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  • 1
    Digitale Medien
    Digitale Medien
    Oxford, UK; Malden, USA : Blackwell Science Ltd/Inc.
    Contact dermatitis 50 (2004), S. 0 
    ISSN: 1600-0536
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Germall 115 and Germall II are well known cosmetic preservatives, widely used as such since the early 1970’s and 1980’s, respectively. This investigation reveals that they have mistakenly been regarded as pure chemical entities with specific structures by the majority of the chemical society. In fact Germall 115 and Germall II both consist of complex mixtures of numerous and fast degradable allantoin-formaldehyde condensation products and may not even contain the conventionally assigned chemical structures of imidazolidinyl urea (Germall 115) and diazolidinyl urea (Germall II). Equilibrium between different structures may be formed in different cosmetic formulations/test materials. This may have led to the discrepancies in the literature: Are the Germalls themselves sensitizers or are the allergic reactions caused by formaldehyde release? The identification and structure assignment of (4-hydroxymethyl-2,5-dioxo-imidazolidin-4-yl)-urea (HU) will be presented, as it is the major and chemically stable degradation product of both Diazolidinyl urea and Imidazolidinyl urea. A guinea pig maximization test has been performed to determine the potential of HU to induce delayed contact hypersensibility in guinea pigs. Separate chemically stable TRUE Test patches containing the mixtures have shown clinical efficacy.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A chiral center in a drug molecule increases the complexity of synthetic, metabolic, pharmacological, and clinical studies, an additional problem being a possible lack of configurational stability. Here, we report detailed kinetic and mechanistic studies on the deuteration and racemization of seven 5-monosubstituted hydantions (= imidazolidine-2,4-diones) used as model compounds. Using 1H-NMR and chiral RP-HPLC, rates of reaction and thermodynamic parameters of activation were determined for the reactions of deuteration and racemization. Energies of deprotonation were obtained by molecular-orbital calculations performed at the AM1 level. It is demonstrated that the deuteration and racemization of 5-monosubstituted hydantoins follow general-base catalysis. The identical (within experimental errors) activation energies of deuteration and racemization indicate that the two reactions share a common reaction mechanism. The fact that the pseudo-first-order rate constants of deuteration are about half of those of racemization suggests that deuteration occurs with inversion of configuration. Very large differences in reaction rates were observed between the seven compounds, indicating the marked influence of substituents on chiral stability. These results, together with the small isotope effects observed, and the comparison between experimental activation energies and calculated energies of deprotonation, suggest a SE2 push-pull mechanism for the racemization of 5-monosubstituted hydantoins.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    ISSN: 0899-0042
    Schlagwort(e): absolute configuration ; muscarinic ; agonists ; chemical resolution ; capillary electrophoresis ; receptor binding ; enantioselectivity ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Methods for the synthesis of each of the four stereoisomers of 6-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[3.2.1]octane (10, 11, 12, and 13) and 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[2.2.1]heptane (18, 19, 20, and 21), and the two stereoisomers of 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[2.2.2]octane (27 and 28) were developed. The relative configuration of the compounds was determined on the basis of previously described 1H NOE experiments, and the absolute configuration of 6-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[3.2.1]octanes (10, 11, 12, and 13) and 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[2.2.2]octane (27 and 28) was determined by single crystal X-ray crystallography. Optical purity was determined by capillary electrophoresis (CE) using chiral selectors as trimethyl-β-cyclodextrin and heparin dissolved in the running buffer. All the 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicycles had low nanomolar affinity for muscarinic receptors as determined by displacement of radiolabelled oxotremorine-M (3H-Oxo-M) and pirenzepine (3H-Pz) from cortical rat brain homogenates. The binding assay discriminated between diastereomers, but only a minor degree of enantioselectivity was observed in the binding assays. Chirality 9:739-749, 1997. © 1997 Wiley-Liss, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 699-704 
    ISSN: 0899-0042
    Schlagwort(e): ormeloxifene ; chiral separation ; sulfated cyclodextrin ; enantiomers ; capillary electrophoresis ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: (-)-Ormeloxifene, a drug candidate under development, was separated from (+)-ormeloxifene using capillary electrophoresis (CE) with sulfated β-cyclodextrin as chiral buffer additive. With conventional long-end injection the method showed high efficiency, since the theoretical plate number for (-)-ormeloxifene was over 1 million per m and the enantiomeric resolution was more than 100. However, the relatively long separation time of ∼22 min was a limiting factor. In order to reduce separation time, short-end injection experiments were carried out. By using the instrumental limits for capillary dimensions and field strength, the separation time was reduced to 〈40 sec. A further and significant reduction was achieved by applying extended short-end injection, which is a novel injection technique presented in this paper. With the extended short-end injection procedure, a plug of run buffer is injected after the sample has been injected, thus moving the sample closer to the detector and resulting in very short effective capillary lengths. Using the extended short-end injection technique, the separation was performed on 1.8 cm capillary (effective length) and the enantiomers were separated within 10 sec, which is a reduction of the original separation time by a factor of ∼155. Chirality 10:699-704, 1998. © 1998 Wiley-Liss, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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