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  • 1980-1984  (6,851)
  • 1981  (6,851)
  • Chemistry  (6,851)
  • Inorganic Chemistry  (704)
  • Nuclear reactions
  • 101
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1615-1623 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nature of peptide bonds in poly(aspartic acid) prepared by debenzylation of poly(β-benzyl-L-aspartate) under various conditions has been studied by means of nmr spectroscopy. It was established that the majority of the polymers prepared, as well as the commercially obtained polymer, contained aspartic acid linked in both α- and β-peptide bonds. The purest polymer, having practically undetectable amounts of β-bond, was prepared by debenzylation by HBr in trifluoroacetic acid. It was established that the β-bonds are formed via succinimides.
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  • 102
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proton magnetic resonance data have been obtained for 6-methyl-2′-deoxyuridine (dT*), its 3′- and 5′-monophosphates, and its 3′,5′-diphosphate, as well as for the corresponding thymine derivatives. The synthesis of the dideoxynucleoside monophosphates - d(TpT), d(T*pT), d(TpT*), and d(T*pT*) - was accomplished, and spectral data were obtained for these four dimers. The data show that the 6-methyluracil base prefers the syn conformation about the N-glycosyl bond at the monomer and dimer levels. The presence of the syn base leads to increases in the cis couplings of the sugar ring, J1′2″ and J2′3′, which indicate a trend towards eclipsing of the substituents on the C1′-C2′ and C2′-C3′ fragments. This trend is discussed in terms of changes in the pseudorotational parameters which describe the pucker of the ring. The syn base destabilizes the g+ conformer about the C4′-C5′ bond, leading to a preference for the t conformer in all dT* residues at the monomer and dimer levels. Preliminary work on the formation of cyclobutane-type photodimers in d(T*pT) and d(T*pT*) is discussed and presented as evidence for the capability of the syn 6-methyluracil base to form base-stacked complexes.
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  • 103
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1727-1739 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complete conformational analysis of B-type DNA was carried out in the independent two-dimensional surface of the hexa-dimensional conformational space of the helical structures. A theoretical double-helical model was derived by locating the deepest minimum of the conformational energy. It is similar to that obtained by x-ray refining methods; significant differences seem to be supported by relevant experimental data. Examination of the energy map allows a direct estimate of the flexibility limits of B-DNA, which are found to be consistent with a smoothly supercoiled DNA in chromatin. The structure of the hypothetical left-handed B-type DNA was predicted to be as stable as the standard right-handed model at high ionic strength. Left- and right-handed helices are, however, not interconvertible without separation of the strands, and mixing of opposite screw sense fragments is unlikely to give coaxial helices, which would prevent their packing in fibers.
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  • 104
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1785-1791 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1. The extent of racemization and the coupling yield in peptide synthesis were studied under high dilution conditions. The azide method yielded the best results. 2. Five linear penta-peptide precursors related to gramicidin S were subjected to cyclization in order to study how the difference in the sequence influences the yield and the ratio of cyclic dimer to monomer. The azide with the sequence of -L-Pro-L-Val-L-Orn(Z)-L-Leu-D-Phe- afforded diZ-gramicidin S in a high yield of 63%. 3. Alternaria mali toxin III, a cyclotetradepsipeptide phytotoxin, was synthesized. The activated linear tetradepsipeptide containing a D-Dap(Z) (N3-Z-D-2,3-diaminopropionic acid) residue at the N-terminus afforded the cyclic precursor (53%). The Dap residue in the precursor was converted into a ΔAla residue by Hofmann degradation to give the desired product.
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  • 105
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1761-1784 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Striking advances have been made in the synthesis of biologically active peptides. The synthesis of fully active crystalline bovine ribonuclease A by Yajima and Fujii [(1981) Biopolymers 20, 1855-1863] represents an exciting milestone. The main factors contributing to this success include sequential coupling of many small segments and a sophisticated multistage protocol for the final acidolytic cleavage of all protecting groups. However, syntheses of large peptides and proteins and even of many medium-sized peptides continue to present formidable challenges. In peptide coupling the challenge is to join large peptide segments efficiently and in good yields. For solid-phase synthesis the challenge is application of polar supports and alternative Nα-protection. With protecting groups the challenge is to achieve quantitive cleavage at the end of synthesis. Concerning racemization the challenge is to develop sensitive and rapid procedures for measuring racemization during coupling. For purification the challenge is to improve the existing procedures and to search for novel alternative separation principles.
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  • 106
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Attachment of the side-chain carboxyl of the protected aspartic or glutamic acid ester to the resin support has been established for the solid-phase synthesis of the asparagine or glutamine peptide. After further elongation of the α-amino deprotected resin-bound peptide ester with protected peptide fragments and the final detachment from the resin support by ammonolysis, the larger peptides containing, or preferably C-terminated with, asparagine or glutamine could be obtained. Thus, the C-peptide of human proinsulin was prepared by coupling to the resin-bound dipeptide derivative, Leu-Glu(OCH2Ph®)·OtBu, with six fragments consecutively. It was obtained in an overall yield of 36% after detaching from the resin with alcoholic ammonia, followed by mild acidolysis, DEAE cellulose chromatography, and gel filtration. This procedure has now been applied to the synthesis of the C-terminal fragment of the insulin A chain ending in asparagine, and also to the synthesis of the threonine or serine peptide, where the anchorage to the resin was designed by the reaction of the sidechain hydroxyl with succinic anhydride in the presence of 4-dimethylaminopyridine to form the hemiester of succinic acid, which in turn was condensed to the aminomethyl resin by the DCC-HOBt procedure. Model experiments on the synthesis of the Z-Thr(CO-CH2CH2CONHCH2Ph®)·OtBu and Bpoc-Lys(Boc)-Thr(COCH2CH2CONHCH2Ph®)·OtBu, as well as their detachment from the resin by amminolysis or hydrazinolysis, have shown the potential for a milder process in the solid-phase synthesis of larger peptides.
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  • 107
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1913-1920 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-Turns are a common feature of cyclic peptides, but judging from recent x-ray and solution studies of cyclic hexapeptides it is not always possible to predict in advance the type of turn and the position of the turns in the sequence. Two or more backbone conformations containing β-turns may be of comparable energy and in rapid solvent- and temperature-dependent equilibrium in solution. The use of differential relaxation effects produced by a nitroxyl radical to locate β-turns with only minor perturbation of such equilibria is noted. Examination of the effect of a nitroxyl on the N-H resonances of the decapeptide hormone luteinizing hormone releasing hormone supports a dominant conformation with a β-turn at Gly6-Leu7. Although this turn is probably part of the biologically active conformation, it is not obvious in the more active [D-Ala6] analog.
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  • 108
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A quinoxaline antibiotic triostin A has a bicyclic octadepsipeptide structure. Proton and carbon-13 nmr spectra showed the presence of two symmetrical conformations favoring polar and nonpolar solvents, respectively. They interconvert slowly on the nmr time scale, and this slow interconversion is due to the cooperative effects of the presence of the quinoxaline ring and the N-methyl peptide bonds. Reversal of the chirality of the disulfide bond as the origin of the slow exchange was excluded by the presence of two conformers for S-benzyltriostin A. Conformer 2, which favors the polar solvent, can form hydrogen-bonded complexes with purine nucleoside derivatives in organic solvents, but conformer 1 does not. The binding sites were elucidated and a mode of interaction with DNA proposed.
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  • 109
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2001-2010 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: There is a general parallelism in the strategy followed in the design of hormonal peptide analogs and protease inhibitors. However, in the latter, one more dimension has been added with the development of mechanism-based inhibitors, a dimension that is not yet available for hormonal peptides because of the lack of knowledge about receptor mechanisms. The recently advanced concepts of transition state and bi-product analogs have made possible the development of highly potent active-site directed reversible protease inhibitors of great therapeutic potential.
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  • 110
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    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2021-2031 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two-dimensional nmr techniques have been carried out for the peak assignment of the spectrum of a somatostatin analog. Two-dimensional J-resolved spectroscopy simplified the rather broad and complicated spectrum to show the center of chemical shifts of each resonance and gave information on the coupling profiles. Another technique, two-dimensional spin-echo correlated spectroscopy, revealed the connectivities between protons which are correlated by weak spin-spin couplings. The combination of the results of these two complementary techniques made it possible for us to assign almost all peaks of the spectrum of the 11-residue somatostatin analog.
