Determination of the in vitro metabolism of (+)- and (−)-epibatidine

The oxidative in vitro metabolism of epibatidine was investigated using liver microsomes from rat, dog, rhesus monkey and human. Analysis was performed using liquid chromatography–mass spectrometry (LC–MS) using both achiral and chiral stationary phases. Comparison of the metabolism of the (+)- and (−)-enantiomers revealed species differences in the extent of metabolism, with rhesus monkey>dog>rat=human. Furthermore, differences in the routes of metabolism for epibatidine enantiomers were also observed, with mass spectra consistent with hydroxylation of the azabicycle for (−)-epibatidine and with the formation of diastereomeric N-oxides for (+)-epibatidine being obtained. For chiral LC–MS, a volatile ion-pair reagent of heptafluorobutyric acid was used in place of pentanesulphonic acid with no deterioration in chiral selectivity. Analysis of the same samples by chiral LC–MS revealed no evidence for metabolic chiral interconversion and chiral analysis from a metabolic time course of racemic material revealed enantiomers to be metabolised to approximately the same extent. Such findings may be important particularly should epibatidine be investigated in non-rodent species.