into living cells, microinjection is a very efficient method. Microinjection has been used extensively for gene transfer into different cell types. We applied the microinjection technique to the adult rat ventricular cardiac muscle cells (AVC) in primary culture and optimized microinjection parameters and the appropriate cell culture conditions. We also optimized the use of particular agents (i.e. 2,3-butanedione monoxime, verapamil) for the prevention of the cell damage caused by the micropuncture. We obtained the expression of a CMV-β-galactosidase reporter gene in up to 20% of the injected cells with efficient maintenance of long term cell viability. Under our experimental conditions direct microinjection is a very advantageous technique to transfer macromolecules into living adult cardiac muscle cells and a powerful system to study and manipulate the biochemistry and molecular biology of the cardiac myocyte.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006867621743
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  • 4
    Electronic Resource
    Electronic Resource
    DNA transfer into vascular smooth muscle using fusigenic Sendai virus (HJV)-liposomes (1997)
    Springer
    Molecular and cellular biochemistry 172 (1997), S. 3-12 
    Details
    ISSN: 1573-4919
    Keywords: smooth muscle ; gene transfer ; DNA ; fibroblast growth factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Manipulation of the genetic machinery of cells both in vitro and in vivo is becoming an ever more important means of elucidating pathways of molecular and cellular biochemistry. In addition, gene therapy has been proposed as a novel and potentially powerful treatment for both inherited and acquired diseases. Successful gene transfer and gene blockade generally depend on high efficiency delivery of exogenous DNA or RNA into living cells, and much effort has therefore been focused on the development of methods for achieving this delivery in a safe and effective manner. We describe here our application of fusigenic Sendai virus (HVJ)-liposome technology toward the effective delivery of DNA into vascular smooth muscle cells (VSMC) in cell culture. Cellular uptake and intracellular distribution of oligodeoxynucleotide (ODN) after transfection with HVJ-liposome complexes was characterized using fluorescent (FITC)-labeled ODN, and the biologic effect of HVJ-liposome mediated transfection was demonstrated via inhibition of DNA synthesis in cultured VSMC using antisense ODN against basic fibroblast growth factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006801807206
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  • 5
    Electronic Resource
    Electronic Resource
    Novel methods for adenovirus-mediated gene transfer to blood vessels in vivo (1997)
    Springer
    Molecular and cellular biochemistry 172 (1997), S. 37-46 
    Details
    ISSN: 1573-4919
    Keywords: gene transfer ; gene expression ; adenovirus ; blood vessel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Adenovirus-mediated gene transfer is a promising method for studies of vascular biology and potentially for gene therapy. Intravascular approaches for gene transfer to blood vessels in vivo generally require interruption of blood flow and have several limitations. We have used two alternative approaches for gene transfer to blood vessels in vivo using perivascular application of vectors. First, replication-deficient adenovirus expressing nuclear-targeted bacterial b-galactosidase was injected into cerebrospinal fluid via the cisterna magna of rats. Leptomeningeal cells over the major arteries were efficiently transfected, and adventitial cells of large vessels and smooth muscle cells of small vessels were occasionally stained. When viral suspension was injected with the rat in a lateral position, the reporter gene was expressed extensively on the ipsilateral surface of the brain. Thus, adenovirus injected into cerebrospinal fluid provides gene transfer in vivo to cerebral blood vessels and, with greater efficiency, to perivascular tissue. Furthermore, positioning of the head may ‘target’ specific regions of the brain. Second, vascular gene delivery was accomplished by perivascular injection of virus in peripheral vessels. Injection of the adenoviral vector within the periarterial sheath of monkeys resulted in gene transfer to the vessel wall that was substantial in magnitude although limited to cells in the adventitia. Approximately20% of adventitial cells expressed the transgene, with no gene transfer to cells in the intima or media. These approaches may provide alternative approaches for gene transfer to blood vessels, and may be useful for studies of vascular biology and perhaps vascular gene therapy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006803202179
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  • 6
    Electronic Resource
    Electronic Resource
    Isozyme Variability in Plants Regenerated from Calli of Cereus peruvianus (Cactaceae) (1997)
    Springer
    Biochemical genetics 35 (1997), S. 189-204 
    Details
    ISSN: 1573-4927
    Keywords: somaclonal variation ; tissue culture ; isozymes ; cactus ; genetic diversity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Morphological and isozyme variation was observed among plants regenerated from callus cultures of Cereus peruvianus. Different morphological types of shoots (68%) were observed in 4-year-old regenerated plants, while no distinct morphological variants were observed in plants grown from germinated seeds. Isozyme patterns of 633 plants regenerated from calli and of 261 plants grown from germinated seeds showed no variation in isocitrate dehydrogenase isozyme, and the differential sorbitol dehydrogenase, alcohol dehydrogenase, malate dehydrogenase, acid phosphatase, and peroxidase isozyme patterns observed in regenerated plants were attributed to nonallelic variation. Allelic variation was detected at three isoesterase loci. The proportion of polymorphic loci for both populations was 13.6% and the deviation from Hardy–Weinberg equilibrium for the Est-1 and Est-7 loci observed in somaclones was attributed to the manner in which the regenerant population was established. The high values for genetic identity among regenerant and seed-grown plant populations are in accordance with the low levels of interpopulation genetic divergence. In somaclones of C. peruvianus, morphological divergence was achieved within a short time but was not associated with any isozyme changes and also was not accompanied by biochemical genetic divergence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021906226291
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  • 7
    Electronic Resource
    Electronic Resource
    Expression of fibroblast growth factor receptor-1 in rat heart H9c2 myoblasts increases cell proliferation (1997)
    Springer
    Molecular and cellular biochemistry 176 (1997), S. 89-97 
    Details
    ISSN: 1573-4919
    Keywords: cell division ; gene transfer ; mitogenic response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Basic fibroblast growth factor (FGF-2) plays an important role in myocardial growth and development and in particular cardiac myocyte proliferation. FGF-2 exerts its effects by binding to cell surface receptors (FGFR-1) of the tyrosine kinase family. We have detected the presence of both long and short isoforms of FGFR-1 in embryonic and adult mouse heart. In this report, we have examined the ability of long and short FGFR-1 isoforms to signal a mitogenic response. Assessment of RNA from rat myoblast H9c2 cells by reverse transcriptase-polymerase chain reaction and RNA blotting revealed that they were deficient in transcripts corresponding to long and short FGFR-1 species. Hybrid genes containing the cDNAs coding for long and short FGFR-1 isoforms directed by the myosin light chain-2 promoter and simian virus 40 enhancer sequences, were used to transiently transfect H9c2 cells. Total tyrosine phosphorylation was increased 2.0 and 2.6 fold in H9c2 cells transfected with the long and short FGFR-1 isoforms, respectively, compared to 'control' transfected H9c2 cells. This was accompanied by a 2.1 and 2.0 fold increase in DNA synthesis, as measured by tritiated thymidine incorporation, in H9c2 cells expressing the long and short FGFR-1 isoforms, respectively. To assess effects on proliferation, H9c2 cells were stably transfected with the myosin light chain-2/FGFR-1 cDNA genes. The rate of proliferation was increased 1.6 and 3.1 fold in H9c2 cells stably expressing the long and short FGFR-1 isoforms, respectively, compared to 'control' H9c2 cells. In contrast to non transfected H9c2 cells, treatment of H9c2 cells stably expressing long FGFR-1 with FGF-2 for 24 h resulted in a slight increase (1.3 fold, p 〈 0.02) in cell number. However, a greater response (1.5 fold, p 〈 0.0005) was observed with H9c2 cells stably expressing short FGFR-1 after treatment with FGF-2. These results suggest that both long and short FGFR-1 isoforms are capable of signalling a mitogenic response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006879029333
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  • 8
    Electronic Resource
    Electronic Resource
    Adenovirus-mediated gene transfer using in-situ perfusion of the liver graft (1997)
    Springer
    Transplant international 10 (1997), S. 202-206 
    Details
    ISSN: 1432-2277
    Keywords: Key words Gene transfer ; adenovirus ; liver transplantation ; Adenovirus ; gene transfer ; liver transplantation ; Liver transplantation ; adenovirus ; gene transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To establish an efficient technique for adenovirus-mediated gene transfer in liver transplantation, we evaluated the in situ perfusion of liver grafts. The grafts were perfused in situ with 1 × 1010 of E1-deleted, replication-defective adenoviral vectors encoding the LacZ gene driven by the human CMV promoter, either through the hepatic artery (group 1) or the portal vein (group 2). Group 3 animals served as negative controls; their liver grafts were perfused with lactated Ringer's solution through the portal vein. PCR confirmed the presence of viral DNA in every graft perfused with viral vectors. In X-gal staining, positive staining was observed almost exclusively at the portal triad in group 1, whereas in group 2 minimal staining was observed, predominantly in the parenchymal area. Protein production from the transfected gene was confirmed by a functional protein assay; the values were 0.16 % ± 0.07 % liver protein in group 1, 0.13 % ± 0.02 % in group 2, and 0.007 % ± 0.0003 % in group 3 on postoperative day 2. In conclusion, in situ perfusion of the viral vectors through the hepatic artery resulted in an effective expression of the transfected gene, predominantly at the portal triad.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001470050042
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  • 9
    Electronic Resource
    Electronic Resource
    Sperm as a carrier to introduce an exogenous DNA fragment into the oocyte of Japanese abalone (Haliotis divorsicolor suportexta) (1997)
    Springer
    Transgenic research 6 (1997), S. 85-95 
    Details
    ISSN: 1573-9368
    Keywords: abalone ; gene transfer ; sperm-electroporation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We investigated gene transfer in abalone via electroporated sperm. The mobility of sperm electroporated either in seawater or in marine invertebrate physiological solution was as good as that of the control group. The fertilization rate reached as high as 94.7--99.6% (93.0-- 99.7% for the control group) when 200 eggs were fertilized by 106 or 107 sperm treated with electroporation at 10 kV and 27 pulses for six cycles. Moreover, the fertilization rate of sperm electroporated in the presence of foreign DNA (opAFP-2000CAT) ranging from 0.1 to 3.2 μg and at voltages ranging from 2 to 10 kV, at 27 or 211 pulses for six or 12 cycles showed no differences from the control sperm. After DNase digestion, the genome of the electroporated sperm was analysed by polymerase chain reaction, and it was shown that a 138-bp product was amplified, corresponding to the transgene's amplification product. Southern blotting also showed that a positive band located at the same position as that of opAFP-2000CAT was found in the electroporated sperm after DNase treatment. Analysis by PCR of the genome isolated from a trochophore-stage abalone larva, derived from sperm electroporated with 3.2 g opAFP- 2000CAT, showed the existence of foreign DNA in 13 out of 20 examined samples (65%). The integration of the transferred DNA into the genome of transgenic abalone was also shown by Southern blot analysis. Furthermore, CAT activity was positive for the experimental larvae, but the level of CAT expression was lower than that of larvae derived from sperm electroporated with pCAT- Control vector, driven by SV40 promoter and enhancer sequences. These results demonstrate the potential for the use of sperm as mass gene transfer strategy in marine mollusks such as abalone
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018413318223
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  • 10
    Electronic Resource
    Electronic Resource
    Expression of cryIA(c) gene of Bacillus thuringiensis in transgenic chickpea plants inhibits development of pod-borer (Heliothis armigera) larvae (1997)
    Springer
    Transgenic research 6 (1997), S. 177-185 
    Details
    ISSN: 1573-9368
    Keywords: cryIA(c) gene ; gene transfer ; toxic to pod-borers ; transgenicchickpea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two strains of chickpea (Cicer arietinum L.) ICCV-1 and ICCV-6, were used for transgenic plant generation. Embryo axis of mature seed devoid of the root meristem and the shoot apex was used as experimental material. The explants were cultured in medium containing MS macro salts, 4 × MS micro salts, B5 vitamins, 3.0 mg l−1 BAP, 0.004 mg l−1 NAA, 30 mg l−1 sucrose and cultured at 26 °C in dark, 24 h prior to bombardment. Gene delivery to the explants was carried out using a Bio-Rad Biolistic 1000/He particle gun. A chimaeric, truncated bacterial cryIA(c) gene construct was developed for plant expression with the CaMV35S promoter, nos terminator, an initiatory kozak sequence and a translational enhancer (STAR-P) sequence of tobacco mosaic virus. This cryIA(c) gene was cotransferred with a plasmid containing nptII gene as the selection marker. Transgenic kanamycin resistant chickpea plants were obtained through multiple shoot formation and repeated selection of the bombarded explants. Molecular analyses of the transformants revealed the presence of the transferred functional cryIA(c) gene in plant. Insect feeding assay indicated that the expression level of the cryIA(c) gene was inhibitory to the development of the feeding larvae of Heliothis armigera Hubner, the chickpea pod-borer
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018433922766
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  • 11
    Electronic Resource
    Electronic Resource
    The application of gene transfer techniques to marine resource management: recent advances, problems and future directions (1997)
    Springer
    Hydrobiologia 352 (1997), S. 263-278 
    Details
    ISSN: 1573-5117
    Keywords: transgenic fish ; gene transfer ; growth enhancement ; lopifection ; particle bombardment ; electroporation ; fish sperm ; fish embryos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Recent advantages in transgenic fish research are reviewed, with special reference to the methods for gene transfer. These include microinjection, electroporation, particle bombardment, and lipofection. The success and problems associated with each of these methods, and the possible applications of transgenic fish research to aquaculture are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003000127867
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  • 12
    Electronic Resource
    Electronic Resource
    Retrotransposons of rice: their regulation and use for genome analysis (1997)
    Springer
    Plant molecular biology 35 (1997), S. 231-240 
    Details
    ISSN: 1573-5028
    Keywords: insertion mutation ; retrotransposon ; rice ; somaclonal variation ; transposable elements ; transposon tagging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Retrotransposons were extensively surveyed in rice using two molecular methods. The total copy number of retrotransposons in the rice genome was estimated to be about 1000 and 32 families were isolated, showing that retrotransposons are a major class of transposable elements in rice. Although these retrotransposons appear inactive during normal growth conditions, 5 out of 32 families were active under tissue culture conditions. The most active element, Tos17, was studied in detail. Its activity was show to be regulated mainly at the transcriptional level. The analysis of target sites of transposition indicated that activation of Tos17 is an important cause of tissue culture-induced mutations in rice. Tissue culture-induced activation of Tos17 was used to develop the site-selected mutagenesis system, in which mutants carrying a Tos17 insertion in the gene of interest can be identified among rice plants regenerated from tissue culture by the PCR using one primer for the ends of Tos17 and another for the gene of interest. This system will contribute to understanding the functions of rice genes whose sequences are being determined by the rice genome project.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005774705893
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  • 13
    Electronic Resource
    Electronic Resource
    Self-Assembling DNA-Lipid Particles for Gene Transfer (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 190-196 
    Details
    ISSN: 1573-904X
    Keywords: gene transfer ; cationic lipid ; DNA complexes ; hydrophobic effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. We have demonstrated that a heteromolecular complex consisting of cationic lipids and DNA can be prepared and isolated (1). Cationic lipids bind DNA through electrostatic interactions. However, when sufficient lipids are bound to DNA the physical and chemical properties of the complex are governed by hydrophobic effects. Here we describe an approach where this hydrophobic complex is used as an intermediate in the preparation of lipid-DNA particles (LDPs). Methods. The approach relies on the generation of mixed micelles containing the detergent, n-octyl β-D-glucopyranoside (OGP), the cationic lipid, N-N-dioleoyl-N, N-dimethylammonium chloride (DODAC), and selected zwitterionic lipids, 1,2-dioleoyl-sn-glycero-3 -phosphoethanolamine (DOPE) or egg sphingomyelin (SM). Results. When these micelles were prepared at low detergent concentrations (20 mM OGP) and combined with pCMVβ DNA, LDPs spontaneously formed. The mean diameter of these particles as measured by quasielastic light scattering was 55−70 nm, a result that was confirmed by negative stain electron microscopy. Further characterization of these LDPs showed that DNA within the particles was inaccessible to the small fluorochrome TO-PRO-1 and protected against DNase I degradation. LDPs could also be prepared in high concentrations of OGP (100 mM), however particles formed only after removal of OGP by dialysis. Particles formed in this manner were large (〉2000nm) and mediated efficient transfection of Chinese hamster ovary cells. Transfection activity was greater when the lipid composition used consisted of SM/ DODAC. Small particles (〈100nm) prepared of SM/DODAC were, however, inefficient transfecting agents. Conclusions. We believe that LDP formation is a consequence of the molecular forces that promote optimal hydrocarbon-hydrocarbon interactions and elimination of the hydrocarbon-water interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012000711033
