Antioxidants eliminate stereomutation and thioether formation during lipase-catalyzed thioesterification and transthioesterification for the preparation of uniform cis- and trans-unsaturated thioesters

The lipase-catalyzed preparation of acyl thioesters from unsaturated fatty acids and alkanethiols is accompanied by the formation of geometrical isome rs via stereomutation and of thioether derivatives via addition at the olef inic bond, both induced by thiyl radicals. Therefore, a method was develope d in order to inhibit radical generation by the addition of antioxidants an d thus prevent the formation of geometrical isomers and thioether derivativ es during the lipase-catalyzed preparation of unsaturated acyl thioesters. In the presence of antioxidants such as 2,6-di-t-butyl-4-methylphenol (BHT) and octyl gallate thioesterification of oleic and elaidic acids with 1-tet radecanethiol as well as transthioesterification of methyl linoleate with 1 -tetradecanethiol led to the corresponding geometrically uniform thioesters without radical-induced side reactions. In the absence of antioxidants rap id stereomutation of unsaturated acyl moieties as well as formation of high proportions of thiyl radical-induced addition products such as isomeric 9( 10)-S-tetradecyl stearic acids and 9(10)-S-tetradecyl stearic acid tetradec yl thioesters were observed. (C) 2000 Elsevier Science Ireland Ltd. All rig hts reserved.