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  • 1995-1999  (2,812)
  • 1955-1959  (2,457)
  • Organic Chemistry  (5,143)
  • Brassica napus
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Year
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  • 1
    Electronic Resource
    Electronic Resource
    Wound-induced increases in the glucosinolate content of oilseed rape and their effect on subsequent herbivory by a crucifer specialist (1999)
    Springer
    Entomologia experimentalis et applicata 91 (1999), S. 163-167 
    Details
    ISSN: 1570-7458
    Keywords: Brassica napus ; Psylliodes chrysocephala ; glucosinolates ; jasmonic acid ; induction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Damage to the oilseed rape plant (Brassica napus L.) by the cabbage stem flea beetle, Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae) induces systemic changes to the glucosinolate profile, most noticeably an increase in the concentration of indole glucosinolates. When jasmonic acid was applied to the cotyledons of the plant, a similar effect was observed. Feeding tests with artificial substrates compared a glucosinolate fraction from jasmonic acid-treated plants with a similar fraction from untreated plants. In these tests, alterations to the glucosinolate profile increased the feeding of a crucifer-specialist feeder (P. chrysocephala). However, in whole plant tests, P. chrysocephala did not feed more on the jasmonic acid treated plants than on the controls. This implies that other aspects of the damage response are being induced by the jasmonic acid treatment and having a negative effect on subsequent herbivory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003661626234
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  • 2
    Electronic Resource
    Electronic Resource
    Comparing responses of grain legumes, wheat and canola to applications of superphosphate (1999)
    Springer
    Nutrient cycling in agroecosystems 53 (1999), S. 157-175 
    Details
    ISSN: 1573-0867
    Keywords: Brassica napus ; Cicer arietinum ; current P ; Lens culinaris ; Lupinus albus ; Lupinus angustifolius ; P concentration response ; P content response ; Pisum sativum ; previous P ; sigmoid response ; single superphosphate ; Triticum aestivum ; Vicia faba ; yield response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Phosphorus (P) is a major deficiency of soils of south-western Australia (WA). The fertilizer P requirements are not known for grain legumes being evaluated for neutral to alkaline, fine textured soils in WA. To rectify this, glasshouse and field experiments were undertaken to compare the responses of several grain legume species, wheat and canola to applications of single superphosphate and the results are reported in this paper. The glasshouse experiments measured responses of dried tops, harvested at 26 to 42 days after sowing, to P that was freshly-applied (current P) and previously-applied (previous P). Responses in the glasshouse were measured using yield, P concentration and P content (P concentration multiplied by yield) of oven dried tops of the following: wheat (Triticum aestivum), canola (Brassica napus), faba bean (Vicia faba), chickpea (Cicer arietinum), lentil (Lens culinaris), field pea (Pisum sativum), albus lupin (Lupinus albus) and narrow leaf lupin (Lupinus angustifolius). Field experiments in 1994 and 1995 compared seed (grain) yield responses of faba bean, chickpea, lentil, albus lupin and wheat to applications of current P. The P was banded (drilled) with the seed while sowing at 5 cm depth. Canola and wheat produced very large yield responses to increasing applications of current P. Responses were much smaller for albus lupin, faba bean and chickpea. Responses for lentil, narrow leaf lupin and field pea, fell in between responses of the small and large seeded species. Similar trends for responses were obtained as measured using yield, P concentration, or P content. For soils treated with previous P, similar trends were observed as for current P, but differences in yield responses between species were much less marked and the response curves tended to become more sigmoid. In the field experiments, grain yield responses to current P of albus lupin and chickpea were less than that for wheat. Relative to wheat, faba bean was the most responsive grain legume to applications of current P, with lentil producing similar responses to wheat in one experiment at a newly cleared, P deficient site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009798506480
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  • 3
    Electronic Resource
    Electronic Resource
    Polyploidization in embryogenic microspore cultures ofBrassica napus L. cv. Topas enables the generation of doubled haploid clones by somatic embryogenesis (1999)
    Springer
    Protoplasma 208 (1999), S. 240-247 
    Details
    ISSN: 1615-6102
    Keywords: Androgenesis ; Brassica napus ; Ploidy ; Pollen ; Rapeseed ; Somatic embryogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Embryogenic microspore and pollen culture followed by subculture of microspore-derived plantlets enabled the production of clones ofBrassica napus cv. Topas. Flow-cytometric analysis revealed that most microspore- and pollen-derived embryos (pEMs) were haploid initially. Spontaneous diploidization occurred at the globular stage of the pEMs, and was expressed as the relative increase of the 2C and 4C nuclear DNA content. Diploidization occurred throughout various organs of the pEMs and resulted in the formation of haploid and doubled haploid chimerics. In some embryos, nearly all cells were doubled haploid. From early cotyledon stage onward, pure haploid embryos were not observed anymore. At late cotyledon and germination stages, pure doubled haploid embryos and plantlets increased in number. Tetraploid pEMs were found occasionally. A culture regime was established to induce somatic embryos on the pEM-derived young plantlets. The ploidy of the somatic embryos varied highly and tended to be the same as that of the tissue at the initiation site on the pEM-plant. The results show that during the embryogenic development ofB. napus microspores, spontaneous diploidization occurs at globular stage, and increases progressively, resulting in the formation of chimerical haploid and doubled haploid plants as well as pure doubled haploid plants; ploidy neither affects pEM development at embryo developmental stages nor somatic embryogenesis, that starts on young pEM-derived plantlets; doubled haploid somatic embryos can be cloned from single pEM-derived plantlets; and doubled haploid embryos develop to fertile plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279095
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  • 4
    Electronic Resource
    Electronic Resource
    The 35S-CaMV promoter is silent during early embryogenesis but activated during nonembryogenic sporophytic development in microspore culture (1999)
    Springer
    Protoplasma 208 (1999), S. 257-264 
    Details
    ISSN: 1615-6102
    Keywords: Brassica napus ; Microspore embryogenesis ; Cauliflower mosaic virus 35S promoter ; Sporophytic development ; Tobacco ; Zygotic embryogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cauliflower mosaic virus 35S (35S-CaMV) promoter, which is generally used as a constitutive promoter in plants, is known to be silent during microspore and pollen development. Here we analyzed whether the 35S-CaMV promoter fused to thegus (β-glucuronidase) gene can be used as a marker for early sporophytic development in embryogenic microspore cultures of tobacco andBrassica napus. In microspore culture ofB. napus, the 35S-CaMV promoter remained off from the start of embryogenic culture up to the mid-cotyledonary embryo stage. 35S-CaMV promoter activity was only present in those microspores that initiated sporophytic development, but failed to enter embryogenic development. Similar results were also obtained with shed-microspore cultures of tobacco, in which rapid, direct embryogenesis takes place. In isolated-microspore cultures, in which embryogenesis is delayed, an intermitting period of sporophytic development was observed, characterized by extensive 35S-CaMV promoter activity. Therefore, the 35S-CaMV promoter discriminates between two classes of sporophytic development: it is activated in microspores which change fate from gametophytic into (temporarily) nonembryogenic sporophytic development, whereas the promoter is silent in sporophytic microspores that enter embryogenic development directly. This mirrors our observation that the 35S-CaMV promoter is also silent in young zygotic embryos.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279097
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  • 5
    Electronic Resource
    Electronic Resource
    Identification of coiled bodies inBrassica napus nuclei during embryogenesis and early germination (1999)
    Springer
    Protoplasma 207 (1999), S. 106-113 
    Details
    ISSN: 1615-6102
    Keywords: Brassica napus ; Coiled bodies ; Embryogenesis ; Germination ; Nucleolus-associated bodies ; Small nuclear RNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nucleolus-associated bodies characterize interphase nuclei of many plant species. The recent demonstration that such bodies contain small nuclear ribonucleoproteins as well as coilin clearly indicates that they belong to a larger family of nuclear structures, known as coiled bodies, that have been intensively studied in a variety of animal cell types. In a previous work, we have shown that coiled bodies were present in close association with the nucleolus inZea mays dry seeds as well as during subsequent stages of germination. This study reveals that similar nuclear structures were also present duringBrassica napus embryogenesis starting at the torpedo stage and that they were, likewise, generally located on the nucleolar surface. As in the case ofZ. mays, coiled bodies were observed in cells of dry seeds as well as in those of early germinating tissues. These bodies were labelled with monoclonal antibody K121, an antibody reacting with the unique 5′-terminal cap structure containing 2,2,7-trimethylguanosine that characterizes small nuclear RNAs. Owing to their intimate association with the nucleolus in all stages studied, the possibility is considered that, in these plant cells, coiled bodies are assembled on an organizer element located within this organelle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01294718
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  • 6
    Electronic Resource
    Electronic Resource
    Interaction between composite elements in the napA promoter: both the B-box ABA-responsive complex and the RY/G complex are necessary for seed-specific expression (1999)
    Springer
    Plant molecular biology 40 (1999), S. 699-709 
    Details
    ISSN: 1573-5028
    Keywords: Brassica napus ; seed ; napin ; promoter ; gene regulation ; ABA ; ABRE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During seed maturation, the transcriptional activity of napin genes is regulated by developmental signals involving the transcriptional activator ABI3 and abscisic acid (ABA). To localize cis elements involved in the seed-specific activity of the napin napA promoter, a systematic analysis was performed focusing on two major element complexes, the B-box and RY/G. Substitution mutation analysis using promoter-reporter gene fusions in stable transgenic tobacco showed synergistic interactions between elements within these complexes. The distal part of the B-box shows similarities to abscisic acid response elements and the proximal portion contains a CA-rich element. In vitro studies involving Exonuclease III protection and electrophoretic mobility shift assays revealed binding by nuclear proteins to elements within the B-box. The distal and proximal parts of the B-box were found to bind distinct nuclear protein complexes. By gain-of-function analysis with a tetramer of the B-box fused to a truncated (−46) cauliflower mosaic virus (CaMV) 35S minimal promoter, it was demonstrated that the B-box mediates strong activity in seeds. Further, it was shown that the elements in the B-box constitute an ABA-responsive complex, since the B-box tetramer mediates ABA-responsiveness in vegetative tissues to a construct containing the CaMV virus 35S enhancer (−343 to −90). Thus, the seed-specific activity of the napA promoter relies on the combinatorial interaction between the RY/G complex and the B-box ABA-responsive complex during the ABA response in seed development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006206124512
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  • 7
    Electronic Resource
    Electronic Resource
    Age-dependent wound induction of a myrosinase-associated protein from oilseed rape (Brassica napus) (1999)
    Springer
    Plant molecular biology 41 (1999), S. 171-180 
    Details
    ISSN: 1573-5028
    Keywords: Brassica napus ; GUS ; jasmonate ; myrosinase-associated protein ; promoter ; wounding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to study the expression of the induced form of myrosinase-associated protein (iMyAP), a genomic clone encoding the protein was isolated from Brassica napus. The coding portion of the gene was found to consist of five exons separated by one long intron of 938 bp and three shorter introns of ca. 100 bp. A 1.9 kb promoter fragment including the 5′-untranslated region was cloned in front of the coding portion of the Escherichia coli iudA gene and transformed into Arabidopsis thaliana. Expression was observed in hypocotyls of 4-day seedlings, but in 7-day seedlings the iMyAP promoter did not direct expression. In flowering plants, only the abscission zone of the young silique displayed promoter activity. In contrast, mechanical wounding of 7-day seedlings induced a systemic expression in all cells of the cotyledons. Wounding of 14-day seedlings gave rise to systemic induced expression mainly in the vascular tissue. However, mechanical wounding and wounding by flea beetles (Phyllotreta undulata) of 4-week old plants only gave rise to a local induction of the promoter, suggesting that the systemic signal system is age-dependent. Methyl jasmonate also induced iMyAP expression. In situ and northern analysis of iMyAP transcripts in young leaves of B. napus showed that the induction was high after 1 h and absent after 24 h. Comparison of the effect of different types of wounding on the iMyAP promoter induction in transgenic Arabidopsis showed that similar degrees of local induction were achieved regardless of the degree of macerated tissue left on the plant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006364607564
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of aluminium on canola roots (1999)
    Springer
    Plant and soil 216 (1999), S. 27-33 
    Details
    ISSN: 1573-5036
    Keywords: Aluminium toxicity ; Brassica napus ; canola ; root growth ; ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract There is little information on the effects of aluminium (Al) on canola (Brassica napus var. napus L.), which is a commercially important crop species in many parts of the world. In this report, we describe the effects of Al on roots of canola seedlings grown hydroponically in a nutrient solution at pH 4.5. The morphological and ultrastructural changes that accompanied these growth effects were examined. Additions to the nutrient solution of Al at concentrations below 40 μM stimulated root growth of canola seedlings, increasing both the size and number of central cap cells. The stimulation of root growth did not appear to be due to the alleviation of a proton toxicity at the root surface. At concentrations of Al above 60 μM, root growth was strongly inhibited, with cellular damage being observed primarily in peripheral root cap cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004789014255
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  • 9
    Electronic Resource
    Electronic Resource
    The promotive effect of combustion products from plant vegetation on the release of seeds from dormancy (1999)
    Springer
    Plant growth regulation 28 (1999), S. 129-132 
    Details
    ISSN: 1573-5087
    Keywords: dormancy ; Lactuca sativa ; lettuce seeds ; Brassica napus ; rapeseed ; combustion products ; Salix viminalis ; Themeda triandra ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In darkness, dormancy was imposed on seeds of lettuce (Lactuca sativa L. cv. Grand rapids) by high temperature and on seeds of oilseed rape (Brassica napus L. cv. Apex) by osmotic stress using polyethylene glycol (PEG 8000). In both cases, dormancy was broken by incubating the seeds in aqueous extracts of combustion products from Salix viminalis wood chips or Themeda triandra leaves. Dormancy of rapeseed, but not lettuce, was also broken by a solution of smoke from burnt straw of Triticum aestivum. The greatest stimulation from burnt vegetation was achieved with an aqueous extract of pyrolysed willow wood chips, which had been subjected to temperatures of up to 800 °C during combustion in a down-draught gasifier. This suggests that some biologically active substances obtained from combustion of plant tissues are highly heat-stable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006222705855
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  • 10
    Electronic Resource
    Electronic Resource
    Perception of Oviposition-Deterring Pheromone by Cabbage Seed Weevil (Ceutorhynchus assimilis) (1999)
    Springer
    Journal of chemical ecology 25 (1999), S. 1655-1670 
    Details
    ISSN: 1573-1561
    Keywords: Oviposition-deterring pheromone ; host marking pheromone ; marker ; electrophysiology ; contact chemoreception ; gustatory sensilla ; antenna ; behavior ; Ceutorhynchus assimilis ; Coleoptera ; Curculionidae ; Brassica napus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Following oviposition into a pod of oilseed rape (Brassica napus), the female cabbage seed weevil (Ceutorhynchus assimilis) marks the pod with oviposition-deterring pheromone (ODP) by brushing it with her eighth abdominal tergite. On an unmarked pod, oviposition site selection was always accompanied by intensive antennation of the pod. Females approaching a freshly ODP-marked pod brought their antennae within 1 mm of the pod but usually did not antennate it before rejecting it for oviposition. Females with the clubs of their antennae amputated continued to discriminate pods from stems or petioles as oviposition sites but showed no behavioral response to ODP. Extracts of volatiles air-entrained from ovipositing weevils failed to inhibit oviposition. Air passed over a behaviorally active extract of ODP did not elicit a detectable electroantennogram response. By contrast, when presented as a gustatory stimulus to the sensilla chaetica of the antennal club, a behaviorally active extract of ODP from postdiapause, gravid females elicited a strong electrophysiological response. This response usually involved more than one cell and displayed a phasic–tonic time course over the recording period of 10 sec. Extract from prediapause (and hence sexually immature) females elicited neither behavioral nor electrophysiological (contact) responses. Thus the ODP of the cabbage seed weevil is sensed primarily by contact chemoreception at the sensilla chaetica of the antennae, and the electrophysiological responses recorded from these gustatory sensilla are of value as the basis of a bioassay to assist identification of the active constituent(s) of the pheromone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1020801319251
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  • 11
    Electronic Resource
    Electronic Resource
    Estimation of seed weight, oil content and fatty acid composition in intact single seeds of rapeseed ( Brassica napus} L.) by near-infrared reflectance spectroscopy (1999)
    Springer
    Euphytica 106 (1999), S. 79-85 
    Details
    ISSN: 1573-5060
    Keywords: Brassica napus ; fatty acid composition ; intact single seeds ; NIRS ; oil content ; seed weight