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  • 14
    Electronic Resource
    Electronic Resource
    In Vivo Gene Transfer by Intravenous Administration of Stable Cationic Lipid/DNA Complex (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 742-749 
    Details
    ISSN: 1573-904X
    Keywords: cationic lipid ; DNA ; in vivo ; gene transfer ; alkaline phosphatase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. A stable cationic lipid/DNA complex has been developed for in vivo gene transfer. The formulation capitalizes on a previously described procedure to obtain stable lipid/DNA complexes for in vitro gene transfer (1). Methods. Conditions for DNA/lipid complex formation were modified to yield a DNA concentration of 1 mg/ml. Heat stable alkaline phosphatase (AP) under a CMV promoter was used as a reporter gene. Results. The resulting complex was completely insensitive to serum inactivation. Tail vein injection of a 80 μg DNA into Balb C mice yielded significant levels of reporter enzyme activity in the lung, heart, spleen, muscle, and liver. Less AP activity was observed in the kidney. No AP activity was observed in blood, bone marrow or brain. A titration of the lipid (DOSPA) to DNA-nucleotide ratio showed the optimal molar ratio for in vivo gene transfer to be 1/1. Using this ratio in a dose response study showed approximately 80 μg of DNA/mouse yielded the highest level of gene expression. Using this dose at a 1/1 lipid to DNA nucleotide ratio, the time course for alkaline phosphatase activity was determined. Maximal AP activity was observed 24 hours after injection for all tissues. By day 5, the activity dropped approximately 10 fold for all tissues. By day 7, residual activity was detected in the lung, heart, and muscle. Histology of the lung showed both interstitial and endothelial cells to be transfected. In all other tissues, however, endothelial cells were the only transfected cell type. Conclusions. These results demonstrate that reformulation of an existing cationic lipid can result in the formation of a stable lipid/DNA complex, which is able to reproducibly transfect lung, heart, spleen, and liver upon intravenous administration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012146305040
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  • 15
    Electronic Resource
    Electronic Resource
    The Absence of Accessible Vitronectin Receptors in Differentiated Tissue Hinders Adenoviral-Mediated Gene Transfer to the Intestinal Epithelium In Vitro (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 1216-1222 
    Details
    ISSN: 1573-904X
    Keywords: adenoviral vector ; Caco-2 ; gene transfer ; integrin ; intestinal epithelium ; vitronectin receptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Adenoviral (Ad) vectors have been used as efficient tools for gene therapy in various tissues, whereas in some differentiated epithelium transduction efficiency is almost abolished. Methods. Caco-2 cell monolayers were chosen as an in vitro model for the differentiated intestinal epithelium. Fluorescence-labeled adenoviral particles were used for binding studies to cell surfaces. Internalization receptors for adenoviral uptake were decteted by a fluorescence-labeled vitronectin antibody. Gene expression was studied by using the β-galactosidase reporter gene. All experiments were done on undifferentiated and differentiated Caco-2 cells. Furthermore, adenoviral particles were allowed to bind to differentiated Caco-2 monolayers followed by a trypsinization step that disintegrates the monolayers and result in a cell suspension. Gene expression was tested after reseeding the cells into dishes. Results. The results from adenoviral binding studies, vitronectin immunofluorescence detection and gene expression are in good agreement and indicate that virion binding as well as the expression of internalization receptors almost disappear in fully differentiated cells. Nonetheless, adenoviral binding to differentiated monolayers seems to be sufficient to cause up to 53% gene expression, but only if internalization of the vector can be induced by disintegrating the monolayers and releasing free vitronectin receptors. Conclusions. These findings indicate that gene transfer to the intestinal epithelium utilizing adenoviral vectors is poor and ineffective, because of the lack of sufficient internalization receptors. If these receptors can be exposed in differentiated epithelium, transduction can be made more efficicient. Alternatively, a viral vector must be developed whose uptake mechanism is independent of integrin receptor expression like the enteral virus Ad40, or Ad5 could be conjugated to ligands that trigger viral internalization by receptor-mediated endocytosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012163025455
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  • 16
    Electronic Resource
    Electronic Resource
    Non-Polarized Secretion of Mouse Interferon-β from Gene-Transferred Human Intestinal Caco-2 Cells (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 483-485 
    Details
    ISSN: 1573-904X
    Keywords: gene transfer ; interferon-β ; Caco-2 cells ; non-polarized secretion ; gene therapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The intestinal epithelium is considered to be a feasible target for somatic gene therapy. To this end, Caco-2 cells derived from human colon carcinoma were transfected with a mouse interferon-β (IFN-β) expression vector and several stable sublines were established; this hetero-specific cytokine allows unexpected cellular effects to be avoided. Using the highest mouse IFN-β-producing sublines, the mode of IFN secretion was examined. Methods. The secretion polarity of mouse IFN-β in its gene-transduced Caco-2 sublines was studied in a bicameral culture system in which the chambers were separated by microporous filters. Results. Mouse IFN-β was secreted to the same extent from both apical and basolateral surfaces of the transduced cells regardless of cell aging. Conclusions. These results suggest that in the intestinal epithelium exogenous gene products such as IFNs can be delivered to both the luminal and blood sides in vivo. Thus, the intestinal epithelium may be suitable for systemic and local delivery of therapeutic proteins by gene transfer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012151616910
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  • 17
    Electronic Resource
    Electronic Resource
    Gene therapy strategies for carcinoma of the breast (1997)
    Springer
    Breast cancer research and treatment 44 (1997), S. 93-114 
    Details
    ISSN: 1573-7217
    Keywords: cancer gene therapy ; gene transfer ; breast carcinoma ; molecular therapeutics ; molecular chemotherapy ; immunotherapy ; loss of heterozygosity (LOH) ; oncogenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005761723853
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  • 18
    Electronic Resource
    Electronic Resource
    Isolation and analysis of different subpopulations of normal human breast epithelial cells early after their infection with a retroviral vector encoding a cell surface marker (1997)
    Springer
    Breast cancer research and treatment 44 (1997), S. 153-165 
    Details
    ISSN: 1573-7217
    Keywords: gene transfer ; human breast epithelial cells ; retrovirus ; selectable marker
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The use of gene transfer procedures has greatlyfacilitated the investigation of cell lineage relationships andother developmental processes in a variety of primarytissues. In this report we describe the infectionand selection of primary human breast epithelial cellsusing retroviral vectors (Jzen-HSA-NEO and MSCV-HSA.NEO) containing thecomplete 228 bp coding sequence of a murinecell surface marker (Heat Stable Antigen, HSA) aswell as the neomycin resistance (neor) gene. Expressionof the transduced HSA gene was detectable usingeither flow cytometry or immunohistochemistry after staining infectedcells with an anti-murine HSA-specific antibody (M1/69). Expressionof the transduced neor gene conferred resistance toG418. In initial experiments with the MCF-7 breastcancer cell line, continued expression of both markerswas demonstrated in a high proportion of cellsfor at least 4 weeks after their infectionby positive M1/69 staining of cells that hadbeen selected by prior incubation in G418. Evidenceof gene transfer to early stage (〈 9days old) primary cultures of normal human breastepithelial cells (15 experiments with cells from 12normal individuals) was also obtained using an infectionprotocol in which these cells were exposed tohelper-free viral supernatants (2 incubations, 4 to 6hr each) after being subcultured for 12 to18 hr to increase their rate of proliferation.The presence of 5–50% (mean=26%) HSA+ cells was demonstrated in these experiments within 5days after their infection and the HSA+populationsincluded both myoepithelial and luminal phenotypes. The transduced(HSA+) cells within both of these subpopulations couldalso be separately isolated by FACS and subcultured.These results should provide an important starting pointfor future studies of genetically modified or markedprimary human breast epithelial cell populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005713419023
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  • 19
    Electronic Resource
    Electronic Resource
    Immunotherapy I: Cytokine gene transfer strategies (1997)
    Springer
    Cancer and metastasis reviews 16 (1997), S. 421-432 
    Details
    ISSN: 1573-7233
    Keywords: cytokine ; tumor ; gene transfer ; immunotherapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The cytokine approach to gene therapy of cancer stems from early studies of direct, repeated injection of recombinant cytokines at the tumor site, and extension of the bystander effect that enables a few cytokine gene transduced cells in a tumor to bring about its total destruction. This effect can be extended through the immune system, since cytokine-activated regression of a small mass of tumor cells can afford systemic protection. Transduced cells used as a vaccine provide a local concentration of both cytokine and tumor antigens. Cytokines sustain antigen uptake and presentation by increasing the immunogenic potential of the environment through the recruitment of antigen presenting cells and leukocytes, and activation of a cascade of events which amplify and tone up the efficacy of a vaccine. The promises and difficulties of this approach are discussed by considering what is still missing from experimental studies and what can best be done as soon as possible in animals and humans to reach compelling conclusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005980418533
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  • 20
    Electronic Resource
    Electronic Resource
    RFLP analysis of Hypericum perforatum L. somaclones and their progenies (1997)
    Springer
    Euphytica 95 (1997), S. 229-235 
    Details
    ISSN: 1573-5060
    Keywords: apomixis ; Hypericum perforatum ; rDNA ; heterogeneity ; RFLP ; progeny ; somaclonal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Three adjacent EcoRI fragments of the rDNA unit from Lycopersicon esculentum, eleven anonymous genomic and two anonymous cDNA clones from Brassica napus and three restriction endonucleases: BamHI, EcoRI and EcoRV were used for RFLP analysis of the genome of Hypericum perforatum L. A polymorphic band identified with EcoRI and two rDNA probes in five somaclones originated from the same genotype was detected in all progenies of two somaclones indicating the inheritance of the molecular changes. rDNA unit heterogeneity represented by two types of RFLP pattern revealed among somaclones and seed-derived control plants using EcoRV and two rDNA probes may indicate an alloploid origin of Hypericum perforatum. The occurrence of the identical RFLP patterns in some R0 somaclones and seed-derived plants and their progenies may be related to the apomictic mode of reproduction which is assumed to be prevalent in Hypericum perforatum. The differences in RFLP patterns of progenies when compared with the maternal plants (1 out of 10 progenies of one control plant and 1 out of 8 progenies of one somaclone) may indicate that some progenies have originated through sexual recombination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002946618273
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  • 21
    Electronic Resource
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    Plant regeneration in sweet potato (Ipomoea batatas L., Convolvulaceae) (1997)
    Springer
    Euphytica 96 (1997), S. 143-152 
    Details
    ISSN: 1573-5060
    Keywords: Sweet potato ; Ipomoea batatas ; plant regeneration ; somatic embryogenesis ; protoplasts ; genetic variation ; somaclonal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The application of new techniques for improvement of sweet potato crops, particularly including the exploitation of somaclonal variation, gene transfer by genetic transformation and somatic hybridization, requires the control of plant regeneration from tissue cultures. Shoots can easily be regenerated from explants of stems, petioles, leaves and roots, while callus cultures do not produce any shoots. The potential of somatic embryogenesis and plant regeneration via embryogenesis was evaluated for 10 cultivars of sweet potato. Protocols for plant regeneration from cultured protoplasts have also been developed. Since mesophyll was resistant to enzyme digestion, fragments of stems and petioles, callus and cell suspensions were used as source of protoplasts of sweet potato. Series of transfers of protoplast-derived calluses, particularly those which had been obtained from in vitro plants, to media containing a high level of zeatin resulted in successful formation of shoots in only two sweet potato cultivars. In addition, the embryogenic potential was irreversibly lost through protoplast culture, since protoplasts isolated from embryogenic cell suspensions developed into non-embryogenic callus. Consequently, an alternative protocol is being successfully developed to improve plant regeneration from cultured protoplasts of sweet potato, involving first root formation from which shoots can then be regenerated. Preliminary evaluation in field conditions in Gabon revealed that plants regenerated from cultured protoplasts exhibited a great genetic variability in their growth and tuber formation in particular.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002997319342
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  • 22
    Electronic Resource
    Electronic Resource
    Use of somaclonal variation and in vitro selection for chilling tolerance improvement in rice (1997)
    Springer
    Euphytica 96 (1997), S. 135-142 
    Details
    ISSN: 1573-5060
    Keywords: Oryza sativa ; chilling tolerance ; in vitro selection ; rice ; somaclonal variation ; field performance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Embryo-derived calli of four rice varieties cultivated at high altitude in Burundi — Facagro 57, Facagro 76, Kirundo 3 and Kirundo 9 — were submitted to different temperature regimes. The percentage of regenerating calli greatly varied depending on variety, length of culture and callus temperature treatment. The reduction of regeneration percentages induced by low temperature was more pronounced in the more sensitive varieties. Regenerated plants (R0) and their progenies in R1, R2 and R3 were cold-screened together with control plants. In all varieties, significantly higher survival rates were obtained in R3 with in vitro plants than with control plants. Such chilling tolerance improvement was not obtained following a massal selection applied during 3 successive generations onto the control plants. In vitro plants regenerated from calli cultivated either at 25 °C, either at 4 °C, were cultivated at different altitudes in Burundi during two successive generations. For most observed traits, the in vitro plants were characterized by lower means, larger variation and higher maximum values than the control plants. The most chilling-tolerant somaclonal families were most usually characterized by extensive differences in fatty acid composition, chilling-induced electrolyte leakage and chlorophyll fluorescence, compared to the varieties they derived from.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002926421430
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    Electronic Resource
    Electronic Resource
    Introduction of new traits into cotton through genetic engineering: insect resistance as example (1997)
    Springer
    Euphytica 96 (1997), S. 163-166 
    Details
    ISSN: 1573-5060
    Keywords: Agrobacterium tumefaciens ; Bacillus thuringiensis ; cotton ; gene transfer ; Gossypium hirsutum ; insect resistance ; protease inhibitors ; regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The main goal of gene transfer into cotton is the development of insect-resistant varieties. The stakes are important since cotton protection against insects uses almost 24% of the world's chemical insecticides market, which is not without consequences on the environment. The first approach was to introduce and express in the cotton genome, genes from the bacterium Bacillus thuringiensis (B.t.) which produces entomopathogenic toxins. The development of an efficient Agrobacterium tumefaciens mediated transformation system was the first step. The expression of B.t. genes was studied and synthetic genes more adapted to a plant genome have been constructed. Studies on their expression in cotton is underway. The second focus was to develop strategies that would minimize the risks of inducing insect resistance. The main approach is to associate several genes coding for entomopathogenic proteins with different modes of action. Genes encoding protease inhibitors were chosen. One possibility is to associate a B.t. gene and a gene encoding a protease inhibitor. Several protease inhibitors were tested in artificial diets on major pests of cotton. The corresponding genes have been introduced into the cotton genome. These various orientations of the research program will be presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002906308304
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    An assessment of somaclonal variation as a breeding tool for generating herbicide tolerant genotypes in wheat (Triticum aestivum L.) (1997)
    Springer
    Euphytica 94 (1997), S. 335-340 
    Details
    ISSN: 1573-5060
    Keywords: somaclonal variation ; in vitro selection ; herbicides ; wheat ; triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The present work was initiated to assess tissue culture techniques as a means of generating and selecting herbicide tolerant genotypes of wheat through exploiting somaclonal variation. Callus was initiated from immature embryos of genetically defined varieties and subcultured onto selective media containing 5 μm, 10 μm and 50 μm concentrations of difenzoquat and atrazine. Plants were regenerated from all the selective media except that media containing the highest herbicide concentration. The progenies of the regenerated plants were tested as whole plants for their response to spray application of the herbicides. For difenzoquat, variation in response from extreme susceptibility to tolerance was observed. However, genetic characterization by progeny testing tolerant lines revealed that the induced variation was not heritable. No plants tolerant to atrazine were obtained. Overall, no clear evidence of heritable mutations was obtained. Alternative strategies to obtain herbicide tolerant genotypes using cell culture techniques are discussed.
