Abstract

The influence of ortho chlorine substituents on 4-toluidine rat liver microsomal metabolism was investigated with 4-toluidine, 2-chloro-4-toluidine, and 2,6-dichloro-4-toluidine as substrates. Microsomal metabolic products were identified and quantified by HPLC, chemical assays, and synthesized reference compounds. Metabolites identified include products from aromatic ring hydroxylation, side-chain C-hydroxylation (benzyl alcohols and benzaldehydes), N-hydroxylation (hydroxylamines, nitrosotoluenes, azoxy, azo, and hydrazo derivatives), and two new types of microsomal metabolites: secondary amines [i.e. (halogenated) N-(4'-aminobenzyl)-4-toluidines] and an imine [i.e. N-(4'-amino-3',5'-dichlorobenzylidene)-2,6-dichloro-4-toluidine]. The secondary amine appeared to be a major microsomal metabolite for all three 4-toluidines studied. Quantification of the metabolite patterns demonstrated several influences of the chlorine substituents on metabolism of the 4-toluidine derivatives. The total conversion increased significantly in the order: 4-toluidine < 2-chloro-4-toluidine < 2,6-dichloro-4-toluidine, especially because of a marked increase in microsomal side-chain C-hydroxylation with increasing number of ortho chlorine substituents. The rate of N-hydroxylation varied much less. Aromatic ring hydroxylation was observed to a significant extent only for nonchlorinated 4-toluidine. Additional data from microsomal binding studies and molecular orbital calculations provided insight in possible mechanisms underlying the observed changes in metabolic profiles with increasing number of chlorine substituents at an ortho position with respect to the amine group.