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The potential of near-infrared reflectance spectroscopy (NIRS) for the simultaneous analysis of seed weight, total oil content and its fatty acid composition in intact single seeds of rapeseed was studied. A calibration set of 530 single seeds was analysed by both NIRS and gas-liquid chromatography (GLC) and calibration equations for the major fatty acids were developed. External validation with a set of 75 seeds demonstrated a close relationship between NIRS and GLC data for oleic (r = 0.92) and erucic acid (r = 0.94), but not for linoleic (r = 0.75) and linolenic acid (r = 0.73). Calibration equations for seed weight and oil content were developed from a calibration set of 125 seeds. A gravimetric determination was used as reference method for oil content. External validation revealed a coefficient of correlation between NIRS and reference methods of 0.92 for both traits. The performance of the calibration equations for oleic and erucic acid was further studied by analysing two segregating F2 seed populations not represented in the calibration set. The results demonstrated that a reliable selection for both fatty acids in segregating populations can be made by using NIRS. We concluded that a reliable estimation of seed weight, oil content, oleic acid and erucic acid content in intact, single seeds of rapeseed is possible by using NIRS technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003592115110
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  • 12
    Electronic Resource
    Electronic Resource
    The restorer Rfo gene acts post-translationally on the stability of the ORF138 Ogura CMS-associated protein in reproductive tissues of rapeseed cybrids (1999)
    Springer
    Plant molecular biology 40 (1999), S. 893-902 
    Details
    ISSN: 1573-5028
    Keywords: Brassica napus ; cytoplasmic male sterility (CMS) ; mitochondrial gene expression ; polysomes ; post-translational degradation ; restoration of fertility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This paper describes the analysis of the effect of the restorer gene Rfo on the expression of the ORF138 protein associated with Ogura cytoplasmic male sterility (CMS) which has been engineered in rapeseed by protoplast fusion. We show that the presence of the Rfo gene in the genome of the plants decreases the amount of ORF138 protein in floral buds, this effect being the most dramatic in anthers at the stage of development when the sterile phenotype is normally expressed. However, the amount of orf138 transcripts is not affected by the Rfo gene in the same organs at the same stages. Total polysome analyses of buds and anthers show that the orf138 transcripts are translated with the same efficiency in sterile and restored plants. From these results we infer that the Rfo gene product acts on the post-translational stability of the ORF138 protein, leading to a decrease in the accumulation of the protein and a restoration of fertility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006223908044
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  • 13
    Electronic Resource
    Electronic Resource
    The promoter of a Brassica napus lipid transfer protein gene is active in a range of tissues and stimulated by light and viral infection in transgenic Arabidopsis (1999)
    Springer
    Plant molecular biology 41 (1999), S. 75-87 
    Details
    ISSN: 1573-5028
    Keywords: Brassica napus ; cauliflower mosaic virus ; epidermis ; gene expression ; light induction ; lipid transfer protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract cDNA and genomic clones encoding Brassica napus non-specific lipid transfer proteins (LTP) were isolated and sequenced. The encoded amino acid sequences were very similar to those reported previously for LTPs from B. napus and other species. Sequence information indicates that B. napus contains an LTP gene family. The 5′-flanking region of one gene, designated BnLTP, was fused to GUS and the fusion introduced into Arabidopsis. LTP transcripts and BnLTP-Gus expression were present predominantly in the epidermis of leaf and stem, consistent with the hypothesised function of LTPs in the deposition of cuticular or epicuticular waxes. However, GUS activity was detected in other tissues, including lateral root initials, anthers, stigmas and vascular tissues, which may suggest additional functions. LTP transcript levels in B. napus and Arabidopsis and BnLTP-GUS expression in transgenic Arabidopsis were stimulated by blue and red light but not UV-B. BnLTP promoter activity was also stimulated upon viral infection, at a time when the virus had spread systemically. No increase in expression was observed in response to cold or wounding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006232700835
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  • 14
    Electronic Resource
    Electronic Resource
    Greenhouse and field evaluations of transgenic canola against diamondback moth, shape Plutella xylostella, and corn earworm, shape Helicoverpa zea (1998)
    Springer
    Entomologia experimentalis et applicata 88 (1998), S. 17-24 
    Details
    ISSN: 1570-7458
    Keywords: transgenic plants ; transgenic canola ; Brassica napus ; Bacillus thuringiensis ; diamondback moth ; corn earworm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Canola (Brassica napus L.) cultivars Oscar and Westar, engineered with a Bacillus thuringiensis (Bt) cryIA(c) gene, were evaluated for resistance to lepidopterous pests, diamondback moth, Plutella xylostella L. (Plutellidae) and corn earworm, Helicoverpa zea (Boddie) (Noctuidae) in greenhouse and field conditions. In greenhouse preference assays conducted at vegetative and flowering plant stages, transgenic plants recorded very low levels of damage. A 100% diamondback moth mortality and ≈90% corn earworm mortality were obtained on transgenic plants in greenhouse antibiosis assays. The surviving corn earworm larvae on transgenic plants had reduced head capsule width and body weight. Mortality of diamondback moth and corn earworm were 100% and ≈95%, respectively, at different growth stages (seedling, vegetative, bolting, and flowering) on the transgenic plants in greenhouse tests. In field tests conducted during 1995–1997, plots were artificially infested with neonates of diamondback moth or corn earworm or left for natural infestation. Transgenic plants in all the treatments were highly resistant to diamondback moth and corn earworm larvae and had very low levels of defoliation. Plots infested with diamondback moth larvae had greater damage in both seasons as compared with corn earworm infested plots and plots under natural infestation. After exposure to defoliators, transgenic plants usually had higher final plant stand and produced more pods and seeds than non-transgenic plants. Diamondback moth injury caused the most pronounced difference in plant stand and pod and seed number between transgenic and non-transgenic plants. Our results suggest that transgenic canola could be used for effective management of diamondback moth and corn earworm on canola.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003209300897
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  • 15
    Electronic Resource
    Electronic Resource
    Influence of nitrogen nutrition and metabolism on ammonia volatilization in plants (1998)
    Springer
    Nutrient cycling in agroecosystems 51 (1998), S. 35-40 
    Details
    ISSN: 1573-0867
    Keywords: ammonia emission ; ammonium ; apoplast ; Brassica napus ; compensation point ; glutamine synthetase ; Hordeum vulgare
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Barley (Hordeum vulgare L. cv. Golf) was grown in solution culture with controlled nitrogen availability in order to study the influence of nitrogen nutrition on ammonia emission from the leaves. Ammonia emission measured in cuvettes connected to an automatic NH3 monitor was close to zero for nitrate grown plants but increased to 0.9–1.3 nmol NH3 m-2 leaf area s-1 after 3–5 days of ammonium nutrition. Increasing concentrations from 0.5 to 10 mM NH4 + in the root medium increased NH3 emission from the shoots, root glutamine synthetase activity and NH4 + concentrations in apoplast, xylem sap and bulk tissue, while apoplastic pH values decreased. Inhibition of glutamine synthetase in nitrate grown barley plants by addition of 1 mM methionine sulfoximine (MSO) to the root medium caused ammonia emission to increase 5 to 10-fold after 2–3 hours. At the same time shoot tissue ammonium concentrations started to increase. Addition of an inhibitor of photorespiration, 1 mM pyrid-2-yl hydroxymethane sulfonate (HPMS) reduced this increase in ammonia emission showing a relation between NH3 emission and photorespiration. Oil seed rape (Brassica napus L. cv. Global) plants grown at 3 different nitogen levels (2N, 4N and 7N) in a sand/soil mixture showed increasing NH3 compensation points with increasing N level. This increase was highly correlated with increasing NH4 + concentrations in the leaf apoplast and total leaf tissue. The NH3 compensation points could be succesfully predicted on basis of the pH and NH4 + concentration in the leaf apoplast.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009796610912
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  • 16
    Electronic Resource
    Electronic Resource
    Brassica napus hsp90 can autophosphorylate and phosphorylate other protein substrates (1998)
    Springer
    Molecular and cellular biochemistry 185 (1998), S. 33-38 
    Details
    ISSN: 1573-4919
    Keywords: hsp90 ; Brassica napus ; protein kinase ; phosphorylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract A Brassica napus cDNA encoding the 90 kDa heat shock protein, hsp90, was modified to add 6 histidines at the C-terminus and expressed in insect cells to prepare a recombinant histidine-tagged hsp90. The recombinant protein was purified over Ni2+-NTA agarose columns and its identity was confirmed by Western blotting, using a plant hsp90-specific antiserum. Incubation of purified hsp90 with [γ-32P] ATP in the presence of Mn2+ resulted in its autophosphorylation on serine residues. The purified hsp90 could also phosphorylate other protein substrates such as histones and casein in the presence of Mn2+. Analysis of phosphorylated casein revealed that serine residues are phosphorylated by hsp90. This is the first demonstration that a cytosolic hsp90 homolog can phosphorylate other protein substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006884306169
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  • 17
    Electronic Resource
    Electronic Resource
    A rapeseed FAE1 gene is linked to the E1 locus associated with variation in the content of erucic acid (1998)
    Springer
    Theoretical and applied genetics 96 (1998), S. 177-186 
    Details
    ISSN: 1432-2242
    Keywords: Key words β-ketoacyl-CoA synthase ; FAE1 ; Brassica napus ; Erucic acid ; E1 locus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The synthesis of very long chain fatty acids occurs in the cytoplasm via an elongase complex. A key component of this complex is the β-ketoacyl-CoA synthase, a condensing enzyme which in Arabidopsis is encoded by the FAE1 gene. Two sequences homologous to the FAE1 gene were isolated from a Brassica napus immature embryo cDNA library. The two clones, CE7 and CE8, contain inserts of 1647 bp and 1654 bp, respectively. The CE7 gene encodes a protein of 506 amino acids and the CE8 clone, a protein of 505 amino acids, each having an approximate molecular mass of 56 kDa. The sequences of the two cDNA clones are highly homologous yet distinct, sharing 97% nucleotide identity and 98% identity at the amino acid level. Southern hybridisation showed the rapeseed β-ketoacyl-CoA synthase to be encoded by a small multigene family. Northern hybridisation showed the expression of the rapeseed FAE1 gene(s) to be restricted to the immature embryo. One of the FAE1 genes is tightly linked to the E1 locus, one of two loci controlling erucic acid content in rapeseed. The identity of the second locus, E2, is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001220050725
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  • 18
    Electronic Resource
    Electronic Resource
    Identification of molecular markers associated with linoleic acid desaturation in Brassica napus (1998)
    Springer
    Theoretical and applied genetics 96 (1998), S. 897-903 
    Details
    ISSN: 1432-2242
    Keywords: Key words RAPD ; Linoleic linolenic acid ; Brassica napus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Linolenic acid is a component of canola oil that is readily oxidized, which results in a reduced frying stability and shelf life of the oil. The reduction of linolenic acid in canola seed has therefore been an important breeding objective for many years. The inheritance of linolenic acid concentrations in seed oil is polygenic and is also strongly influenced by the environment. For these reasons, molecular markers are sought to assist in early and reliable selection of desired low linolenic acid genotypes in breeding programmes. Molecular markers associated with low linolenic acid loci were identified in a doubled-haploid population derived from a cross between the Brassica napus lines, ‘Apollo’ (low linolenic)×YN90-1016 (high linolenic) using RAPDs and bulked segregant analysis. A total of 16 markers were distributed over three linkage groups, which individually accounted for 32%, 14% and 5% of the phenotypic variation in linolenic acid content. The rapeseed fad3 gene was mapped near the locus controlling 14% of the variation. The mode of inheritance appeared to be additive, and a QTL analysis showed that collectively the three loci explained 51% of the phenotypic variation within this population. PCR fragments for low linolenic acid ‘Apollo’ alleles (3% linolenic acid) were identified at all three loci. Simultaneous selection for low linolenic acid ‘Apollo’ alleles at each locus resulted in a group of DH lines with 4.0% linolenic acid. The use of these makers in the breeding programme will enhance the breeding of low linolenic acid B. napus cultivars for production in Canada.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001220050817
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  • 19
    Electronic Resource
    Electronic Resource
    A pollen-dispersal experiment with transgenic oilseed rape. Estimation of the average pollen dispersal of an individual plant within a field (1998)
    Springer
    Theoretical and applied genetics 96 (1998), S. 886-896 
    Details
    ISSN: 1432-2242
    Keywords: Key words Risk assessment ; Pollen flow ; Transgene ; Fourier transforms ; Brassica napus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In order to help establish a basis for the assessment of gene flow associated with the large-scale release of transgenic oilseed rape, we previously designed a method which makes it possible to retrieve the average pollen dispersal of a single plant from that of a large source plot. The ‘individual’ pollen distribution thus obtained is less dependent on the experimental design than pollen distributions usually published and could therefore be used to model the possible escape of a transgene from commercial transgenic crops. In this study we report on a field experiment set up to study the pollen dispersal from an herbicide-resistant transgenic variety of oilseed rape and to test the applicability of the method on the experimental data. Two techniques were used to determine the individual pollen dispersal, and their outcomes are compared. The results suggest that approximately half of the pollen produced by an individual plant fell within 3 m and that the probability of fertilisation afterwards decreased slowly along a negative exponential of the distance. Comparison with the global pollen distribution from the source plot indicates that pollen-dispersal distributions based on dispersal from whole plots instead of individual plants would have underestimated the proportion of pollen that was dispersed over average or long distances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001220050816
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  • 20
    Electronic Resource
    Electronic Resource
    Targeted mapping approaches to identify DNA markers linked to the Rfp1 restorer gene for the ‘Polima’ CMS of canola (Brassica napus L.) (1998)
    Springer
    Theoretical and applied genetics 97 (1998), S. 431-438 
    Details
    ISSN: 1432-2242
    Keywords: Key words Targeted mapping ; RFLP ; RAPD ; Brassica napus ; Polima CMS ; Nearly isogenic line ; Bulked segregant analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We have used two targeting approaches [pairs of nearly isogenic lines (NILs) and bulked segregant analysis] to identify DNA markers linked to the Rfp1 restorer gene for the pol CMS of canola (Brassica napus L.). We were able to target the Rfp1 locus as efficiently by comparing NILs as by bulked segregant analysis, and it was demonstrated in this instance that double-screening strategies could significantly improve the overall targeting efficiency. The chance occurrence of shared homozygosity at specific unlinked chromosomal regions in the bulks was found to limit the efficiency of bulked segregant analysis, while the efficiency of NIL comparison was limited by residual DNA from the donor cultivar at scattered sites throughout the genome of the NILs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001220050913
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  • 21
    Electronic Resource
    Electronic Resource
    Heterologous and homologous transgenic expression directed by a 2S seed storage promoter of Brassica napus (1998)
    Springer
    Transgenic research 7 (1998), S. 165-172 
    Details
    ISSN: 1573-9368
    Keywords: pollen ; seed ; storage protein ; Brassica napus ; heterologous expression ; homologous expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Few plant genes have been analysed in both homologous and heterologous transgenic systems. In this study, deletion mutants of the storage protein promoter napA fused to the receptor gene uidA (GUS) were analysed for their ability to direct tissue-specific expres sion in transgenic tobacco as well as transgenic Brassica napus. In seeds, qualitatively similar results have previously been obtained, demonstrating that transcription factors in the heterologous tobacco system recognized the napA promoter cis elements, more or less in the same way as in B. napus (Ellerstrom et al., 1996; Stalberg et al., 1996). However, in anthers of the transgenic plants, clear differences were noted. The napA promoter constructs were inactive in transgenic B. napus anthers. In contrast, tobacco anthers displayed activities of similar magnitudes to those previously found in the seed for the respective promoter constructs. Interestingly, in seven constructs the activity in the anthers was retained dow nstream from an imperfect ABRE element, whereas no activity could be detected in the seed. Another clear difference was that a region from −211 to −152 silenced the expression in anthers whereas this region had no effect on the activity in the seed. Likewise, in tobacco the napA promoter showed a low activity in leaves. Histochemical staining of young tobacco leaves showed that this activity was considerably higher in stomata guard cells than in the mesophyll cells while the leaves of the B. napus plants had a diffuse and barely detectable staining in the mesophyll cells. The high level of napA transcription in tobacco anthers indicates that the set of transcription factors and corresponding cis-sequences that direct tissue-specific transcription in this organ are similar to those responsible for seed-specific expression. However, comparison of the levels of expression in anthers and seeds in individual plants revealed that there was no correlation between the activities in the two organs, which suggests that positional effects influence the transcription complexes differently in seeds and anthers. Further, this study shows that careful analysis of expression directed by promoter mutants in a heterologous transformation system might reveal important cis-elements, not discernible in the tighter homologous situation
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008884728643
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  • 22
    Electronic Resource
    Electronic Resource
    sn-1-Acylglycerol-3-phosphate acyltransferase of Escherichia coli causes insertion of cis-11 eicosenoic acid into the sn-2 position of transgenic rapeseed oil (1998)
    Springer
    Molecular breeding 4 (1998), S. 39-46 
    Details
    ISSN: 1572-9788