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    URL: http://dx.doi.org/10.1023/A:1002966309224
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  • 25
    Electronic Resource
    Electronic Resource
    Long-term ploidy stability of shoot primordium cultures and produced plants of melon (1997)
    Springer
    Plant cell, tissue and organ culture 48 (1997), S. 31-35 
    Details
    ISSN: 1573-5044
    Keywords: Cucurbitaceae ; Cucumis melo ; polyploidy ; regeneration ; somaclonal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The chromosome number of cells in the shoot primordium aggregates and produced plants of melon [Cucumis melo L. 'Prince' (2n=2x=24)] was examined. Shoot primordium aggregates were induced from shoot-tips cultured in liquid medium and shaken at low speed (2 rpm). They were maintained by subculturing small pieces (5mm〈) every 4 weeks. Shoot primordium aggregates just after induction contained about 97 diploid and 3 tetraploid cells, which was similar to those maintained in shoot primordium cultures for 6 years. This indicates that the ploidy level was maintained stably. On the other hand, plants produced from the shoot primordium aggregates just after induction were either diploid, tetraploid or mixoploid with both diploid and tetraploid cells. These ploidies were again observed among plants produced from shoot primordium cultures that were 2, 3 or 4 years old. A majority of produced plants were diploid while the total frequency of tetraploids and mixoploids was less than 8 of plants produced from all ages. Therefore, the frequency of somaclonal variation with respect to ploidy among plants produced from shoot primordium aggregates is likely to be stable at a low level over the long term.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005854523278
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  • 26
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    Naphthopyranquinone Antibiotics: Novel enantioselective syntheses of frenolicin B and some of its stereoisomers (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 43-58 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new enantioselective syntheses of the naphthopyranquinone antibiotic frenolicin B (1), of its enantiomer 2, and of its diastereoisomers 3 and 4 were accomplished using two different routes from optically active β-Hydroxy esters (R)- and (S)-11 and 18. β-Hydroxy esters (R)- and (S)-11 were prepared stereoselectively from optically active sulfenylacetates (S)- and (R)-10, respectively (Scheme 2, Method A). Alternatively, compound 18 was obtained in excellent yield by enantioselective hydrogenation of the corresponding β-keto ester 17, using a chiral ruthenium-complex catalyst (Scheme 3, Method B). Subsequently, compounds (S)-11 and 18 were transformed into frenolicin B (1). In analogy, Stereoisomers 2-4 were prepared from (S)- and (R)-11 in good yields.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800104
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  • 27
    Electronic Resource
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    Oligonucleotides Containing Consecutive 2′-Deoxyisoguanosine Residues: Synthesis, duplexes with parallel chain orientation, and aggregation (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 73-85 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2′-deoxyisoguanosine phosphonates 3a and 4a and the phosphoramidites 3b and 4b were prepared as building blocks for solid-phase oligonucleotide synthesis. The diphenylcarbamoyl (dpc) residue was introduced as 2-oxo protecting group which stabilizes the N-glycosylic bond against hydrolysis and prevents the molecule from side reactions. The dpc-protected building blocks 4a, b were employed in solid-phase synthesis and were found to be much more efficient than the unprotected compounds 3a, b. Oligonucleotides with alternating (11) or consecutive isoguanine residues (13-15) were synthesized. They form duplexes with parallel chain orientation. The aggregate d(T4-iG4-T4) (15) containing four consecutive 2′-deoxyisoguanosine is shown to be a tetramer similar to that of d(T4-G4-T4).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800107
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  • 28
    Electronic Resource
    Electronic Resource
    Synthesis and Odor of Chiral Partial Structures of Khusimone. Part 1Dedicated with best personal wishes to Prof. Dr, W. Fleischhacker on the occasion of his 65th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 139-145 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Khusimone (1), one of the main odor-donating compounds of vetiver oil is subject of the following study on structure/odor relationship. The omittance of the ethano bridge of the tricyclic khusimone leads to a bicyclic system. The stereoselective approach to this degraded structure is described, and the olfactory properties are studied. The key step of the synthesis of the hydrindane nucleus is based on a highly diastereoselective conjugate addition to a chiral oxo-cyclopentene-2-carboxylate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800114
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  • 29
    Electronic Resource
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    Nucleotides. Part LPart IL:[1]. Aglycone protection by the (2-dansylethoxy)carbonyl (= {2-{[5-(dimethylamino)naphthalen-l-yl]sulfonyl}ethoxy}carbonyl; dnseoc) group a new variation in oligodeoxyribonucleotide synthesis (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 200-212 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The (2-dansylethoxy)carbonyl (= {2-{[5-(dimethylamino)naphthalen-l-yl]sulfonyl}ethoxy}carbonyl; dnseoc) group was employed for protection of the amino functions of the aglycone residues. The lactam function of 2′-deoxyguanosine was on the one hand unprotected and on the other hand alkylated at O6 of the aglycone with the 2-(4-nitrophenyl)ethyl (npe) and 2-(phenylsulfonyl)ethyl (pse) group, respectively. The syntheses of monomeric building blocks, both phosphoramidites and nucleoside- functionalized supports, are described for the three common 2′-deoxynucleosides (2′-deoxycytidine, 2′-deoxyadenosine, 2′-deoxyguanosine). As kinetic studies with the tritylated nucleosides showed, the dnseoc group is more labile towards DBU cleavage than the corresponding 2-(4-nitrophenyl)ethyl-(npe) and [2-(4-nitrophenyl)ethoxy]carbonyl(npeoc)-protected analogues (see Table 2). These results were confirmed by the very fast deprotection rate of the dnseoc groups at some oligonucleotides.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800118
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    The Absolute Configuration of 3-Methylpyrrolidine Alkaloids from Poison Glands of Ants Leptothoracini (Myrmicinae) (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 267-272 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The absolute configuration of 3-methylpyrrolidine alkaloids isolated from the poison gland of ants Leptothoracini was determined as (3R). The enantiomeric separation by chiral gas chromatography and unambiguous structural assignment of the target compounds are described.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800124
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    Mitteilungen (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 317-318 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800127
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  • 32
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    New Heptalenes Substituted with Extended π-Systems (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 253-266 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of π-substituted heptalenecarboxylates or -dicarboxylates, starting with the easily available dimethyl 9-isopropyl-1, 6-dimethylheptalene-4, 5-dicarboxylate (2b), are described. Treatment of 2b with t-BuOK and C2Cl6 at -78° leads to the chemoselective introduction of a Cl substituent in Me-C(1) (see 5b in Scheme 1). Formation of the corresponding triphenylphosphonium salt 7b via the iodide 6b (Scheme 2) allowed a Wittig reaction with cinnamaldehyde in the two-phase system CH2Cl2/2N NaOH. Transformation of the 4, 5-dicar-boxylate of 2b into the corresponding pseudo-ester 10b allowed the selective reduction of the carbonyl function at C(4) with DIBAH to yield the corresponding 4-carbaldehyde 11b (Scheme 3). Wittig reaction of 11b with (benzyl) triphenylphosphonium bromide led to the introduction of the 4-phenylbuta-1, 3-dienyl substituent at C(4). The combination of both Wittig reactions led to the synthesis of the 1, 4-bis(4-phenylbuta-1, 3-dienyl)-substituted heptalene-5-carboxylate (all-E)-17b (Scheme 5). In a similar manner, by applying a Horner-Wadsworth-Emmons reaction, followed by the Wittig reaction, the donor-acceptor substituted heptalene-5-carboxylate (E;E)-22b was synthesized (Scheme7). Most of these new heptalenes are in solution, at room temperature, in thermal equilibrium with their double-bond shifted (DBS) isomers. In the case of (all-E)-17b and (E;E)-22b, irradiation of the thermal equilibrium mixture with light of λ -(439 ± 10) nm led to a strong preponderance ( 〉 90%) of the DBS isomers 17a and (E;E)-22a, respectively (Schemes 6 and 7). Heating of the photo-mixtures at 40° re-established quickly the thermal equilibrium mixtures. Heptalenes-carboxylates (all-E)-17a and (E;E)-22a which represent the off-state of a 1,4-conjugative switch (CS) system show typical heptalene UV/VIS spectra with a bathochromically shifted heptalene band III and comparably weak heptalene bands II and I which appear only as shoulders (Figs. 4 and 5). In contrast, the DBS isomers (all-E)-17b and (all-E)-22b, equivalent to the on-state of a 1,4-CS system, exhibit extremely intense heptalene bands I and, possibly, II which appear as a broad absorption band at 440 and 445 nm, respectively, thus indicating that the CSs (all-E)-17a⇌(all-E)-17b and (E;E)-22a⇌(E;E)-22b are perfectly working.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800123
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    Konfigurations- und konformationsisomere antiaromatische [28]Tetraoxaporphyrinoide(4.2.4.2) und aromatische [26]Tetraoxaporphyrin(4.2.4.2)-dikationen. Eine neue Form molekularer Dynamik in makrocyclischen Systemen (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 14-42 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Configurational and Conformational Isomeric Antiaromatic [28]Tetraoxaporphyrinoids(4.2.4.2) and Aromatic [26]Tetraoxaporphyrin(4.2.4.2) Dications. A New Type of Molecular Dynamics in Macrocyclic SystemsThe [28]tetraoxaporphyrinoids(4.2.4.2) 6 are synthesized by cyclizing Wittig reaction of (E, E)-5, 5′-(buta-1, 3-diene-1, 4-diyl)bis[furan-2-carbaldehyde] (8) with (E, E)-{(buta-1, 3-diene-diyl)bis[(furan-5, 2-diyl)methylene]}bis-[triphenylphosphonium] dibromide (9) and 3, 3′-{[(E)-ethene-1, 2-diyl]bis(furan-5, 2-diyl)}bis[(E)-prop-2-enal] (22) with (E)-{(ethene-1, 2-diyl)bis[(furan-5.2- diy)methylene]}bis[triphenylphosphonium] dibromide (23). An alternative path to get 6 is the McMurry condensation of 8. Four different configurational isomers of 6 could be isolated and characterized by 1H-NMR spectroscopy. The (Z, EE, Z, EE)-isomer 6a is the first macrocyclic system where the inner and outer protons of the (E, E)-dienediyl bridges exchange by rotation around the adjacent single bonds. In the (Z, EE, E, EE)-isomer 6b, the (E)-ethenediyl bridge is rotationally active, while in the (E, ZE, E, EZ)-isomer 6c and in the (E, EZ, E, EZ)-isomer 6e, the rotation of both (E)-ethenediyl bridges is observed. When in the dynamic systems the rotation of the active (E)-double bonds at temperatures T 〈 -90° is frozen, all configurational isomers of 6 appear to be antiaromatic and paratropic. The oxidation of the [28]tetraoxaporphyrinoids 6c and 6e with DDQ yields the aromatic, diatropic [26]tetraoxaporphyrin(4.2.4.2) dications 21e/21e′ both with (E, EZ, E, EZ)-configuration but different fixed conformations. (Z, EE, Z, EE)-Isomer 6a is oxidized to give the (Z, EE, Z, EE)-dication 21a, while the oxidation of 6b yields a mixture of 21a and 21e/21e′. The standard formation enthalpies of the obtained and expected [28]tetraoxaporphyrinoids 6 and [26]tetraoxaporphyrin dications 21 have been calculated with the AM1 method, showing good accordance with the experimental results.
    Additional Material: 15 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800103
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    Diastereoselective Synthesis of Cyclododeca-1,6-diallenes ( = cyclododeca-l,2,6,7-tetraenes) (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 414-420 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of substituted cyclododeca-1,6-diallenes.( = cyclododeca-1,2,6,7-tetraenes) from cyclododeca-5,11-diyne-1,4-diols is described (Schemes 1 and 3). The ca. 1:1 mixtures of the stereoisomers of the cyclododeca-1,6-diallenes were formed in high yields from the ca. 1:1 diastereoisomer mixtures of the 1,4-disubstituted cyclododeca-5,11-diynes by reactions with Me2CuLi or t-BuMgCl/CuII. In mechanistically relevant experiments with the pure diastereoisomers of 1,4-dimethylcyclododeca-5,11-diyne-1,4-diol, it is demonstrated that the configuration is conserved in these reactions. The first synthesis of a 1-substituted cyclododeca-2,8-diyne bearing only one propargylic leaving group gives access to a mixed 12-membered allen-yne (Scheme 5).
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    Lipophilicity Behavior of Model and Medicinal Compounds containing a suilfide, sulfoxide, or sulfone moiety (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 449-462 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This study was designed to unravel lipophilicity changes associated with the oxidation state of the S-atom in model compounds, drugs, and metabolites, special attention being given both to intermolecular and intramolecular effects. The methods used were experimental (potentiometry, CPC, and shake-flask techniques to measure lipophilicity, 13C-NMR spectroscopy to investigate tautomeric equilibria) and computational (quenched molecular dynamics and molecular lipophilicity potential). Simple, monofunctional model compounds were used to assess intermolecular forces, as revealed by the Δlog Poct-alk and Δlog Poct-chf parameters. Drugs and their metabolites proved to be good probes to study intramolecular effects in both neutral and anionic forms, as revealed by the difference between calculated and experimental log Poct values (the diff(log Pexp-calc) parameter). Sulindac and its metabolites showed a normal partitioning behavior, whereas the lipophilicity of sulfmpyrazone and its metabolites' was markedly affected by tautomeric and conformational equilibria.
