5-substituted, 6-substituted, and unsubstituted 3-heteroaromatic pyridine analogues of nicotine as selective inhibitors of cytochrome P-450 2A6

A series of 5- and 6-substituted and unsubstituted 3-heteroaromatic analogues of nicotine were synthesized in an effort to delineate the structural requirements for selectively inhibiting human cytochrome P-450 (CYP) 2A6, the major nicotine metabolizing enzyme. Thiophene, substituted thiophene, furan, substituted furan, imidazole, substituted imidazole, pyridine, substituted pyridine, thiazole, and quinoline moieties were used to replace the N-methylpyrrolidine ring of nicotine. Bromo and methyl groups were introduced at the 5-position of the pyridine ring and fluoro, chloro, and methoxy groups were placed at the 6-position of the pyridine ring in order to explore the structure-activity relationship (SAR) of inhibition of CYP2A6. The inhibitory activity of the most potent CYP2A6 inhibitors on the functional activity of human cytochrome P450s 3A4, 2E1, 2136, 2C9, 2C19, and 2D6 was also examined to determine inhibitor selectivity. We identified 36 compounds that were more potent than nicotine at inhibition of coumarin 7-hydroxylase (CYP2A6) activity. We also found a number of compounds to be highly selective for the inhibition of human CYP2A6 versus the other human CYPs examined.