    Keywords: sn-1-acylglycerol-3-phosphate acyltransferase ; Brassica napus ; cis-11 eicosenoic acid ; Escherichia coli ; triacylglycerol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The plsC gene of Escherichia coli encoding sn-1-acylglycerol-3-phosphate acyltransferase was modified by inserting an endoplasmic reticulum retrieval signal to its 3′ end and introduced into rapeseed (Brassica napus L.) plants under the control of a napin promotor. In developing seeds from transgenic plants an sn-1-acylglycerol-3-phosphate acyltransferase activity was detectable which showed substrate specificities typical of the E. coli enzyme. Moreover, seed oil from the transformants unlike that from untransformed plants contained substantial amounts of triacylglycerol species esterified with very-long-chain fatty acids at each glycerol position. Analysis of fatty acids at the sn-2 position of triacylglycerol showed hardly any very-long-chain fatty acids in untransformed plants, but in certain transformants these fatty acids were present, namely about 4% erucic acid and 9% eicosenoic acid. These data demonstrate that the bacterial acyltransferase can function in developing rapeseed and alters the stereochemical composition of transgenic rape seed oil by directing very-long-chain fatty acids, especially cis-11 eicosenoic acid, to its sn-2 position.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009615229344
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  • 23
    Electronic Resource
    Electronic Resource
    Reaction of Brassica juncea (Indian Mustard) Lines to Australian Isolates of Leptosphaeria maculans under Glasshouse and Field Conditions (1998)
    Springer
    European journal of plant pathology 104 (1998), S. 895-902 
    Details
    ISSN: 1573-8469
    Keywords: Brassica napus ; Brassica carinata ; field resistance ; pathogenicity ; plant breeding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Brassica juncea (Indian mustard) lines from diverse geographical locations around the world and from Australian breeding programs were screened for resistance to the blackleg fungus, Leptosphaeria maculans, in both glasshouse and field trials. The five Australian L. maculans isolates used in glasshouse trials could be classified into two groups; those that attacked all B. juncea lines, and those that attacked none. All these isolates caused lesions on cotyledons of B. napus cultivars including Westar, Glacier and Quinta, suggesting that they are in Pathogenicity Group 4 as described by Koch et al. (1991). The two isolates that attacked B. juncea also attacked B. napus lines to a similar extent, but did not attack the two B. carinata lines tested. Brassica lines were sown in a blackleg disease nursery at Lake Bolac, Victoria, Australia, and five indicators of blackleg disease were measured (survival rate, disease rating, disease incidence, external and internal lesion length). All 92 B. juncea lines developed blackleg symptoms. Although they displayed a high disease incidence in the field, almost all of the B. juncea lines were more blackleg-resistant than a B. napus cultivar, Dunkeld, which is amongst the most resistant cultivars in commercial production in Australia. Four B. carinata lines were more resistant than any of the B. juncea lines, suggesting that this species may be a useful source of blackleg resistance in B. napus breeding programs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008609131695
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  • 24
    Electronic Resource
    Electronic Resource
    Estimating the fatty acid composition of the oil in intact-seed rapeseed (Brassica napus L.) by near-infrared reflectance spectroscopy (1998)
    Springer
    Euphytica 101 (1998), S. 221-230 
    Details
    ISSN: 1573-5060
    Keywords: Brassica napus ; fatty acid composition ; NIRS ; rapeseed ; reflectance spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The objective of this work was to evaluate the potential of near-infrared reflectance spectroscopy (NIRS) as a rapid method to estimate the fatty acid composition of the oil in intact-seed samples of rapeseed. A total of 549 samples (3 g intact seed) from selected mutant and breeding lines were scanned by NIRS, and 220 of them were selected and scanned again by using two different adapters, which reduced the sample size to 300 and 60 mg, respectively. Selected samples were analysed by gas liquid chromatography and calibration equations for individual fatty acids were developed. Calibrations for oleic, linoleic, linolenic, and erucic acid were highly accurate, with values of r2 in cross validation from 0.95 to 0.98 (samples of 3 g), from 0.93 to 0.97 (300 mg), and from 0.84 to 0.96 (60 mg). Calibrations for palmitic and stearic acid were less accurate, with values of r2 in cross validation always lower than 0.8, probably because of the narrow range available for these fatty acids. The accuracy of the calibration equations for eicosenoic acid was very low (r2 = 0.69 in 3 g samples), although improved equations were developed (r2 from 0.78 to 0.91) when the relationship between erucic and eicosenoic acid was taken into account. We conclude that NIRS is a powerful technique to estimate the fatty acid composition of the oil in rapeseed, provided that samples covering a wide range of fatty acid levels are available, with the advantage that such estimation is possible with few additional costs when NIRS is used for the determination of other seed quality traits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018358707847
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  • 25
    Electronic Resource
    Electronic Resource
    Efficacy of bulked DNA samples for RAPD DNA fingerprinting of genetically complex Brassica napus cultivars (1998)
    Springer
    Euphytica 102 (1998), S. 65-70 
    Details
    ISSN: 1573-5060
    Keywords: Brassica napus ; RAPD ; bulked DNA ; DNA fingerprinting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Since DNA-based markers are unaffected by environmental or physiological factors, they have potential utility in the description of plant cultivars required for award of proprietary rights (i.e. Plant Breeders' Rights). The high discriminating power of this class of markers, however, can also make demonstration of uniformity and stability of such a marker within a cultivar difficult, especially for genetically-complex cultivars. This report examines the usefulness of bulking equal quantities of DNA from 14 to 20 individuals of a cultivar to identification of RAPD DNA markers that distinguish between Brassica napus cultivars of varying genetic complexity. For the four cultivars assessed (Quantum, OAC Springfield, Innovator and AC Excel), it is shown that consistent presence/absence scores are obtained from bulked DNA samples for three different RAPD markers despite a significant degree of variation among samples from individuals. Use of bulked DNA samples thus may enable identification of a distinguishing profile of RAPD markers whose presence/absence is uniform and stable even in complex cultivars. Nevertheless, RAPD markers remain limited in that they are not strictly quantitative in nature. This limitation is discussed with respect to cultivar description for plant breeders' rights applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018378304701
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  • 26
    Electronic Resource
    Electronic Resource
    Field observations on nitrogen catch crops (1998)
    Springer
    Plant and soil 201 (1998), S. 149-155 
    Details
    ISSN: 1573-5036
    Keywords: Brassica napus ; cover crop ; Raphanus sativus ; Secale cereale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Nitrogen catch crops help to reduce the loss of nitrogen from arable cropping systems during autumn and winter. The ability of catch crops to absorb nitrogen from the soil profile is affected by rate and depth of colonization of the soil by roots. The aim of the current work was to analyze total root length and root length density of catch crops in relation to above ground growth, nitrogen supply and crop species. In two field experiments roots were sampled with an auger. Experimental factors included crop species (winter rye, Secale cereale and forage rape, Brassica napus ssp. oleifera (Metzg.) Sinsk., or oil radish, Raphanus sativus spp. oleiferus (DC.) Metzg.), two sowing dates S1 and S2 (end of August and three weeks later) and two nitrogen treatments: N0, no nitrogen applied, and N1, nitrogen applied at non-limiting rate. The natural logarithm of the total root length, measured in the top 40 cm, L0–40 (km m-2), was linearly related to natural logarithm of the dry weight of the shoot, W (g m-2). There was no effect of species or sowing date on this relation. For a given W, N1 treatments showed lower values of L0–40 than N0 treatments. The decline in root length density, D (cm cm-3), with depth, X (cm), was described with the function ln D = ln D0 − qX, where D0 is the value of D at zero depth and q the linear coefficient. D0 was linearly related to L0–40, without effect of species, time of observation or N supply. The ratio D0/q, an estimate of the absolute root length, was 1.24 × L0–40. Together the relations enable estimates to be made of total root length and of root length distribution with depth using shoot dry weight of catch crops and its change with time as input. The generation of such estimates of root distribution is necessary for model studies in which the efficacy of catch crops to prevent N losses is evaluated in relation to sowing dates, distribution of N in the soil profile and the distribution of rainfall in the season.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004367530320
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  • 27
    Electronic Resource
    Electronic Resource
    A Brassica cDNA clone encoding a bifunctional hydroxymethylpyrimidine kinase/thiamin-phosphate pyrophosphorylase involved in thiamin biosynthesis (1998)
    Springer
    Plant molecular biology 37 (1998), S. 955-966 
    Details
    ISSN: 1573-5028
    Keywords: bifunctional enzyme ; Brassica napus ; cDNA ; hydroxymethylpyrimidine phosphate kinase ; thiamin ; thiamin phosphate pyrophosphorylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We report the characterization of a Brassica napus cDNA clone (pBTH1) encoding a protein (BTH1) with two enzymatic activities in the thiamin biosynthetic pathway, thiamin-phosphate pyrophosphorylase (TMP-PPase) and 2-methyl-4-amino-5-hydroxymethylpyrimidine-monophosphate kinase (HMP-P kinase). The cDNA clone was isolated by a novel functional complementation strategy employing an Escherichia coli mutant deficient in the TMP-PPase activity. A biochemical assay showed the clone to confer recovery of TMP-PPase activity in the E. coli mutant strain. The cDNA clone is 1746 bp long and contains an open reading frame encoding a peptide of 524 amino acids. The C-terminal part of BTH1 showed 53% and 59% sequence similarity to the N-terminal TMP-PPase region of the bifunctional yeast proteins Saccharomyces THI6 and Schizosaccharomyces pombe THI4, respectively. The N-terminal part of BTH1 showed 58% sequence similarity to HMP-P kinase of Salmonella typhimurium. The cDNA clone functionally complemented the S. typhimurium and E. coli thiD mutants deficient in the HMP-P kinase activity. These results show that the clone encodes a bifunctional protein with TMP-PPase at the C-terminus and HMP-P kinase at the N-terminus. This is in contrast to the yeast bifunctional proteins that encode TMP-PPase at the N-terminus and 4-methyl-5-(2-hydroxyethyl)thiazole kinase at the C-terminus. Expression of the BTH1 gene is negatively regulated by thiamin, as in the cases for the thiamin biosynthetic genes of microorganisms. This is the first report of a plant thiamin biosynthetic gene on which a specific biochemical activity is assigned. The Brassica BTH1 gene may correspond to the Arabidopsis TH-1 gene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006030617502
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  • 28
    Electronic Resource
    Electronic Resource
    Influence of Increasing Herbivore Pressure on Modification of Glucosinolate Content of Swedes (Brassica napus spp. rapifera) (1998)
    Springer
    Journal of chemical ecology 24 (1998), S. 2003-2019 
    Details
    ISSN: 1573-1561
    Keywords: Herbivore pressure ; glucosinolate ; induced response ; turnip root fly ; Delia floralis ; Brassica napus ; root damage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The effect of increasing herbivore pressure, in the form of larval feeding damage by the turnip root fly, Delia floralis, on the glucosinolate content of swede roots (Brassica napus ssp. rapifera) was investigated. Only one of the 14 root glucosinolates detected, 3-indolyl methyl glucosinolate, rose significantly with increasing levels of insect attack. Although other root glucosinolate concentrations altered following damage, the induced changes were no greater from inoculation with 20 eggs/root than with 5 eggs/root. Swedes roots that had been damaged by D. floralis contained approximately three times the concentration of total indolyl glucosinolates of control roots. This change was strongly influenced by a fourfold increase in the concentration of 1-methoxy-3-indolyl methyl glucosinolate. The total glucosinolate concentration found in swede roots remained unchanged overall as a result of a fall in the concentration of five of the aliphatic glucosinolates, which balanced the rise in aromatic glucosinolates. The relevance of these results to studies of crucifer–insect interactions are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1020729524818
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  • 29
    Electronic Resource
    Electronic Resource
    Response of Cabbage Seed Weevil (Ceutorhynchus assimilis) to Baits of Extracted and Synthetic Host-Plant Odor (1998)
    Springer
    Journal of chemical ecology 24 (1998), S. 2101-2114 
    Details
    ISSN: 1573-1561
    Keywords: Anemotaxis ; Ceutorhynchus assimilis ; Brassica napus ; host-plant extracts ; wind tunnel ; isothiocyanates ; α-farnesene ; trapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The effect of extracted and artificial oilseed rape (Brassica napus ssp. oleifera) odors on the behavioral response of male and female cabbage seed weevils (Ceutorynchus assimilis) was investigated in a wind tunnel. Odor-mediated upwind anemotaxis was induced by leaf extract and its artificial equivalent. Omission of two isothiocyanates from the artificial extract significantly reduced the upwind movement of females. Increasing the wind speed within the tunnel significantly reduced upwind movement in response to the odor of leaf and flower extracts. The artificial baits proved less attractive than simple extracts from oilseed rape. Field trapping confirmed that extracted leaf material was more attractive than artificial equivalents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1020741827544
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  • 30
    Electronic Resource
    Electronic Resource
    Visualization of the Brassica self-incompatibility S-locus on identified oilseed rape chromosomes (1998)
    Springer
    Plant molecular biology 38 (1998), S. 1081-1087 
    Details
    ISSN: 1573-5028
    Keywords: fluorescence in situ hybridization ; Brassica napus ; S-locus ; rDNAs ; image analysis ; quantitative chromosome map
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Seventy years after Karpechenko [15] first reported the accurate chromosome number of oilseed rape (Brassica napus L., 2n=38), we have developed a quantitative chromosome map of rape using computer imaging technology. The capacity to identify individual rape chromosomes will facilitate a wide range of genetic studies. Here we demonstrate the use of imaging methods in combination with fluorescence in situ hybridization to localize, on identified chromosomes, the single copy S-locus glycoprotein and S-locus-related genes involved in the self-incompatibility system of Brassica. These techniques have a broader application in plant genome research involving the mapping of single-copy genes and markers, irrespective of the plant species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006036100987
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  • 31
    Electronic Resource
    Electronic Resource
    The production of yellow-seeded Brassica napus (AACC) through crossing interspecific hybrids of B. campestris (AA) and B. carinata (BBCC) with B. napus (1998)
    Springer
    Euphytica 103 (1998), S. 329-333 
    Details
    ISSN: 1573-5060
    Keywords: Brassica napus ; yellow-seed coat ; B. campestris and B. carinata interspecific hybridization ; hexaploid (AABBCC) ; pentaploid (AABCC)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract To transfer the genes for yellow seed coat from both genomes A and C to B. napus (AACC), the hexaploid of Brassica (AABBCC) was synthesised from reciprocal interspecific crosses between yellow-seeded B.campestris (AA) and B.carinata (BBCC). The hexaploid with 27 pairs of chromosomes was red-seeded which showed that genic interaction existed in the trigenomic plants for the colour of the seed coat. Hundreds of hybrid seeds were obtained from crosses between the red-seeded hexaploid and partial yellow or brown-seeded varieties of B. napus as pollen donor. The majority of the hybrid plants (AABCC) were self fertile with brown seeds. It appeared that the chromosomes of the B genome were excluded during the meiosis of the pentaploid and a high proportion of the genetically balanced AC gametes could be produced. The fertility of the F2 population was increased and even reached normal levels for some plants. Seventy-three plants with the yellow-seeded character were isolated from 2590 open-pollinated F2 plants, most with increased fertility. After two successive self-pollinations, 18 lines produced yellow seeds and no brown seeds segregated from these populations. The morphology of the novel yellow-seeded plants was basically towards B. napus. Esterase isoenzyme electrophoresis showed that the plants contained some of the genetic background of B. campestris, B. carinata and B. napus. Cytological analysis has shown that at least some yellow-seeded lines have the B.napus AACC genome composition with 38 chromosomes and normal meiotic pairing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018646223643
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  • 32
    Electronic Resource
    Electronic Resource
    Promoter regions of the extA extensin gene from Brassica napus control activation in response to wounding and tensile stress. (1998)
    Springer
    Plant molecular biology 37 (1998), S. 675-687 
    Details
    ISSN: 1573-5028
    Keywords: Brassica napus ; extensin ; promoter analysis ; repressors ; tensile stress ; wounding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To identify controlling cis acting promoter regions in the B. napus extA extensin gene, expression in transgenic tobacco of 5′ −159, −433, −664, −789 and −940 bp promoter truncations linked to the uidA (B-glucuronidase) reporter coding sequence were analysed. The −159 and −433 bp truncations directed non specific expression in all cell types within the plant. An activator region which increased expression levels 10 fold in all cell types was located between −159 to −433 bp. A repressor region was found between −664 to −789 bp; removal of this region resulted in a 15 fold increase in expression. Histochemical analysis showed that transgenics containing the −664, −789 and −940 bp truncations directed expression of the fusion gene only in the phloem. A negative regulatory region located between −433 to −664 bp repressed expression in non-phloem cell types. In areas of the plant subject to tensile stress, the repression exerted by the negative regulatory region was overcome, allowing expression in all cell types. The quantitative repressor and activator regions which controlled absolute expression levels in all cell types were seperate from the negative regulatory region which controlled cell type specific expression in response to tensile stress. A wound responsive region was found to be located between −940 to −3500 bp. Thus, the extA gene is under complex control, being regulated by 4 sets of positively and negatively acting cis regions, which control wound inducibility, activation in response to tensile stress, and quantitative expression levels.