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    Methanofullerene Molecular Scaffolding: Towards C60-substituted poly(triacetylenes) and expanded radialenes, preparation of a C60-C70 hybrid derivative, and a novel macrocyclization reaction (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 293-316 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of (E)-hex-3-ene-l, 5-diynes and 3-methylidenepenta-1, 4-diynes with pendant methano[60]-fullerene moieties as precursors to C60-substituted poly(triacetylenes) (PTAs, Fig. 1) and expanded radialenes (Fig. 2) is described. The Bingel reaction of diethyl (E)-2, 3-dialkynylbut-2-ene-1, 4-diyl bis(2-bromopropane-dioates) 5 and 6 with two C60 molecules (Scheme 2) afforded the monomeric, silyl-protected PTA precursors 9 and 10 which, however, could not be effectively desilylated (Scheme 4). Also formed during the synthesis of 9 and 10, as well as during the reaction of C60 with thedesilylated analogue 16 (Scheme 5), were the macrocyclic products 11, 12, and 17, respectively, resulting from double Bingel addition to one C-sphere. Rigorous analysis revealed that this novel macrocyclization reaction proceeds with complete regio- and diastereoselectivity. The second approach to a suitable PTA monomer attempted N, N′-dicyclohexylcarbodiimide(DCC)-mediated esterification of (E)-2, 3-diethynylbut-2-ene-l, 4-diol (18, Scheme 6) with mono-esterified methanofullerene-dicarboxylic acid 23; however, this synthesis yielded only the corresponding decarboxylated methanofullerene-carboxylic ester 27 (Scheme 7). To prevent decarboxylation, a spacer was inserted between the reacting carboxylic-acid moiety and the methane C-atom in carboxymethyl ethyl 1, 2-methano[60]fullerene-61, 61-dicarboxylate (28, Scheme 8), and DCC-mediated esterification with diol 18 afforded PTA monomer 32 in good yield. The formation of a suitable monomeric precursor 38 to C60-substituted expanded radialenes was achieved in 5 steps starting from dihydroxyacetone (Schemes 9 and 10), with the final step consisting of the DCC-mediated esterification of 28 with 2-[1-ethynyl(prop-2-ynylidene)]propane-1, 3-diol (33). The first mixed C60-C70 fullerene derivative 49, consisting of two methano[60]fullerenes attached to a methano[70]fullerene, was also prepared and fully characterized (Scheme 13). The Cs-symmetrical hybrid compound was obtained by DCC-mediated esterification of bis[2-(2-hydroxy-ethoxy)ethyl] 1, 2-methano[70]fullerene-71, 71-dicarboxylate (46) with an excess of the C60-carboxylic acid 28. The presence of two different fullerenes in the same molecule was reflected by its UV/VIS spectrum, which displayed the characteristic absorption bands of both the C70 and C60 mono-adducts, but at the same time indicated no electronic interaction between the different fullerene moieties. Cyclic voltammetry showed two reversible reduction steps for 49, and comparison with the corresponding C70 and C60 mono-adducts 46 and 30 indicated that the three fullerenes in the composite fullerene compound behave as independent redox centers.
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    Bis- through Tetrakis-Adducts of C60 by Reversible Tether-Directed Remote Functionalization and systematic investigation of the changes in fullerene properties as a function of degree, pattern, and nature of functionalization (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 343-371 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By the tether-directed remote functionalization method, a series of bis- to hexakis-adducts of C60, i.e., 1-7 (Fig. 1), had previously been prepared with high regioselectivity. An efficient method for the removal of the tether-reactive-group conjugate was now developed and its utility demonstrated in the regioselective synthesis of bis- to tetrakis(methano)fullerenes ( = di- to tetracyclopropafullerenes-C60-Ih) 9-11 starting from 4, 5, and 7, respectively (Schemes 2, 4, and 5). This versatile protocol consists of a 1O2 ene reaction with the two cyclohexene rings in the starting materials, reduction of the formed mixture of isomeric allylic hydroperoxides to the corresponding alcohols, acid-promoted elimination of H2O to cyclohexa-1,3-dienes, Diels-Alder addition of dimethyl acetylenedicarboxylate, retro-Diels-Alder addition, and, ultimately, transesterification. In the series 9-11, all methano moieties are attached along an equatorial belt of the fullerene. Starting from C2v-symmetrical tetrakis-adduct 15, transesterification with dodecan-1-ol or octan-1-ol yielded the octaesters 16 and 17, respectively, as noncrystalline fullerene derivatives (Scheme 3). The X-ray crystal structure of a CHCl3 solvate of 11 (Fig. 3) showed that the residual conjugated π-chromophore of the C-sphere is reduced to two tetrabenzopyracylene substructures connected by four biphenyl-type bonds (Fig. 5). In the eight six-membered rings surrounding the two pyracylene (= cyclopent[fg]acenaphthylene) moieties, 6-6 and 6-5 bond-length alteration (0.05 Å) was reduced by ca. 0.01 Å as compared to the free C60 skeleton (0.06 Å) (Fig. 4). The crystal packing (Fig. 6) revealed short contacts between Cl-atoms of the solvent molecule and sp2- and sp3-C-atoms of the C-sphere, as well as short contacts between Cl-atoms and O-atoms of the EtOOC groups attached to the methano moieties of 11. The physical properties and chemical reactivity of compounds 1-11 were comprehensively investigated as a function of degree and pattern of addition and the nature of the addends. Methods applied to this study were UV/VIS (Figs. 7-11), IR, and NMR spectroscopy (Table 2), cyclic (CV) and steady-state (SSV) voltammetry (Table 1), calculations of the energies of the lowest uunoccupied mmolecular orbitals (LUMOs) and electron affinities (Figs. 12 and 13), and evaluation of chemical reactivity in competition experiments. It was found that the properties of the fullerene derivatives were not only affected by the degree and pattern of addition but also, in a remarkable way, by the nature of the addends (methano vs. but-2-ene-1, 4-diyl) anellated to the C-sphere. Attachment of multiple thano moieties along an equatorial belt as in the series 8-11 induces only a small perturbation of the original fullerene π-chromophore. In general, with increasing attenuation of the conjugated fullerene π-chromophore, the optical (HOMO-LUMO) gap in the UV/VIS spectrum is shifted to higher energy, the number of reversible one-electron reductions decreases, and the first reduction potential becomes increasingly negative, the computed LUMO energy increases and the electron affinity decreases, and the reactivity of the fullerene towards nucleophiles and carbenes and as dienophile in cycloadditions decreases.
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    Variants of Solid-State and Solution Structures of (η3-Allyl)- {2-[2′-(diphenylphosphino)phenyl]-4,5-dihydrooxazole-P,N}palladium(II) hexafluorophosphates and tetraphenylborates (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 463-471 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crystal and solution structures of the enantiomerically pure and the racemic pairs of (η3-allyl) {2-[2′-(diphenylphosphino)phenyl]-4,5-dihydro-4-phenyloxazole}palladium(II) hexafluorophosphates (1, and rac-1, resp.) and tetraphenylborates (2, and rac-2, resp.) as well as (η3-allyl){2-[2′-(diphenylphosphino)phenyl]-4,5-dihydro-4-isopropyloxazole}palladium(II) tetraphenylborate (3) were characterized by X-ray crystallography and 1H-NMR spectroscopy. In the solid state, rac-1 and rac-2 proved to be disordered with both diastereoisomeric complexes in the crystal. The complexes 2 and 3 exist only in the ‘exo’ form. The X-ray structures show that the [PdII(η3-allyl)] moiety may adopt different configurations between a nearly symmetrical three-electron PdII(π3-allyl) system and an asymmetrical allyl group with a η1- and a η2-bonding to the metal center. The [PdII(η3-allyl)] system of rac-1 and of ‘endo’ rac-2 is closer to the former, and that of 2, ‘exo’-rac-2, and 3 closer to the later geometry. The 1H-NMR spectra of the hexafluorophosphates 1 and rac-1 show two sets of signals of the allylic protons in an ‘exo’/‘endo’ ratio of 2:3. The tetraphenylborates 2, rac-2, and 3 give only one set of broad signals of the allylic protons.
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    Oligosaccharide Analogues of Polysaccharides. Part 12Part 11: [1]. Synthesis of ‘acetyleno-saccharide’-derived cyclodextrin analoguesDedicated to Prof., Dr. Dieter Seebach on the occasion of his 60th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1027-1052 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ‘Acetyleno-oligosaccharides’ in which two terminal ethynyl substituents enclose an angle (significantly) below 180° are building blocks for the preparation of cyclodextrin analogues. This is illustrated by the preparation of a cyclotrimer and a cyclotetramer; the C3-symmetrical cyclotrimer 18 (Scheme 1) was synthesized in 13 steps (7.7%) and the C4-symmetrical cyclotetramer 51 (Scheme 3) in 14 steps (4.3%) from the known dialkyne 21. The solubilities of 18 and 51 in H2O were determined by gravimetry; a saturated solution is 130 mM in the trimer 18 and 12.8 mM in the tetramer 51. The dependence of the optical rotation of 18 and 51 in H2O on the concentration, and the concentration dependence of the 1H-NMR chemical shift of the signals of the 1CH groups of 51 (D2O) suggest that there is no significant self-association of 18 and 51.
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    Synthesis of Chiral Bicyclic Bis-lactam Components for the controlled self-assembly of hydrogen-bonded arrays (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 856-875 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral biyclic bis-lactams of structures 3 and 4 were synthesized from the key intermediate 2′b, the N,N′-bis(4-methoxybenzyl) derivative of 2 (X = MeO) (Scheme 6). The synthesis of this intermediate involved two key steps: (1) a double condensation of glyoxylic acid/anisamide (= oxoacetic acid/4-methoxybenzamide) adduct 11c with veratrole (1,2-dimethoxybenzene; 10) allowed the introduction of two glycine units at the 4,5-positions of the veratrole ring to give 18c (Schemes 3 and 4); (2) in order to circumvent the hydrolysis of 4-methoxybenzoyl protective groups which proved to be unfeasible, these groups were transformed into 4-methoxybenzyl groups through a sequence involving thiocarbonylation followed by reduction (Scheme 5). Thereafter, the double intramolecular cyclization of the resulting diamino diester 22c proceeded easily to afford 2′b. This intermediate may be transformed via the tetrol 2′g or the diol 2′h into the N-protected derivatives of 2 (X = OR) and of 3 (X = OCOR). Cleavage of the 4-alkuxybenzyl groups was achieved by ceric ammonium nitrate. However, when the aromatic ring bore ether functions (N-protected 2), this normal reaction was accompanied by the oxidative ring cleavage to give the diene-diester structure 4 (Schemes 5 and 6).
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    Metal Complexes with Macrocyclic Ligands. Part XLIVPart XLIII:[1] Kinetics of the Cu2+ incorporation into a macrocyclic ligand conjugated to proteins: Model studies for the d‘post-labeling’ technique (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 934-947 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the Cu2+ complexation by macrocycles 1 (4-[(l,4,8,11-tetraazacyclotetradec-1-yl)methyl]-benzoic acid) and 2 (N-propyl-4-[(1,4,8,11-tetraazacyclotetradec-1-yl)methyl]-benzamide) as well as by macrocycle 1 conjugated to bovine serum albumin (bsa) and to ribonuclease A (rnase) were studied by stopped flow techniques. For 1 and 2, the kinetics were followed in the mM range monitoring the d-d* absorption band of the Cu2+ complex. From the pH dependence of kobs, the rate law is v = [Cu2+] (kLH[LH] + kLH2[LH2]), where kLH and kLK2 are the bimolecular rate constants for Cu2+ with the diprotonated (LH2) and monoprotonated (LH1) form of the ligand, respectively. The values are kLH2 = 1.7(1) M-1s-1 and kLH = 2.3(1) 105 M-1s-1 for 1, and kLH2, = 0.28(9) M-1s-1 and kLH = 2.0(1) 105 M-1s-1 for 2. The kinetics of the Cu2+ incorporation into 1,2 and 1 conjugated to bsa and rnase, i.e., 3 and 4, respectively, were also followed using nitroso-R salt as a metal indicator in the μM range, i.e., under conditions typical for the ‘post-labeling’ technique to give radiolabeled monoclonal antibodies. In these cases, the reaction takes place between the 1:1 complex of Cu2+ with nitroso-R-salt and the macrocycle. At pH 6.5, the rates are very similar to each other indicating that the complexation properties of the macrocycle attached to a protein are not very different from those of the free ligand under comparable conditions.
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    Synthesis of Medium- and Large-Ring Compounds Initiated by Photochemical Decarboxylation of ω-PhthalimidoalkanoatesDedicated to Prof. Waldemar Adam and Prof. Dieter Seebach on the occasions of their 60th birthdays on July 26th and October 31st 1997, respectively (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 912-933 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a variety of hydroxylactams from ω-phthalimidoalkanoates using a triplet-sensitized photodecarboxylation reaction initiated by intramolecular photo electron transfer is described. Ring sizes available by this method span from 4 (benzazepine-1,5-dione 7) to 26 (cyclodipeptide 26e). Ground-state template formation is proposed as the explanation for the high efficiency of this reaction and for the decrease in reactivity in the presence of organic bases instead of metal carbonates. The crucial step in this macrocyclization reaction seems to be the protonation of the intermediary ketyl radials (Scheme 4). Spacer groups investigated were alkyl chains (C3-C11: 5c-h, 11a, 12), ether (16, 18), ester (20, 22), and amide (26a-f) linkages. Within the detection limits, no dimeric (= decarboxylative coupling) products were observed, indicating the high preference for intra-vs. intermolecular photoelectron transfer. The C,C radical combination step proceeds with low stereoselectivity (cf, products 11 and 12) in contrast to comparable singlet reactions. Except for the lactones 22, all products were stable under the photolysis conditions. Prolonged irradiation of 22 led to the formation of the spiro compounds 23, probably via an intermediary acyliminium betaine (Scheme 8). One serious limitation of the decarboxylative macrocyclization is its incompatibility with the glycine spacer (as in 27a and 27b), probably the consequence of a strong intramolecular H-bond (Scheme 10).
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    Mitteilungen (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 988-988 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800330
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    Synthesis of a Novel Tricyclic Dipeptide Template and Its Incorporation into a Cyclic Peptide Mimetic Containing an NPNA Motif (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1513-1527 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel tricyclic dipeptide template, formally derived by coupling (2S,4S)-4-aminoproline (Pro(NH2)) and (S)-2-(carboxymethyl)proline (Pro(CH2COOH)) as a diketopiperazine, has been synthesized in a form suitable for solid-phase peptide synthesis using Fmoc chemistry. This template was incorporated into the cyclic molecule cyclo(-Ala1-Asn2-Pro3-Asn4-Ala5-Ala6-Temp-) (Temp = template), whose conformation in H2O was studied by NMR methods. Average solution structures derived by restrained simulated annealing point to a highly populated βI-turn within the Asn-Pro-Asn-Ala motif and also indicate which conformations are likely to be preferred by the template.
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    URL: http://dx.doi.org/10.1002/hlca.19970800514
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    Aza-Claisen Rearrangement: Synthesis of 5′-branched 5′-aminothymidinesDedicated with best personal wishes of D. B. to Professor Oskar Jeger on the occasion of his 80th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1589-1606 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of both diastereoisomers of 5′-ethyl-substituted thymidine dimers, the (5′R)- and (5′S)-configurated 33a and 33b respectively, in which the natural phosphodiester linkage is replaced by an amide group (C(3′)-CH2CONH-CH(5′)(Et)), arc described. Their fully protected derivatives 35a and 35b, respectively, are suitable for incorporation into antisense oligonucleotides. Unexpectedly, an attempted PdII-catalysed aza-Claisen rearrangement of trichloroacetimidate 7 provided the diastereoisomerically pure cyclopropane derivative 17, whose structure was confirmed by X-ray analysis.
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  • 46
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    Neue Wege zu Pentalen-Vorstufen17. Mitteilung über Kupplungsreaktionen 16. Mitteilung (Kurzmitteilung): [1] (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1627-1638 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New Pathways to Precursors of PentalenePentalene dimers 2 and 3 are easily available in moderate yields by CuCl2-induced oxidative coupling of dilithium-pentalenediide (5) (Scheme 1). On the other hand, NBS bromination of 1,5-dihydropentalene (4) or of 1,2-dihydropentalene (8) gives unstable 1-bromo-1,2-dihydropentalene (9), while subsequent in-situ elimination with Et3N exclusively gives syn-cis-pentalene dimer 2 in moderate yields (Scheme 3). NMR-Spectroscopic evidence for compounds 2, 3, and 9 is presented, and mechanistic alternatives for the formation of pentalene dimers 2 and 3 are discussed.