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  • 111
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    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2093-2120 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of excluded volume on the thermodynamic activity of globular macromolecules and macromolecular complexes in solution is studied in the hard-particle approximation. Activity coefficients are calculated as a function of the fraction of total volume occupied by macromolecules using relations obtained from scaled particle and lattice models. Significant and readily observable effects are predicted to occur as the fraction of volume occupied by globular macromolecules increases, including the following: (i) Compact quasi-spherical macromolecular conformations become increasingly energetically favored over extended anisometric conformations. (ii) Self- and heteroassociation processes are enhanced, particularly those leading to the formation of compact quasi-spherical aggregates. (iii) Depending upon the details of the reaction mechanism, the rate of an enzyme-catalyzed reaction may monotonically decrease, go through a maximum, or exhibit more complex behavior. A given degree of volume occupancy by larger macromolecules is predicted to have less effect on the structure and self-association of smaller macromolecules than the same degree of volume occupancy by smaller macromolecules has on the structure and self-association of larger macromolecules.
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  • 112
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    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2143-2163 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measurements have been made on the flow dichroism of T7 DNA as a function of NaCl concentration. In high salt, our results are compatible with an optical factor of -1.4 and a persistence length of 470 Å. The former is in agreement with expectations from the x-ray diffraction structure of fibrous B-DNA, and the latter is in the midrange of recent determinations. As salt concentration is decreased, the persistence length increases. The relation of our study to other recent investigations and with current theories of the electrostatic contribution to persistence length is discussed. We note that the separation of the electrostatic expansion factor into long- and short-range effects is somewhat arbitrary and might affect the interpretation of different experimental results in different ways. Finally, our hydrodynamic factors are consistent with a chain which is partially free-draining. This goes against the traditional interpretation but is in agreement with two recent observations.
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  • 113
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformations of a pentapeptide L-His-L-Arg-L-Trp-Gly with weak adrenocorticotropin (ACTH) activity and its analogs, where each L-amino acid residue is substituted by D-residue, were investigated by means of proton and carbon-13 nmr spectroscopy on their DMSO-d6 solutions. The spectra indicated the presence of slowly exchangeable conformation isomers for D-Phe and D-Arg analogs, due to steric hindrance around the arginine residue. The activation energy of the hindered rotation of the arginine side chain was estimated to be more than 19 ∼ 20 kcal/mol. Spin-lattice relaxation times of carbon-13 nuclei also indicated slow segmental motion of the arginine side chain of the D analogs. An effect on proton chemical shifts by intermolecular electrostatic interaction between the arginine side chain and the C terminal carboxylic residue was observed. We did not observe, however, a direct correlation between pentapeptide activity and molecular conformation at this stage of the experiments.
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  • 114
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simultaneous curve fitting for the ionization parameters of oxidized and reduced horse heart cytochrome c in 0.15M KCl and 20°C yields values for the ionization constants (as pK′) and the heats of ionization (ΔHi) which can reconstruct either the potentiometric or thermal titration curves. Reduced cytochrome c requires 8 sets of groups, whereas oxidized cytochrome c requires 10 sets of groups. The additional groups in the oxidized preparation appear to involve the ferriheme (pK′, 9.25; ΔHi, 13.7 kcal/mol) and a tyrosine (pK′ ≃ 10.24) that is not present in the reduced form. The potentiometric and thermal difference curves (reduced - oxidized) involve the appearance of 17 kcal/mol centered at pH 9.7 and 5.8 kcal/mol centered at pH 4.9. The carboxyl groups in both species appear to be normal for the hydrogen-bonded form. Only one histidine has normal ionization properties (pK′, 6.7; ΔHi, 7.5 kcal/mol), as do 17 of the lysine residues (pK′, 10.8; ΔHi, 11.5 kcal/mol).
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  • 115
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    New York : Wiley-Blackwell
    Biopolymers 20 (1981) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 116
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    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2369-2380 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transient electric birefringence measurements of the rotational diffusion constant of five short restriction fragments of the plasmid pBR322 show that the hydrodynamic length is independent of sodium ion concentration in the range of 0.2 to 2.5 mM. The fragments are too stiff to be modeled as wormlike molecules. The rotational relaxation times of the fragments, which range from 64 to 124 base pairs, have been used to calculate the rise per base pair using six different theoretical expressions for the length dependence of the rotational diffusion coefficient of straight cylinder. The best estimate for the rise per base pair of Na-DNA in solution is 3.3 ± 0.1 Å.
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  • 117
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    New York : Wiley-Blackwell
    Biopolymers 20 (1981) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 118
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    Biopolymers 20 (1981), S. 2509-2531 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermodynamic parameters for the double-strand formation of the molecules rCAmG + rCUnG, m,n = 5-7, and dCAmG + dCTnG, m,n = 5,6, were measured from optical melting curves. Normal helices are formed when m = n. The deoxyoligomers are more stable than the ribo-oligomers, due to a more favorable enthalpy. Double helices with mismatched bases can be formed by mixing oligomers with m ≠ n. Such helices may form several possible structures. A structure with a dangling base is favored over a structure with a bulged base. The destabilization of the double strands by the formation of a bulged base was determined to be greater than 1.6 kcal/mol at 10°C. The extent of aggregation in the oligomer double strand rCA7G·rCU7G was determined using ultracentrifugation equilibrium. The possible effects of aggregation on the determination of the thermodynamic parameters for double-strand formation are discussed.
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  • 119
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    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2635-2648 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An azo pyrimidine nucleotide has been prepared and enzymatically attached to oligo(A) primers. The nucleotide's azo pyrimidine group has previously been shown to initiate polymerization of methacrylate esters designed to bind marker groups for visualization by microscopy. When attached to RNA molecules complementary to a chromosomal DNA segment, these nucleotides may allow localization of the DNA segment following in situ hybridization of the probe, methacrylate polymerization, and marker attachment. Since mRNA molecules of potential interest as probes bear a 3′-poly(A) tail, the modified nucleotides were added to oligo(A) primers as models. First, N4-ureidocytosine nucleotides were enzymatically added to ApApA, (Ap)9A, or [5′-32P]-(pA)10, using the modified cytidine 5′-diphosphate and “primer-dependent” polynucleotide phosphorylase (M. luteus). In the case of the ApApA-primed reaction, the N4-ureidocytosine nucleotides in the product polynucleotide were converted into azo nucleotides by oxidation with N-bromosuccinimide. The other two primers were employed to study the time course of polynucleotide formation and to verify that primer was indeed being utilized by the enzyme. The suitability of the modified nucleotide for in situ hybridization studies was examined. Poly(N4-ureidocytidylic acid) was prepared from poly(C) and semicarbazide by the bisulfite-catalyzed transamination reaction. It was found that 95% of the N4-ureidocytosine nucleotides in this polynucleotide survive the elevated temperatures typically required for DNA:DNA denaturation and RNA:DNA annealing. When poly(N4-ureidocytidylic acid) was mixed with poly(I) in buffered aqueous salt solutions, no evidence for hybridization was found, so binding of the probe RNA to the denatured chromosomal DNA molecule via the modified nucleotides is not expected. Upon oxidation of poly(N4-ureidocytidylic acid) with N-bromosuccinimide, the azo nucleotides were formed, as judged by the appearance of a characteristic peak at approximately 350 nm in the uv-absorption spectrum of the yellow-orange product, azoRNA. The azo nucleotides in azoRNA exhibited the expected acid lability, which is known to be accompanied by 1-glyceryl methacrylate polymerization in the case of the simple azo pyrimidine. Because 1-glyceryl metharcylate bears substituent glycol groups for attaching heavy atoms or fluorescent markers, it is possible that probe RNA molecules bearing azo nucleotides may be useful for localizing low-multiplicity genes along eukaryotic chromosomes.
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  • 120
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    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2671-2690 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We show that the persistence length a of DNA, derived from total intensity laser light scattering of linear Col E1 DNA and corrected for excluded-volume effects, varies from about 68 nm in 0.005M NaCl to about 40 nm in 0.2M NaCl, leveling off to a constant value (about 27 nm) at high NaCl (1-4M) concentration. These observations do not agree with current views on the effect of electrostatic charge and ionic conditions on DNA dimensions. The apparent diffusion constant Dapp, determined from laser light scattering autocorrelation as a function of scattering vector q, at NaCl concentrations 0.005-4M, correctly yields the translational diffusion coefficient Dt at low values of q and scales with molecular dimensions rather than segment length at high values of q; thus, Dapp/Dt yields a universal curve when plotted against q2Rg2, where Rg is the radius of the gyration. The sedimentation coefficients s at 0.1 and 0.2M NaCl concentration closely agree with the well-tested empirical relations, and a combination of s, Dt, and the appropriate density increments yield correct molar masses over the whole salt concentration range. Approximate constancy of DtRg indicates limited draining in translational flow. We present some observations and thoughts on the regimes in which a dependence of the correlation decay times on q3 rather than q2 applies. We conclude that quasielastic laser light scattering discloses little information about dynamics of internal motion of DNA chains.
