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

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. Mammalian cytochrome P450 drug metabolizing enzymes rarely cleave C−C bonds. Here we report the mechanisms of two unusual CYP3A‐mediated cleavages of non‐polar, unstrained C(sp2)−C(sp3) bonds in the metabolism of tyrosine kinase inhibitor pexidartinib. One bond is cleaved by CYP3A‐mediated ipso‐addition of activated oxygen, and the other occurs by a pseudo‐retro‐aldol reaction after hydroxylation of a C(sp3) site.