CYP3A Mediates an Unusual C(sp²)−C(sp³) Bond Cleavage via Ipso‐Addition of Oxygen in Drug Metabolism

Abstract

Mammalian cytochrome P450 drug‐metabolizing enzymes rarely cleave carbon–carbon (C‐C) bonds and the mechanisms of such cleavages are largely unknown. We identified two unusual cleavages of non‐polar, unstrained C(sp2)‐C(sp3) bonds in the FDA‐approved tyrosine kinase inhibitor pexidartinib that are mediated by CYP3A4/5, the major human phase I drug metabolizing enzymes. Using a synthetic ketone, we rule out the Baeyer‐Villiger oxidation mechanism that is commonly invoked to address P450‐mediated C‐C bond cleavages. Our studies in 18O2 and H218O enriched systems reveal two unusual distinct mechanisms of C‐C bond cleavage: one bond is cleaved by CYP3A‐mediated ipso‐addition of oxygen to a C(sp2) site of N‐protected pyridin‐2‐amines, and the other occurs by a pseudo‐retro‐aldol reaction after hydroxylation of a C(sp3) site. This is the first report of CYP3A‐mediated C‐C bond cleavage in drug metabolism via ipso‐addition of oxygen mediated mechanism. CYP3A‐mediated ipso‐addition is also implicated in the regioselective C‐C cleavages of several pexidartinib analogs. The regiospecificity of CYP3A‐catalyzed oxygen ipso‐addition under environmentally friendly conditions may be attractive and inspire biomimetic or P450‐engineering methods to address the challenging task of C‐C bond cleavages.