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  • 121
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    Biopolymers 20 (1981), S. 1747-1750 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 122
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A strategy suitable for the synthesis of larger peptides is proposed. It involves the following four considerations: (1) all of the side-chain functional groups are protected by benzyl-type protective groups; (2) a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide, is used for the fragment-condensation reactions together with 1-hydroxybenzotriazole as the additive; (3) all the protective groups are cleaved simultaneously by the HF method in the final stage of the synthesis; and (4) side products formed are detected and removed by an efficient high-performance liquid chromatography procedure. The usefulness of these procedures is demonstrated taking the synthesis of human parathyroid hormone [hPTH(1-84)] as an example.
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  • 123
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    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1877-1899 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several examples are cited to demonstrate how conformational-energy calculations provide information about the manner in which interatomic interactions influence the structure and stability of polypeptides and proteins, and of intermolecular complexes involving these same species. These include the screw senses of α-helical polyamino acids, helix-coil transition parameters, properties of β-bends, and the structures of gramicidin S and of synthetic poly-(tripeptide) models of collagen. In all of these calculations, the multiple-minimum problem has been surmounted. A description is provided as to how the multiple-minimum problem is being approached in calculations on globular proteins. These computational methods have also been applied to protein structure refinement and to the calculation of structures of homologous proteins and of enzyme-substrate complexes.
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  • 124
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    Biopolymers 20 (1981), S. 1921-1927 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Dnp-pNA derivatives of more than 30 tetrapeptides were synthesized and subjected to CD measurements in MeOH. The CD spectra were analyzed on the basis of exciton chirality theory and were found to be useful for estimating β-turn preference of the parent tetrapeptides based on the following facts: (1) when a compound of the series takes the βturn conformation, a pair of strong CD bands with opposite sign are observed at 305 and 350 nm, and (2) when it is in a random or nonfolded conformation, no significant bands are observed at the wavelengths. The intensity of the 350-nm band reflects especially well the βturn preference. The CD spectra can be classified into two groups according to the sign of the band at 350 nm, and the groups seem to correspond to the type of βturn. By summarizing the results obtained, some generalizations concerning the sequence-conformation relationship are proposed.
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  • 125
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 15 (1981), S. coi 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 126
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    Chemie in unserer Zeit 15 (1981), S. 27-34 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 127
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 15 (1981), S. coi 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 128
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    Chemie in unserer Zeit 15 (1981), S. A16 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 129
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    Chemie in unserer Zeit 15 (1981), S. 71-77 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 8 Ill.
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  • 130
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    Chemie in unserer Zeit 15 (1981), S. 102-102 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 131
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    Chemie in unserer Zeit 15 (1981), S. 197-200 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 132
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    Chemie in unserer Zeit 15 (1981), S. 179-189 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
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  • 133
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    Chemie in unserer Zeit 15 (1981), S. 208-209 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 134
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    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981) 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 135
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The isotope partition coefficient α between cyclohexane, cycloheptane and hydrogen has been determined between 80 and 180° and pressures around 1 atm. The values decrease with increasing deuterium content y of the hydrogen and can be expressed by the simple equation Ina = Δ S/R + (ΔH + δ · y)/RT with an error of ±1%. However it was not possible to achieve good agreement with theoretical calculations using a unique average value for the partition function of the hydrocarbon.
    Additional Material: 1 Ill.
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  • 136
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of reactions of p-chlorobenzenediazonium ions in aqueous buffer solutions (pH 9.0-10.6) under N2 (〈 5 ppb of O2) have been measured between 20 and 50°C. The formation of trans-diazotate is first-order with respect to the concentration of hydroxyl ions and to the equilibrium concentration of diazonium ions, if the diazonium ion⇄cis-diazotate equilibrium is considered as a fast prior equilibrium. This indicates that the p-chlorobenzenediazonium ion, in contrast to all previous investigations with the p-nitrobenzenediazonium ion and benzenediazonium ions carrying similar substituents with a -M effect, rearranges from the cis- to the trans-configuration as diazohydroxide and not as diazotate. The formation of trans-diazotate is catalyzed by carbonate and inhibited by hydrogen carbonate ions; mechanisms of these catalyses are discussed, and the solvent isotope effect KH2O/KD2O measured by an 1H-NMR. technique reported. The kinetics of the dediazoniations can be analyzed as a mixture of two reactions, a relatively fast first reaction, reaction A, which is responsible for about 5% of the total reaction, and a second reaction F. Both are first-order with respect to diazonium ion; reaction A is also first-order in hydroxyl ions. There are some indications that reaction A corresponds to the hydrolysis of the diazonium ion to give eventually amine and nitrite ions. Reaction F shows a complex dependence on hydroxyl ions; it is related to the homolytic dediazoniation.
    Additional Material: 10 Ill.
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  • 137
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 23Na-chemical shifts for the NaClO4 solute depend markedly upon the composition of binary solvent mixtures of THF with amines (pyridine, piperidine, pyrrolidine, aniline, propylamine, and isopropylamine). These changes, analyzed in a novel application of the Hill formalism, show equality of the intrinsic equilibrium constant K for the successive steps, upon displacement of THF from sodium coordination by one of these amines. The results, which are entirely consistent with tetracoordination of the sodium cation by these solvents, also indicate proportionality of the K values to the amine chemical shifts.
    Additional Material: 3 Ill.
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  • 138
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    Helvetica Chimica Acta 64 (1981), S. 568-571 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenylglycine esters react with pyruvic acid to give α-methylsuccinic amides 9 instead of the expected Schiff bases 8, analogously to p-anisidine but unlike aniline.
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  • 139
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compounds have been isolated and their structures determined by X-ray crystallography. Their relative stability is discussed in terms of theory and experiment. The endo-adduct is the thermodynamically more stable one.
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  • 140
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    Helvetica Chimica Acta 64 (1981), S. 572-578 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Notes on the Synthesis of Sulfonated Derivatives of 5,6,7,8-Tetrahydro-1-naphthylamine and 5,6,7,8-Tetrahydro-2-naphthylamineSulfonation of 5,6,7,8-tetrahydro-1-naphthylamine (1) with sulfuric acid gave a mixture of 1-amino-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (2), 4-amino-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (13) and 4-amino-5,6,7,8-tetrahydronaphthalene-1-sulfonic acid (3). The same reaction with 5,6,7,8-tetrahydro-2-naphthylamine (20) yielded 3-amino-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (21); formation of 2-amino-5,6,7,8-tetrahydronaphthalene-1-sulfonic acid (16) or of 3-amino-5,6,7,8-tetrahydronaphthalene-1-sulfonic acid (24) was not observed. Treatment of 4-bromo-5,6,7,8-tetrahydro-1-naphthylamine (4) or of its 4-chloro analogue 5 with amidosulfuric acid gave 1-amino-4-bromo-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (9) and its 4-chloro analogue 10, respectively, which were dehalogenated to 2. Preparations of 13 and 24 were achieved by sulfonation of 5-nitro-1,2,3,4-tetrahydronaphthalene (14) and 6-nitro-1,2,3,4-tetrahydronaphthalene (22) to 4-nitro-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (15) and 3-nitro-5,6,7,8-tetrahydronaphthalene-1-sulfonic acid (23), respectively, followed by Béchamp reductions. The sulfonic acid 13 was also obtained by hydrogenolysis of 4-amino-1-bromo-5,6,7,8-tetrahydronaphthalene-2-sulfonic acid (11) or of its 1-chloro analogue 12; compounds 11 and 12 were synthesized from N-(4-bromo-5,6,7,8-tetrahydro-1-naphthyl)acetamide (7) and from its 4-chloro analogue 8, respectively, by sulfonation with oleum and subsequent hydrolysis. By ‘baking’ the hydrogensulfate salt of 1 or 20 compounds 3 and 21 were obtained, respectively. Synthesis of 16 was achieved by sulfur dioxide treatment of the diazonium chloride derived from 2-nitro-5,6,7,8-tetrahydro-1-naphthylamine (17) giving 2-nitro-5,6,7,8-tetrahydronaphthalene-1-sulfonyl chloride (18), followed by hydrolysis of 18 to the corresponding sulfonic acid 19 and final reduction.
