Thiol esters of 2-mercaptoethanol and 3-mercapto-1,2-propanediol

2-Mercaptoethanol and 3-mercapto-1,2-propanediol are selectively S-acylated by fatty acids with dicyclohexylcarbodiimide (DCC) catalyzed by 4-dimethylaminopyridine. Since reaction of such thiols with acid halides produces mixtures of S- and O-acylated materials, the procedure using DCC is more efficient. Such thiol esters are valuable as substrates in the study of lipase activity, using Ellman's Reagent in a continuous spectrophotometric assay. This selective synthesis will facilitate the study of fatty acid residues that are less available. Rearrangement of S- to O-acylated compounds occurs only slowly under the conditions of the lipase assay and should not significantly affect activity measurements. Using DCC, it is possible to sequentially esterify 2-mercaptoethanol to form unsymmetrical diesters.