ASYMMETRIC METABOLIC N-OXIDATION OF N-ETHYL-N-METHYLANILINE BY PURIFIED FLAVIN-CONTAINING MONOOXYGENASE

The prochiral tertiary amine N-ethyl-N-methylaniline (EMA) is known to be metabolically N-oxygenated in vitro with microsomal preparations. This biotransformation is thought to be mediated predominantly by the flavin-containing monooxygenase (FMO) enzyme system. Microsomal N-oxyg enation of EMA is known to be stereoselective and varies between speci es. In order to further characterise this metabolic transformation, we have examined the in vitro metabolism of EMA using purified porcine h epatic FMO. Following incubation of EMA with purified FMO, EMA N-oxide , the only metabolite detected, was found to be produced stereoselecti vely [ratio (-)-(S):(+)-(R), ca. 4:1]. The enantiomeric ratio of the N -oxide product did not change markedly with respect to time, enzyme or substrate concentration. Determination of the kinetics of formation o f the N-oxide indicated a single affinity for the prochiral substrate with differential rates of formation of the enantiomers. The extent of EMA N-oxide formation was shown to be affected by activators and inhi bitors of FMO and pH, but its stereoselectively was unaltered. (C) 199 4 Wiley-Liss, Inc.