Enzymatic synthesis of alpha-butylglucoside lactate: A new alpha-hydroxy acid derivative

An alpha-hydroxy acid derivative, alpha-butylglucoside lactate, was success fully prepared by enzymatic transesterification of alpha-butylglucoside wit h a lactate alkyl ester in a non-aqueous medium using immobilized lipase as biocatalyst. Ester synthesis in organic solvent was optimized. Solvent cho ice was made on the basis of substrate solubility and enzyme stability in t he medium. A solvent-free reaction using butyllactate as lactate donor led to the highest yields. In the presence of 0.5 M alpha-butylglucoside and 10 0 g/L Novozym(R), a 67% yield could be obtained within 40 h at 50 degrees C . However, the presence of butanol by-product limited the reaction to a max imum that could not be exceeded in closed systems. The elimination of the a lcohol under reduced pressure resulted in the complete equilibrium shift of the transesterification reaction in favor of synthesis; below 15 mbars, mo re than 95% of 0.5M alpha-butylglucoside could be converted within 30 h. Mo reover, simultaneous evaporation of water allowed hydrolysis of butyllactat e to be eliminated. Consequently, a very high a-butylglucoside lactate conc entration (170 g/L) could be obtained in a single batch reaction. A single purification procedure, consisting of butyllactate extraction with hexane, enabled the product to be obtained at a purity above 95% (w/w). H-1 and C-1 3 NMR analysis later demonstrated that lactic acid was exclusively grafted onto the primary hydroxyl group of alpha-butylglucoside. (C) 1999 John Wile y & Sons, Inc. Biotechnol Bioeng 62: 225-234, 1999.