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  • 141
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    Helvetica Chimica Acta 64 (1981), S. 1023-1025 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deprotonation of ethyl (E)-2-alkenoates 1, 3 and 4 yields after protonation the double bond migrated (3 Z)-isomers 5, 7 and 9 as major products. In contrast, deprotonation and reprotonation of ethyl (Z)-2-pentenoate (2) gives the (3 E)-isomer 6 exclusively. These findings are explained by reaction paths starting from different ester conformations.
    Additional Material: 1 Tab.
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  • 142
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    Helvetica Chimica Acta 64 (1981), S. 1026-1031 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A New Route to 1, 3-Dicarbonyl Derivatives, Model Investigations on the A/B-Part of-3-Oxo-5α-steroidsStarting from 1 the 1, 3-dicarbonyl compounds 4a-d were synthetized via the enynes 2a-e and the relatively unstable epoxides 3a-d. The latter were reacted with 95% formic acid to gave 4a-d; small amounts of the furane derivatives 5a-c were identified as by-products in this last step. In the presence of catalytic amounts of HgSO4 the epoxides 3a-c yielded with 95% formic acid the furanes 5a-c, but no detectable amounts of 4a-c.
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  • 143
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    Helvetica Chimica Acta 64 (1981), S. 1032-1039 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It was found that analysis of the 1H-NMR. signals (at 360 (preferably) and/or 100 MHz) of the protons at C (4) and of the equatorial α-proton at C (6), particularly when these are located in the 2-3 ppm region and therefore convenient for detection and identification, may be of valuable aid in the structural and configurational characterization of 5-hydroxy- and 5-acetoxy-steroids (unsubstituted or containing a hydroxy or acyloxy substituent at C (3)).
    Additional Material: 1 Tab.
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  • 144
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heterodiamantanes and Structurally Related Compounds. Part III. The Pentacyclic C11-Diethers 5, 13-Dioxapentacyclo [6.5.0.02,6.03,12.04,9]tridecane, 4, 13-Dioxapentacyclo [6.4.1.02,7.03,10.05,9]tridecane, and 3, 10-Dioxapentacyclo [7.3.1.02,7.04,12.06,11]tridecaneIn connection with the studies on heterodiamantanes and structurally related compounds the three novel pentacyclic diethers 3-5 were prepared starting from the cyclopentadienone dimer 6. All four compounds have as common features a central carbocyclic 6-membered ring with four axial alkyl substituents and two oxygen functions in 1, 4 position. The required eleventh C-atom was introduced by dichlorocarbene addition either to 6 ( → 7) (Scheme 2) or to 29 ( → 28) (Scheme 4).Diether 3 was obtained by reduction of 26 (Scheme 2), a suitable precursor prepared either by intramolecular addition (24 → 26; Scheme 2) or substitution (30 → 26, 31 → 26; Scheme 4), as well as by direct substitution (44 → 3, 42 → 3; Scheme 5). Diether 4 was the product of a direct substitution (39 → 4, 36 → 4; Scheme 5). The synthesis of diether 5 was achieved from the addition product 51 (resulting from the alcohols 47 and 48; Scheme 6).Diether 4 is the thermodynamically least stable of the three diethers 3-5. It was easily isomerized to 5 on treatment with concentrated sulfuric acid in benzene whereas 3 and 5 remained unchanged under these conditions.
    Additional Material: 1 Tab.
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  • 145
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    Helvetica Chimica Acta 64 (1981), S. 1040-1057 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spherical Cryptates. Synthesis and Inclusion-Complexes of Spherical Macrotricyclic LigandsA general strategy for the synthesis of spherical macrotricyclic ligands has been developed. Four spherical cryptands, SC-24, SC-25, SC-26 and SC-27 have been obtained by this route. The synthesis and cation-complexing properties of these compounds are described in detail. Stability constants and cation exchange rates of the spherical cryptates obtained with alkali and alkaline-earth cations have been determined. Highly stable complexes are formed by SC-24; the Rb+ and Cs+ cryptates of SC-24 are the most stable complexes of these cations known to date. The size of the intramolecular cavity affects the complexation selectivity. The cation exchange rates are very slow, and the corresponding free energies of activation are even larger than, for macrobicyclic cryptates of similar stability. Both the high complex stabilities and the high activation energies required for cation exchange indicate a marked ‘spherical cryptate effect’ resulting from the highly connected nature of the molecular architecture of spherical macrotricyclic ligands.
    Additional Material: 6 Ill.
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  • 146
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    Helvetica Chimica Acta 64 (1981), S. 1058-1062 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates of proton transfer from 2, 4-hexadiene, 1, 3-cycloheptadiene, cyclopentadiene and acetone to t-butoxide have been measured in the gas phase using pulsed-ion-cyclotron-resonance spectroscopy. The rate constants are (units of 10-10 cm3 molecule-1 s-1): 2.7 ± 0.4, 3.8 ± 0.4, 6.1 ± 0.7 and 10.8 ± 1.5, respectively. These results are analyzed in terms of the properties of the encounter complex and reaction transition states. The reaction profile for t-butoxide + cyclopentadiene is modeled using RRKM theory and an estimate for the central barrier height is obtained.
    Additional Material: 1 Ill.
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  • 147
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 2- and 3-Phenyl Substituted Alkylalkylidene Iminium Ions in the Gas PhaseThe collision-induced fragmentations of 2- and 3-phenyl substituted alkylalkylidene iminium ions are reported. Besides the homolytic cleavage of the azaallyl bond a nucleophilic attack of the unsubstituted phenyl group at the iminium function is observed in the gas phase, yielding carbonium ions such as cyclopropanspirobenzenium (3), indanylium (10) and indenylium ions (11).
    Additional Material: 1 Tab.
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  • 148
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A modification of a previously reported synthesis of zeaxanthin (1), and routes to both zeaxanthin and rhodoxanthin (2) from α-ionone, are described.
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  • 149
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition metal complexes often have low-lying excited electronic states and, as a consequence, tend to be electronically labile, i.e., their electronic properties exhibit pronounced sensitivity to external perturbations. Often drastic changes in various spectroscopic properties indicating substantial electronic rearrangements can be induced be relatively weak intermolecular forces as provided by nonpolar solvents or solid molecular host lattices. This behaviour can be explained by crossing of potential surfaces in the vicinity of the absolute minimum. Many physical properties of a given orbitally (near-) degenerate system depend strongly on the relative magnitude of some characteristic parameters determining the shape of the ground Born-Oppenheimer potential surface(s), e.g. barrier height versus zero-point energy, distance between minima versus zero-point amplitude, energy difference between minima, etc. Typical examples are systems exhibiting Jahn-Teller activity, spin-crossover, mixed valence, exchange coupling and other types of electronic near-degeneracies. In paramagnetic systems changes in the electronic wavefunction can be most conveniently detected and analyzed by using EPR. spectroscopy.In paramagnetic sandwich complexes we studied two types of orbital degeneracies: Jahn-Teller degeneracies (d7-systems such as Co (cp)2, Ni(cp)2+ and Fe (cp) (bz), low-spin d5-systems such as Mn (cp)2) and low-spin/high-spin equilibria (d5-systems such as Mn (cp)2). By diluting these complexes and ring-substituted derivatives in a large variety of diamagnetic host systems we have been able to control the 6A/2E equilibrium of Mn (cp)2 by influencing the metal-to-ring distance and by changing the degree of ring alkylation; similarly we have been able to vary the relative weights of the two electronic states contributing to the two-fold degenerate electronic ground state of d5- and d7-systems to a large degree by variation of the local asymmetric fields offered by the lattice sites of the host systems.For comparison the electronic ground state properties of octahedral Cu(II) complexes with CuN6 CuO6 chromophores, of V (CO)6 and tetrahedral VCl4 were also studied by EPR. between 4K and room temperature in several host systems. Characteristic differences in the details of the temperature and host dependence of the EPR. spectra in all these electronically labile systems can be explained in terms of differences in the vibronic coupling type (E ⊗ e vs. T ⊗ e, t), the strength of linear and/or quadratic JT-coupling and the effects produced by spin-orbit coupling.
