REGIOSELECTIVE ACETYLATIONS OF ALKYL BETA-D-XYLOPYRANOSIDES BY USE OF LIPASE PS IN ORGANIC-SOLVENTS AND APPLICATION TO THE CHEMOENZYMATIC SYNTHESIS OF OLIGOSACCHARIDES

Aglycon structure and solvent can change the regioselectivity of the acetylation of alkyl beta-D-xylopyranosides, catalyzed by lipase PS. The acetylation of methyl beta-D-xylopyranoside (3) in acetonitrile gave the 3,4-diacetate 4 exclusively, whereas the reaction of octyl beta-D-xylopyranoside (5) gave a mixture of 2,4- and 3,4-diacetates (6 and 7) in 1.0:1.3 and 3.6:1.0 ratios, in acetonitrile and hexane, respectively. The effect of several solvents on the selectivity in the monoacetylation of 5 was studied. The 2-monoacetate 8 was preferentially formed over the 3- and 4-monoacetates (9 and 10) in hydrophobic solvents. High yields of partially acetylated xylose derivatives were obtained, which were used in the syntheses of a disaccharide showing liquid crystal properties, an intermediate for the synthesis of proteoglycan fragments, and a trisaccharide potential inhibitor of plant growth.