Use of liquid chromatography in the synthesis of isoluminol-labeled medroxyprogesterone acetate and zeranol

A high-performance liquid chromatographic (HPLC) method for monitoring the syntheses of two isoluminol-labelled drugs, medroxyprogesterone acetate (MPA) and zeranol, has been developed. MPA and the ketone derivative of zeranol, zearalanone, were conjugated to N-(4-aminobutyl)-N-ethylisoluminol through the carboxymethyloxime derivative of the drug by using the N-succinimide ester as an intermediary. Reaction mixtures were sampled periodically and chromatographed directly by HPLC on a silica gel column, by using isocratic elution with mixtures of hexane-ethanol-acetic acid in several different proportions. The degree of reaction completion was determined by comparison of the peak area of the initial reactant to that present at sampling time. MPA oxime production was found to be complete after 15 min; 97.0% of the oxime was converted to succinimide ester in 24 h; 99.0% of the available ester reacted within 2.5 h to form the final labelled product. Zearalanone oxime production was found to be complete after 2 h; 93.3% of the oxime was converted to the activated ester within 24 h; 89.6% of available ester had reacted in 30 min to form the final labelled product. The chromatography can be performed in real time, permitting modification in the conditions of the reaction while in progress.