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  • 150
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Structure of Porphine-type Nickel Complexes Containing Axially Oriented SidechainsThe structure of (±)-[1, 11-dimethoxy-10 H-HDP (2-)]nickel (3), the product of the thermodynamically controlled addition of methanol to [6 H-HDP]nickel-bis-(tetrafluoroborate) (1), was determined by X-ray analysis. The two methoxy groups in 3 are cis-oriented. The syntheses and spectroscopic properties of [1, 11-diethoxy-10 H-HDP (2-)]nickel (5), [1, 11-dineopentyloxy-10 H-HDP (2-)]nickel (6) as well as the bridged complexes [1, 11-pentamethylenedioxy-10 H-HDP (2-)]nickel (4) and [1, 11-(E)-2,3-(dimethyl-2-butenylenedioxy)-10 H-HDP (2-)]nickel (7) are described. Reaction of 1 with bromide ions or 4-methylpyridine leads to the formation of the corresponding hexacoordinated, paramagnetic complexes dibromo [6 H-HDP]-nickel (II) (8) and bis (4-methylpyridine)[6 H-HDP]nickel-bis (tetrafluoroborate) (9).
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  • 151
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe a flexible, stereocontrolled synthesis of enantiomerically pure substituted cyclopentenes and cyclopentanes - including 11α-hydroxy-13-oxaprostanoic acid 20 - (-)-quinic acid via an acyclic precursor 6 by an intramolecular aldolisation-dehydration reaction.
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  • 152
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute conformation of 7-chloro-5-phenyl-1-[(S)-α-phenylethyl]-1, 3-dihydro-2H-1, 4-benzodiazepin-2-one (1c) in crystal, and its inversion rate in solution were determined, enabling prognosis of direction of asymmetric induction during C(3)-alkylation.
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  • 153
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Application of the α-Alkynone Cyclization: Synthesis of rac-Modhephenerac-Modhephene 1, the first sesquiterpene with a propellane C-skeleton and its epimer rac-epi-modhephene 27, were synthesized starting from bicyclo[3.3.0]oct-1(5)-en-2-one (2). The key step in the construction of the [3.3.3]-propellane system is an application of the α-alkynone cyclization, namely 3 → 4 and 11 → 14. The preferred formation of the propellanes 4 and 14 in this step shows that the insertion of the postulated alkylidene carbene intermediate into tertiary C,H-bonds outweighs the one into the secondary ring-C,H-bonds leading to 12/13 and 15/16, respectively. The two starting materials for the α-alkynone cyclization, 3 and 11, were prepared from 2 by the reactions shown in Scheme 3. The further elaboration and separation of the cyclization products 4 and 14 to rac-modhephene 1 and its epimer 27 are outlined in Scheme 5.
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  • 154
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    Helvetica Chimica Acta 64 (1981), S. 389-398 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transformations of 13 alcohols and 13 diols in the presence of a small amount dimethylsulfoxide (1/16 mol) were studied. Relationships were found between the type of the hydroxy compound and the selectivity of the transformation, and conclusions were drawn regarding the transformation mechanism. The ether formation observed with certain alcohols proceeds via a carbenium cation. The reaction conditions applied were found suitable for inducing water elimination from the ditertiary 1,2- and 1,3-diols (pinacol rearrangement, 1,2-elimination). From the 1,4- and 1,5-diols the corresponding oxacycloalkanes can be obtained in good yield. Cyclodehydration occurs by intramolecular nucleophilic substitution, via a concerted mechanism. The effect of DMSO is exerted directly, and protoncatalysis occurs simultaneously.
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  • 155
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    Helvetica Chimica Acta 64 (1981), S. 425-429 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Novel Example of Unsaturated Branched-chain Sugar Nucleoside: 3′-Deoxy-3′-methylidene-adenosineStarting from 5-O-benzoyl-3-C-methylidene-3-deoxy-1,2-O-isopropylidene-α-D-erythro-pentofuranose (11) the title compound 8 has been prepared. Its α-anomer (9) and the acyclic sugar nucleoside 10 have been obtained as by-products. Adenosine deaminase slowly deaminated 8, 9 being not affected. Compound 8 exhibited no antiviral activity, whereas one of its saturated analogues (13) inhibited the multiplication of the herpes-1 (HF) virus.
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  • 156
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    Helvetica Chimica Acta 64 (1981), S. 449-457 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configurational isomers of astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4′-dione) from the flesh of salmon (Salmo salar and Oncorhynchus) caught at different places in Europe and Canada were isolated and analyzed as (-)-camphanic acid diesters by means of HPLC. The biological variation in the composition of the configurational isomers in seven fish was surprisingly similar: 78 to 85% of (3S, 3′S)-astaxanthin, 12 to 17% (3R, 3′R)-astaxanthin and 2 to 6% meso-astaxanthin.
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  • 157
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An interactive system of programs has been developed to assist in structure elucidation based on mass spectral data. The program relies on algorithms for generating all the structural isomers that constitute alternative explanations of the observed data and it associates relative plausibility values with the different isomers. The structure assembly part of the program allows for the use of overlapping substructural components, such as substructures inferred from the appearance of particular ion patterns in the spectrum of an unknown compound. Mass spectrum interpretation procedures used with this structure assembly process could exploit any form of spectrum-substructure correlation scheme. In this work, the emphasis has been on the use of detailed and class specific spectrum-substructure correlations. Applications of the program are illustrated by means of an example analysis of the mass spectra of a variety of marine sterols.
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  • 158
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selective Modification of the Terminal Amide Group of Linear Polyamides via 2-Oxazolin-5-ones as IntermediatesTreatment of aqueous or alcoholic solutions of diamides of type 2 with HCl leads to the formation of amide-acids and amide-esters of type 3 (Scheme 1 and Table). It has been shown, that 2-oxazolin-5-ones of type 4 are intermediates of this selective transformation of the disubstituted terminal amide group. The selectivity of the transformation is demonstrated by the reaction sequence shown in Scheme 3. No selectivity has been observed in the acid-catalyzed hydrolysis of triamide 9 with a monosubstituted terminal amide group (Scheme 4). Hydrolysis of the optically active dipeptide derivatives (+)-(L)-13 and (+)-(L)-15 with HBr in nitromethane at 60-80° yields the pure enantiomer (+)-(L)-14 and (+)-(L)-16, respectively (Scheme 5), i.e., no racemization takes place under the reaction conditions.These results show the usefulness of the dimethylamide group as a protecting group for carboxylic acids for example in the peptide synthesis.
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  • 159
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 15N-CIDNP. spectra recorded during the reaction of diazonium cations with OH- in weakly alkaline aqueous solutions show that the dediazoniation is at least partially homolytic. The polarizations observed for the diazonium and trans-diazotate ions can be explained by reaction proceeding via a cage involving diazenyl and diazotate radicals using Kaptein's rules and simple intensity considerations.
    Additional Material: 2 Ill.
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  • 160
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of dediazoniation of p-chlorobenzenediazonium tetrafluoroborate have been studied in buffer solutions in the pH-range 9.0-10.0, ionic strength I = 0.10, at 20.0° in glass and polytetrafluoroethylene vessels. The presence of oxygen (〈5 ppb of O2, 60 to 100 ppb of O2, air, 〉 99% of O2) has a decisive influence on the rate and kinetic order of the dediazoniation. Iodoacetic acid inhibits the reaction, whereas p-chlorophenol has a catalytic effect, and in air and 〉99% of O2 it acts as an autocatalyst. The reaction is subject to general-base catalysis by water, hydroxyl ions, hydrogen carbonate and carbonate ions. The kinetic results are interpreted in conjunction with data concerning the reaction products [2] and a 15N-CIDNP. investigation of a related system [3]. Specific radical chain mechanisms are consistent with the results.
    Additional Material: 10 Ill.
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  • 161
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The product distribution of compounds 2, 3 and 4 formed in the electrohydrodimerization (EHD) of 1 was determined as function of the water content of the solvent (CH3CN). The presence of water favours the formation of the glycols 4 and reduces the relative amounts of 1,6-diketones 2 and hydroxyketones 3, as determined by GC./MS.-analysis.
    Additional Material: 1 Ill.
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  • 162
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    Helvetica Chimica Acta 64 (1981), S. 1575-1578 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The unusual propellane skeleton of the sesquiterpene modhephene (1) has been synthesized starting from cyclopentenone (2). The key step 6 → 7 is an efficient and highly stereoselective intramolecular thermal ene-reaction. Further elaboration of the propellane 7 gave the enone 10 which had been previously converted to (±)-modhephene (1) in three steps.
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  • 163
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present work a mixing-reaction model is developed to describe the influence of the space- and time-dependent concentration of the leaving group on the pre-equilibria of the reactants and thus on the product distribution of mixing-disguised reactions. The modelling is carried out using a typical example of such reactions, namely azo coupling, where the leaving group is a proton. For this reaction, the existence of characteristic sets of parameters is established, for which the product distribution does not depend on the initial pH-value. These sets of parameters define the isoselectivity points.
    Additional Material: 6 Ill.
