Dmd057141 890..898

We investigated an uncommon biotransformation of pyrimidine during the metabolism of GNE-892 ((R)-2-amino-1,39,39-trimethyl79-(pyrimidin-5-yl)-39,49-dihydro-29H-spiro[imidazole-4,19-naphthalen]5(1H)-one), a b-secretase 1 inhibitor. Three novel metabolites, formed by conversion of pyrimidine to pyrazole, were observed in the C-radiolabeled mass balance study in rats. Their structures were characterized by high-resolution mass spectrometry and nuclear magnetic resonance. Although these metabolites accounted for <5% of the administered dose, their unique nature prompted us to conduct further investigations. The pyrazolecontaining metabolites were formed in vitro with rat hepatocytes and liver microsomes, which supported that they were formed during hepatic metabolism. Further, their generation was inhibited by 1-aminobenzotriazole, indicating involvement of cytochrome P450s. Studies with rat recombinant enzymes identified that CYP2D2 generated the N-hydroxypyrazole metabolite from GNE-892. This biotransformation proceeded through multiple steps from the likely precursor, pyrimidine N-oxide. On the basis of these data, we propose a mechanism in which the pyrimidine is activated via N-oxidation, followed by a second oxidative process that opens the pyrimidine ring to form a formamide intermediate. After hydrolysis of the formamide, a carbon is lost as formic acid, together with ring closure to form the pyrazole ring. This article highlights a mechanistic approach for determining the biotransformation of the pyrimidine to a pyrazole for