title: Enol lactone inhibitors of serine proteases. The effect of regiochemistry on the inactivation behavior of phenyl-substituted (halomethylene)tetra- and -dihydrofuranones and (halomethylene)tetrahydropyranones toward alpha-chymotrypsin: stable acyl enzyme intermediate.
abstract: We have found that alpha-aryl-substituted halo enol lactones (I and II) are effective mechanism-based inactivators for chymotrypsin. In this study, we have investigated, for comparative purposes, halo enol lactones with aryl functions situated beta and gamma to the lactone carbonyl group. We synthesized 4-phenyl-5(E)-(iodomethylidene)tetrahydro-2-furanone (1), 4-phenyl-5(E)-(iodomethylidene)dihydro-2-furanone (2), 4-phenyl-6(E)-(iodomethylidene)tetrahydro-2-pyranone (3), and 5-phenyl-6(E)-(iodomethylidene)tetrahydro-2-pyranone (4), using a halolactonization reaction to convert the appropriate phenyl-substituted acetylenic acid precursor into the corresponding 5(E)-(halomethylidene)furanone and 6(E)-(halomethylidene)pyranone system. The 4-phenylfuranone (1 and 2) and the 5-phenylpyranone (4) proved to be only reversible, competitive inhibitors. By contrast, the 4-phenyltetrahydropyranone (3) inactivated alpha-chymotrypsin in a time-dependent manner. This inactivation was very rapid but reversible, with regeneration of enzyme activity being spontaneous and hydrazine-accelerated, suggestive of the intermediacy of a stable acyl enzyme. Kinetic comparison of the iodomethylene lactone 3 with the corresponding protio lactone 25 indicates that the iodine accelerates the rate of chymotrypsin acylation but produces an acyl enzyme that is more hydrolytically labile than that formed from lactone 25. From the results of this study, we conclude that a phenyl group situated at C-3 (alpha to the lactone carbonyl group) in both the 5(E)-(iodomethylidene)tetrahydro-2-furanone (I) and 6(E)-(iodomethylidene)tetrahydro-2-pyranone (II) series is essential for their activity as mechanism-based irreversible inactivators of chymotrypsin. The corresponding beta-aryl-substituted lactones, by contrast, are potent acylating agents that lead to acyl enzymes of high stability.
mesh_terms: D000215:Acylation; D001667:Binding, Competitive; D002850:Chromatography, Gel; D002918:Chymotrypsin / Q000037:antagonists & inhibitors*; D006834:Hydrazines / Q000494:pharmacology; D007783:Lactones / Q000494:pharmacology*; D011480:Protease Inhibitors; D012697:Serine Endopeptidases; D013329:Structure-Activity Relationship
chemical_list: D006834:Hydrazines; D007783:Lactones; D011480:Protease Inhibitors; C029424:hydrazine; D012697:Serine Endopeptidases; D002918:Chymotrypsin