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    URL: http://dx.doi.org/10.1023/A:1005918816630
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    Conserved structure and function of the Arabidopsis flowering time gene CONSTANS in Brassica napus (1998)
    Springer
    Plant molecular biology 37 (1998), S. 763-772 
    Details
    ISSN: 1573-5028
    Keywords: Arabidopsis thaliana ; Brassica napus ; constans ; flowering ; zinc finger
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Arabidopsis thaliana CONSTANS (CO) gene which promotes flowering in long days was recently isolated by chromosome walking. The mapping of QTLs controlling flowering time in Brassica species has identified genomic regions that contain homologues of the CO gene. Four genes homologous to the Arabidopsis CO gene were isolated from a pair of homoeologous loci in each of two doubled-haploid Brassica napus lines displaying different flowering times, N-o-1 and N-o-9. The four genes, BnCOa1, BnCOa9, BnCOb1 and BnCOb9, are located on linkage groups N10 and N19, and are highly similar to each other and to the Arabidopsis CO gene. Two regions of the proteins are particularly well conserved, a N-terminal region with two putative zinc fingers and a C-terminal region which may contain a nuclear localization signal. All four genes appear to be expressed in B. napus. The BnCOa1 allele was shown to complement the co-2 mutation in Arabidopsis in a dosage-dependent manner causing earlier flowering than in wild type under both long- and short-day conditions.
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    URL: http://dx.doi.org/10.1023/A:1006064514311
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    Structure and Dynamics of Hydrogen Chelates. Part 1. NMR-spectroscopic studies in the quinazoline-2-acetonitrile series (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 236-250 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To get informations on both the structure and dynamics of hydrogen chelates 1 of heteroaromatic systems, a great variety of quinazoline-2-acetonitrile chelates were synthesized (see 2-4). Similarly to the situation of the corresponding H-chelates in the pyrimidine-2-acetonitrile series, the investigation of these new derivatives 2-4 by NMR spectroscopic methods (DNMR, COSY, NOESY, ROESY, EXSY, HMQC, HMBC) confirms the presence of an equilibrium of the two possible H-chelate structures (two ‘rotamers’ I and II, i.e., (E)/(Z) isomers; see Scheme). The corresponding equilibria I ⇌ II were determined by complete 1H-NMR signal assignment at low temperatures (after freezing the rotational processes). In addition, the tautomer equilibria A ⇌ B (relative energies of the two minima of the nonsymmetrical double-well potential) for both ‘rotamers’ are ascertained by H,H and C,H couplings. The results are an important basis for the interpretation of both the UV/VIS absorptions and the dependence of fluorescence and fluorescence quantum yields on temperature.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810206
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    Stereoselective Reactions of Phthalimido-Substituted Radicals Derived from (±)-Threonine: A comparison with reactions of N-phthaloyliminium ions (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 268-284 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective reactions of phthalimido-substituted radicals derived from (±)-threonine with different radical traps are reported (Scheme 3, Table 1). A strong influence of the nature of the radical trap on the stereoselectivity was noticed. Small nucleophilic radical traps gave preferentially the syn products. The observed selectivities are explained with the A1,3 strain model and depend on steric and electronic effects (Fig. 2). Reactions with electrophilic radical traps such as diphenyl diselenide gave the anti diastereoisomers with moderate stereocontrol, presumably due to stereoelectronic effects. The same stereochemical outcome, i.e., preferential formation of the anti products, was observed for the reactions of the related N-phthaloyliminium ion (Scheme 5, Table 2). The stereochemistry of the ionic reaction is rationalized by a Felkin-Anh model (Fig. 3).
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810208
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    Cyclopalladation of 1,1′-Azonaphthalene (= Di(naphthalen-1-yl)diazene): Isolation and characterization of two isomeric complexes (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 307-316 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cyclopalladation of 1,1′-azonaphthalene (= di(naphthalen-1-yl)diazene; 2) with bis(hexafluoroacetyl-acetonato)palladium(II) (3; [Pd(hfa)2]) yields the ortho-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[1-(naphthalen-1-ylazo-κN2)naphthalen-2-yl-κC2]palladium(II) (4) as well as the peri-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[8-(naphthalen-1-ylazo-κN2)naphthalen-1-yl-κC1]-palladium(II) (5); their structures were corroborated by X-ray analyses. The formation of the novel peri-metallated product 5 containing a six-membered palladacycle strongly depends upon the reaction conditions.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810211
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    The Photoisomerization Behavior of the (4-Hydroxycinnamoyl)-spermidines (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 342-352 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photoisomerization behavior of three mono[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 1, 2, and 3, and three bis[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 4, 5, and 6, are investigated. The synthetic product (E)-1 could be almost quantitatively (〉 96%) converted into its isomer (Z)-1 under UV light irradiation. In the cases of (E)-2 and (E)-3, a mixture of (E)/(Z) ca. 1:2 was obtained, when the same conditions were applied. The comparison of their UV spectra provides the possible explanation for these different behaviors. Furthermore, it was noticed that the (Z) → (E) isomerization of the C=C bond took place during the purification by reverse-phase high-performance liquid chromatography (RP-HPLC), and the (E)/(Z)-mixture is thus inseparable. The same feature could be observed during the isolation of the (Z,Z)-N,N′-bis[3-(4-hydroxyphenyl)prop-2-enoyl]-spermidines, (Z,Z)-4, (Z,Z)-5, and (Z,Z)-6. Nevertheless, the fractions of (Z,Z)-5 and (Z,Z)-6 were in almost pure state collected, and their 1-NMR spectra are presented.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810215
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    Preparation and Absolute Configuration of (-)-(E)-α-trans-Bergamotenone (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 153-162 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, absolute configuration, and olfactive evaluation of (-)-(E)-α-trans-bergamotenone (= (-)-(1′S,6′R,E)-5-(2′,6′-dimethylbicyclo[3.1.1]hept-2′-en-6′-yl)pent-3-en-2-one; (-)-1), as well as its homologue (-)-19 are reperted. The previously arbitrarily attributed absolute configuration of 1 and of (-)-α-trans-bergamotene (= (-)-(1 S,6R)-2,6-dimethyl-6-(4-methylpent-3-enyl)bicyclo[3.1. 1]hept-2-ene; (-)-2), together with those of the structurally related aldehydes (-)-3a,b and alcohols (-)-4a,b, have been rigorously assigned.
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    URL: http://dx.doi.org/10.1002/hlca.19980810114
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    New Synthesis and Chirality of (-)-4,4,4,4′,4′,4′-Hexafluorovaline (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 182-186 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (-)-(R)-4,4,4,4′,4′,4′-Hexafluorovaline hydrochloride ((R)-5) of 98% ee is prepared from β,β-bis(trifluoromethyl)acrylic acid (= benzyl 4,4,4-trifluoro-3-(trifluoromethyl)but-2-enoate; 1) in 4 steps with an overall yield of 9.6%. Key step is the separation of the TsOH salts of the diastereoisomers obtained by anti-Michael addition of (+)-(R)-1-phenylethylamine (2) to 1 (→ (R,R)-3). In contrast to the published (S)-chirality, the X-ray structure analysis of (R,S)-6 reveals, that (R)-chirality has to be assigned to the levorotatory (-)-4,4,4,4′,4′,4′-hexafluorovaline hydrochloride.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810117
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    Tripodal Dodecadentate Ligands with Salicylamide and bipyridine binding sites for iron(II) and iron(III) coordination (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 207-218 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterization of tripodal dodecadentate ligands with salicylamide and bipyridine binding sites for iron(II) and iron(III) are presented.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810203
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    N,N-Dialkylcarbamato Complexes of the d10 cations of copper, silver, and gold (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 219-230 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of CuO'Bu with CO2, and iPr2NH in the presence of PPh3, gives the dialkylcarbamato complex [Cu(O2CNiPr2)(PPh3)2] (1). The CO2/R2NH system (R = Me, Et) in an appropriate organic medium reacts with Ag2O giving the corresponding N,N-dialkylcarbamato complexes of analytical formula [Ag(C2CNR2)] (R = Me, 2; R = Et, 3). The methyl derivative 2 was characterized by X-ray diffraction methods. Crystal data of 2: for [Ag2(O2CNMe2)2], C6H12Ag2N2O4, mol. wt. 391.9; monoclinic, space group P21/c, a = 12.08(1), b = 3.797(2), c = 11.316(7) Å, β = 113.37(6)°, V = 476.3 Å3, Z = 2, Dc = 2.732 g cm-3; μ(MoKα) = 40.64 cm-1, F(000) = 376.0; R = 0.059, Rw = 0.067; g.o.f. 1.27. The structure consists of dinuclear [(Ag2OCNMe2)2] units with slightly distorted linearly two-coordinated Ag-atoms containing bridging carbamato groups to form a substantially planar eight-membered ring with an intra-annular Ag—Ag distance of 2.837(2) Å; the dinuclear units are further joined by Ag—O bonds to form an infinite array. Compound 3, which is presumably dinuclear, as suggested by cryoscopic measurements in benzene, undergoes a structural fission with PPh3, giving the mononuclear triphenylphosphine derivative [Ag(O2CNEt2)(PPh3)2] (4). The amine-catalyzed conversion of Ag2O into Ag2CO3, in the presence of the iPr2NH/CO2 system, is also reported. Cl-Exchange from [AuCl(PPh3)] with [Ag(O2CNEt2)] (3) gives the first N,N-dialkylcarbamato complex of gold, namely [Au(O2CNEt2)(PPh3)] (5), which crystallizes in the monoclinic system: C23H25AuNO2P · 0.5 C7H16, mol. wt. 625.5, space group P21/c; a = 13.212(5), b = 12.25(1), c = 16.795(6) Å, β = 109.09(2)°, V = 2568(2) Å3, Z = 4, Dc, = 1.618 g cm-3; μ(AgKα) = 31.40 cm-1, F(000) = 1236.0; R = 0.058; Rw = 0.064; g.o.f. 2.121. The compound contains two-coordinated Au-atom, namely to the P-atom and to the O-atom of the monodentate carbamato group, the P—Au—O bond angle being 174.7(3)°. The reaction with MeI showed these compounds to react predominantly at the carbamato O-atom giving the corresponding urethanes R2NCO2Me. Evidence was gathered for the transient coordination of CO to Ag in 3.
