Isocoumarin-based inhibitors of pancreatic cholesterol esterase

Pancreatic cholesterol esterase (CEase), which is secreted from the exocrine pancreas, is a serine hydrolase that aids in the bile salt-dependent hydrolysis of dietary cholesteryl esters and contributes to the hydrolysis of triglycerides and phospholipids. Additional roles for CEase in intestinal micelle formation and in transport of free cholesterol to the enterocyte have been suggested. There also are studies that point to a pathological role(s) for CEase in the circulation where CEase accumulates in atherosclerotic lesions and triggers proliferation of smooth muscle cells. Thus, there is interest in CEase as a potential drug target. 4-Chloro-3-alkoxyisocoumarins are a class of haloenol lactones that inhibit serine hydrolases and serine proteases and have the potential to be suicide inhibitors. In the present study, we have developed 3-alkoxychloroisocoumarins that are potent inhibitors of CEase. These inhibitors were designed to have a saturated cycloalkane ring incorporated into a 3-alkoxy substituent. The size of the ring as well as the length of the tether holding the ring was found to be important contributors to binding to CEase. 4-Chloro-3-(4-cyclohexylbutoxy)isocoumarin and 4-chloro-3-(3-cyclopentylpropoxy)isocoumarin were demonstrated to be potent reversible inhibitors of CEase, with dissociation constants of 11nM and 19nM, respectively. The kinetic results are consistent with predictions from molecular modeling.