文摘
The 2,3-diaminopyridine (DAP) moiety was found to represent a core structure essential forthe potency of a new series of human bradykinin B1 receptor antagonists. However, incubationof 14C-labeled 2,3-DAP derivatives with rat and human liver microsomes resulted in substantialirreversible binding of radioactive material to macromolecules by a process that was NADPH-dependent. Trapping the reactive species with GSH led to significant reduction of theirreversible binding of radioactivity, with concomitant formation of abundant GSH adducts.One type of thiol adducts (detected in both human and rat liver microsomes), resulting fromaddition of 305 Da to the parent compound, was observed with all 2,3-DAP compounds. Theseadducts also were detected in rat hepatocyte incubates, as well as in rat bile, followingintravenous administration of 2,3-DAPs. Formation of the conjugates appeared to involvemodification of the DAP ring, based upon mass spectral analysis of a number of representativeGSH adducts; this was corroborated by detailed LC NMR analysis of one compound. Formationof this type of GSH conjugate was markedly reduced when the 2-amino methyl group linkingthe 2,3-DAP and the biphenyl moiety was replaced with an ether oxygen atom. It is postulated,therefore, that oxidation of the 2-amino group serves as a key step leading to the formation ofreactive species associated with the DAP core. In addition, this step appears to be mediatedprimarily by P450 3A, as evidenced by the marked decrease in both the irreversible binding ofradioactivity and the formation of the GSH adducts in human liver microsomes followingtreatment with ketoconazole and monoclonal antibodies against P450 3A. A mechanism forthe bioactivation of 2,3-DAP is proposed wherein oxidation (dehydrogenation or N-hydroxylationfollowed by dehydration) of the 2-amino group, catalyzed by P450 3A, results in the formationof a highly electrophilic species, pyridine-2,3-diimine.
