N-hydroxylation and N-dealkylation by P4502C3 of N-methylbenzamidine: N-oxygenation and N-oxidative dealkylation of one functional group

Abstract

1. The first detection of a microsomal N-hydroxylation of an N-alkylated benzamidine possessing α-H atoms by P450 is now reported in the present in vitro biotransformation studies.

2. The newly found metabolites, N-hydroxy-N-methylbenzamidine and N-methylbenzamidoxime, were identified after hplc separation by comparison of their retention times with those of synthetic reference compounds and by comixing methods. N-hydroxy-N-methylbenzamidine exists predominantly in the aminonitrone form and constitutes a novel type of metabolite.

3. By means of reconstitution experiments with purified P4502C3 from rabbit liver and with purified variants of 2C3 expressed in Escherichia coli, it has been shown that the N-hydroxylation and the N-dealkylation of N-methylbenzamidine are catalysed by the same P450 isoenzyme.

4. A reaction mechanism is proposed in which the P450-dependent N-oxygenations and N-dealkylation of N-methylbenzamidine are derived from a common intermediate. It is obvious that if α-H atoms are present N-dealkylation is observed; however, in contrast with previous concepts, N-oxygenation is also possible.