Zur Methodik der chemischen Vitamin A- und D-Bestimmung mit elektrophilen Metallhalogeniden

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Analogs of tetrahydrofolic acid. XXXIX . selective bromoacylation of polyfunctional molecules for synthesis of active-site-directed irreversible enzyme inhibitors

A number of methods for selective bromoacylation of side-chain amino groups on 2-amino-4-pyrimidinols or 2,4,6-triaminopyrimidines have been developed for these extremely sensitive products. The choice of method depends upon whether (a) the aminopyrimidine is a stronger base than the amine to be bromoacylated, (b) as weak a base as the amine to be bromoacylated but the amine is more reactive, (c) the amine group to be bromoacylated is a strong aliphatic amine. In case (a) the aminopyrimidine can be protonated to protect it from acylation with an anhydride; in case (b), the reaction with an anhydride is controlled by temperature, stoichiometry, and time of reaction; in case (c), the reaction is selectively controlled by use of the less reactive p-nitrophenyl esters. Other difficulties were solved such as (a) proper characterization of the products when combustion analyses were unsatisfactory due to polymerization; in these cases a combination of thin layer chromatography, color reactions, and derivatization were employed; and (b) insolubility leading to overreaction on the aminopyrimidine which was solved with partial aqueous systems.