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    Masthead (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800601
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    Iridoid Glucosides with Free Radical Scavenging Properties from Fagraea blumei (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1144-1152 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four new iridoid glucosides 1-4, named blumeosides A-D, were isolated from the methanolic stem-bark extract of Fagraea blumei G. DON. (Loganiaceae). They were accompanied by the benzyl-alcohol derivative di-O-methylcrenatin (5) and the flavone C-glucoside swertisin (6). The structures of 1-4 were established by spectroscopic methods, including FAB-MS, and 1H- and 13C-NMR, and by alkaline hydrolysis. Blumeosides A (1) and C (3) are 10-O-(2,5-dihydroxytercphthalo) adoxosidic acid and 10-O-(2-hydroxyterephthalo)adoxosidic acid, respectively. In blumeosides B (4) and D (2), both carboxylic groups of the terephthalic-acid moiety are esterified by adoxosidic-acid units, Blumeosides A-D (1-4) inhibited bleaching of crocin induced by alkoxyl radicals. Blumeosides A (1) and D (2) also demonstrated scavenging properties towards the 2,2-diphenyl-1-picryl-hvdrazvl (CDPPH) radical in TLC autographic and spectrophotometric assays.
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    Reformulating the Kinetic Approach of Column Chromatography for a Single Component (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1176-1182 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetic model of column chromatography is revisited to explicitly show that this approach yields, when neglecting axial dispersion, a rather simple analytical expression depending only on two dimensionless parameters, namely a dimensionless kinetic retention parameter and a dimensionless time parameter. An expression for the time corresponding to the maximum of the peak is also proposed.
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    URL: http://dx.doi.org/10.1002/hlca.19970800415
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    Synthesis of Unnatural Lipohilic N-(9H-Fluoren-9-ylmethoxy)carbonyl-Substituted α-Amino Acids and Their Incorporation into Cyclic RGD-Peptides: A structure-activity studyDedicated to Peter Welzel on the occasion of his 60th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1280-1300 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The αv/β3 integrin is implicated in human tumor metastasis and angiogenesis. It has been shown that structures of the sequence cyclo(-Arg1-Gly2-Asp3-D-Phe4-Xaa5-) (I) and cyclo(-Arg1-Gly2-Asp3-Phe4-D-Xaa5-) (II) bind with high affinity and the latter with high selectivity to this receptor. The residues Xaa and D-Xaa accept a broad variety of amino acids. Here, we report on the synthesis, activities, and conformational analysis of cyclic Arg-Gly-Asp (RGD) peptides containing liophilic amino acids Xaa or D-Xaa in position 5. For I, these were (2S)-2-aminohexadecanoic acid (Ahd) and N′-hexadecylglycine (Hd-Gly) and in II, D-Ahd and Hd-Gly, and, for control purposes, Ahd were incorporated (Fig. 1). The enantiomerically pure a-amino acids were obtained by non-enantioselective synthesis and subsequent enzymatic separation of isomers using acylase I (Scheme). Hd-Gly was prepared in a modified procedure according to Stewart from ethyl bromoacetate and hexadecylamine (Scheme). The synthesis and physicochemical properties of the corresponding (9H-fluoren-9-ylmethoxy)carbonyl (Fmoc) derivatives, compatible with solid-phase peptide synthesis, are described. Structure elucidation by NMR reveals that the lipid modification has no significant impact on the template structures when incorporated into them. For peptides I with Xaa = Ahd or Hd-Gly (1 or 2), a βII′/γ-turn-like arrangement with D-Phe in i+1 position of the β-turn is found. Peptides II with D-Xaa = D-Ahd or Hd-Gly (3 or 4) exhibit a βII′/γ-turn conformation with Gly in i+1 position of the β-turn, whereas II with Ahd instead of D-Xaa, i.e., lacking a D-amino acid in position 4 or 5 (5). adopts no defined conformation. However, in assays of receptor specificity employing human αvv/β3 integrin, the compounds exhibit IC50 values ranging from nanomolar to less than millimolar. These results indicate that although the arrangement of the pharmacophoric groups is preserved in the target compounds, the biological activity is highly dependent on spatial requirements of the lipid anchor in the receptor binding pocket. Obviously, only certain positions do not affect the binding.
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    URL: http://dx.doi.org/10.1002/hlca.19970800423
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    Cyclic Heptapeptides Axinastatin 2, 3, and 4: Conformational analysis and evaluation of the biological potentialDedicated to Ernst Bayer on the occasion of his 70th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1338-1354 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational analysis of naturally occurring cytostatic cyclic heptapeptides axinastatin 2, 3, and 4 was carried out by two-dimensional NMR spectroscopy in combination with distance-geometry (DG) and molecular-dynamics (MD) calculations in explicit solvents. The synthesized secondary metabolites were examined in (D6)DMSO. Axinastatin 2 was also investigated in CD3OH. In all structures, Pro2 is in the i + 1 position of a βI turn and Pro6 occupies the i + 2 position of a βVIa turn about the cis amide bond between residue 5 and Pro6. In all peptides, a bifurcated H-bond occurs between residue 4 CO and the amide protons of residue 1 and 7. For axinastatin 2 and 3, an Asn Ig turn was found about Asn1 and Pro2. We compared these structures with conformations of cyclic heptapeptides obtained by X-ray and NMR studies. A β-bulge motif with two β turns and one bifurcated H-bond is found as the dominating backbone conformation of cyclic all-L-heptapeptides. Axinastatin 2, 3, and 4 can be characterized by six trans and one cis amide bond resulting in a β/βVI(a)-turn motif, a conformation found for many cyclic heptapeptides. Detailed biological tests of the synthetic compounds in different human cancer cell lines indicates these axinastatins to be inactive or of low activity.
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    URL: http://dx.doi.org/10.1002/hlca.19970800503
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    Synthesis via a Carbohydrate-Derived Münchnone of Pyrrolopyridines (Indolizines) and imidazopyridines, and their evaluation as inhibitors of β-D-glucosidasesDedicated to Oscar Jeger on the occasion of his 80th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1443-1456 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the presence of activating agents, the N-acylglycine 8 reacts with electrophilic alkynes via the münchnone9 to the pyrrolopyridines (= indolizines) 10, 18, and 19 (Scheme 1 ), Depending on the nature of the activating agent and the reaction temperature, the formation of the pyrroles was accompanied by partial epimerization to the manna-configurated epimers 16 and 17. The gluco-configurated pyrrolopyridine 10 was deprotected to 12. Silylation of 12, followed by reduction and desilylation, gave the hexol 15. Cycloaddition of 9 to 4-toluenesulfonyl cyanide yielded 53% of the imidazole 23, while cycloaddition to phenyl cyanate gave the phenoxyimidazole 28 in low yields only (Scheme 2). As expected, the deprotected pyrroles 12, 15, 20, and 21 are weak inhibitors of retaining β-glucosidases, while the deprotected imidazole 24 derived from 23 proved a good inhibitor of sweet-almond β-glucosidases and a powerful inhibitor of Caldocellum saccharolyticum β-glucosidase.
    Additional Material: 3 Ill.
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    Introduction of Amino Alcohols in the Ring-Opening Reaction of 3-bromo-2,5-dimethylthiophene 1,1-dioxide. A short diastereoselective synthesis of substituted ‘tetrahydrobenzo[a]pyrrolizidines’ (= octahydro-1H-pyrrolo[2,1-a]isoindoles) using L-prolinolDedicated to Prof. Dr. h. c. Dieter Seebach on the occasion of his 60th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1483-1493 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetrahydrobenzo[a]pyrrolizidines (= octahydro-1H-pyrrolo[2,1-a]isoindoles) and tetrahydrobenzo[a]indo-lizidines, (= decahydropyrido[2,1-a]isoindoles) were prepared stereoselectively in four steps through an amineinduced ring-opening of 3-bromo-2,5-dimethylthiophene 1,1-dioxide (1) with L-prolinol (9), piperidine-2-methanol (10), and piperidine-2-ethanol (11), yielding the dienes (2S)-1-[(2E,4Z)-4-bromohexa-2,4-dienyl]pyrrolidine-2-methanol (12), 1-[(2E,4Z)-4-bromohexa-2,4-dienyl]piperidine-2-methanol (13), and 1-[(2E,4Z)-4-bromo-hexa-2,4-dienyl]piperidine-2-ethanol (14; Scheme2), which, after conversion into their α,β-unsaturated esters, cyclized in a TiCl4-catalyzed intramolecular Diets-Alder reaction (Scheme3). A discussion on the mechanism of the ring opening reaction including semiempirical and ab initio calculations is also presented.
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    X-Ray Structure Analyses of Alkyl-Substituted N-Acryloyl- and N-CrotonoyltoluenesultamsDerived from saccharine (= 1,2-benzoisothiazol-3(2H)-one, 1,1-dioxide)Dedicated to the memory of Professor Wolfgang Oppolzer (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1607-1612 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray crystal-structure analyses of two N-enoyl-toluenesultam derivatives 1 are reported. The structural differences with their bornanesultam analogues 2 as well as stereochemical aspects with respect to their [4 + 2] and [3 + 2] cycloadditions are discussed.
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  • 55
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    Boophiline, an Antimicrobial Sterol Amide from the cattle tick boophilus microplus (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2066-2072 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Boophiline (1), a new sterol amide was isolated from the cattle tick Boophilus microplus (Ixodidae). The structure was assigned as N-[3-(sulfooxy)-25ξcholest-5-en-26-oyl]-L-isoleucine by detailed 2D NMR investigations in conjunction with FAB mass spectrometry and acidic hydrolyses. Complete assignment of the diastereotopic methylene protons of the ring system could be deduced from the NMR data. In agar dilution assays, 1 exhibited antifungal properties against Cladosporium cucumerinum and antibacterial activity against Bacillus subtilis and Escherichia coli.
    Additional Material: 2 Tab.
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    Comparative Study of the Cope rearrangement of hexa-1,5-diene and barbaralane (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2112-2123 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The classical rules for Cope rearrangements predict a transition state with chair form to be favored over the boat form. On the other hand, bridged homotropylidenes, which allow only a boat-form transition state by steric reasons, have extremely low barriers. A controversy about the correct pathway and the different possible intermediates and transition states of the reaction has gone on for years. In this work, the hypersurfaces of barbaralane, in comparison with the boat- and chair-form of hexa-1,5-diene, are computed by the ab inito CASSCF (6,6)/6-31G** method starting with UMP2/6-31G** natural orbitals (NO's). All three hypersurfaces show characteristic features, and, moreover differ from each other. A hitherto undiscussed intermediate, bicyclo[2.2.0]hexane, was localized on the boat-hexa-1,5-diene pathway. So it is noteworthy that our transition state for the boat-hexa-1,5-diene does not correspond to the transition states found by other authors for this conformation. The computed enthalpies of activation of boat- and chair-hexa-1,5-diene, and barbaralane are in good agreement with the experimental data.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800711
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  • 57
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    Novel Leptomycins from a Streptomyces strain A92-308902: Inhibitors of the Nucleo-cytoplasmic translocation of the HIV-1 regulatory protein Rev (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2157-2167 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As one of the regulatory gene products in the HIV-1 genome, Rev protein must be translocated from the nucleus to the cytoplasm to exert its function. Therefore, inhibition of Rev protein translocation could be a useful target for HIV therapy. An extract from the Streptomyces strain A92-308902 with very potent inhibitory activity was found in the course of a high throughput screening with a Rev translocation assay (RTA). Bioassay-guided fractionation with gel filtration, normal-phase and reversed-phase chromatography yielded six RTA-active metabolites belonging to the leptomycin family, the known leptomycin A (1), leptomycin B (2), kazusamycin B (3), and kazusamycin A (4). and the hitherto unknown dilactonmycin (5) and delactonmycin (6), together with an inactive cyclic hexadepsipeptide L-156,620 (7). The structures were established mainly by spectroscopic methods (UV, FT-IR, FAB-MS, 1H-NMR, 13C-NMR(JMOD), DQ-COSY, ROESY, HSQC, and HMBC). The configuration of all C=C bonds of 1-6 was unambiguously established by analysis of coupling constants and ROESY spectra. All isolated leptomycins 1-6 inhibit Rev translocation at nanomolar concentrations. Six derivatives (2a-c and 4a-c) of leptomycin B (2) and kazusamycin A (4) were also prepared and tested in the RTA for preliminary investigations on structure-activity relationships.
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    URL: http://dx.doi.org/10.1002/hlca.19970800715
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    The Enantioselective Copolymerisation of allylbenzene, 1-allyl-4-(trifluoromethyl)benzene, and 1-allyl-4-methoxybenzene with carbon monoxide (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2204-2214 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The olefins mentioned in the title were copolymerized with CO in the presence of palladium catalysts modified with dicyclohexyl{(R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}phosphine. Productivities up to 95 g/(gPd · h) were achieved. The obtained copolymers were recovered in the pure, regio- und stereoregular polyketone structures3. The isotactic poly[2-benzyl-1-oxopropane-1,3-diyl] (3a) and its analogues 3b, c were found to isomerize to the corresponding spirocyclic poly[3-(arylmethyl)tetrahydrofuran-2,2-5,5-tetrayl-2-oxy-2-methylene]s 4 in a suspension in CHC13, thus indicating that the spiroketal structure is thermodynamically the most stable for these copolymers. However, the atactic material did not undergo any structural transformation. These results show that regularity at the centers of chirality in the main chain is a prerequisite for the conversion of the polyketone to the spiroketal structure.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800719
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    Methyl and Phenylmethyl 2-Acetyl-3-{[2-(dimethylamino)-1-(methoxycarbonyl)ethenyl]amino}prop-2-enoate in the Synthesis of heterocyclic systems: Preparation of 3-amino-4H-pyrido-[1,2-a]pyrimidin-4-ones (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2418-2425 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methyl 2-acetyl-3-{[2-(dimethylamino)-1-(methoxycarbonyl)ethenyl]amino}prop-2-enoate (4) and phenyl-methyl 2-acetyl-3-{[2-(dimethylamino)-1(methoxycarbonyl)ethenyl]amino}prop-2-enoate (5) were prepared in three steps from the corresponding acetoacetic esters, and used as reagents for the preparation of N3-protected 3-amino-4H-pyrido[1,2-a]pyrimidin-4-ones 10-12, 5H-thiazolo[3,2-a]pyrimidin-5-one 13, 4H-pyrido[1,2-a]-pyridin-4-one 19 and 2H-1-benzopyran-2-ones 20-23. Free 3-amino-4H-pyrido[1,2-a]pyrimidin-4-ones 24-26 were prepared from 10-12 by removal of the 2-(methoxycarbonyl)-3-oxobut-1-enyl or 3-oxo-2-[(phenyl-methoxy)carbonyl]but-1-envl as N-protecting group by various methods.
