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  • 1
    Electronic Resource
    Electronic Resource
    The so-called “interconversion” of stereoisomeric drugs: An attempt at clarification (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 105-111 
    Details
    ISSN: 0899-0042
    Keywords: enantiomers ; racemization ; epimers ; epimerization ; configurational stability ; nonenzymatic reactions ; oxazepam ; amfepramone ; thalidomide ; atropine ; chlorthalidone ; pilocarpine ; 16α-substituted 3-methoxyestrones ; chlorpromazine ; telenzepine ; tofisopam ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A variety of reactions can be categorized under the global concept of the “interconversion of stereoisomers.” Thus, racemization or epimerization can result from inversion of labile chiral centers. From the examples available, some predictive rules are suggested for a chiral center of the type R″R′RC—H undergoing base-catalyzed inversion and a provisional table of affecting groups is presented. Unimolecular inversion of nonsymmetrical, nonplanar ring systems can also result in racemization or epimerization, but no generalization can yet be offered. Beside these cases of nonenzymatic reactions, a limited variety of enzymatic reactions can operate to interconvert stereoisomers, the outcome rarely being a racemic mixture. An important aspect of stereoisomer interconversion is the time scale in which the phenomenon is observed. Thus, several reactions to nonezymatic racemization or epimerization are fast compared to the duration of action of the drug and therefore have pharmacological significance, while other are slower and are of pharmaceutical relevance only. © 1993 Wiley-Liss, Inc.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050302
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  • 2
    Electronic Resource
    Electronic Resource
    Racemization, enantiomerization, diastereomerization, and epimerization: Their meaning and pharmacological significance (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 396-400 
    Details
    ISSN: 0899-0042
    Keywords: configurational lability ; enantiomers ; diastereomers ; epimers ; macroscopic processes ; microscopic processes ; pharmacological time scale ; pharmaceutical time scale ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configurational lability of enantiomers can be characterized by different terms, each defining a specific process. Racemization relates to the macroscopic and statistical process of the irreversible transformation of one of the enantiomers into the racemic mixture. Enantiomerization refers to the microscopic and molecule process of the reversible conversion of one enantiomer into the other. Methods allowing the experimental determination of rate constants of racemization (krac) and enantiomerization (kenant) are discussed, and it is shown that kenant = 1/2 krac. Neglect of this fact is a source of some confusion in the literature. When two or more elements of chirality are present in a molecule and one of them is configurationally labile, epimerization occurs, a particular case of diastereomerization. These processes of interconversion between diastereomers are kinetically more complicated than racemization and enantiomerization since the rate constants of the forward and reverse reactions are always different (kdiast/A-to-B ≠ kdiast/B-to-A), however small the difference. An important aspect of the configurational lability of stereoisomeric drugs is the time scale of the phenomenon. When interconversion occurs to a significant extent during the residence time of a drug in the body, a pharmacological time scale is implied. In contrast, the pharmaceutical time scale refers to slower rates of interconversion that affect the configurational purity of a drug during its shelf-life. © 1995 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070603
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