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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2909-2914 
    ISSN: 1434-193X
    Keywords: Methyl methacrylate ; 13C label ; Mass spectrometry ; 1H NMR ; 13C NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthetic scheme has been developed to prepare methyl methacrylate specifically 13C-labelled at all different positions and in any combination of positions, from simple, commercially available starting materials. According to this scheme methyl (1-13C)- and methyl (2-13C)methacrylate (1a and 1b) have been prepared with high label incorporation (99%).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    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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  • 3
    ISSN: 1434-193X
    Keywords: Astaxanthin ; Carotenoids ; Isotopic labeling ; Isotopic labeling ; Total synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The all-E isomer of (4,4′-13C2)astaxanthin (1a) has been prepared by total synthesis starting from commercially available 99% 13C enriched acetonitrile. The labelled astaxanthin was obtained in high purity and with high isotope incorporation. For this synthesis, the C15 + C10 + C15 strategy was used. The central C10-synthon, 2,7-dimethylocta-2,4,6-triene-1,8-dial (3), was coupled with 13C-enriched C15-phosphonium salt 2a. The new synthetic scheme for the preparation of the C15-phosphonium salt is discussed in this paper; the same scheme can be used to label all positions and combinations of positions of the C15-phosphonium salt.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-193X
    Keywords: DNA ; Dihydroxyacetone monophosphate ; Aldolase ; Carbon-13 ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A synthesis of [3′,4′-13C2]thymidine (1) is described in which [13C2]acetic acid (2) is converted into the nucleoside in twelve steps with 9% overall yield. D-2-Deoxyribose-5-phosphate aldolase (DERA, EC 4.1.2.4) and triosephosphate isomerase (TPI, EC 5.3.1.1) are used for the stereocontrolled formation of D-[3,4-13C2]-2-deoxyribose-5-phosphate (8) from [2,3-13C2]dihydroxyacetone monophosphate (DHAP, 7) and acetaldehyde in 80% yield. The route permits the introduction of isotopically enriched carbon atoms at any position or combination of positions in the furanose ring and the product can be coupled with any of the four naturally occurring base moieties.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-193X
    Keywords: Amino acids ; Isotopic labelling ; Ethyl benzoate ; Benzonitrile ; Sodium phenylpyruvate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthetic route to stable-isotope-substituted L-phenylalanine is presented, which allows the introduction of 13C, 15N, and deuterium labels at any position or combination of positions. For labelling of the aromatic ring, a synthetic route to ethyl benzoate (or benzonitrile) has been developed, based on the electrocyclic ring-closure of a 1,6-disubstituted hexatriene system, with in situ aromatization by elimination of one (amino) substituent. Several important (highly isotopically enriched) synthons have been prepared, namely benzonitrile, benzaldehyde, ethyl benzoate, and ethyl diphenyloxyacetate. Labelled L-phenylalanines have been synthesized from both aromatic precursors by initial conversion into sodium phenylpyruvate and subsequent transformation of this intermediate into the L-α-amino acid by an enzymatic reductive amination reaction. In this manner, highly enriched phenylalanines are obtained on the 10-gram scale and with high enantiomeric purities (≥ 99% ee). The method has been validated by the synthesis of [1′-13C]-L-Phe and [2-D]-L-Phe. In addition, two methods are described for the introduction of isotopes into L-tyrosine starting from the isotopically enriched precursors benzonitrile and ethyl benzoate.
    Type of Medium: Electronic Resource
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  • 6
    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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