THE REGIOSELECTIVITY OF THE LIPASE-CATALYZED ACYLATION OF 1,6-ANHYDRO-BETA-D-GLYCOPYRANOSES

Transesterification of anhydroglucose, anhydrogalactose and anhydroman nose with ethyl butanoate was catalyzed by Candida antarctica lipase i n the presence of zeolite CaA. Anhydroglucose and anhydromannose were predominantly acylated at the 4-position whereas anhydrogalactose reac ted slowly with low regioselectivity. The selectivity observed is in a ccordance with the selectivity rules of Ciuffreda et al. and Colombo e t al.. That is, all pyranosides are acylated at the same terminus of t he three secondary hydroxyl groups. If this specific hydroxyl group ha s the axial orientation then the regioselectivity is low. These result s contribute to the prediction of the regioselectivity of the lipase-c atalyzed acylation of glycopyranosides.