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  • 164
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: rac.-Ajmalicine (31) and 19-epi-ajmalicine (30) have been synthesized by a convergent route from the preformed D, E-ring moieties 25 and 27 and tryptophyl bromide. Two syntheses of the trans-1-benzoyl-3-vinyl-4-piperidineacetic acid (13), used in the preparation of 25 and 27, are also described.
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  • 165
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    Helvetica Chimica Acta 64 (1981), S. 1653-1662 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: X-ray Structure Analyses of Chiral Ionophores: The NH4NCS Complex of 9,9′-Spirobifluorene-22-crown-5In the crystalline NH4NCS complex of 9,9′-spirobifluorene-22-crown-5 (1) the NH4+ ion sits in the centre of the polyether ring, with distances of 2.92-3.15 Å to the five O-atoms and shows at least twofold orientational disorder. In one orientation, three H-atoms point toward O-atoms and the fourth to the N-atom of the anion situated 2.78 Å above the polyether ring. In another, only two H-bonds are formed. The mean planes of the two fluorene parts of the molecule are perpendicular to each other.Crystals of 2,2′-bis (hydroxymethyl)-9,9′-spirobifluorene (2), an intermediate for the synthesis of 1, contain occluded benzene, which cannot be removed under vacuum. X-ray analysis shows that the benzene molecule does not interact with the spirobifluorene in a specific way but merely occupies cages in the crystal packing.
    Additional Material: 5 Ill.
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  • 166
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    Helvetica Chimica Acta 64 (1981), S. 1717-1717 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 167
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    Helvetica Chimica Acta 64 (1981) 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 168
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    Helvetica Chimica Acta 64 (1981), S. 1717-1727 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The N-diazo coupling of p-chloroaniline with p-chlorobenzenediazonium tetrafluoroborate in acetonitrile at 30° shows non-linear base catalysis by water. The results are interpreted in terms of the SE2 mechanism with rate-limiting proton loss at low base concentration; it is postulated, moreover that the reaction proceeds via transition states in which varying degrees of H-bonding from the amine and the intermediate ω-complex to different water species influence the initial step and the base catalysis.
    Additional Material: 2 Ill.
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  • 169
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleotides. XV. Synthesis and Properties of 2′O-t-Butyldimethylsilyl-5′-O-monomethoxytritylribonucleoside-3′-phosphotriesters, Starting Materials for Oligonucleotide SynthesesThe syntheses of two types of fully blocked ribonucleoside 3′-phosphotriesters 6-14 have been achieved in excellent yields from 2′-O-t-butyldimethylsilyl-5′-O-monomethoxytrityl-ribonucleosides 1-5 by phosphorylation with 2-chloro- and 2,5-dichlorophenylphosphorodichloridate respectively and subsequent treatment by cyanoethanol to 6, 8, 10, 12 and 14 and by p-nitrophenylethanol to 7, 9, 11 and 13. These phosphotriesters are valuable starting materials for oligonucleotide syntheses due to the fact that the corresponding phosphotriesters 15-23 with free HO—C(5′) could be obtained by detritylation and the 3′-phosphodiester triethylammonium salts 24-32 by deblocking of the cyanoethyl and the 2,5-dichlorophenyl group respectively. All newly synthesized compounds have been characterized by UV.-and NMR.-spectra as well as C, H, N elementary analyses.
    Additional Material: 4 Tab.
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  • 170
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: XIV. Substituted β-Phenyl-ethyl Groups. New Blocking Groups for Oligonucleotide Syntheses by the Phosphotriester ApproachVarious o- and p-substituted β-phenylethanols (2-10) have been synthesized and investigated as blocking groups in the phosphotriester approach. A large number of 5′-O-tritylated thymidine-3′-phosphotriesters (13-36) with two different phosphate protecting groups have been prepared, characterized, and studied according to their chemical stability and usefullness for oligonucleotide syntheses. The combination of a 5′-O-monomethoxytrityl- and a 3′-(2,5-dichlorophenyl, p-nitrophenylethyl)-phosphate function as in 18 turned out to possess optimal properties as a monomeric nucleotide building block due to the fact that these blocking groups can be quantitatively and selectively be removed without harming each other by trifluoroacetic acid in chloroform to 41, by oximate to 42, and by DBU to 43. The base-catalyzed removal of the monosubstituted phenylethyl groups by DBU or DBN respectively as well as the disubstituted phenylethyl groups by triethylamine in aprotic solvents is a β-elimination process leading to phosphodiesters without attack on the P-center.
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  • 171
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various free radicals formed during UV.-irradiation of aliphatic dicarboxylic acids in aqueous and methanolic solution are identified by ESR.-spectroscopy. Their structures point to α-cleavage and photoreduction as the dominant primary photochemical decay processes. The relative contributions of these reactions to the overall photodecomposition depend on solvent and degree of α-alkylation of the acid. Emission ESR.-spectra are found for radicals formed by C, CO-bond cleavage of α-dimethyl substituted acids. The polarization is referred to the triplet mechanism of CIDEP. and indicates this cleavage reaction occurs from a triplet molecular state.
    Additional Material: 6 Ill.
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  • 172
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    Helvetica Chimica Acta 64 (1981), S. 1910-1929 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperature and solvent dependence of the ESR. spectra of a number of semiquinone- and semidione-type radicals have been investigated with the aim of obtaining structural and kinetic information about intramolecular hydrogen bonding. Systematic variation of the chemical structure of the radicals indicates that in many cases formation and/or exchange of intramolecular H-bonds is disturbed or even precluded by steric hindrance or concomitant dynamic processes, such as internal rotation and/or intermolecular proton exchange.
    Additional Material: 8 Ill.
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  • 173
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    Helvetica Chimica Acta 64 (1981), S. 1943-1948 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, surface activity and micelle formation of three novel cyanine dyes with amphiphilic character is described. It is illustrated by combined surface tension and absorption measurements that in one case self-assembly is highly cooperative leading to aggregates with unique absorption properties.
    Additional Material: 5 Ill.
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  • 174
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    Helvetica Chimica Acta 64 (1981), S. 1964-1967 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Naturally occurring kaempferol 3-O-β-D-(6″-O-coumaroyl)glucopyranoside (tiliroside) has been synthesized thereby confirming its structure. This is the first acylated flavonoid glycoside to be synthesized.
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  • 175
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    Helvetica Chimica Acta 64 (1981), S. 1968-1968 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 176
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Juliprosine, a Further Alkaloid Isolated from Prosopis juliflora A.DC.By catalytic hydrogenation of the second base juliprosine (2) isolated from Prosopis juliflora (Leguminosae) the hexahydroderivative 5 was formed. The same product was obtained also by catalytic hydrogenation of juliprosopine (1) of known structure. The absolute configuration of 2 was deduced by comparison of [M]D values of Prosopis alkaloids of known absolute configuration.
    Additional Material: 1 Tab.
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  • 177
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    Helvetica Chimica Acta 64 (1981), S. 1985-1990 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,5-Octadiyne cation in its lowest excited state has been studied in the gas phase by laser-induced fluorescence and photoelectron-photon coincidence techniques. The excitation spectrum of the Ã2″←2A″ transition has been obtained and yields vibrational frequencies of some of the fundamentals for the excited cationic state. The fluorescence quantum yields and lifetimes at selected energies within the Ã2A″ state have been determined from the coincidence measurements. This provides quantitative data for the discussion of the relaxation behaviour of such an excited open-shell cation.
    Additional Material: 2 Ill.
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  • 178
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    Helvetica Chimica Acta 64 (1981), S. 2002-2021 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deprotonation of the 3-trialkylsilyloxy-1,4-diene 3a and subsequent electrophilic substitution of the non-isolated 3-trialkylsilyoxypentadienyllithium 4 gives the α- and γ-products 8 and/or 6 in good yields. Whereas alkylation of 4 proceeds with variable regioselectivity (Table 1) aldehydes and ketones attack preferentially the γ-position of 4 (Table 2). The desired γ-products 6 may be directly subjected to inter- and intramolecular [4 + 2]-additions as demonstrated by the reactions 5a (≡ 6d) → 7 and 6h → 19 (Schemes 4 and 12). Alternatively, smooth fluoride-promoted silylether-cleavage 6 → 11 (Scheme 8) provides a convenient approach to substituted vinyl ketones such as to the natural products 11f (Table 3). The stereoselective conversion 6k → 23 (Scheme 13) implies an endo-selective intramolecular Diels-Alder addition (26 → 23) and exemplifies the use of 4 as an equivalent of the hypothetical anion IV. Furthermore, some electrophilic substitutions of the hexadienyllithium 15 have been studied (Scheme 10).