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    URL: http://dx.doi.org/10.1002/hlca.19970800811
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    New Cyclophanes as Initiator Cores for the Construction of Dendritic Receptors: Host-guest complexation in aqueous solutions and structures of solid-state inclusion compounds (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2368-2390 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclophanes 3 and 4 were prepared as initiator cores for the construction of dendrophanes (dendritic cydophanes) 1 and 2, respectively, which mimic recognition sites buried in globular proteins. The tetra-oxy[6.1.6.1]paracyclophane 3 was prepared by a short three-step route (Scheme 1) and possesses a cavity binding site shaped by two diphenylmethane units suitable for the inclusion of flat aromatic substrates such as benzene and naphthalene derivatives as was shown by 1H-NMR binding titrations in basic D2O phosphate buffer (Table 1). The larger cyclophane 4, shaped by two wider naphthyl(phenyl)methane spacers, was prepared in a longer, ten-step synthesis (Scheme 2) which included as a key intermediate the tetrabromocyclophane 5. 1H-NMR Binding studies in basic borate buffer in D2O/CD3OD demonstrated that 4 is an efficient steroid receptor. In a series of steroids (Table 1), complexation strength decreased with increasing substrate polarity and increasing number of polar substituents; in addition, electrostatic repulsion between carboxylate residues of host and guest also affected the binding affinity strongly. The conformationally flexible tetrabromocyclophane 5 displayed a pronounced tendency to form solid-state inclusion compounds of defined stoichiometry, which were analyzed by X-ray crystallography (Fig. 2). 1,2-Dichloroethane formed a cavity inclusion complex 5a with 1:1 stoichiometry, while in the 1:3 inclusion compound 5b with benzene, one guest is fully buried in the macrocyclic cavity and two others are positioned in channels between the Cyclophanes in the crystal lattice. In the 1:2 inclusion compound 5c, two toluene molecules penetrate with their aromatic rings the macrocyclic cavity from opposite sides in an antiparallel fashion. On the other hand, p-xylene (= 1,4-dimethylbenzene) in the 1:1 compound 5d is sandwiched between the cyclophane molecules with its two Me groups penetrating the cavities of the two macrocycles. In the 1:2 inclusion compound 5e with tetralin (= 1,2,3,4-tetrahydronaphthalene), both host and guest are statically disordered. The shape of the macrocycle in 5a-e depends strongly on the nature of the guest (Fig. 4). Characteristic for these compounds is the pronounced tendency of 5 to undergo regular stacking and to form channels for guest inclusion; these channels can infinitely extend across the macrocyclic cavities (Fig. 6) or in the crystal lattice between neighboring cyclophane stacks (Fig. 5). Also, the crystal lattice of 5c displays a remarkable zig-zag pattern of short Br…O contacts between neighboring macrocycles (Fig. 7).
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    Use of the Wolff Rearrangement of Diazo Ketones from Amino Acids as a synthetic method for the formation of oligonucleo-peptides: A novel approach to chimeric biomolecules (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1-13 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photolysis and Ag-benzoate-catalyzed decomposition of the diazo ketones 2 and 4 derived from Z-Ala-OH and Z-Ala-Ala-OH in the presence of oligonucleotide derivatives bearing at the 5′-terminus an NH2 instead of the OH group, or an aminohexyl phosphate group lead to Z-protected 3-aminobutanoyl and to Z-Ala-β-HAla derivatives, respectively (conjugates 12, 13, and 17-23, Schemes 3-5), In solution, this amide-forming acylation reaction could be realized only with oligomers containing up to 8 unprotected nucleotide building blocks (Schemes 3 and 4). With the analogous polymer-bound and protected oligonucleotide derivatives as amino nucleophiles, excellent yields were obtained with all chain lengths tested (up to 15mer Scheme 5), The products were purified by reversed-phase HPLC and characterized by MALDI-TOF mass spectrometry (Figs. 2-4, Table 2) and by capillary gel electrophoresis (Fig.2).
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    URL: http://dx.doi.org/10.1002/hlca.19970800102
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    A Novel and Efficient Approach for the Combinatorial Synthesis of Structurally Diverse Pyrimidines on solid supportPresented in part at the ‘Random & Rational Conference’ in Princeton on September 16, 1996 (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 65-72 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe a versatile novel approach for the synthesis of 2, 4, 6-trisubstituted pyrimidines on solid support. Thus, polymer-boun J thiouronium salt 2 reacted in high yield in a cyclocondensation reaction with the acetylenic ketones 3 to form, after tert-butyl-ester cleavage, the polymer-bound carboxylic acids 4, which were cleaved by oxidation with 3-chloroperbenzoic acid and pyrrolidine to form the 2-pyrrolidinylpyrimidine-4-carboxylic acids 6a-c in high yields and purities without further purification (Scheme 1). Alternatively, acid 4a was subjected to an Ugi four-component condensation which gave the polymer-bound Ugi products 9a-e in good yields (Scheme 2). Multidirectional cleavage reaction of sulfone 8a with different nucleophiles resulted in the clean formation of pyrimidine-4-carboxamides 10-13 (Scheme 3). This strategy combines efficiently solid-phase chemistry with a multicomponent reaction and a multidirectional cleavage step to form highly diverse pyrimidines in a parallel array.
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    URL: http://dx.doi.org/10.1002/hlca.19970800106
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    6-Azabicyclo[3.1.0]hex-30-en-2-ol Derivative, photochemically generated building blocks for bicyclic β-lactamsDedicated to Fabian Gerson to commemorate a long-standing collaboration (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 121-127 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compounds 4 are obtained by photolysis of simple N-alkylpyridinium salts in H2O or alcohol. On reaction with [Fe2(CO)9] in THF, 4 gives bicyclic tricarbonyliron complexes 13a-d, which on oxidative decomplexation with ceric ammonium nitrate afford cis-fused cyclopenteno-β-lactams 15a-d.
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    Models for the Active Center of Pterin-Containing Molybdenum Enzymes: Crystal structure of a molybdenum complex with sulfur and pterin ligands (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 103-110 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first crystal structure of a molybdenum complex 9 with a hydrogenated pterin and a sulfur ligand contributes to the discussion about the active center of molybdenum and tungsten enzymes containing a molybdopterin cofactor. Complex 9 was synthesized through a redox reaction of [MoVIO2 (LN-S2)] (8; LN-S2 = pyridine-2, 6-bis(methanethiolato)) with 5, 6, 7, 8-tetrahydropterin (7). 2 HCl (H4Ptr.2 HCl). The complex crystallizes, with a non-coordinating Cl-atom acting as a counterion, in the monoclinic space group C2/c (No. 15) with cell dimensions a = 22.900(5), b = 10.716(2), c = 17.551(4) Å, β = 120.36(3)°, and Z = 8. We interpret 9 as [MoIVO(LN-S2)(H+-q-H2Ptr)]Cl (q = quinonoid; H2Ptr = dihydropterin), i.e., a MoIV monooxo center coordinated by a pyridine-2, 6-bis(methanethiolato) ligand and a protonated dihydropterin. The spectroscopic properties of this new complex are comparable to those of other crystalline molybdenum complexes of hydrogenated pterins without additional S-coordination. The slightly H2O-soluble complex 9 reacts with the natural enzyme substrate DMSO very slowly, possibly due to the lack of easily dissociable ligands at the metal center.
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    URL: http://dx.doi.org/10.1002/hlca.19970800110
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    Cyclo-β-peptides: Structure and tubular stacking of cyclic tetramers of 3-aminobutanoic acid as determined from powder diffraction dataDedicated to Professor Hans Paulsen on the occasion of his 75th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 173-182 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solid-state structures of three stereoisomer, 1-3, of the cyclic tetramer of 3-aminobutanoic acid are presented. These cyclo-β-peptides were found to be highly insoluble materials, and it proved to be impossible to grow crystals of sufficient quality for X-ray single-crystal analysis. The samples of 1-3 were, however, suitable candidates for structure determination from powder diffraction data (Fig. 1), and the application of this method is described. All three isomers have been found to adopt tubular structures (Figs. 2-4) in a fashion similar to those already observed for certain cyclo-α-peptides. The stacks of 16-membered rings are held together by four nonlinear C=O…H—N H-bonds between pairs of molecules (Fig.5).
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    URL: http://dx.doi.org/10.1002/hlca.19970800116
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    Partial Synthesis and Characterization of the Mono-and Diepoxides of β-Cryptoxanthin (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 221-229 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-Cryptoxanthin (1) was acetylated and then epoxidized with monoperoxyphthalic acid. After hydrolysis, repeated chromatography, and crystallization, (3S,5R,6S)-5,6-epoxy-β-cryptoxanthin (3), (3S,5S,6R)-5,6-epoxy-β-cryptoxanthin (4), (3R,5′R,6′R)-5′,6′-epoxy-β-cryptoxanthin (5), (3S,5R,6S,5′R,6′S)-5,6:5′,6′-diepoxy-β-cryp-toxanthin (6), and (3S,5S,6R,5′S,6′R)-5,6:5′,6′-diepoxy-β-cryptoxanthin (7) were isolated as main products and characterized by their UV/VIS, CD, 1H- and 13C-NMR, and mass spectra. The comparison of the carotenoid isolated from yellow, tomato-shaped paprika (Capsicum annuum var. lycopersiciforme flavum) with 3-5 strongly supports the structure of 3 for the natural product.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800120
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  • 67
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    Metal Complexes with Macrocyclic Ligands. Part XLIIIPart XLII [1]. Tetraazamacrocyclic nickel(II) and copper(II) complexes with aliphatic methylthio- and methoxy-substituted pendant chains (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 241-252 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 14-membered tetraazamacrocyclic Ni2+ and Cu2+ complexes of 4 (1, 4, 8-trimethyl-11-[(2-methylthio)ethyl]-1, 4, 8, 11-tetraazacyclotetradecane), 5. (1, 4-dimethyl-8, 11-bis[2-(methylthio)ethyl]-l, 4, 8, 11-tetraazacyclotetradecane), and 7 (1, 4, 8, ll-tetrakis[2-(methylthio)ethyl]-1, 4, 8, 11-tetraazacyclotetradecane), with pne, two, and four methylthio-substituted pendant chains, respectively, and the Ni2+ complex of 6 (1, 4-dimethyl-8, 11-bis (2-methoxyethyl)-1, 4, 8, 11-tetraazacyclotetradecane), with two methoxy-substituted pendant chains, were synthesized and their chemistry studied with regard to modelling F430. Solution spectra in H2O, MeCN, and DMF indicate participation of the side chain in metal coordination when the donor group is a thioether, whereas no coordination with the metal ion is observed with the ether group. Similarly the X-ray structures of the thioether-containing compounds [Ni(5)](ClO4)2, [Cu(5)](ClO4)2, and [Cu(7)](ClO4)2 show a coordination number of 5, whereas that of [Ni(6)](ClO4)2 with ether pendant chains, shows a coordination number of 4. Cyclic voltammetry of these complexes in MeCN reveals that Ni2+ is reversibly reduced to Ni+ between -0.64 and -0.77 V vs. SCE, the potential being influenced by the nature and number of the pendant chains. At more negative potentials, the thioether is cleaved, whereby a thiol is formed; the thiol is then oxidized at ca. + 0.8 V vs. SCE, when a glassy carbon electrode is used, or at ca. 0 V vs. SCE at a dropping Hg electrode. No cleavage of the ether bond in [Ni(6)](ClO4)2 is observed under similar conditions.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800122
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  • 68
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    Electronic Resource
    Masthead (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800201
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  • 69
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    Synthesis of Indole Derivatives by [2 + 2] Photocycloaddition of Indoline-2-thiones with alkenes and photodesulfurization of indoline-2-thiones (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 388-397 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photochemical synthesis of indole derivatives starting from the indoline-2-thiones 1 is described. Irradiation of indoline-2-thiones 1 in the presence of alkenes 3 gave 2-alkyl-3H-indoles 4-7 or 2-alkylindoles 8-22 through the ring cleavage of the intermediates, spirocyclic amino-thietanes, initially derived by [2 + 2] cycloaddition of the C=S bond of 1 and the C=C bond of 3. Irradiation of 1 in the presence of trialkylamines 26 gave desulfurization products 27-32 and unexpected 3-alkylindoles 33-40. N-Acylindoline-2-thiones 11-p yielded the deacylated products, indoline-2-thiones 1a-b, and ethyl esters 43 through γ-H abstraction by the excited thioamide S-atom when irradiated in CDC13/EtOH or benzene/EtOH. Oxygen analogues 2a-d also underwent intramolecular H abstraction to give the indolin-2-ones 2e-f and ethyl esters 43 in a similar way.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19970800205
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  • 70
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    Isolation, Structure, and Biological Activities of Long-Chain Catechols of Plectranthus sylvestris (Labiatae) (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 436-448 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Antioxidant activity guided fractionation of extracts of the aerial parts of the title plant and HPLC separation yielded a series of oxygenated long-chain alkylcatechols. Their structures were inferred by spectroscopic methods and chemical transformations to be the novel 4-[(2S,4R,6S)-4-(acetyloxy)tetrahydro-6-pentyl-2H-pyran-2-yl]benzene-1,2diol (1a), 4-[(2S,4R6S)-tetrahydro-4-hydroxy-6-pentyl-2H-pyran-2-yl]benzene-1,2-diol (1b), 4-[(3S,5S)-5-(acetyloxy)-3-hydroxydecyl]benzene-1,2-diol (2a), 4-[(3S,5S)3-(acetyloxy)-5-hydroxydecyl]benzene-1,2-diol (2b), (3S,13Z)-1-(3,4-dihydroxyphenyl)-3-hydroxydocos-13-en-5-one (3a), (Z)-1-(3,4-dihydroxyphenyl)docos-13-en-5-one (4), besides the known l-(3,4-dihydroxyphenyl)icosan-5-one (5). The absolute configurations of the optically active compounds which are structurally related to the [n]-gingerols (6) and -diols (7) were established by the high-field 1H-NMR application of Mosher's method. All compounds are in vitro potent antioxidants, inhibiting the Fe2+-catalysed autoxidation of linoleic acid in the same order of magnitude as the commercial antioxidant 2,6-di(tert-butyl)-4-methylphenol (BHT). The dose-dependent inhibitory effects on soybean-lipoxygenase are in the μmol range, that of the most effective compound (3a) in the nmol range, hence being significantly more potent than the Known anti-inflammatory and analgesic drugs indomethacin and nordihydroguaiaretic acid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800209
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  • 71
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    Synthesis and Structure of a Macrocyclic Europium Complex and its possible role as a catalyst for phosphodiester transesterification (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 487-494 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and X-ray crystal structure of a europium macrocyctic complex 1, an important catalyst used for the sequence-specific cleavage of RNA, is reported. The role of this metal complex in facilitating phosphate transesterification is discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800213
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  • 72
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    A Novel Approach towards 2,3,5-Trisubstituted Thiophenes via tandem Michael addition/intramolecular Knoevenagel condensation (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 531-537 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from the easily available, highly functionalized acetylenic ketories 4a-i (Scheme 1), novel 2,3,5-trisubstituted thiophenes 1a-i (Scheme 2) were synthesized in good yields using a tandem Michael-addition/intramolecular Knoevenagel-condensation strategy, featuring Cs2CO3/MgSO4 (1:2) as an efficient base to effect the cyclization. Subsequent simple one-step transformations yielded 2,3-disubstituted thiophene-5-carbaidehydes 7a-c, carboxylic-acid derivatives 8, 9, and 11, and alcohol 10 (Scheme 3). These molecules constitute interesting novel thiophene-containing building blocks, useful for the preparation of low-molecular-weight compound libraries by combinatorial and parallel-chemistry techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800217
