title: Stereoselective metabolism of conformational analogues of warfarin by beta-naphthoflavone-inducible cytochrome P-450.
abstract: Previous studies have shown that the structurally related oral anticoagulants warfarin and phenprocoumon are regioselectively hydroxylated in the 6- and 8-positions by hepatic microsomes obtained from 3-methylcholanthrene (3-MC) or beta-naphthoflavone (BNF) pretreated rats. Stereoselectivity for hydroxylation is also observed and favors (R)-warfarin but (S)-phenprocoumon. The possibility that the stereoselectivity of warfarin hydroxylation is a function of the solution conformation of the drug was tested with conformationally restricted analogues. In these experiments the analogues were incubated with microsomes obtained from BNF-pretreated rats and any stereoselectivity associated with 6- and 8-hydroxylation was determined. The R enantiomer of cyclocoumarol, the cyclic ketal analogue of warfarin, was found to be selectively hydroxylated, in contrast to the S enantiomer of warfarin 4-methyl ether, the ring-opened analogue. The latter compound is known to have a preferred solution conformation similar to that of phenprocoumon. The results suggest that at the active site of BNF-induced cytochrome P-450 (R)-warfarin is metabolized in its cyclic hemiketal tautomer, a form which spatially mimics the preferred solution conformation of (S)-phenprocoumon.
mesh_terms: D000818:Animals; D001571:Benzoflavones / Q000494:pharmacology*; D003577:Cytochrome P-450 Enzyme System / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology*; D006900:Hydroxylation; D066298:In Vitro Techniques; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D008968:Molecular Conformation; D010644:Phenprocoumon / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013237:Stereoisomerism; D014859:Warfarin / Q000031:analogs & derivatives / Q000378:metabolism*; D019324:beta-Naphthoflavone
chemical_list: D001571:Benzoflavones; D005419:Flavonoids; D014859:Warfarin; D019324:beta-Naphthoflavone; D003577:Cytochrome P-450 Enzyme System; D010644:Phenprocoumon