    Additional Material: 4 Tab.
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  • 179
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    Helvetica Chimica Acta 64 (1981), S. 1937-1942 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zinctetramethylpyridylporphyrin (ZnTMPyP4+) in acidic aqueous solution sensitizes efficiently oxygen generation by visible light in the presence of acceptors such as Fe3+ - and Ag+-ions and colloidal RuO2/TiO2 redox catalyst. Hydrogen and oxygen are cogenerated under visible light illumination of ZnTMPyP4+ solutions when a bifunctional catalyst (Pt and RuO2 codeposited onto TiO2) is employed.
    Additional Material: 3 Ill.
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  • 180
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Effects of the Nature of the C(1) Substituent on the Conformational Equilibrium of (E)-derivatives of 3-Methoxypropene: Determination of the origin of the phenomenon using energy partitioning techniquesIntermolecular interactions taking place in the compounds of the general formula (E)-CH3OCH2CH=CHX were analyzed in terms of one- and two-center interaction energies within the framework of SCF ab initio (STO-3G), Extended Hückel and CNDO methods. The results confirmed the important role of unoccupied orbitals in the stabilization of the different conformers.
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  • 181
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    Helvetica Chimica Acta 64 (1981), S. 1969-1970 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 182
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    Helvetica Chimica Acta 64 (1981) 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 183
    ISSN: 0018-019X
    Keywords: All-trans-retina ; N-butyl-(all-trans-retinylidene)amine ; 1H-NMR. ; l, 13C-NMR. ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Schiff base of all-trans-retinal was investigated in organic solution by 1H- and 13C-NMR. at high field. Complete assignment of the 1H-NMR. peaks of N-butyl-(all-trans-retinylidene)amine (2) and the N-butyl-(all-trans-retinylidene)-ammonium ion (3) was achieved by INDOR (internuclear double resonance). The vicinal proton coupling constants of the polyene chain show that the π-bond orders remain unchanged in N-butyl-(all-trans-retinylidene)amine relative to all-trans-retinal (1), but change towards larger π-delocalization in the N-butyl-(all-trans-retinylidene)ammonium ion. At --61° only one isomer of N-butyl-(all-trans-retinylidene)ammonium was observed. This was shown to be trans at the imine linkage and independent of the solvent. The trifluoroacetic acid counter-ion can approach the positive charge of the N-atom in the weakly polar solvent dichloromethane but not in the leveling solvent methanol. In dichloromethane the nature of the 1:1 complex is a H-bonded (O-…H-N+) ion-pair whose rate of breaking and forming is rapid at RT. Strong stabilization of the ion-pair resulted from homo-conjugation with a second molecule of trifluoroacetic acid. Excess of acid efficiently diminished the isomerization rate at the C,N-bond.
    Additional Material: 6 Ill.
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  • 184
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    Helvetica Chimica Acta 64 (1981), S. 2022-2028 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: γ-Selective sulfenylation of the triethysilyloxypentadienyllithium 1 gave the versatile alkylthiodene 4 which on successive deprotonation and alkylation furnished with high regioselectivity the γ-products 6. Fluoride-promoted silylether cleavage 6 → 7 may be followed by intramolecular [4 + 2]-addition 7c → 8 and sulfoxide elimination 8 → 9. The conversions 7b → 12 and 7a → 17 demonstrate the feasibility of 5 to serve as an equivalent of the hypothetical β-deprotonated divinylketone 13 whose two enone units may be unmasked separately.
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  • 185
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    Helvetica Chimica Acta 64 (1981), S. 2056-2064 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new metabolites have been isolated from cultures of Chaetomium globosum. The structures of 19-O-acetylchaetoglobosin B (4) and 19-O-acetylchaetoglobosin D (5) are assigned. The 13C-NMR. spectra of chaetoglobosin A (1), 19-O-acetylchaetoglobosin A (2), chaetoglobosin C (3), 19-O-acetylchaetoglobosin B (4), 19-O-acetylchaetoglobosin D (5) and of cytochalasin G (6), a (3-indolyl)-[11]cytochalasan isolated from Pseudeurotium zonatum, have been interpreted.
    Additional Material: 2 Ill.
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  • 186
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The products of the thermolysis of N-(1-pyridinio)-2-nitroanilides (1) had previously been interpreted as tris (2-nitrophenyl)-triaziridines (3). The present work shows them to be actually 1, 2-bis[(Z)-(2′-nitrophenyl)-ONN-azoxy]benzenes (5). The revised structural assignment is based on the chemical and the spectroscopic (especially 1H-NMR.) properties of 5 and on the results of a X-ray structural analysis.
    Additional Material: 1 Tab.
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  • 187
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    Helvetica Chimica Acta 64 (1981), S. 2148-2153 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The appearent first-order rate constants for the oxidation of water by iron tris (bipyridyl) (Fe (bpy)3+3), and reduction of water by methylviologen (MV+) catalyzed by a stabilized RuO2 or Pt-sol, respectively, were measured. Rate constants for water oxidation at pH 7 of 0.4 s-1 and water reduction at pH 4.7 and pH 1 of up to 460 s-1 for different sols were found.
    Additional Material: 3 Ill.
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  • 188
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photophysical and electron transfer properties of the lowest excited state of nine ruthenium (polypyridine) complexes have been characterized. The complexes studied are Ru (bpy)3-n (LL)2+n, where n varies from 0 to 3, and LL is 4, 4′-di-t-butyl-2,2′-bipyridine (DTB-bpy), 3, 3′-dimethyl-2, 2′-bipyridine (DM-bpy), or a 2, 2′-diquinolyl derivative (DMCH). The results obtained show that the Ru (bpy)2(DMCH)2+ complex is expected to be a more efficient mediator than Ru (bpy)2+3 in the water-splitting reaction by solar energy.
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  • 189
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    Helvetica Chimica Acta 64 (1981), S. 2183-2188 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational behaviour of sulpiride has been investigated by the quantum mechanical PCILO method and by CD. measurements. The results indicate the predominance of a folded, intramolecularly H-bonded conformer, with extended conformers being only slightly less stable. The pharmacological relevance of these results is briefly discussed.
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  • 190
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    Helvetica Chimica Acta 64 (1981), S. 2193-2202 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermolysis of the potassium 2-substituted bicyclo [2.2.2]oct-5-en-2-alkoxides derived from alcohols 2-17 at 90-120° in hexamethylphosphoric triamide affords unsaturated ketones resulting from allylic bond cleavage. The mechanistic and synthetic aspects of this anionic fragmentation are discussed with reference to the formation of 1-(3′-cyclohexenyl)-2-alkanones 18-28 via initial heterolytic C(1), C(2)-bond cleavage in the substrate alkoxide and regioselective, intramolecular protonation of the resultant transient allylic anion.
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  • 191
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    Helvetica Chimica Acta 64 (1981), S. 2219-2226 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hitherto unknown diterpenoid 14-hydroxytaxodione (10a) has been prepared by oxidation of 6β-hydroxyroyleanone. Its solutions exhibit a dynamic structural behaviour (UV./VIS/. and NMR.) and lead to an equilibrium mixture of the 11, 14- and the 6, 12-dioxo forms. By methylation and acetylation the 6, 12-dioxo form can be isolated. Chloroform solutions of 14-hydroxytaxodione slowly set up a mixture of coleon V (2a), coleon U (3) and dimeric products (later established as grandidone C, grandidone D and 7-epigrandidone D). Therefore, coleon V (2a) owing to its strong intramolecular H-bond is more stable than 7, 14-dihydroxy-taxodione (2b).
    Additional Material: 1 Ill.
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  • 192
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Isolation of 14-Hydroxytaxodione from Plectranthus grandidentatus GÜRKE and of Seven New Dimeric Diterpenoids from P. grandidentatus, P. myrianthus and Coleus carnosus Structures of Grandidone A, 7-Epi-A, B, C, D and 7-Epi-DFrom the leaf-glands of the title plant the following abietane diterpenes have been isolated and their structures established by chemical, spectroscopical and X-ray methods: 14-hydroxytaxodione (5, 0,57%), new as a natural product, the already known coleons U (6, 0,17%) and V (7, 0,024%), and furthermore 7 novel dimeric compounds named grandidones (ca. 0,09%), Both grandidone A (1a) and 7-epigrandidone A (1b) as well as grandidone B (2a) and 7-epigrandidone B (2b) are C(7) acetals of 6, 7-Dioxoroyleanone with catecholes such as coleon U (→ 1a, 1b) or coleon V (→ 2a, 2b). Based on the relative configuration at C(7) of 1a which was established by X-ray analysis, the constitutions of 1b, 2a and 2b were assigned by HPLC. - controlled interconversions. The unstable grandidone C (3) is a C(7)-C(7′) linked bis-6-oxoroyleanone with C2-symmetry. Grandidone D (4a) and 7-epigrandidone D (4b) are spiro-dihydrofurans formed from 3 via a hypothetical bis (14-hydroxytaxodione) by intramolecular addition of HO-C(14) or HO-C(14′) to C(7′) to C(7′) or C(7). The relative configuration of 4a was established by X-ray analysis of its diacetate 4c. The absolute configuration of all dimers was established by the partial syntheses from 14-hydroxytaxodion (5) (entirely described in the following communication).
