Synthetic Inhibitors of Cytochrome P-450 2A6: Inhibitory Activity, Difference Spectra, Mechanism of Inhibition, and Protein Cocrystallization.

A series of 3-heteroaromatic analogues of nicotine were synthesized to delineate structural and mechanistic requirements for selectively inhibiting human cytochrome P450 (CYP) 2A6. Thiophene, substituted thiophene, furan, substituted furan, acetylene, imidazole, substituted imidazole, thiazole, pyrazole, substituted pyrazole, and aliphatic and isoxazol moieties were used to replace the N-methylpyrrolidine ring of nicotine. A number of potent inhibitors were identified, and several exhibited high selectivity for CYP2A6 relative to CYP2E1, -3A4, -2B6, -2C9, -2C19, and -2D6. The majority of these inhibitors elicited type II difference spectra indicating the formation of a coordinate covalent bond to the heme iron. The majority of inhibitors were reversible inhibitors although several mechanism-based inactivators were identified. Most of the inhibitors were also relatively metabolically stable. X-ray crystal structures of CYP2A6 cocrystallized with three furan analogues bearing methanamino side chains indicat...