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  • 73
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    Synthesis, Characterization, and Crystal Structure of Complexes of Lanthanide Picrates with N,N,N′,N′-tetraphenyl-3,6-dioxaoctanediamide (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 586-592 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lanthanide picrate complexes with the ligand N,N,N′,N′-tetraphenyl-3,6-dioxaactanediamide (tdd): [Ln(Pic)3(tdd)] (Ln = La, Nd, Eu, Tb, Er) have been prepared in a nonaqueous medium and characterized by elemental analysis, conductivity measurements, IR, and 1H-NMR spectra. The crystal structures of the complexes for Ln = Nd and Er were determined. The early lanthanide, NdIII, crystallizes as the nona-coordinate complex [Nd(Pic)3(tdd)]. 2 CH3CN in the monoclinic space group P21n with a = 11.384(2), b = 18.805(4), c = 27.526(5) Å, β = 99.41(1)°, V = 5832(2) Å3, and Dc = 1.58 gcm-3 for Z = 4. The structure was refined to R = 0.0505, based on 4772 observed Deflections. The late lanthanide, ErIII, forms an octa-coordinate complex [Er(Pic)3(tdd)]; crystals are triclinic, P1, with a = 12.449(2), b = 17.065(2), c = 26.243(4) Å, α = 72.12(1), β = 87.86(1), γ = 84.60(1)°, V = 5282(1) Å3, and Dc = 1.68 g cm-3 for Z, = 4. The structure was refined to R = 0.0469, based on 10666 observed reflections, The results reveal that tdd forms a ring-like structure with its four O-atoms, coordinating to the metal ions as multidentate ligand, together with one O-atom of the bidentate picrate. The structure of the complexes is greatly affected by the ionic radius due to participation of the picrates in coordination.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800221
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  • 74
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    Mitteilungen (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 622-622 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800225
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  • 75
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    Palladium-Catalysed Intramolecular Cyclisations of Olefinic Propargylic Carbonates and application to the diastereoselective synthesis of enantiomerically pure (-)-α-thujone (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 623-639 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intramolecular [Pd2(dba)3]/tri(2-furyl)phosphine-catalysed (dba = dibenzylideneacetone, PhCH=CHCOCH=CHPh) cyclisations of olefinic propargylic carbonates I provided alk-1-enyl-(3-aza)bicyclo[3.1.0]-hexanes VIII in good yields. A palladium cascade sequence I → II → III → IV → VII → VIII is proposed. Furthermore, chiral propargylic carbonates such as 23, 24 and 25 allowed diastereoselective formation of bicyclo[3.1.0]hexanes 29, 30 and 31, respectively. The first diastereoselective synthesis of the monoterpene, (-)-α-thujone 40 illustrates the potential of the method.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800302
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  • 76
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    Rogioldiol A, a new obtusane diterpene, and rogiolal, a degraded derivative, of the red seaweed Laurencia microcladia from II rogiolo along the coast of tuscany: A Synergism in Structural Elucidation (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 684-694 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of rogioldiol A ((-)-1), isolated from the red seaweed Laurencia microcladia, was determined. Employing the exciton-coupling technique for rogioldiol A p-bromobenzoate (2), the absolute configuration at C(9) of (-)-1 was assigned, and, together with extensive NMR experiments, the absolute configuration at C(10) and preferred conformations of (-)-1 were determined. The absolute configuration of the hetero-substituted cyclohexane ring was deduced in analogy from the X-ray structure of 4, a derivative of the aldehyde 3, which was isolated from the same seaweed and is believed to be a degradation product of (-)-1.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800306
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  • 77
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    Synthesis and Photochromic Behaviour of Naphthopyrans, Pyranoquinolines, Pyranoquinazolines and Pyranoquinoxalines (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 725-738 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New chromenes annulated with different six-membered azaheterocycles were prepared, i.e., the 3H-pyra-no[3,2-f]quinolines 9/10 and 14, the 8H-pyrano[2,3-h]isoquinoline 11, the 8H-pyrano[3,2-f]quinazolme 12, the 8-H-pyrano[3,2-f]quinoxaline 13, and the 2H-pyrano[2,3-f]isoquinoline 15. The synthesis was achieved using conveniently substituted α,β-unsaturated aldehydes and organotitanium intermediates arising from azaheterocyclic phenols. Their photochromic behaviour (photocolouration yield, UV/VIS spectrum of photomerocyanines, rate constant of thermal bleaching) were studied besides those of corresponding naphthopyrans. The heterocycle effect and the role of substituents in the pyran moiety were investigated quantitatively through the study of the photochromic properties and the solvent effects. Diaryl-substituted azino-fused chromenes, especially isoquinoline derivatives, exhibit increased colourabilities and bathochromically shifted spectra for photomerocyanines which open up new prospects for photochromic applications.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800310
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  • 78
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    Selective N3- and 5′-O-Alkylation of 2′,3′-O-isopropylideneuridine with methyl iodide (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 851-855 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2′,3′-O-isopropylideneuridine (1) reacts with MeI in the presence of an excess of NaH in THF giving 2′,3′-O-isopropylidene-5′-O-methyluridine (2). Prolonged reaction time gives rise to 2′,3′-O-isopropylidene-3,5′-O-dimethyluridine (4). The use of an equimolar amount of base and alkylating agent results predominantly in methylation at N(3) (→ 3).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800319
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  • 79
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    A Short Synthesis of the Factor-Xa Inhibitor DX-9065a using palladium-catalyzed key stepsPart of the Ph. D. Thesis of C. Kehr, University of Heidelberg, 1996Dedicated to Professor Dr. Rolf Gleiter, Heidelberg, on the occasion of his 60th birthday with best wishes (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 892-896 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe a new, efficient synthesis of DX-9065a (4), a potent inhibitor of the blood coagulation enzyme factor Xa (fXa) which has previously been prepared in more than 20 steps. We saved approximately 10 steps starting with a Pd-catalyzed cyanation of the triflate 10 of 7-methoxynaphthalen-2-ol (9). After cleavage of the MeO group with boron tribromide, the triflate 6 was coupled to acrylate 5 in a Heck reaction (→3). The subsequent transformations led to DX-9065 a.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800322
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  • 80
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    Metal Complexes with Macrocyclic Ligands. PartXLVPart XLIV: [1] Axial coordination tendency in reinforced tetraazamacrocyclic complexes (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 948-959 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Cu2+ and Ni2+ complexes of three reinforced tetraazamacrocycles, containing a piperazine subunit and one or two alkyl substituents at the other two N-atoms have been prepared and their structural properties studied. In solution, the Ni2+ complexes are square-planar and show no tendency to axially coordinate a solvent molecule or an N3- ion. In contrast, the Cu2+ complexes change their geometry depending upon the donor properties of the solvent, being square-planar in MeNO2 and pentacoordinate in DMF. They also easily react in aqueous solution with N3- to give ternary species with pentacoordinate geometry, the stabilities of which have been determined. In the solid state, the X-ray crystal structures of three Cu2+ complexes also show both geometrical arrangements, two having a square-planar, the other one a distorted square pyramidal geometry. The difference behavior of Ni2+ and Cu2+ stems from the fact that the structural change from square-planar to square-pyramidal can easily be accomplished for Cu2+, whereas, for Ni2+, it is accompanied by an electronic rearrangement from the low-spin to the high-spin configuration. The relatively rigid ligands cannot Adapt to the somewhat larger high-spin Ni2+ion.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800326
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  • 81
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    Selective Synthesis of Polyamine Derivatives: Efficient derivatization of the secondary amino group of N-monosubstituted 1,3-diaminesDedicated to Professor Klaus Schreiber on the occasion of his 70th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 966-978 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Monosubstituted 1,3-diamines were selectively functionalized at the secondary N-atom via 2-Ph-substituted hexahydropyrimidine intermediates. Reaction of the diamines with benzaldehyde, followed by treatment with an electrophile and hydrolysis, provided the desired products with excellent selectivity and in high yields. N4,N9-bis[3-phenylprop-2-enoyl]spermine (4a), which was further converted to N1,N1 2-bis[3-phenylprop-2-enoyl]spermine (15) by a transamidation reaction, was prepared by this way in 82% yield from spermine (1). Compound 4a was alternatively synthesized in 83% yield, equally from 1, by a sequence involving intermediary protection of the terminal amino groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800328
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  • 82
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    Synthesis of Monodisperse Macromolecular Bicyclic and dendriticPartially published in a preliminary communication [1] compounds from (R)-3-hydroxybutanoic acid and benzene-1,3,5-tricarboxylic acid and analysis by fragmenting MALDI-TOF mass spectroscopyDedicated to Professor Waldemar Adam on the occasion of his 60th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 989-1026 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As previously shown, oligo- and poly(β-hydroxyalkanoates) have a high tendency to form lamellar crystallites with ca. 50-Å thickness which corresponds to chain lengths of 16 units (Fig. 1). To have monodisperse model compounds, we have now prepared bicyclic derivatives with three parallel (27-29) or two parallel and an antiparallel chain (68-70) consisting of up to 16 3-hydroxybutanoate (3-HB) units. We also prepared dendritic compounds (71-75, 82-85) containing oligo(3-HB) chains which cannot possibly be arranged as in the lamellae; the branching units were prepared from trimesic acid (= benzene-1,3,5-tricarboxylic acid). So far, none of the prepared samples formed crystals or contained crystalline domains which would have been suitable for single-crystal or powder-diffraction X-ray analysis. The terminally deprotected dendrimers (74, 75, and 85) are multi-anionic (up to 12 peripheral CO2H groups) and biodegradable. The macromolecular HB derivatives (molecular weight up to 10150 Da) have been fully characterized by IR, 1H- and 13C-NMR, [α]D, and elemental analysis. Especially important is the analysis by mass spectrometry with the MALDI-TOF technique (Fig. 2), proving that the products are monodisperse; application of a new variation of this MS method (post source decay = PSD or fragment analysis by structural time of flight = FASTTM) allows for the observation of metastable fragment ions and, thus, is a tool for structural oligomer analysis (Fig. 3).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800402
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  • 83
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    Flash Photolysis of 5-Methyl-1,4-naphthoquinone in Aqueous Solution: Kinetics and mechanism of photoenolization and of enol trappingDedicated to our colleague Fabian Gerson who is venturing to new shores (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1106-1121 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5-Methyl-1,4-naphthoquinone (1) is a remarkable probe to study hydrogen and proton transfer reactions. The photoenol 4-hydroxy-5-methylidene naphthalen-1 (5H)-one (2) is formed in the ground state within 2 ps of excitation and with a quantum yield of unity, presumably through a conical intersection of the S0 and S1 hypersurfaces. In aqueous acid, enol 2 is hydrated to 5-(hydroxymethyl)naphthalene-1,4-diol 3 (X = OH, Scheme 1). The rate of hydration of 2 increases linearly with acid concentration from ca. 1.5 × 104 s-1 at pH 6 to reach a maximum value of 9 ×107 s-1 when the remaining carbonyl function is protonated, pKa(2+) = 1.1. Contrary to an earlier suggestion, the rate-determining step in the acid-catalyzed hydration of 2 is addition of water to the conjugate acid 2+. Pronounced acceleration of the decay rate of 2 by hydrazoic-acid buffers indicates competitive trapping of 2+ by the azide ion. In neutral-to-weakly-basic solutions, enol 2 reacts by ionization, pKa(2) = 6.5, and nearly diffusion-controlled condensation of the carbanionic species 2- with quinone 1. Proto-nation at the methylidene C-atom does not compete measurably with protonation on carbonyl O-atom, despite a Substsial thermodynamic basic for carbon Portoation of ca. 50 kJ mol-1 for 2 and 100 mol-1 for 2-.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800408
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  • 84
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    Synthesis and Evaluation of 2-{[(2-Oxo-1H-quinolin-8-yl)oxy]methyl}-Substituted α-Methylidene-γ-butyrolactones (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1161-1168 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: O-Alkylation of 8-hydroxy-1H-quinolin-2-one (1) afforded 8-(2-oxopropoxy)-1H-quinolin-2-one (2) which was immediately cyclized to form the tricyclic 2,3-dihydro-3-hydroxy-3-methyl-5H-pyrido[1,2,3-de][1,4]benzoxazine,-5-one (3). The Reformatsky-type condensation of 3 furnished antiplatelet 8-[(2,3,4,5-tetrahydro-2-methyl-4-methylidene-5-oxofuran-2-yl)melhoxy]-1H-quinolin-2-one (4). Its counterparts 7a-f, Ph-substituted at C(2) of the furan ring, were obtained from 1 via alkylation and the Reformatsky-type condensation. Although compound 4 was less active against platelet aggregation than 7a-f, it was the only compound which exhibited significant inhibitory activity on high-K+ medium, Ca2+-induced vasoconstriction and was more active than most of its Ph-substituted counterparts against norepinephrine-induced vasoconstrictions.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19970800413
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  • 85
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    Photolysis of Steroidal 20-Aryl-Substituted 11-NitritesDedicated to Prof. O. Jeger on the occasion of his 80th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1221-1228 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The two structurally similar 20-phenyl- and 20-(4-methoxyphenyl)-11-(nitrosooxy)pregnan-20-ol derivatives 4 and 7 behave differently under photolytic conditions, the former nitrous acid ester affording, as a main product, the benzo-fused hexacyclic compound 9, and the latter the 21-nitro derivative 12. Mechanistic aspects of these transformations are discussed.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800419
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  • 86
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    Design and Synthesis of Potent Macrocyclic Benzolactam Growth Hormone SecretagoguesDedicated to the Memory of Professor Wolfgang Oppolzer.2Deceased March 15, 1996. (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1244-1259 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a variety of potent macrocyclic growth hormone secretagogues, i.e. 5, 9, 12, and 20-22, based on the known lead structure L-692,429 (1) is described. These conformationally constrained growth hormone secretagogues were prepared by joining the two essential pharmacophores, the amino-acid side chain at the 1H-1-benzazepine moiety and the 1,1′-biphenyl moiety with a variety of linkers. The most potent analog was found to be L-744,080 (21), a derivative in which a 2′-carboxamide moiety at 1,1-biphenyl is N,O-joined to the OH group of the (2-hydroxypropyl)amino-acid side chain by a C4 ester linker. This potent analog may be useful in determining the bound conformation of the benzolactam class of growth hormone secretagogues at the newly identified GHS receptor, L-744,080 (21) with an ED50 of 20 nM was up to fifty times more potent than the seco-acid precursor and 3-fold more potent than the parent 2′-tetrazole compound L-692, 429 (1).
