3-Alkyl-6-chloro-2-pyrones: selective inhibitors of pancreatic cholesterol esterase.

A series of 3-alkyl-6-chloro-2-pyrones with cyclohexane rings tethered to the 3-position was synthesized. The tether ranged from 0 to 4 methylene units. Inhibition of pancreatic cholesterol esterase by this series of pyrones was markedly dependent upon the length of the tether. Dissociation constants as low as 25 nM were observed for 6-chloro-3-(1-ethyl-2-cyclohexyl)-2-pyranone. This class of cholesterol esterase inhibitors functioned as simple competitive inhibitors of substrate binding rather than as suicide substrates or active site inactivators. Trypsin and chymotrypsin were not strongly inhibited by this class of pyrones. Selectivities for cholesterol esterase were greater than 10(3). This is in contrast to 3-aryl-6-chloro-2-pyrones which are nonselective, irreversible inactivators of serine hydrolases. Thus, replacement of the 3-aryl group by an appropriately tethered 3-alkyl ring can produce highly selective inhibitors of cholesterol esterase. A second series of halogen-containing esters was prepared in which cholesterol was esterified with alpha-haloacyl halides. These haloesters were simple substrates of cholesterol esterase with no evidence of irreversible inactivation.