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    URL: http://dx.doi.org/10.1002/hlca.19980810204
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    1,3-Oxathiole and Thiirane Derivatives from the Reactions of Azibenzil and α-diazo amides with thiocarbonyl compounds (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 285-302 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of α-diazo ketones 1a,b with 9H-fluorene-9-thione (2f) in THF at room temperature yielded the symmetrical 1,3-dithiolanes 7a,b, whereas 1b and 2,2,4,4-tetramethylcyclobutane-1,3-dithione (2d) in THF at 60° led to a mixture of two stereoisomeric 1,3-oxathiole derivatives cis- and trans-9a (Scheme 2). With 2-diazo-1,2-diphenylethanone (1c), thio ketones 2a-d as well as 1,3-thiazole-5(4H)-thione 2g reacted to give 1,3-oxathiole derivatives exclusively (Schemes 3 and 4). As the reactions with 1c were more sluggish than those with 1a,b, they were catalyzed either by the addition of LiClO4 or by Rh2(OAc)4. In the case of 2d in THF/LiClO4 at room temperature, a mixture of the monoadduct 4d and the stereoisomeric bis-adducts cis- and trans-9b was formed. Monoadduct 4d could be transformed to cis- and trans-9b by treatment with 1c in the presence of Rh2(OAc)4 (Scheme 4). Xanthione (2e) and 1c in THF at room temperature reacted only when catalyzed with Rh2(OAc)4, and, in contrast to the previous reactions, the benzoyl-substituted thiirane derivative 5a was the sole product (Scheme 4). Both types of reaction were observed with α-diazo amides 1d,e (Schemes 5-7). It is worth mentioning that formation of 1,3-oxathiole or thiirane is not only dependent on the type of the carbonyl compound 2 but also on the α-diazo amide. In the case of 1d and thioxocyclobutanone 2c in THF at room temperature, the primary cycloadduct 12 was the main product. Heating the mixture to 60°, 1,3-oxathiole 10d as well as the spirocyclic thiirane-carboxamide 11b were formed. Thiirane-carboxamides 11d-g were desulfurized with (Me2N)3P in THF at 60°, yielding the corresponding acrylamide derivatives (Scheme 7). All reactions are rationalized by a mechanism via initial formation of acyl-substituted thiocarbonyl ylides which undergo either a 1,5-dipolar electrocyclization to give 1,3-oxathiole derivatives or a 1,3-dipolar electrocyclization to yield thiiranes. Only in the case of the most reactive 9H-fluorene-9-thione (2f) is the thiocarbonyl ylide trapped by a second molecule of 2f to give 1,3-dithiolane derivatives by a 1,3-dipolar cycloaddition.
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    URL: http://dx.doi.org/10.1002/hlca.19980810209
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    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810301
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    Synthesis of Chiral C2-Symmetric Binucleating Ligands (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 491-506 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a series of chiral enantiomerically pure C2-symmetric binucleating ligands is reported. Ligands of type 1-4, which consist of a phenolic or heterocyclic unit bridging two chiral dihydrooxazole rings. are readily accessible from chiral amino alcohols. Ligands 5a and 5b are composed of a cyclic urea or thiourea unit, respectively, and two 3,4-dihydro-2H-pyrrole rings containing a stereogenic center next to the N-atom. Compounds of this type are readily assembled from ethane-1,2-diamine and an imidothioic ester derived from pyroglutamic acid. These new ligands, which can coordinate two metals in close proximity to each other, are of interest regarding possible applications in asymmetric catalysis.
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    URL: http://dx.doi.org/10.1002/hlca.19980810304
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    Stability and Lability of Dicopper Double-Stranded Helicates in Solution (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 548-557 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stability constants have been measured for a series of ligands based on a 2,2′-(pyridine-2,6-diyl)bis[1H-benzimidazole] unit which forms dinuclear double-stranded helical complexes with copper(I). Variation of different structural parameters confirms the importance of the coordinate bond, the stacking interactions, and the weakly bridging pyridine units observed by X-ray crystallography. The stabilities of the complexes depend strongly on the solvent, and in MeCN, which is a good solvent for copper(I), the complexes are less stable and assemble in a stepwise manner. The interconversion of the enantiomers may be followed by 1H-NMR and takes place on a millisecond time scale around room temperature. The trends in lability are similar to those found for the stability of the complexes.
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    7-Deazapurine Oligodeoxyribonucleotides: The effects of 7-deaza-8-methylguanine on dna structure and stability (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 570-583 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oligodeoxyribonucleotides containing 7-deaza-2′-deoxy-8-methylguanosine (m8c7Gd; 2b) were prepared. For this purpose, the phosphonate 3a and the phosphoramidite 3b were synthesized and employed in solidphase oligodeoxyribonucleotide synthesis. The structures and the thermodynamic data of duplex formation of oligodeoxyribonucleotides containing 2b were investigated by temperature-dependent CD and UV spectra and compared with those containing 7-deaza-2′-deoxy-7-methylguanosine (m7c7Gd) or 7-deaza-2′-deoxy-guanosine (c7Gd; 2a). In general, compound 2b reduces the duplex stability. In case of the sequence d(m8c7G-C)4 (18), the B → Z transition was facilitated by the incorporation of 2b. Moreover, a single 7-deaza-8-methylguanine residue present in an oligodeoxyribonucleotide tract of guanine residues destabilizes the dG quadruplex significantly. This destabilization is more pronounced than in the case of 7-deazaguanine or 7-deaza-7-methyl-guanine.
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    Absolute rate Constants for the Addition of Malonyl Radicals to Alkenes in Solution (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 770-780 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute rate constants and their Arrhenius parameters are obtained for the addition of a cyclic malonyl radical derived from Meldrum's acid to 20 mono- or 1,1-disubstituted alkenes in (±)-propylene oxide and for the addition of the open-chain di(tert-butyl)malonyl radical to six mono- or 1,1-disubstituted alkenes in 1,1,2-trichloro-1,2,2-trifluoroethane by time-resolved electron spin resonance spectroscopy. At room temperature, the radicals add at the unsubstituted C-atoms with rate constants ranging from 1.1. 105 M-1S-1 (acrolein) to 2.4. 106 M-1S-1 (1,1-diphenylethene). The frequency factors are in the narrow ranges of log (A/M-1S-1) = 8.7 ± 0.1 for the cyclic and log (A/M-1S-1) = 8.2 ± 0.2 for the open-chain malonyl species, whereas the activation energies vary from 12.9 kJ/mol (1,1-diphenylethene) to 21.7 kJ/mol (acrylonitrile). They correlate with the alkene ionization potentials and, more weakly, with the reaction enthalpy. No correlation was found between the activation energies and the alkene electron affinities. Hence, the results confirm and quantify the electrophilic nature of malonyl radicals in addition reactions.
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    URL: http://dx.doi.org/10.1002/hlca.19980810327
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    Synthesis of the Spermidine Alkaloid (-)-(4R)-Dihydroisomyricoidine (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1303-1318 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An asymmetric synthesis of (-)-(4R)-dihydroisomyricoidine (28), a 13-membered amino lactam of type A, was performed by a diastereoselective Michael addition between the spermidine derivative 3 and the commercially available optically active ethyl carboxylate 4, and the cyclization of the resulting ω-amino acid 7 using diethyl phosphorocyanidate ((EtO)2POCN), followed by a Wittig reaction to introduce the (Z)-side chain. Some side reactions are also discussed.
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    URL: http://dx.doi.org/10.1002/hlca.19980810541
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    New Types of Potentially Antimalarial Agents: Epidioxy-substituted norditerpene and norsesterpenes from the marine sponge Diacarnus levii (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1285-1292 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Natural free carboxylic acids from the hadromerid sponge Diacarnus levii (Kelly-Borges and Vacelet) were esterified to yield the new cyclic norditerpene peroxides ent-muqubilin benzyl ester (= (αR,3S,6R)-α,6-dimethyl-6-[(E)-4-methyl-6-(2,6,6-trimethyl-cyclohex-1-en-1-yl)hex-3-enyl]-1,2-dioxan-3-acetic acid benzyl ester; 6, diacarnoate B methyl ester(= (αS,3R,6R)-α,6-dimethyl-6-{2-(4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-3-oxo-2,5,5,8a-tetramethylnaphthalen-1-yl)ethyl}-1,2-dioxan-3-acetic acid methyl ester; 9), and deoxydiacarnoate B benzyl ester (= (αS,3R,6R)-α,6-dimethyl-6-{2-[(4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-2,5,5,8a-tetramethyl-1-naphthalenyl]ethyl}-1,2-dioxan-3-acetic acid benzyl ester; 10), which were isolated following extensive chromatography. The relative configuration of the peroxide/α-methylacetate moiety of 6, 9, and 10, was directly determined from their NMR spectra. The absolute configurations of the peroxide/α-methylacetate moiety was deduced from comparative 1H-NMR data of the (S)- and (R)-phenylglycine methyl ester derivatives 7 and 8 as well as 11/13 and 12/14, all obtained from a mixture of the precursors of 3, 6, and 10. The absolute configuration at the carbobicyclic moiety of enone 9 and of 10, is identical, as established by chemical interconversion, 9 and 10 belong to the normal labdane series according to empirical CD rules, applied either directly to 9 or to the parent (+)-sclareolide-derived enone 20. In contrast, molar rotation additivity rules suggest the ent-labdane configuration for 9 and 10. The epidioxides 1-3, 6, and 10 proved active in vitro against the malaria parasite Plasmodium falciparum; especially the previously isolated methyl 3-epinuapapuanoate (2) was active against a chloroquine-resistant strain, and this with a good security index.
    Additional Material: 1 Tab.
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    3-Hydroxy-2-cyanoalk-2-enamides, and 2-Cyano-2-(tetrahydrofuran-2-ylidene)- and 2-Cyano-2-(tetrahydropyran-2-ylidene)acetamides: Synthesis, structure, and solvent-dependent (Z)/(E)-isomerismDedicated to Professor D. Seebach on the occasion of his 60th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1319-1328 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3-Hydroxy-2-cyanoalk-2-enamides, and 2-cyano-2-(tetrahydrofuran-2-ylidene)- and 2-cyano-2-(tetrahydropyran-2-ylidene)acetamides with N-alkyl and N-aryl substituents have been synthesized in three steps from cyanoacetic acid. Their conformations were investigated by X-ray crystallography and 1H-NMR ROESY spectroscopy at room temperature. The enolic compounds 1-3 adopt an extended conformation stabilized by a strong intramolecular O—H … O=C bond both in the solid state and in (D6)DMSO solution. In contrast, the structure of the cyclic derivatives 5a,b-8a,b is solvent-dependent. In the solid state and in CDCl3 solution, the compounds adopt an extended conformation of type I or III, while, in (D6)DMSO solution, their structures undergo time-dependent (Z)/(E)-isomerization structures (of type II or IV). This observation is compatible with a dipolar transition state of rotation. The kinetics of the isomerization are controlled by the N-substituent, the N-(t-Bu) derivatives 7a and 7b having the highest barrier of rotation around the C=C bond. The whole body of experimental evidence together with the results of molecular-mechanics calculations with I-IV, indicate that, in DMSO, two (E)/(Z)-isomers with two conformations are present, and that they undergo interconversion at room temperature with four different constants. The very fast exchange rates kI,II and kIII,IV in the NMR time-scale might be responsible for the detection of only two isomers.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810542
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    Monoterpene Dimers from Lisianthius seemannii (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1393-1403 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new acylated dimeric secoiridoid glycoside, seemannoside A (2), has been isolated from the aerial parts of Lisianthius seemannii (GRISEB) O. KUNTZE (Gentianaceae). The structure was established by spectroscopic analysis (UV, MS, 1H- and 13C-NMR, and 2D-NMR experiments) and chemical reactions as (E-4′-O-p-coumaroyl)lisianthioside. The structure of the (Z)-isomer (seemannoside B, 3), also present in the plant, was confirmed by LC/UV/1H-NMR analysis. The active principle, 6, responsible for the antifungal activity of the apolar extract against Cladosporium cucumerinum, has been isolated. Its structure has been established by NMR spectroscopy and X-ray crystallographic analysis as a rare type of aglycone monoterpene dimer.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810548
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  • 52
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    Asymmetric synthesis of pentono- and 6-deoxyhexono-δ-lactams via hetero-Diels-Alder reactions with nitroso dienophile (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1417-1428 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Asymmetric Diels-Alder reaction of the pentadienoic and hexadienoic acids 2a,b with the chiral chloronitroso derivative 3 gave the primary adducts 4a,b with good-to-excellent enantioselectivity. Subsequent as- or trans-dihydroxylation and hydrogenolytic cleavage of the N—O bond led to the 5-amino-5-deoxypentono-δ-lactams 13a, 14, 15a, and 16 in the D-ribose, L-arabinose, D-xylose, and L-lyxose series, respectively, and to the 5-amino-5,6-dideoxyhexono-δ-lactams 13b and 15b in the D-allose and D-glucose series, respectively.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810550
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  • 53
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    Distamycin-NA: A DNA Analog with an Aromatic Heterocyclic Polyamide Backbone. Part 1. Synthesis and structural analysis of monomers and dimers containing the nucleobase uracil (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 14-34 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the monomeric building block 13 and its constitutional isomer 12 of a new type of DNA analog, distamycin-NA, is presented (Schemes 1 and 2). This building block consists of a uracil base attached to a thiophene core unit via a biaryl-like axis. Next to the biaryl-like axis on the thiophene chromophore, a carboxy and an amino substituent are located allowing for oligomerization via peptide coupling. The proof of constitution and the conformational preferences about the biaryl-like axis were established by means of X-ray analyses of the corresponding nitro derivatives 10 and 11. Thus, the uracil bases are propeller-twisted relative to the thiophene core, and bidentate H-bonds occur between two uracil bases in the crystals. The two amino-acid building blocks 12 and 13 were coupled to give the dimers 15 and 16 using dicyclohexylcarbodiimide (DCC) in THF/LiCl and DMF, respectively. While the dimer 15 showed no atropisomerism on the NMR time scale at room temperature, its isomer 16 occurred as distinct diastereoisomers due to the hindered rotation around its biaryl-like axis. Variable-temperature 1H-NMR experiments allowed to determine a rotational barrier of 19 ± 1 kcal/mol in 16. The experimental data were complemented by AM1 calculations.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810103
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    [2+3] Cycloadditions of ‘Thiocarbonyl Ylides’ (= (Alkylidenesulfonio)methanides) and diazoalkanes with N,N′-(thiocarbonyl)diimidazole (= 1,1′-(carbonothioyl)bis[1H-imidazole])Part of the planned Ph.D. Thesis of T.G., University of Łódź.Dedicated to Professor Romuald Bartnik (University of Łódź) on the occasion of his 60th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 66-77 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heating of a mixture of N,N′-(thiocarbonyl)diimidazole (= 1,1′-(carbonothioyl)bis[1H-imidazole]; 1) and 2,5-dihydro-1,3,4-thiadiazole 2a or 2b gave the 1,3-dithiolanes 4a and 4b, respectively, via a regiospecific 1,3-dipolar cycloaddition of the corresponding ‘thiocarbonyl methanides’ 3a,b onto the C=S group of 1 (Schemes 1 and 2). The adamantane derivative 4b was not stable in the presence of 1H-imidazole and during chromatographic workup. The isolated 1,3-dithiole 5 is the product of a base-catalyzed elimination of 1H-imidazole from the initial cycloadduct 4b. The formation of the S,N-acetal 6 can be rationalized by a protonation of the ‘thiocarbonyl ylide’ 3b followed by a nucleophilic addition of 1H-imidazole. With the diazo compounds 8a-e (Scheme 3) 1 underwent a regiospecific 1,3-dipolar cycloaddition to give the corresponding 2,5-dihydro-1,3,4-thiadiazole derivatives 9, which spontaneously eliminated 1H-imidazole to yield (1H-imidazol-1-yl)-1,3,4-thiadiazoles 10. The structures of 10a and 10d were established by X-ray crystallography. In the case of diazodiphenylmethane (8f), the initial cycloadduct 9f decomposed via a ‘twofold extrusion’ of N2 and S to give 1,1′-(2,2-diphenylethenylidene)bis[1H-imidazole] (11; Scheme 3).
