Long-chain acyl thioesters prepared by solvent-free thioestrification and transthioesterification catalysed by microbial lipases

Long-chain acyl thioesters (thio wax esters) have been prepared in high (80 % to more than 90%) yields by solvent-free esterification of fatty acids (l auric, myristic, palmitic and stearic acids) with long-chain thiols, such a s decane thiol, dodecane thiol, tetradecane thiol and hexadecane thiol, cat alysed by lipases from Candida antarctica (Novozym) and Rhizomucor miehei ( Lipozyme) in the presence of a 0.4-nm molecular sieve. In the thioesterific ation reaction Novozym was a more effective biocatalyst than Lipozyme. The extent of thioesterification increased with increasing molar ratio of fatty acid to alkane thiol (1:1 to 3:1) and with temperature (40 degrees C compa red to 60 degrees C), as well as with the amount of the enzyme preparation and the amount of 0.4-nm molecular sieve. Decreasing the chain length of th e alkane thiol from C-16 to C-10 also increased the extent of thioesterific ation, Lipase-catalysed solvent-free transthioesterification of fatty acid methyl esters with alkane thiols was less effective for the preparation of acyl thioesters than was thioesterification of fatty acids with alkane thio ls. In transthioesterification, Lipozyme was slightly more effective as a b iocatalyst than Novozym.