MECHANISM-BASED INHIBITORS OF PROSTAGLANDIN OMEGA-HYDROXYLASE - (R)-12-HYDROXY-16-HEPTADECYNOIC AND (S)-12-HYDROXY-16-HEPTADECYNOIC ACID AND 2,2-DIMETHYL-12-HYDROXY-16-HEPTADECYNOIC ACID

12-Hydroxy-16-heptadecynoic acid has been shown to selectively inactiv ate cytochrome P450 4A4, a pulmonary cytochrome P450 enzyme that catal yzes the omega-hydroxylation of prostaglandins [Muerhoff, A.S.; Willia ms, D.E.; Reich, N.O.; CaJacob, C.A.; Ortiz de Montellano, P.R.; aster s, B. S. S. J. Biol. Chem. 1989,264, 749-756]. Potent, specific inhibi tors of this enzyme are required to explore its physiological role. In a continuing effort to develop such agents, the two enantiomers of 12 -hydroxy-16-heptadecynoic acid have been stereospecifically synthesize d, their absolute stereochemistry confirmed, and the dependence of enz yme inactivation on absolute stereochemistry determined using cytochro me P450 4A4 purified from the lungs of pregnant rabbits. The 12S enant iomer is roughly twice as active (K(I) = 1.8 muM, t1/2 = 0.7 min) as t he 12R enantiomer (K(I) = 3.6 muM, t1/2 = 0.8 min), but the chirality of the hydroxyl group is not a major determinant of the specificity fo r the prostaglandin omega-hydroxylase. The flexibility of the acyclic skeleton of the inhibitor may account for the relatively low enantiome ric discrimination. 2,2-Dimethyl-12-hydroxy-16-heptadecynoic acid, an analogue that cannot undergo beta-oxidation, has also been synthesized as a potential in vivo inhibitor of the enzyme and has been shown to inactivate the purified enzyme with K(I) = 4.9 muM and t1/2 = 1.0 min. These acetylenic agents, particularly the dimethyl analog, are promis ing in vivo inhibitors of cytochrome P450 4A4.