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    Synthesis of New Nucleosides by coupling of chloropurines with 2- and 3-deoxy derivatives of N-methyl-D-ribofuranuronamide (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 145-152 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of new deoxyribose nucleosides by coupling chloropurines with modified D-ribose derivatives is reported. The methyl 2-deoxy-N-methyl-3-O-(p-toluoyl)-α-D-ribofuranosiduronamide (α-D-8) and the corresponding anomer β-D-8 were synthesized starting from the commercially available 2-deoxy-D-ribose (1) (Scheme 1). Reaction of α-D-8 with the silylated derivative of 2,6-dichloro-9H-purine (9) afforded regioselectively the N9-(2′-deoxyribonucleoside) 10 as anomeric mixture (Scheme 2), whereas β-D-8 did not react. Glycosylation of 9 or of 6-chloro-9H-purine (17) with 1,2-di-O-acetyl-3-deoxy-N-methyl-β-D-ribofuranuronamide (13) yielded only the protected β-D-anomers 14 and 18, respectively (Scheme 3). Subsequent deacetylation and dechlorination afforded the desired nucleosides β-D-11, β-D-12,15, and 16. The 3′-deoxy-2-chloroadenosine derivative 15 showed the highest affinity and selectivity for adenotin binding site vs. A1 and A2A adenosine receptor subtypes.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810113
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    Asymmetric Synthesis of (S)-5,5,5,5′,5′,5′,5′-Hexafluoroleucine (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 174-181 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (S)-5,5,5,5′,5′,5′-Hexafluoroleucine ((S)-13) of 81 % ee is prepared from hexafluoroacetone (l) and ethyl bromopyruvate (= ethyl 2-oxopropanoate) in 7 steps with an overall yield of 18% (Schemes 1 and 2). Key step in this sequence is the highly enantioselective reduction of the carbonyl group in α-keto ester 4 either by bakers' yeast (91 % ee) or by ‘catecholborane’ 6 utilizing an oxazaborolidine catalyst, yielding hydroxy ester (R)-5 with 99% ee. The absolute configuration was determined by X-ray analysis of the HCl adduct (S,R)-9b of (2S)-N-[(R)- l-phenylethyl]-5,5,5,5′,5′,5′-hexafluoroleucine ethyl ester.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810116
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    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810201
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    Preparation of N-Fmoc-Protected β2- and β3-Amino Acids and their use as building blocks for the solid-phase synthesis of β-peptidesPartially published in a preliminary communication [1]; β2 means that the NH2, group ist at C(3)(= C(β)) and the side chain at C(2) of the amino acid, and β3 indicates that both the NH2 group and the side chain are at C(3)( = C(β)). Fmoc = (9H-Fluoren-9-ylmethoxy)carbonyl.Dedicated to Professor A. I. Meyers, University of Colorado, Fort Collins, on the occasion of his 65th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 187-206 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Fmoc-Protected (Fmoc = (9H-fluoren-9-ylmethoxy)carbonyl) β-amino acids are required for an efficient synthesis of β-oligopeptides on solid support. Enantiomerically pure Fmoc-β3-amino acids β3: side chain and NH2 at C(3)(= C(β)) were prepared from Fmoc-protected (S)- and (R)-α-amino acids with aliphatic, aromatic, and functionalized side chains, using the standard or an optimized Arndt-Eistert reaction sequence. Fmoc-β2- Amino acids (β2 side chain at C(2), NH2 at C(3)(= C(β))) configuration bearing the side chain of Ala, Val, Leu, and Phe were synthesized via the Evans' chiral auxiliary methodology. The target β3-heptapeptides 5-8, a β3- pentadecapeptide 9 and a β2-heptapeptide 10 were synthesized on a manual solid-phase synthesis apparatus using conventional solid-phase peptide synthesis procedures (Scheme 3). In the case of β3-peptides, two methods were used to anchor the first β-amino acid: esterification of the ortho-chlorotrityl chloride resin with the first Fmoc-β-amino acid 2 (Method I, Scheme 2) or acylation of the 4-(benzyloxy)benzyl alcohol resin (Wang resin) with the ketene intermediates from the Wolff rearrangement of amino-acid-derived diazo ketone 1 (Method II, Scheme 2). The former technique provided better results, as exemplified by the synthesis of the heptapeptides 5 and 6 (Table 2). The intermediate from the Wolff rearrangement of diazo ketones 1 was also used for sequential peptide-bond formation on solid support (synthesis of the tetrapeptides 11 and 12). The CD spectra of the β2- and β3-peptides 5, 9, and 10 show the typical pattern previously assigned to an (M) 31 helical secondary structure (Fig.). The most intense CD absorption was observed with the pentadecapeptide 9 (strong broad negative Cotton effect at ca. 213 nm); compared to the analogous heptapeptide 5, this corresponds to a 2.5 fold increase in the molar ellipticity per residue!
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    URL: http://dx.doi.org/10.1002/hlca.19980810202
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  • 59
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    Photoaddition of Ethyl 2,2-Dimethyl-5-oxo-5,6-dihydro-2H-pyridine-1-carboxylate to 2,3-dimethylbut-2-ene (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 303-306 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On irradiation (350 nm) in the presence of excess 2,3-dimethylbut-2-ene, the newly synthesized title compound 5 affords as main products the unexpected cyclopropylpyrrolidine 10 (50%) and the spiro-oxetane 9 (25%).
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    URL: http://dx.doi.org/10.1002/hlca.19980810210
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    Influence of Lewis Acids on the [4 + 2] Cycloaddition of N,N′-Fumaroylbis[(2R)-bornane-10,2-sultam] to Cyclopentadiene and application to various dienes (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 324-329 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Among seventeen different Lewis acids, TiCl4 was found to be the best catalyst for the [4 + 2] cycloaddition of cyclopentadiene to N,N′-fumaroylbis[(2R)-bornane-10,2-sultam] ((-)-1). Independently of the TiCl4 molar concentration, almost constant and complete (98-89% d.e.) diastereofacial π-selection was achieved in the Diels-Alder addition of (-)-1 to cyclopentadiene, cyclohexadiene, isoprene, and 2,3-dimethylbuta-1,3-diene.
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    N,Se-Acetals: Preparation and use in diastereoselective radical reactionsFor a preliminary communication of this work, see [1]. (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 353-373 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new facile synthesis of N,S- and N,Se-acetals starting from aldehydes and primary amines is presented (Schemes 3-5). These acetals are used as precursors for stereoselective radical deuteration and allylation reactions (Schemes 6 and 7, Tables 1 and 2). The stereochemical outcome of the reactions depends on the radical trap and the substituents at the N-atom. Deuterations give always anti products with moderate to high selectivities. The allylation reactions give either syn or anti products with low to moderate selectivities. The observed stereoselectivities can be explained with a model based on minimization of A1,3 strain and are controlled by steric and stereoelectronic effects.
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    Syntheses of O-Methylasparvenone-Derived Serotonin-Receptor Antagonists (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 525-538 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on O-methylasparvenone (1), a N-free 5HT2C antagonist with moderate affinity (pKi = 6.7), derivatives bearing dimethylamino (7), (dimethylamino)methyl (17, 18, 21, and 22), and aminomethyl substituents (26) in place of the benzylic OH group of 1 as well as pyrrolidine- (33) and piperidine-fused derivatives (29, 43, and 45) were synthesized. In contrast to the lead structure 1, these new ligands were active in vivo in the rat. The tricycles 33 and 45 display high affinities for the 5HT2C receptor (pKi = 8).
    Additional Material: 5 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19980810306
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    [2+3] Cycloadditions of Azomethine Ylides with 1,3-Thiazole-5(4H)-thionesDedicated to Professor Max Viscontini on the occasion of his 85th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 558-569 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermal reactions of 1,2,3-trisubstituted aziridines 1 with 1,3-thiazole-5(4H)-thiones 6 in toluene yielded, in general, a mixture of two diastereoisomeric spirocyclic [2+3] cycloadducts. The formation of these products can be explained by a stereoselective electrocyclic ring opening of 1 to give an azomethine ylide 2 as the reactive intermediate, which is trapped immediately by 6 via a stereoselective 1,3-dipolar cycloaddition. Only in the case of trans-dimethyl 1-(4-methoxyphenyl)aziridine-2,3-dicarboxylate (trans-1a), four diastereoisomeric cycloadducts were formed (Scheme 4). This result is rationalized by an isomerization of the intermediate azomethine ylide cis-2a to trans -2a.
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    Protonic Quantum Correlations in the H-Bond Dynamics of Nucleic Acids. Part II. Correlations along the helical axis of protein-coding DNA of living organisms (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 584-601 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Due to their small mass, adjacent protons (or H-atoms) of molecular systems may exhibit quantum entanglement (or quantum correlations), even at ambient conditions. The considerable thermal disturbance and/or manybody interactions of condensed matter and the associated decoherence effect, however, cause this protonic entanglement to be restricted in space and time. Some aspects of entanglement and decoherence are mentioned. Extending our previous theoretical work, in the present paper the focus is on the possible existence of entangled protons belonging to the H-bonds of adjacent base pairs of B-type DNA. Based on the ‘working hypothesis’ that this effect does really exist, the most probable ‘positions’ for the appearance of protonic entanglement in DNA sequences are qualitatively determined. Furthermore, these ‘positions’ appear to correspond uniquely to dimers of adjacent base pairs of DNA. As a consequence, one can straightforwardly search for an enhanced appearance of such entangled H-bonds in DNA sequences of living organisms, using the existing DNA databases. A quantitative analysis of protein-coding DNA sequences of various organisms has been performed, the results of which provide strong evidence for the existence of the considered effect. The most striking finding may be summarized as follows: Quantum entanglement appears preferably between the third base of a codon and the first base of the following one. Quantitative estimates of this and further obtained results are presented. It is also shown that quantum-chemical considerations of stacking energies cannot account for the results. The new findings provide first evidence for the biological significance of entangled H-bonds.
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    URL: http://dx.doi.org/10.1002/hlca.19980810311
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    An Advantageous Synthesis of 1D- and 1L-1,2,3,5/4-Cyclohexanepentol (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 688-694 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compounds D-10 and L-10 were prepared from 1 in eight steps and in a combined overall yield of 41-49%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810319
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    Reaction of N,N'-dimethyl-2-nitroethene-1, 1-diamine with α,ß-unsaturated acyl isothiocyanates: Preparation of 1,3-thiazin-4-one and 4-nitro-1,2-thiazol-5(2H)-imine derivativesPresented in preliminary form at the ‘XII seminario cientifico’, centro nacional de investigaciones cientificas, habana, cuba, 1995 (M. I. G. T.) and at the ‘tenth international conference on organic synthesis’, Bangalore, India, 1994 (D. M. A.). (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 718-728 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of N,N'-dimethyl-2-nitroethene-1,1-diamine (8) with α,ß-unsaturated acyl isothiocyanates 9 affords 3,3-diamino-2-nitroacrylthioamides 10 (Scheme 2) in moderate-to-good yields. Cyclization of 10 under acidic conditions gives 1,3-thiazin-4-one derivatives of type 11. Oxidative cyclization of 10 with diethyl azodicaboxylate leads to 4-nitro-1,2-thiazol-5(2H)-imine derivatives 12.
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    Prenylated Flavanones from Monotes engleri: On-line Structure Elucidation by LC/UV/NMR (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 754-763 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The CH2Cl2 extract of Monotes engleri Gilg. (Dipterocarpaceae) showed antifungal activity against the yeast Candida albicans in our bioautographic TLC assays. After a first fractionation of the crude extract, the bioactivity was located in one of the fractions. To perform an efficient targeted isolation of the active compounds, LC/UV/MS and LC/UV/NMR analyses of the crude extract and the active fraction were performed. LC/UV/, LC/MS, and LC/NMR data (1D and 2D) allowed the identification of 1 as (2S)-2,3-dihydro-5,7-dihydroxy-{3-hydroxy-4-[(3-methylbut-2-enyl) oxy]phenyl}-4H-1-benzopyran-4-one, a new prenylated flavanone, named monoteson A. Subsequent isolation of 1 has permitted the determination of its absolute configuration on the basis of CD measurements. Theree other prenylated flavanoes 2-4 were isolated from the same extract. Compound 3 was identified as 2- (3, 5-dihydroxyphenyl) -2,3-dihydro-5, 7-dihydroxy-6, 8-bis (3-methylbut-2-enyl)-4 H-1-benzopyran-4-one, another new natural product, named monotesone B. The structures of 2 and 4 were established as selinone and lonchocarpol A, respectively. The antifungal activity against Candida albicans was determined for all compounds.
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    Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds part VIPart V: [1] Derivatives with Bidentate Ligands, Crystal Structures of tetrahedro- Decacarbonyl{μ-[1,1-bis(methylthio-χS)ethane]}tetrairidium ([Ir4(CO)10-(μ2-(MeS)2CHMe)]), tetrahedro-Tri-μ-carbonylheptacarbonyl{μ-{ethylidenebis- [diphenylphosphine]-χP:χP'}}tetrairidium ([Ir4(CO)10(μ2-(Ph2P)2CHMe)]), and tetrahedro-Tri-μ-carbonylheptacarbonyl{μ-{propane-1,3-diylbis[diphenylphosphine]-χP:χP'}}tetrairidium ([Ir4(CO)10(μ2-Ph2P(CH2)3PPh2)]) (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 781-791 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The disubstituted clusters[Ir4(CO)10(μ2-L—L)] with one edge-bridging ligand have a ground-state geometry with all COs terminal (L—L = (MeS)2CHMe, cluster 1) or with three edge-bridging COs (L—L = (Ph2P)2CHMe, cluste 2; L—L =Ph2P(CH2)3PPh2, cluster 3) in the solid state and in solution. A comparative 13C-NMR study of 1-3 shows that their respective ground-state geometries are merely relative minima of energy in the same kinetic profile of successive fluxional processes consisting of a merry-go-round of six COs about a unique trangular face and the rotation of terminal COs about one Ir-atom. The factors affecting the activation energy of the merry-go-round result from the relative bites of the bidentate ligands in the ground-state geometry, as shown by a comparison of the molecular structures of 2 and 3.
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    Kinetic Study of the Reaction of Pyridoxal 5′-Phosphate with Hydrazino Compounds of Pharmacological Activity (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 837-844 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the reaction between pyridoxal 5′-phosphate (PLP) with carbidopa, hydralazine, and isoniazid, in aqueous solution at variable pH and constant ionic strength of 0.1M was studied spectrophotometrically. The rate constants of formation and hydrolysis of the resulting Schiff base, and its stability were determined in a wide range of pH. A comparison is made of the formation rate constants with those of PLP with hydrazine. The reactivity shows the sequence isoniazid 〉 hydrazine 〉 carbidopa 〉 hydralazine in the whole range of pH studied. The Schiff bases studied are more stable than those formed by PLP and hexylamine and as stable as those described for the reactions of PLP with poly(L-lysine) or copolypeptides containing L-lysine.
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    Structure and Properties of Transition-Metal Complexes with Chiral C2-symmetric binucleating ligands (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 507-524 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coordination behavior of chiral binucleating ligands of type 1-4 with various transition metals has been investigated. 1H-NMR Titration experiments with zinc(II) salts gave detailed structural information about the structure of the resulting zinc complexes. Ligand 1 forms an unusual C3-symmetric dinuclear zinc complex [Zn2CIL3] (8a) which was characterized by X-ray crystallography. Treatment of complex 8a with various carboxylic acids resulted in ligand-exchange reactions. With ligand 2, a hydroxo-bridged dinuclear copper complex 15 was synthesized and its structure elucidated by X-ray analysis. Solution studies UV and 1H-NMR spectroscopy of the reaction of ligand 3 with ZnII and NII salts revealed the formation of dimeric species of the type [M2X4L2]. Ligand 4 formed well-defined dinuclear complexes with NiII and CuII salts of which the corresponding NiII complex [Ni2(AcO)2(ClO4)2L] (22a) was characterized by crystal-structure analysis.
