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 a-Chymotrypsin: Stable Acyl Enzyme Intermediate

Michael J. Sofia, John A. Katzenellenbogen

Research output: Contribution to journalArticlepeer-review

Abstract

We have found that α-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 β and γ to the lactone carbonyl group. We synthesized 4-phenyl-5(£)-(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 α-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 (a 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 β-aryl-substituted lactones, by contrast, are potent acylating agents that lead to acyl enzymes of high stability.

Original languageEnglish (US)
Pages (from-to)230-238
Number of pages9
JournalJournal of Medicinal Chemistry
Volume29
Issue number2
DOIs
StatePublished - 1986

ASJC Scopus subject areas

  • Molecular Medicine
  • Drug Discovery

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