Abstract
We investigated an uncommon biotransformation of pyrimidine during the metabolism of GNE-892 ((R)-2-amino-1,3′,3′-trimethyl-7′-(pyrimidin-5-yl)-3′,4′-dihydro-2′H-spiro[imidazole-4,1′-naphthalen]-5(1H)-one), a β-secretase 1 inhibitor. Three novel metabolites, formed by conversion of pyrimidine to pyrazole, were observed in the 14C-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 pyrazole-containing 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 GNE-892.
Footnotes
- Received January 16, 2014.
- Accepted March 4, 2014.
↵1 Current affiliation: Novartis Institutes for BioMedical Research, Emeryville, California.
Parts of this work were previously presented at The 18th North American Meeting of the International Society for the Study of Xenobiotics, 2012 Oct 14–18; Dallas, TX.
The authors were employees of Genentech, XenoBiotic Laboratories, or Array BioPharma at the time this work was completed.
↵This article has supplemental material available at dmd.aspetjournals.org.
- Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics
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