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    Warum Pentose- und nicht Hexose-Nucleinsäuren??. Teil VTeile I-IV der Reihe ‘Warum Pentose- und nicht Hexose-Nucleinsäuren?’, vgl. [1-4]. Die vorliegende Arbeit gilt als 9. Mitteilung in der Reihe ‘Chemie von α-Aminonitrilen’ 8. Mitteilung dieser Reihe vgl. [4]. Teile der hier publizierten Ergebnisse sind von J. H. an der Herbstversammlung der Schweizerischen Chemischen Gesellschaft in Bern am 16.10.1991 vorgetragen sowie in mehreren von A. E. gehaltenen und im Druck erschienenen Vorträgen erwähnt worden; vgl. [5-8].. (Purin-Purin)-Basenpaarung in der homo-DNS-Reihe: Guanin, Isoguanin, 2,6-Diaminopurin und Xanthin (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 375-474 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Why Pentose- and Not Hexose-Nucleic Acids? Purine-Purine Pairing in homo-DNA: Guanine,Isoguanine, 2,6-Diaminopurine, and XanthineThis paper concludes the series of reports in this journal [1-4] on the chemistry of homo-DNA, the constitutionally simplifie dmodel system of hexopyranosyl-(6′ → 4′)-oligonucleotide systems stidued in our laboratory as potentially natural-nucleic-acid alternatives in the context of a chemical aetiology of nucleic-acid structure. The report describes the synthesis and pairing properties of homo-DNA oligonucleotides which contain as nucleobases exclusively purines, and gives, together with part III of the series [3], a survey of what we know today about purine-purine pairingin homo-DNA. In addition, the paper discusses those aspects of the chemistry of homo-DNA which, we think, influence the way how some of the structural features of DNA (and RNA) are to be interpreted on a qualitative level.Purine-purine pairing occurs in the homo-DNA domain in great variety. Most prominent is a novel tridentate Watson-Crick pair between guanine and isoguanine, as well as one between 2,6-diaminopurine and xanthinone, both giving rise to very stable duplexes containing the all-purine strands in antiparallel orientation. For the guanine-isoguanine pair, constitutional assignment is based on temperature-dependent UV and CD spectroscopy of various guanine- and isoguanine-containg duplexes in comparison with duplexes known to be paired in the reverse guanine is replaced by 7-carbauguanine. Isoguanine and 2,6-diaminopurine also have the capability of self-pariring in the reverse-Hoogsteen mode, as previously observed for adenine and guanine [3]. In this type of pairing, the interchangeably. Fig. 36 provides an overall survey of the relative strength of pairing in all possible purine-purine combinations.Watson-Crick pairing of isoguanine with guanine demands the former to participate in its 3H-tautomeric form; hitherto this specific tautomer had not been considered in the pairing chemistry of isoguanine. Whereas (cumulative) purine-purine pairing in DNA (reverse-Hoogsten or Hoogsteen) seems to occur in triplexes and tetrapalexes only, its occurrence in duplexes in a characteristic feature of homo-DNA chemistry. The occurrence of purine-purine Watson-Crick base pairs is probably a consequence of homo-DNA's quasi-linear ladder structure [1][4]. In a double helix, the distance between the two sugar C-atoms, on which a base pair is anchored, is expected to be constrained by the dimensions of the helix; in a linear duplex, however, there would be no restrictions with regard to base-pair length. Homo-DNA's ladder-like model also allows one to recognize one of the reasons why nucleic-acid duplexes prefer to pair in antiparallel, rather than parallel strand orientation: in homo-DNA duplexes, (averaged) backbone and base pair axes are strongly inclined toward one another [4]; the stronger this inclination, the higher the preference for antiparallel strand orientation is expected to be (Fig. 16).In retrospect, homo-DNA turns out to be one of the first artificial oligonucleotide systems (cf. Footnote 65) to demonstrate in a comprehensive way that informational base pairing involving purines and pyrimidines is not a capability unique to ribofuranosyl systems. Stability and helical shape of pairing complexes are not necessary conditions of one another; it is the potential for extensive conformational cooperativity of hte backbone structure with respect to the constellational demands of base pairing and base stacking that determines whether or nor a given type of base-carrying backbone structure is an informational pairing system. From the viewpoint of the chemical aetiology of nucleic-acid structure, which inspired our investigations on hexopyranosyl-(6′ → 4′)-oligonucleotide systems in the first place, the work on homo-DNA is only an extensive model study, because homo-DNA is not to be considered a potential natural-nucleic-acid altenratie. In retrospect, it seems fortunate that the model study was carried out, because without it we could hardly have comprehended the pairing behavior of the proper nucleic-acid alternatives which we have studied later and which will be discussed in Part VI of this series.The English footnotes to Fig. 1-49 provide an extension of this summary.
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    Synthesis and Properties of Monodisperse Chiral Dendrimers (up to Fourth Generation) with doubly branched building blocksPartially published in preliminary communications [1][2].: An intriguing solvent effect (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 603-631 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ‘Fully chiral’ dendrimers, containing a stereogenic center at each and every branching point, have been prepared using a chiral core triol with aromatic elongating units (cf. 27) and chiral branch diols (cf. 8, 12, and 24) as building blocks. The biggest dendrimer prepared is of the 4th generation (33: 46 building blocks, 93 stereogenic centers, 1028 possible stereoisomers), and has been obtained by a convergent growth approach in 32 steps starting from the biopolymer poly[(R)-3-hydroxybutanoic acid] (P(3-HB)). All compounds were shown to be monodisperse by MALDI-TOF mass spectrometry. Spin-lattice relaxation-time (T1) measurements and size-exclusion chromatography show typical features of structurally related achiral dendrimers. The influence of the chiral building blocks on the shape of the whole dendrimer has been investigated by chiroptical measurements: the specific rotation can be considered as average of all chiroptical properties of its constituent chiral units, independent of the solvent, the concentration, and the temperature. On the other hand, regularity in the circular dichroism (CD) spectra is completely lost with variation of the solvent (cf. Fig. 13).
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    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810101
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    Enantioselective Dicarbonylation of Styrene to Isotactic Poly[1-oxo-2-phenylpropane-1,3-diyl] with phosphinodihydrooxazole-palladium(ii) complexes: Model studies for enantioface selection preliminary communication (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 764-769 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first steps, believed to be involved in the highly enantioselective copolymerization of styrene and carbon monoxide to poly[1-oxo-2-phenylpropane-1,3-diyl] with phosphinodihydrooxazole-palladium(II) complexes, were investigated. The insertion of carbon monoxide into [Pd(Me)(P^N)(solvent)] TfO (P^N = (S)-2-[2-(5H-benzo[b]phosphindol-5-yl)phenyl]4-benzyl-4,5-dihydrooxazole (1)) and of styrene into [Pd(Me)(P^N)(solvent)] TfO were highly regioselective (alkyl and acyl substituents trans to N); moreover, the olefin insertion took place with essentially complete enantioface discrimination.
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    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810501
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    A Novel Hydrocarbon, 8,10-Dimethylidenetricyclo[7.1.1.02,7]undeca-2,4,6-triene: Synthesis of benzopinane skeleton via di-π-methane rearrangement of benzonorbornadiene systemDedicated to Professor Özer Bekaroǧlu on the occasion of his 65th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 828-836 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The [4 + 2] cycloadduct 17 of 2,3-dimethylidene-1,2,3,4-tetrahydro-1,4-methanonaphthalene and 4-phenyl-4H-1,2,4-triazole-3,5-dione (PTAD) was subjected to a triplet-sensitized di-π-methane rearrangement. Hydrolysis of the resulting urazol 18 gave the hydrocarbon 7. Hydrolysis of 18 at lower base concentrations led to isomeric stable semicarbazides 24 and 25, which were submitted NiO2 or MnO2 oxidation, to give the target compound 7, and oxidation products 26 and 27.
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    Cooperative Interactions of the Catalytic Nucleophile and the Catalytic Acid in the Inhibition of β-Glycosidases. Calculations and their validation by comparative kinetic and structural studies of the inhibition of glycogen phosphorylase b (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 853-864 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The difference between the strong inhibition of retaining β-glucosidases by the tetrazole 1 and the weak inhibition by the triazole 3 has been explained by the protonation by the enzymic catalytic acid of N(3) of 1, replaced by CH in 3. One also expects a contribution to the inhibition from the charge-dipole interaction between the enzymic catalytic nucleophile and the azole ring. The extent of this contribution was estimated from the calculated, distance-dependent heats of formation of the acetate-azole complexes. The calculations were validated by comparison of the charge-dipole interaction between phosphate and the inhibitors 1 and 3 in the glycogen phosphorylase b (GPb)-azole-phosphate complexes, as derived from differences in the Ki values for 1 and 3, while the structural invariance of the complexes was demonstrated by X-ray analysis. The difference between the charge-dipole interactions of (dihydrogen) phosphate and 1 or 3 as derived from Δ Ki is 1.1 kcal mol-1, while the calculated difference is 1.3 kcal mol-1. The calculated difference for the interaction of 1 or 3 with acetate, representing the catalytic nucleophile in β-glycosidases, is 2.0 kcal mol-1, while the differences of the binding energies as derived from the Ki values for the inhibition by 1 or 3 of different β-glycosidases range from 2.4 to 5.3 5 kcal mol-1. The calculated difference for 1 and the imidazole 6 is 2.5 kcal mol-1 in favour of 1, whereas the Ki-derived difference is 3.7 kcal mol-1 in favour of 6, equal to the calculated difference between 1 and the protonated imidazole 6. Thus, protonation by the catalytic acid and the charge-dipole interaction with the catalytic nucleophile contribute cooperatively to the binding of inhibitors possessing a trigonal anomeric centre bonded to a heteroatom.
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    Heterosupramolecular Chemistry: Synthetic strategies for the covalent and noncovalent assembly and organization of nanocrystals and molecules (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 902-915 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Described are the preparation of nanocrystals and the synthesis of molecules that may be covalently or noncovalently assembled in solution to yield heterosupermolecules possessing a well-defined heterosupramolecular function. Also described are preparative and synthetic methods that yield organized assemblies of heterosupermolecules possessing an addressable heterosupramolecular function. Finally, the development of these synthetic strategies to permit the covalent and noncovalent assembly and organization of a wide range of condensed phase and molecular components is outlined.
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    γ-Peptides Forming More Stable Secondary Structures than α-Peptides: Synthesis and helical NMR-solution structure of the γ-hexapeptide analog of H-(Val-Ala-Leu)2-OHDedicated to Professor E. J. Corey on the occasion of his 70th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 983-1002 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For a comparison with the corresponding α- and β-hexapeptides H-(Val-Ala-Leu)2-OH (A) and H-(β-HVal-β-HAla-β-HLeu)2-OH (B), we have now prepared the corresponding γ-hexapeptide 1 built from the homochirally similar (S)-4-aminobutanoic acid, (R)-4-amino-5-methylhexanoic acid, and (R)-4-amino-6-methylheptanoic acid. The precursors were prepared either by double Arndt-Eistert homologation of the protected amino acids Boc-Val-OH, Boc-Ala-OH, and Boc-Leu-OH (Schemes 1 and 2), or by the superior route involving olefination/hydrogenation of the corresponding aldehydes (Boc-valinal, Boc-alaninal, and Boc-leucinal; Scheme 3). Conventional peptide-coupling methodology (EDC/HOBt) furnished the γ-hexapeptide 1 (through the intermediate γ-di- and γ-tripeptide derivatives 9-11). Analysis of NMR measurements in (D5)pyridine and CD3OH solution (COSY, TOCSY, HSQC, HMBC, ROESY) reveals that the γ-hexapeptide 1 adopts a right-handed helical structure ((P)-2.61 helix of ca. 5-Å pitch, containing 14-membered H-bonded rings) which is to be compared with the left-handed helix of the corresponding β-peptide B ((M)-31 helix of 5-Å pitch, 14-membered H-bonded rings) and with the familiar right-handed, so-called α-helix of α-peptides ((P)-3.61 helix of 5.4-Å pitch, 13-membered rings). Like the helix sense, the helix dipole reverses when going from α-, (N + → C) to β-(C + → N) to γ-peptides (N + → C). The surprising difference between the natural α-, and the analogous β- and γ-peptides is that the helix stability increases upon homologation of the residues.
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    Antitumor Agents. Part 184.Part 183: [1]. Syntheses and antitubulin activity of compounds derived from reaction of thiocolchicone with amines: Lactams, alcohols, and ester analogs of allothiocolchicinoidsDedicated to Prof. Dieter Seebach on the occasion of his 60th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1023-1037 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 7-O-Substituted analogs of deaminodeoxycolchinol thiomethyl ether were synthesized and evaluated for their inhibitory effects on tubulin polymerization in vitro. Ketone 9, a key compound in this study, was derived from thiocolchicone 6 by reaction with aniline. Reaction of compound 6 with MeNH2 or BuNH2 gave tetracyclic lactams 7 and 8, respectively. Optically active alcohols 11a and 11b were obtained from racemic 11 by chemical resolution including a separation of the comphanate diastereoisomers 12a and 12b, followed by basic hydrolysis. The (aR,7R)-configuration of 12b was verified by X-ray crystallographic analysis. Almost all racemic and optically active 7-O-acyl or 7-O-aroyl compounds had strong inhibitory effects on the tubulin polymerization reaction, with IC50 values from 1.7 to 5.1 μM. A few agents, such as the lactams 7 and 8, the camphanates 12a and 12b, the cyclohexanecarboxylates 19a and 19b, and, most notably, the (7S)-benzoate 15a, had negligible effects on polymerization, yielding IC50 values greater than 40μM. Ketone 9 showed strong inhibition of tubulin polymerization comparable to that of thiocolchicone (6). Optically active alcohol 11a and acyl esters 13a and 14a with a (7S)-configuration were more active than the (7R)-esters 13b and 14b. However, the esters 15a-17a with a (7S)-configuration were less active than the (7R)-isomers 15b-17b, in which the (7R)-benzoate 15b was at least 15-fold more inhibitory than the (7S)-isomer 15a. For the most part, the agents causing strongest inhibition of polymerization also caused the greatest inhibition of [3H]colchicine binding. NMR and optical rotatory data indicate that, in polar solvents, the equilibrium in esters with a 7-O-aroyl substituent, i.e., 15a,b, 16a,b, and 17a,b, is reversed from (aS) to (aR) or from (aR) to (aS), as compared to nonpolar solvents.
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    α-Methylidene-γ-butyrolactones: Synthesis and evaluation of quinolin-2(1H)-one derivatives (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1038-1047 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As a continuation of our previous studies on the synthesis and antiplatelet activity of quinolin-2(1H)-ones with an α-methylidene-γ-butyrolactone substituted at O(8), the O(6)- and N(1)-substituted isomers were synthesized and evaluated for antiplatelet activity against thrombin (Thr)-, arachidonic acid (AA)-, collagen (Col)-, and platelet-activating-factor (PAF)-induced aggregation in washed rabbit platelets. These compounds were synthesized from 6-hydroxyquinolin-2(1H)-one via alkylation and Reformatsky-type condensation (Schemes 1 and 2). All of them were found to inhibit the platelet aggregation perfectly which was induced by AA and Col. 6-Substituted isomers 5b-g exhibited very strong inhibitory activities against AA- and PAF- induced aggregation and are approximately ten times more potent than their 8-substituted counterparts. However, the 1-substituted (11a and 11b) and the 1,6-disubstituted (6) counterparts were relatively inactive. Their effects on the Ca2+-dependent vasoconstriction induced by high K+, and the phasic and tonic vasoconstrictions induced by norepinephrine (NE) in rat aorta were also evaluated. Except 5g, all of them were found to have significant inhibitory activity on the NE-induced phasic and tonic vasoconstrictions. Compounds 6 and 11b also exhibited strong inhibitory activity on high-K+ medium, Ca2+-induced vasoconstriction.
