Studies on drug metabolism by use of isotopes. XII. Quantitative analysis of 22H-labeled compounds on benzene ring by mass spectrometry (author's transl)

Abstract

Mass spectral problems on the applicability of a drug labeled with deuterium on the benzene ring for the metabolic studies in man were investigated using benzoic acid [arom.-2H5] and hippuric acid [arom.-2H5]. By comparing the mass spectra of deuterated compounds with those of unlabeled analogues, an intramolecular exchange reaction between deuterium on the benzene ring and hydrogen on the side chain was recognized slightly in the phenyl ion and remarkably in the benzoyl ion from the deuterated benzoic acid. However, such an exchange reaction was not observed in any ion from the deuterated hippuric acid. Deuterium radical from the M-CO2+ of labeled hippuric acid was lost during the fragmentation. Moreover, an isotope effect of a few percent was obsirved in the production of the phenyl ion and the C4H3+ ion by examination of the mass spectrum of an equimolar mixture of nonlabeled and labeled compounds. From these results, the molecular ion and the benzoyl ion of benzoic acid, and the benzoyl ion of hippuric acid were chosen as the main peak for quantitative analysis. By comparing the total peak height in the region of the ±1 mass unit of the main peak from deuterated compound with those from protiated counterpart, the former diluted in the order of 100-fold amount of the latter was determined with a precision within 3%.