Microbial transformation of the antihistamine pyrilamine maleate. Formation of potential mammalian metabolites.

Fourteen fungi were found to metabolize pyrilamine (2-[(2-dimethylaminoethyl)(p-methoxybenzyl)amino]pyridine). Two Cunninghamella elegans strains transformed essentially all of the pyrilamine added after 144 hr. After 48 hr of incubation, C. elegans ATCC 9245 metabolized 76% of the antihistamine into methylene chloride-extractable pyrilamine metabolites. These organic-soluble metabolites were isolated by HPLC and the major metabolites were characterized by comparison of their chromatographic, mass, and 1H-NMR spectral properties with those of authentic compounds. The major metabolite was identified as 2-[(2-dimethyloxyaminoethyl)(p-methoxybenzyl)amino]pyridine (N-oxide derivative of pyrilamine). Other metabolites identified were 2-[(2-dimethylaminoethyl)(p-hydroxybenzyl)amino]pyridine, 2-[(2-methylaminoethyl)(p-methoxybenzyl)amino]pyridine, and 2-[(2-methylaminoethyl)(p-hydroxybenzyl)amino]pyridine. These metabolites represent O-demethylated, N-demethylated, and O- and N-demethylated derivatives of pyrilamine, respectively. The mutagenic activities of the N-oxide and the N- and O-dealkylated pyrilamine derivatives, and pyrilamine maleate were measured by reversion of Salmonella typhimurium strains TA97, TA98, TA100, and TA102. Pyrilamine maleate and the three microbial metabolites showed no appreciable mutagenic activity in any of the S. typhimurium tester strains. The metabolism of pyrilamine by 12 other filamentous fungi and yeast strains was much less when compared to C. elegans and ranged from 3.8% to 12.2%. The fungal metabolism of pyrilamine may be useful in predicting results of mammalian metabolism and in readily providing sufficient quantities of metabolites for further toxicological studies.