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800421
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  • 87
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    Glyconothio-O-lactones. Part III. Thermolysis of a 4,5-Dihydro-1,2,3- and a 2,5-Dihydro-1,3,4-thiadiazole (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1260-1279 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Addition of CH2N2 to 2,3:5,6-di-O-isopropylidene-1-thio-mannono-1,4-lactone (1) gave the 2,5-dihydro-1,3,4-thiadiazole 2 and the 4,5-dihydro-1,2,3-thiadiazole 3. First-order kinetics were observed for the thermolysis of 3 (Scheme 3) at 80-110° in C6D5Cl solution and of 2 (Scheme 3) at 20-35° in CDC13, respectively. The 1,2,3-thiadiazole 3 led to mixtures of the thiirane 9, the starting thionolactone 1, the thiono-1,5-lactone 8, and the enol ether 7, while the isomeric 1,3,4-thiadiazole 2 led to mixtures of the anomeric thiiranes 9 and 12, the O-hydrogen S,O,O-ortholactone α-D-14, the S-methyl thioester 15, the S,S,O-ortholactone 13, and the 2,3:5,6-di-Oisopropylidene-mannono-1,4-iactone (16). Pure products of the thermolysis were isolated by semipreparative supercritical fluid chromatography (SFC), whereas preparative HPLC led to partial or complete decomposition. Thus, the β-D-mannofuranosyl β-D-mannofuranoside 10, contaminated by an unknown S species, was isolated by preparative HPLC of the crude product of thermolysis of 3 at 115-120° and partially transformed in CD3OD solution into the symmetric di(α-D-mannofuranosyl) tetrasulfide 11. Its structure was evidenced by X-ray analysis. Similarly, HPLC of the thermolysis product of 2 gave the enethiol 17, the sulfide 19, and the mercapto alcohol 18 as secondary products. Thermolysis of the thiirane 9 at 110-120° (Scheme 4) led to the anomeric thiirane 12 which was transformed into mixtures of the enethiol 17 and the enol ether 7. Addition of H2O to 17 and 7 gave the corresponding hemiacetals 18 and 20. The mechanism of the thermolysis of the dihydrothiadiazoles 2 and 3, and the thiiranes 9 and 12 is discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800422
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  • 88
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    Non-destructive Removal of the Bornanesultam Auxiliary in α-Substituted N-Acylbornane-10,2-sultanis under Mild Conditions: An efficient synthesis of enantiomerically pure ketones and aldehydes (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1319-1337 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: α-Substituted N-acylbornane-10, 2-sultams 6, 9, and 10 can be converted into enantiomerically pure ketones 5. 13, and 14, respectively, via a two-step procedure involving a known mercaptolysis reaction followed by an [Fe(acac)3]-mediated coupling of the resulting S-benzyl thioesters with Grignard reagents. Furthermore, enantiomerically pure aldehydes 23 can be obtained from α-substituted N-acylbornane-10,2-sultams 6 via a one-step reduction with (i-Bu)2AIH. No epimerization at the α-chiral center is observed during the cleavage reaction whereby the chiral auxiliary, bornane-10,2-sultam 1 or ent-l, was recovered. By using this methodology, several natural products or precursors thereof can be prepared.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19970800502
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  • 89
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    Synthesis of Benzo[a]heptaleneDedicated to Oscar Jeger on the occasion of his 80th birthday. (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1375-1407 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Benzo[a]heptalene has been synthesized by two different approaches. The first one follows a pathway to hexahydrobenzo[a]heptalenone 19a that has been already described by Wenkert and Kim(Scheme). Indeed, 19a was obtained in a mixture with its double-bond-shifted isomer 19b. Reduction of this mixture to the corresponding secondary alcohols 26a/26b and elimination of H2O lead to a mixture of the tetrahydrobenzo[a]heptalenes 23a-d (Scheme7 and 8). Reaction of 23a-d with 2 equiv. of triphenylmethylium tetrafluoroborate in boiling CHCl3, followed by treatment with Me3N in CH2Cl2, generated directly 2, unfortunately in a mixture with Ph3CH that could not be separated from 2 (Scheme 10 and 11). The second approach via dimethyl benzo[a]heptalene-6,7-dicarboxylate (30) (Scheme 12) that was gradually transformed into the corresponding carbaldehydes 37 and 43 (Scheme 14) both of which, on treatment with the Wilkinson catalyst [RhCl(PPh3)3] at 130° in toluene, smoothly decarbonylated, finally gave pure 2 as an unstable orange, viscous oil. UV/VIS, NMR, and mass spectra of 2 are discussed in detail (cf. Chapt.3).
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800506
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  • 90
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    Synthesis of Polysubstituted Pyrrolizidines from Proline Derivatives and Conjugated NitroolefinsDedicated with best wishes to Professor Dieter Seebach on the occasion of his 60th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1457-1472 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemistry of 1,3-dipolar cycloaddition of azomethine ylides derived from aromatic aldehydes and i-proline alkyl esters with several nitroolefins was investigated. Cyclic and acyclic nitroolefins add to the anti form of the ylide in a highly diastereoselective but poorly regioselective manner to give pyrrolizidine derivatives. In a few cases, the stereochemical results strongly support a stepwise mechanism.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19970800510
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  • 91
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    Synthesis and Properties of 2′-Deoxy-1′,2′-seco-D-ribosyl (5′ → 3′)oligonucleotides (= 1′,2′-seco-DNA) containing adenine and thymineThis work was made possible of Prof. Albert Eschenmoser and was carried out in his laboratory in the context of the studies on the chemistry of homo-DNA[1-11] (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1494-1512 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some 2′-deoxy-1′,2′-seco-D-ribosyl (5′→3′)oligonucleotides (= 1′,2′-seco-DNA), differing from natural DNA only by a bond scission between the centers C(1′) and C(2′), were synthesized and studied in order to compare their structure properties and pairing behavior with those of corresponding natural DNA and homo-DNA oligonucleotides (2′,3′-dideoxy-β-D-glucopyranosyl oligonucleotides). Starting from (-)-D-tartaric acid, 2′-deoxy-1′,2′-secoadenosine derivative 9a and 1′,2′-secothymidine (9b) were obtained in pure crystalline form. Using the phosphoramidite variant of the phosphite-triester method, a dinucleotide monophosphate 1′,2′-seco-d(T2) was synthesized in solution, while oligonucleotides 1′,2′-seco-d[(AT)6], 1′,2′-seco-d(A10) and 1′,2′-seco-d(T10) were prepared on solid phase with either automated or manual techniques. Results of UV- and CD-spectroscopic as well as gel-electrophoretic studies indicated that neither adenine-thymine base pairing (as observed in natural DNA and homo-DNA), nor the adenine-adenine base pairing (as observed in homo-DNA) was effective in 1′,2′-seco-DNA, Furthermore, hybrid pairing was observed neither between 1′.2′-seco-DNA and natural DNA nor between 1′,2′-seco-DNA and homo-DNA.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800513
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  • 92
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    Catalytic Cyclophanes. Part XI. A flavo-thiazolio-cyclophane as a biomimetic catalyst for the preparative-scale electro-oxidation of aromatic aldehydes to methyl estersFor a preliminary communication of parts of this work, see [1] (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1555-1588 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Flavo-thiazolio-cyclophane 6 was prepared on a gram scale by an 18-step synthesis (Schemes 3 and 4). This pathway involved the very efficient preparation of bromo-cyclophane 32 (37% yield over 13-steps), which can be readily modified to create various multiply functionalized receptors. This bromide 32 was subsequently converted into the corresponding boronic acid and connected to the 7-bromoflavin 10 (Scheme 2) via Suzuki coupling to give flavo-cyclophane 36. The thiazolium unit was then introduced after quaternization of the tertiary amino groups of 36. Flavo-thiazolio-cyclophane 6, with both prosthetic groups attached in proximity to the well-defined cyclophane binding site, is a functional model for the enzyme pyruvate oxidase. In basic methanolic solution, 6 catalyzes the oxidation of aromatic aldehydes to their corresponding methyl esters. Cyclophane 6 shows saturation kinetics, and the turnover number calculated for the oxidation of naphthalene-2-carbaldehyde to methyl naphthalene-2-carboxylate (kcat = 0.22 s-1) is one of the highest reported for an artificial enzyme. Control experiments showed that the catalytic advantages of 6 result from the macrocyclic binding and reaction site as well as from the covalent attachment of both cofactors to this site. The catalytic cycle is completed by electrochemical re-oxidation of the reduced flavin moiety at a low working electrode potential (- 0.3 V vs. Ag/AgCl), and up to ca. 100 catalytic cycles can be performed on a preparative scale, The intramolecular nature of the electron transfer from the active aldehyde intermediate to the flavin is particularly conducive to the oxidation of unreactive aldehydes.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800516
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  • 93
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    Mitteilungen (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1682-1682 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800523
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  • 94
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    7-Deazaguanine DNA: Oligonucleotides with hydrophobic or cationic side chainsDedicated to Prof. Dr. H. Seliger on the occasion of his 60th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1809-1822 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The phosphoramidites 6b and 9 as well as the phosphonate 6a derived from 7-(hex-1-ynyl)- and 7-[5-(trifluoroacetamido)pent-1-ynyl]-substituted 7-deaza-2′-deoxyguanosines 1 and 10, respectively, were prepared (Scheme 1). They were employed in solid-phase oligodeoxynucleotide synthesis of the alternating octamers d(hxy7c7G-C)4 (12), d(C-hxy7c7G)4 (13), and d(npey 7c7G-C)4 (15) as well as of other oligonucleotides (see 22-25; Table 2; hxy = hex-1-ynyl, npey = 5-aminopent-1-ynyl). The Tm values and the thermodynamic data of duplex formation were determined and correlated with the major-groove modification of the DNA fragments. A hexynyl side chain introduced into the 7-position of a 7-deazaguanine residue (see 1) was found to fit into the major groove without any protrusion. The incorporation of the (5-aminopent-1-ynyl)-modified 7-deaza-2′-deoxyguanosine 2 into single-stranded oligomers of the type 24 and 25 did not lead to change in duplex stability compared to the parent oligonucleotides. The self-complementary oligomer 15 with alternating npey7c7Gd (2) and dC units did not lead to a cooperative melting, either due to orientational disorder or interaction of the 5-aminopent-1-ynyl moiety with a base or with phosphate residues nearby or on the opposite strand.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800605
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  • 95
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    Determination of the Chemical Structure of novel colored 1H-pyrrol-3(2H)-one derivatives formed by Maillard-type reactions (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1843-1856 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The determination of the chemical structure of a previously unknown Maillard reaction product with an amino acid incorporated in a four-ring structure is reported. The red compounds 1a and 1b, isolated from a thermally treated aqueous solution of furan-2-carbaldehyde and L-alanine, were identified as (S)-4{(E)-1-formyl -2-(2-furyl)ethenyl}-5-(2-furyl)-2-{(E)-(2-furyl)methylidene}-2, 3-dihydro-α-methyl-3-oxo-1H-pyrrole-1-acetic acid and its 2-{(Z)-(2-furyl)methylidene}isomer, respectively, by several 1D- and 2D-NMR techniques, MS, UV, and IR spectroscopy as well as by synthetic experiments. 2D-NOESY and 2D-ROESY experiments performed for conformation analysis indicated the existence of two atropisomers.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800608
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  • 96
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    Photochemistry of Isothiocoumarin (= 1H-[2]benzothiopyran-1-one) (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1865-1868 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation (λ = 350 nm) of 1H-[2]benzothiopyran-1-one (2) in the solid state affords selectively and in good yield 6aα, 6bα, 12bα, 12cα -tetrahydrocyclobuta[1, 2-c:4, 3-c′]bis([2]benzothiopyran)-5, 8-dione (3), the head-to-head (HH) cis-cisoid-cis-cyclodimer of 2, X-Ray analysis of 2 confirms that this reaction proceeds according to the well-established topochemical principles. The same dimer 3 is obtained in low yields on irradiation of 10-1 M solutions of 2 in either MeOH or MeCN, while no conversion at all is observed in benzene. On irradiation of 2 in MeCN in the presence of tetrachloroethene, the [2 + 2] photocycloadduct 4 is formed in good yield, the conversion 2 → 4 being efficiently quenched by naphthalene. In contrast, no reaction is observed -on irradiation of 2 in the presence of 2, 3-dimethylbut-2-ene, neither in polar nor in apolar solvents.
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  • 97
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    Reduction Potentials of Tetraaminecopper(II/I) Couples (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1983-1991 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The difference in steric strain between the oxidized and the reduced forms of tetraaminecopper complexes is correlated with the corresponding reduction potentials. The experimentally determined data considered range from -0.54 to -0.04 V (vs. NHE) in aqueous solution and from -0.35 to -0.08 V (vs. NHE) in MeCN. The observed and/or computed geometries of the tetraaminecopper(II) complexes are distorted octahedral or square-pyramidal (4 + 2 or 4+1) with (distorted) square-planar CuN4 chromophores (CuII—N = 1.99-2.06 Å; Cu—O4+2Ax ≈ 2.5 Å; Cu—O4+1ax ≈ 2.3 Å), those of the tetraaminecopper(I) complexes are (distorted) tetrahedral (four-coordinate; CuI—N = 2.12-2.26 Å; tetrahedral twist angle ∅ = 30-90°). The reduction potentials of CuII/I couples with primary-amine ligands and those with macrocyclic secondary-amine ligands were correlated separately with the corresponding strain energies, leading to slopes of 70 and 61 kJ mol-1 V-1, with correlation coefficients of 0.89 and 0.91, respectively. The approximations of the model (entropy, solvation, electronic factors) and the limits of applicability are discussed in detail and in relation to other approaches to compute reduction potentials of transition-metal compounds.
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    URL: http://dx.doi.org/10.1002/hlca.19970800616
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  • 98
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    ‘Three-Component Reaction’ with aromatic thioketones, phenyl azide, and dimethyl fumarate (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1992-2001 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of thiobenzophenone (= diphenylmethanethione; 8a) or 9H-fluorene-9-thione (8b) and methyl fumarate (9) in excess PhN3 at 80° yields a mixture of diastereoisomeric thiiranes 10 and 11 (Scheme 1). A mechanism involving the initial formation of 1-phenyl-4, 5-dihydro-1H-1, 2, 3-triazole-4, 5-dicarboxylate 12 by 1, 3-dipolar cycloaddition of PhN3 and 9 is proposed in Scheme 2. The diazo compound 13, which is in equilibrium with 12, undergoes a further 1, 3-dipolar cycloaddition with thioketones 8 to give 2, 5-dihydro-1, 3, 4-thiadiazoles 14. Elimination of N2 yields the thiocarbonyl ylide 15 which cyclizes to the corresponding thiirane. Desulfurization of the thiiranes 10 and 11 with hexamethylphosphorous triamide leads to the olefinic compounds 16 (Scheme 3). The crystal structures of 10a, 11a, and 16b were determined.
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    URL: http://dx.doi.org/10.1002/hlca.19970800617
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  • 99
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    ‘Mixed’ β-Peptides: A unique helical secondary structure in solution. Preliminary communication (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2033-2038 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-Hexapeptides 1-5 and a β-dodecapeptide 6 with sequences containing two different types of β-amino acids (aliphatic proteinageous side chains in the 2- or in the 3-position) have been prepared. CD (Fig. 1) and NMR measurements indicate that, with one exception, the secondary structures formed by these new β-peptides differ from those of isomers studied previously. Detailed NMR analysis of the β-hexapeptide 5 (with alternating β2,β3-building blocks) and molecular-dynamics simulations have produced a minimum energy conformation (Fig. 2,b)which might be described as a novel irregular helix containing ten- and twelve-membered H-bonded rings. This demonstrates the great structural variability of β-peptides, since three different helical secondary structures have been discovered to date.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19970800703
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  • 100
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    Control of Regio-, Diastereo-, and Enantioselectivity in the [Ti(OTs)2(TADDOLato)]-catalyzed 1,3-dipolar cycloaddition reaction between 3-acryloyloxazolidin-2-one and nitronesDedicated to Professor Dieter Seebach on the occasion of his 60th birthday (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2039-2046 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Catalytic control of regio-, diastereo-, and enantioselectivity in the 1,3-dipolar cycloaddition of 3-acryl-oyloxazolidin-2-one (4) with different nitrones 2 by the application of a [TiX2(TADDOLato)] complex as the catalyst was developed (TADDOL = α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanol). In the absence of a catalyst, the 1,3-dipolar cycloaddition of 4 with 2 proceeded to give a mixture of regioisomers, whereas, in the presence of a catalyst, the regioselectivity of the reaction could be controlled. Three asymmetric [TiX2(TADDOLato)] catalysts were tested, and it was found that use of the [Ti(OTs)2(TADDOLato)] complex gave complete regioselectivity, high ‘endo’-selectivities (〉 90% d.e.), and enantioselectivities corresponding to 48-70% e.e.
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    URL: http://dx.doi.org/10.1002/hlca.19970800704
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