    Additional Material: 1 Ill.
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    Aminocyclopentitols from N-Alkylpyridinium Salts: A photochemical approach (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1095-1104 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photolysis of N-alkylpyridinium halides 9a-e in alkaline H2O gave 6-azabicyclo[3.1.0]hexenol derivatives 10a-e. N-Substituents bearing ether, acetal, and alcohol functions were found to do not adversely influence the photochemical reaction course. The free OH groups of the N-(3-hydroxypropyl) derivative 10d were protected by benzoylation. The ensuing dibenzoate 14 underwent stereocontrolled opening of the aziridine ring on reaction with MeSH/BF3 to give a thioether 15. With benzoic acid in CHCI3, 10d gave the 4-hydroxy-5-aminocyclopent-2-enyl benzoate 11. The meso-2-aminocyclopent-4-ene-1,3-diol 12 was obtained by hydrolysis of 11. On reaction with Boc2O and NaI, the aziridine ring of 14 was converted to a bicyclic compound 17. Hydrolysis of 17 provided the trans-1,3-diol 18, the epimer of 12. Face-selective dihydroxylation of Boc-protected 12 gave a meso-aminocyclopentanetetrol 23 which was characterized upon peracetylation. Dihydroxylation of 15 provided a racemic analogue of epi-mannostatin A (26).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810523
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  • 83
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    An Alternative Synthesis of the Enantiomerically Pure Competitive NMIDA Antagonists SDZ 220-581 and SDZ EAB 515 (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 729-733 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An alternative synthesis of enantiomerically pure SDZ 220-881 (1a) and SDZ EAB 515 (1b) starting from L-Z-tyrosine is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810322
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  • 84
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    Diastereo- and Regioisomeric Bicyclic Thiohydantions from Chiral 1,3-Thiazolidine-2,4-dicarboxylic acids (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 744-753 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bicyclic thiohydantoins were synthesized in a stereoselective manner by reacting (2R)/(2S)-diastereoisomer mixtures of 1,3-thiazolidine-2,4-dicarboxylic acids or their dimethyl diesters with PhNCS. 5,5-Dimethyl-1,3-thiazolidine-2,4-dicarboxylic acid with PhNCS led to a cyclization involving the C=O group at the C(2) center of the thiazolidine ring, while the acid's dimethyl diester gave cyclization involving the C=O group at C(4). In contrast, reactions involving unsubstituted 1,3-thiazolidine-2,4-dicarboxylic acid or its dimethyl diester led to thiohydantoins in which the ring closure had taken place only with the COO group at C(4). Independently of the direction of the ring closure, all reactions produce exclusively products with the (R)-configuration at C(2). The configurational assignments were based on 1H- and 13C-NMR studies, and confirmed by X-ray crystallographic analyses.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810324
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  • 85
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    New Axially Chiral Bis(dihydrooxazoles) as Ligands in Stereoselective Transition-Metal Catalysis (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 676-687 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new, axially chiral bis(4,5-dihydrooxazoles) 4 have been synthesized in a straightforward manner, starting from the substituted, racemic 1,1′-biphenyl-2,2′-dicarboxylic acids 1 and optically active amino alcohols 2. The adducts were resolved by medium-performance liquid chromatography (MPLC; see Scheme 1). Formation of Cu1 complexes of 4 was followed by 1H-NMR spectroscopy. The catalytic behavior of these complexes has been investigated by asymmetric cyclopropanation of styrene with ethyl diazoacetate. Beside the influence of steric factors, a significant electronic effect on asymmetric induction could also be observed (see Scheme 2 and Table).
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810318
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  • 86
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    Synthesis of Bridgehead-Functionalized Bicyclo[3.2.1]octanes via intramolecular titanium- and tributylstannane-induced pinacol coupling (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 734-743 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the enantiomerically pure, bridgehead-functionalized bicyclo[3.2.1]octanes 11 and 16, containing a conformationally fixed trihydroxypropyl (aminodihydroxypropyl) unit, as well as the X-ray structure of 11 are described. These compounds are of interest as sugar surrogates in the preparation of DNA analogs. Compounds 11 and 16 became available in 10 and 12 steps, respectively, and in an overall yield of 11 and 4% from D-arabinose via a highly stereoselective pinacol coupling as the key step.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810323
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  • 87
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    Synthesis and Structure Elucidation of a New Potent Sandalwood-Oil Substitute (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1349-1358 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New derivatives of campholenaldehyde (= 2-(2,2,3-trimethylcyclopent-3-enyl)ethanal bearing two cyclopropane moieties were synthesized, and the structure of the stereoisomer responsible for its exceptionally strong, diffusive, and natural sandalwood-oil scent, ((1S,2S)-1-methyl-2-{[1S,3R,5R)-1,2,2-trimethylbicyclo[3.1.0]hex-3-yl]methyl}cyclopropyl)methanol (13a), was elucidated.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810545
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  • 88
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    Glycosylidene Carbenes. Part 27.Part 26: [1] Glucosidation of titanium dioxide with 1-aziglucoses: Preparation and characterization of modified titanium-dioxide surfaces (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1359-1372 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Titanium-dioxide surfaces have been glycosylated with the benzyl-, 4-fluorobenzyl-, and acetyl-protected diazirines 1-3. The modified TiO2 surfaces were characterized by contact-angle measurement, X-ray photoelectron spectroscopy (XPES), and time-of-flight secondary-ion mass spectrometry (ToF-SIMS). The main by-products of the glucosidation (mostly azines and trehaloses) were identified. Their physisorption slightly reduces the efficiency of the glucosidation by 1 mM solution of 1 or 2 in CH2Cl2, but this influence is neutralized by repeating the glucosidation, or by using a 100 mM solution of the diazirines. The immobilized, acetylated glucosyl moieties were deacetylated in situ. Calculations based on the XPES peaks of Ti 2p and F 1s for the TiO2 surface modified with 2 indicated 1.5 ± 0.9 immobilized glucosyl moieties per nm2.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810546
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  • 89
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    Minor Coumarins from Calophyllum teysmannii var. inophylloide and Synthesis of Cytotoxic Calanone Derivatives (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1404-1416 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Chemotaxonomic survey for biologically active compounds from Malaysian Calophyllum species led to the findings of the four new benzoylcoumarins 1a, 2, 3, and 4a (including the unusual prenylated 6-benzoylcoumann 1a), two uncommon coumarins 5 and 6a with a pyran-4-one moiety fused at C(6) and C(7), and compounds 7a, 9, and 10, all isolated from the bark of C. teysmannii var. inophylloide. Their structures were determined by spectroscopic analysis and chemical transformations. X-Ray crystal-structure determination of 2 provided information on the conformational preferences of substituents in this class of coumarins. The syntheses of the cytotoxic calanone (7a) and of some related coumarins are described.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810549
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  • 90
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    New Enzyme Models of Chloroperoxidase: Improved stability and catalytic efficiency of iron porphyrinates containing a thiolato ligand (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1506-1520 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The heme-thiolate protein chloroperoxidase (CPO) catalyzes the chlorination of activated C—H bonds. A reaction mechanism is proposed for this enzymatic transformation (Scheme 1), and a new iron(III) porphyrinate complex 13 is synthesized containing pentafluorophenyl groups at two meso-positions and a thiophenolato ligand coordinating to the Fe-atom (Schemes 2 and 3). Due to the presence of the electron-withdrawing substituents, the catalyst 13 is appreciably resistant to oxidants (HOCl) and chlorinates, e.g., monochlorodimedone (5), with turnover numbers up to 1530. The redox potential of 13, E0 = - 134 mV, and the Soret band (λmax 448 nm) of the CO adduct of the reduced state of 13 are close to the corresponding values of the enzyme CPO.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810554
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  • 91
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    Nucleotides. Part LVII.Part LVI: [1].. Synthesis of phosphoramidite building blocks of 2′-amino-2′-deoxyribonucleosides: New compounds for oligonucleotide synthesis (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1528-1544 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical synthesis of 2′-amino-2′-deoxyribonucleosides of uracil, cytosine, adenine, and guanine, and their conversion into suitably protected 3′-phosphoramidite building blocks 35-40 for oligonucleotide synthesis are described. The aglycone and the 2′-amino functions were protected using the 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) group. The synthesis of the 3′-O-succinyl (3′-O-(3-carboxypropanoyl))-substituted starting nucleoside 41 is described and its behavior examined in solution and on solid phase with regard to an anticipated migration during 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) deprotection. Oligonucleotides were prepared using the new building blocks, and their hybridization properties were studied by UV-melting techniques.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810556
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  • 92
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    Erratum (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1583-1583 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810559
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  • 93
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    Supramolecular Chirality: Chiral hydrogen-bonded supermolecules from achiral molecular components (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1-13 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral supermolecules may be obtained from suitable achiral molecular constituents associated through a dissymmetrizing interaction mode. This is the case for the supermolecules I-IV formed by hydrogen-bonding association between the achiral complementary components 1a,b and 2a,b,c. The crystal structures of the supermolecular pairs I-III and of the homochiral aggregate of two ternary supermolecules IV have been determined. The structural data are discussed.
    Additional Material: 11 Ill.
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  • 94
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    Nucleotides. Part LVPart LIV: [1].. Synthesis and application of a novel linker for solid-phase synthesis of modified oligonucleotides (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 46-58 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various bifunctional amino-protecting groups such as the phthaloyl, succinyl, and glutaryl group were investigated as potential linker molecules for attachment to solid-support materials. Pentane-1,3,5-tricarboxylic acid 1,3-anhydride (16) offered the best properties and reacted with the amino groups of differently sugar-protected adenosine (see 20 and 22), cytidine (see 29), and guanosine derivatives (see 32) to the corresponding 2-(2-carboxyethyl)glutaryl derivatives 23, 24, 30, and 33. The usefulness of the new linker-type molecules was demonstrated by the solid-support synthesis of the potentially antivirally active 3′-deoxyadenylyl-(2′-5′)-2′-adenylic acid 2′-{2-[(adenin-9-yl)methoxy]ethyl} ester (38) starting from the 2′-end with N6,N6-[2-(2-carboxyethyl)glutaryl]-9-{{2-[(4,4′-dimethoxytrityl)ethoxy]methyl}adenine (12).
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  • 95
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    Biocatalytic Deracemization of 1,4-Benzodiazepines in the Synthesis of Enantiomerically Pure Serine (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 85-92 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient stereocontrolled synthesis of (S)-N-Cbz-serine (Cbz = benzyloxycarbonyl; 12) and of its (R)-enantiomer is reported. Kinetic resolution of the easily available racemic 3-(hydroxymethyl)-1,4-benzodiazepin-2-ones is performed in the key step via acetylation by the immobilized Mucor miehei lipase (Lipozyme IM) at 60°. This method is characterized by high enantiomer purity (ee's ges; 99%) of the intermediary alcohols (+)-8 and (+)-9 and acetates (-)-10 and (-)-11, as well as of the final products (S)- and (R)-N-Cbz-serine, simple recycling of the biocatalyst, complete recovery of 2-aminobenzophenones (3 and 4) and their recycling into production of 1,4-benzodiazepines, and possibility to selectively racemize ‘wrong’ enantiomers of the alcohols 8 and 9 in the presence of Amberlite CG 400.
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    URL: http://dx.doi.org/10.1002/hlca.19980810110
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  • 96
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    A Study of the Metabolic Degradation of an insect juvenile hormone analog using different radiolabeling (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 163-173 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fate of an insect juvenile hormone analog applied to the insect body of the flesh fly (Sarcophaga bullata) or the tsetse fly (Glossina palpalis), respectively, was studied using three different radiolabeled positions in the parent biologically active compound 1. Several metabolites were found and analyzed. A mechanism of degradation of the applied molecule was designed using a combination of several radioanalytical methods. A unique monitoring of the applied compound and its metabolites was provided, based on the different radiolabeling of the structure (cf. 1a-1c), and established their fate in an insect body during a 10-day experiment. A 14C and 3H radiolabeling, respectively, was employed to synthesize three different radiolabeled forms 1a-1c derived from the parent non-labeled 1. A combination of three different ways of radiolabeling resulted in an advantage in tracing the metabolic pathway of degradation of the employed compound 1 in its radiolabeled forms 1a-1c.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810115
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  • 97
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    3rd Swiss course on medicinal chemistry (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 187-187 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810118
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    Orbital-Symmetry Effects in Bimolecular Electron-Transfer Reactions: Back Electron TransferDedicated to Prof. Nicholas J. Turro on the occasion of his 60th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 670-675 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous work has indicated orbital-symmetry effects upon forward electron transfer in bimolecular systems, with magnitude similar to that encountered in rigid monomolecular systems. The present work, which employs back electron transfer, supports and extends these earlier findings.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19980810317
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  • 99
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    Glycosylidene Carbenes part 26Part 25: [1]. The intramolecular F…HO hydrogen bond of 1,3-diaxial 3-fluorocyclohexanols (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 695-717 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: According to ab-initio calculations, the CF…HO H-bond in 1,3-diaxial 3-fluorocyclohexanol is characterized by d(F…H) = 2.08 Å, and ∠ (F…H—O) = 138°, and by ΔE between 1.2 and 4.1 kcal/mol, depending upon the reference system. Relative to the OH stretching frequency of axial cyclohexanol, the OH stretching frequency of 1,3-diaxial 3-fluorocyclohexanol is shifted by Δω = 7 cm-1. The rigid fluoro diols D-4 and L-4 were prepared from tetrahydroxy-p-benzoquinone in 11 steps and 1% overall yield. The IR spectrum of 4 in CCl4 soln. is characterized by Δν = 7 cm-1 for the axial and Δν = 44 cm-1 for the equatorial OH group. A relatively strong intramolecular CF…HO bond of 4 in CCl4 is evidenced by the large through-space coupling 5J(F,HO) of 9.3 Hz. Nevertheless, this FHO bond is disrupted in ethereal solvents, while the bifurcated O…HO bond subsists. In CCl4, the carbene generated from the glucosylidene-derived diazirine 5 reacted more rapidly with the axial OH group of D-4 and L-4 than with the equatorial one. This regioselectivity is in keeping with the weaker H-bond of the axial OH group. The regioselectivity is lower in ethers, but its solvent dependence does not parallel solvent basicity. This is not satisfactorily explained by the differential interaction of the ether solvents with the axial and equatorial OH groups, as evidenced by the solvent dependence of their chemical shift, but must also reflect the different interaction of the solvents with the carbene derived from 5, leading to ylides. The lower solvent dependence of the anomeric selectivity for the glycosidation of the equatorial OH group is a consequence of the coordination of the intermediate oxycarbenium ion with O—C(1) and O—C(3) rather than with the solvent. Under conditions of competitive glycosylation in CCl4, the fluoro alcohol D-22 reacted more slowly than the alcohol L-24, evidencing the intramolecular F…HO H-bond.
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    URL: http://dx.doi.org/10.1002/hlca.19980810320
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  • 100
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    Synthesis and Odor of Chiral Partial Structures of Khusimone. Part 3Part 2: [1].. Short communication (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 40-45 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Khusimone (1), one of the main odor-donating compounds of vetiver oil, is subject of the following study on structure/odor relationship. The omittance of the methano bridge of the tricyclic khusimone should lead to the bicyclic partial structure (-)-2. Unexpectedly, (-)-2 could not be obtained since epimerization favored (-)-16. The stereochemical key step of the synthesis of the hydrazulene nucleus is based on a highly diastereoselective conjugate addition to a chiral oxocyclopent-1-ene-1-carboxylate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810105
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