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  • Carbanions  (2)
  • 13C MAS NMR  (1)
  • Biochemistry and Biotechnology  (1)
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  • 1
    ISSN: 1573-5079
    Keywords: 13C MAS NMR ; EPR ; FTIR ; spheroidene ; stable isotope labelling ; ubiquinone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this minireview the information at the atomic level that has been obtained by studying photosynthetic reaction centers with site-directed isotope labelling is discussed. The required isotopically labelled RCs are prepared using isotopically labelled amino acids and cofactors that have been prepared via organic total synthetic chemistry. In some cases the results of isotopically labelled RCs that are prepared via other methods are also discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 193-208 
    ISSN: 1075-2617
    Keywords: peptaibol ; antibiotic ; peptide synthesis ; NMR spectroscopy ; mass spectrometry ; isotope labelling ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For the first time the total synthesis of the peptaibol antibiotic zervamicin IIB is described. Synthesis of this peptaibol was achieved by the Fmoc/tert-butyl strategy in solution using a fragment condensation approach. Three fragments of zervamicin IIB were obtained by stepwise elongation with Fmoc amino acids using BOP as a coupling reagent. For the introduction of the highly sterically hindered α-aminoisobutyric acid residues BOP/DMAP activation was applied. The Fmoc group was removed by reaction with 0.1 M NaOH in dioxane/methanol/water (30/9/1, v/v/v). Peptide fragments were coupled by means of a new coupling reagent, CF3-PyBOP. Using the strategy developed, zervamicin IIB and two analogues specifically deuterium-labelled at different positions of the glutamine-11 residue have been synthesized in 40% overall yield based on the isotopically labelled amino acid and with 98±2% of isotope enrichment. FAB mass spectroscopy, 600 MHz 1H-NMR spectroscopy and high-performance liquid chromatography provided convincing evidence that the synthetic products, zervamicin IIB and its deuterium-labelled analogues, fully correspond to the naturally occurring zervamicin IIB. © 1997 European Peptide Society and John Wiley & Sons, Ltd.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1907-1914 
    ISSN: 1434-193X
    Keywords: Reductive alkylation ; Acenaphthylene ; Carbanions ; Polycycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dianion of acenaphthylene can be converted into the 5-hydroanion by protonation with one equivalent of methanol. Subsequent reaction with electrophiles such as allyl bromide and propargyl bromide occurs selectively at position 1, resulting in the formation of the novel 1-allylacenaphthene and 1-propargylacenaphthene. In addition to what was observed in the case of methyl iodide, the hitherto unknown 1,1-dialkylated acenaphthene derivatives are formed as minor products; probably the lower reactivity of the unsaturated bromides is responsible for this side reaction. From the products of the reactions with 3,3-dimethylallyl bromide and (bromomethyl)cyclopropane the mechanism was found to be SN2. Reaction of the hydroanion with benzyl bromide takes place at position 1 as well as at position 2a. The reactivity of carbon 2a towards the soft electrophile benzyl bromide is attributed to the high HOMO coefficient at this position.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 713-721 
    ISSN: 1434-193X
    Keywords: Reductive alkylation ; Acenaphthylenes ; Carbanions ; Polycycles ; Single-electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Reaction of the 5-hydroacenaphthylene anion with benzyl halides proceeds at carbon atom 1 as well as at carbon atom 2a, in the latter case creating a quaternary centre. The hardness-softness of the electrophiles was shown to play only a minor role in determining the regioselectivity of the reaction of the hydroanion with several benzyl and alkyl halides: the leaving group hardly affects the ratio of 1- and 2a-substituted products. This indicates that the alkylation might proceed by an electron transfer (SET) instead of an SN2 mechanism. Further evidence for SET was obtained by the use of free radical and electron scavengers. The substitution products 1-benzylacenaphthene and 2a-benzyl-2a,5-dihydroacenaphthylene could be isolated and purified.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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