Relationship between the structures of S-acyl thiol compounds and their rates of hydrolysis by pancreatic lipase and hepatic carboxylic esterase.

About 100 S-fatty acyl thiol compounds designed as substrates for pancreatic lipase [EC 3.1.1.3] were synthesized and tested for susceptibility to hydrolysis by hog pancreatic lipase and hog hepatic carboxylic esterase [EC 3.1.1.1] using 5,5'-dithiobis(2-nitrobenzoic acid) as a chromogenic reagent to determine the hydrolytic rates of their S-acyl bonds. In general, the hydrolytic rates of S-acyl bonds by the lipase were fast with thioglycerol type thiol moieties, slow with dithioethyleneglycol type or monothiol type, and negligible with thiopolyol type. As for the acyl moieties, the hydrolysis of the S-acyl bonds was fast with C3-5 acyl groups, followed by C6-8 acyl groups, and the rate decreased as the acyl chain length deviated from these values or branched. On the other hand, the hydrolysis of S-acyl bonds by the esterase occurred with all types of S-acyl esters except for esters of long S-acyl chains. Of all the compounds tested with the lipase, the rate of hydrolysis of S-acyl bond was maximum with 2,3-dimercaptopropan-1-ol tributyroate [I], high with 3-mercaptopropane-1,2-diol tributyroate [II], but negligible with the analogous compound, 1,3-dimercaptopropan-2-ol tributyroate. Compounds [I] and [II] may be practically useful as substrates for lipase assay in human serum samples pretreated with phenylmethylsulfonyl fluoride, a potent inhibitor against both serum arylesterase [EC 3.1.1.2] and hepatic esterase, which attack [I] and [II].