ENZYMATIC PREPARATION OF BOTH ENANTIOMERS OF 4,4,4-TRIFLUORO-3-(INDOLE-3-)BUTYRIC ACID, A NOVEL PLANT-GROWTH REGULATOR

Efficient optical resolution of both enantiomers of 4,4,4-trifluoro-3-(indole-3-)butyric acid (TFIBA), a novel plant growth regulator, was achieved by two enzyme-catalyzed steps using lipase AK (a lipase from Pseudomonas sp.). S-(+)-TFIBA and R-(-)-TFIBA ethyl ester were prepared with 98% e.e. by the first step of lipase-catalyzed enantioselective hydrolysis in a 0.1 M acetate buffer (pH 5.0) containing 10% t-BuOH at 55-degrees-C for 45 h. The % e.e. in S-(+)-TFIBA was further improved to > 99% e.e. by lipase-catalyzed enantioselective esterification with ethanol in heptane and subsequent hydrolysis using PLE-A (an esterase from pig liver). R-(-)-TFIBA was prepared with > 99% e.e. by the second step of lipase-catalyzed enantioselective hydrolysis under the same conditions as described above and subsequent hydrolysis using PLE-A. The root growth-promoting activity of S-(+)-TFIBA was about 10-fold higher than that of R-(-)-TFIBA for black matpe, Chinese cabbage, lettuce, and rice plants (Ohgonbare and Tan-ginbozu).