    Additional Material: 10 Ill.
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  • 193
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Contributions to the Knowledge of the Corrin Chromophore: XII [1]. Chemical Behaviour of the Reaction Product of Heptamethyl Dicyano-cobyrinate with Hypochlorous AcidHeptamethyl chloro-cyano-5α, 10, 15-trichloro-6α, 14-dihydroxy-5,6,14,15-tetrahydrocobyrinate (2) in CH3OH/H2SO4 yields with RuO2 under 50 bar hydrogen and at 100° during 2 h a mixture of heptamethyl dicyanocobyrinate (1) with an epimeric ester. Using deuterium instead of hydrogen in this reaction, C(13) comes out as the probable epimerization center.
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  • 194
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 2251-2256 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Partial Synthesis of Grandidones A, 7-Epi-A, B, 7-Epi-B, C, D and 7-Epi-D, from 14-HydroxytaxodioneOxydative addition of coleon U (6) to 14-hydroxytaxodione (5) in the presence of Fétizon's reagent mainly leads to grandidone A (1a) and 7-epigrandidone A (1b) (ca. 15:1), whereas coleon V (7) and 5 under the same conditions yield grandidone B (2a) and 7-epigrandidone B (2b) (ca. 3:1). Dimerization of 14-hydroxytaxodione (5) gives grandidone C (3; ca. 40%), grandidone D (4a; ca. 50%) and 7-epigrandidone D (4b; ca. 10%). All these compounds obtained by partial synthesis are in every respect identical with the natural products, thus establishing their absolute configurations. The thermal transformation of grandidone C (3) to grandidone D (4a)/7-epigrandidone D (4b) and interconversions of 4a and 4b were achieved.Oxydative addition of coleon U (6) to 14-hydroxytaxodione (5) in the presence of Fétizon's reagent mainly leads to grandidone A (1a) and 7-epigrandidone A (1b) (ca. 15:1), whereas coleon V (7) and 5 under the same conditions yield grandidone B (2a) and 7-epigrandidone B (2b) (ca. 3:1). Dimerization of 14-hydroxytaxodione (5) gives grandidone C (3; ca. 40%), grandidone D (4a; ca. 50%) and 7-epigrandidone D (4b; ca. 10%). All these compounds obtained by partial synthesis are in every respect identical with the natural products, thus establishing their absolute configurations. The thermal transformation of grandidone C (3) to grandidone D (4a)/7-epigrandidone D (4b) and interconversions of 4a and 4b were achieved.Oxydative addition of coleon U (6) to 14-hydroxytaxodione (5) in the presence of Fétizon's reagent mainly leads to grandidone A (1a) and 7-epigrandidone A (1b) (ca. 15:1), whereas coleon V (7) and 5 under the same conditions yield grandidone B (2a) and 7-epigrandidone B (2b) (ca. 3:1). Dimerization of 14-hydroxytaxodione (5) gives grandidone C (3; ca. 40%), grandidone D (4a; ca. 50%) and 7-epigrandidone D (4b; ca. 10%). All these compounds obtained by partial synthesis are in every respect identical with the natural products, thus establishing their absolute configurations. The thermal transformation of grandidone C (3) to grandidone D (4a)/7-epigrandidone D (4b) and interconversions of 4a and 4b were achieved.Oxydative addition of coleon U (6) to 14-hydroxytaxodione (5) in the presence of Fétizon's reagent mainly leads to grandidone A (1a) and 7-epigrandidone A (1b) (ca. 15:1), whereas coleon V (7) and 5 under the same conditions yield grandidone B (2a) and 7-epigrandidone B (2b) (ca. 3:1). Dimerization of 14-hydroxytaxodione (5) gives grandidone C (3; ca. 40%), grandidone D (4a; ca. 50%) and 7-epigrandidone D (4b; ca. 10%). All these compounds obtained by partial synthesis are in every respect identical with the natural products, thus establishing their absolute configurations. The thermal transformation of grandidone C (3) to grandidone D (4a)/7-epigrandidone D (4b) and interconversions of 4a and 4b were achieved.
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  • 195
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Novel Types of C-Glycosyl-derivatives from Acetylenic Sugars or Partial Synthetic Equivalents thereofThe concept of synthetic equivalent is not unequivocal and, for example, α-fluoroenamines may behave in some cases as synthetic equivalents of ynamines and, in other situations, quite differently. Some uses of these α-fluoroenamines, ‘partial synthetic equivalents’ of ynamines, for the synthesis of C-glycosyl derivatives of coumarins, chromones, quinolines, quinolones, thietenes and isoxazoles are described.We also report the preparation of a series of mono- and diglycosylthiophenes by reacting HS- with mono- and diglycosylbutadiynes. Acetylenic sugar derivatives have also been used for the synthesis of a diglycosylazaphosphorine and a spirooxolenone.
    Additional Material: 2 Tab.
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  • 196
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Occurrence of New Bifunctional Esters In Roman Camomile Oil (Anthemis nobilis L.)Some novel aliphatic esters of the unusual 3-hydroxy-2-methylidenebutyric acid have been found in the commercially available essential oil. Additionally, esters of (Z)-2-methyl-2-butenoic acid of structurally similar diols or other bifunctional alcohols have also been identified. Spectral data as well as a synthetic approach to the new esters of 3-hydroxy-2-methylidenebutyric acid are given.
    Additional Material: 4 Ill.
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  • 197
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CD.-Based Configurational Assignments of GlycosylaziridinesThe relationship between CD.-curves and the configuration of the trans-2-benzoyl-3-phenylaziridines was known. By studying a series of cis- and trans-2-glycosyl-3-benzoylaziridines we have shown that CD. allows the assignment of the configuration at both asymetric C-atoms. As benzoylaziridines can easily be obtained from cyano- or alkoxycarbonylaziridines without configurational change, the absolute configuration of these last two classes of compounds can also be assessed by this method.
    Additional Material: 1 Tab.
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  • 198
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactivity and Electronic Structure of Porphine-type Nickel ComplexesThe electronic structure of the porphine-type hexaaza[16]annulene-nickel dikation 1′ as well as its mono- and diaddition products 2′ and 3′ (Scheme 2) has been considered by an extended Hückel treatment (SCCC-MO including charge iteration on the central metal atom). Correlations between calculated data and reactivity of the porphinoid compounds 1, 2 and 3 (Scheme 1) are discussed.
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  • 199
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 2378-2382 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: One-bond 13C, 13C-spin-coupling constants have been measured, with natural isotope abundance, in η4-diene, η3-allyl and η2-ene transition-metal carbonyl complexes. Typical values of 1J(C,C) are given for Fe-, Ru- and Os-complexes with the three types of olefinic ligands. The effects of substituents and the structural significance of the C,C-coupling constants are discussed.
    Additional Material: 4 Tab.
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  • 200
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 2383-2392 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism (CD.) spectra of all-trans-(3S, 3′S) astaxanthin diacetate and its 9-cis, 13-cis, 9,9′-di-cis, 9,13′-di-cis, and 9,13-di-cis isomers conform to the rules previously formulated for optically active carotenoids with a 4-oxo-β-end ring containing an asymmetric C-atom [1]. Thus the CD. bands of the all-trans and the di-cis isomers show the same signs whereas those of the mono-cis isomers have opposite signs. The CD. spectra of all the astaxanthin diacetate isomers invert sign upon cooling to -180°. The CD. spectra of the 9-mono-cis and 9,9′-di-cis isomers and to a lesser extent also those of the 9, 13′-di-cis and 9, 13-di-cis isomers are concentration dependent at -180°, with the longest wavelength band giving at the higher concentration a bisignate CD. curve under the main absorption characteristic of aggregation. This phenomenon has been observed only in isomers with a 9-cis linkage. It is suggested that steric hindrance prevents such aggregation taking place in the other isomers.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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