Preparation of optically active trifluoromethylated (3'-indolyl) thiacarboxylic acids, novel plant growth regulators, through lipase-catalyzed enantioselective hydrolysis

Among a variety of lipases tested, that obtained from Candida antarctica (SP 435) induced enantioselective hydrolysis of trifluoroethyl 5,5,5-trifluoro-4-(3'-indolyl)-3-thiapentanoate (1c). The selectivity could be increased by optimizing the reaction conditions. Thus, good selectivity was achieved (E = 37) in a buffer containing 10% dichloroethane. In order to improve the optical yields, a sequential kinetic resolution was utilized for the preparative-scale enantioselective hydrolysis of 1c using SP 435. Hydrolysis of trifluoroethyl 6,6,6-trifluoro-5-(3'-indolyl)-4-thiahexanoate (2c) with the lipase of Pseudomonas aeruginosa (LIP) in a buffer containing 20% tert-amyl alcohol at 25 degrees C gave excellent selectivity (E=357).