The Regioselectivity of the Lipase-Catalyzed Acylation of 1,6-Anhydro-β-d-glycopyranoses

Abstract

Transesterification of anhydroglucose, anhydrogalactose and anhydromannose with ethyl butanoate was catalyzed by Candida antarctica lipase in the presence of zeolite CaA. Anhydroglucose and anhydromannose were predominantly acylated at the 4-position whereas anhydrogalactose reacted slowly with low regioselectivity. The selectivity observed is in accordance with the selectivity rules of Ciuffreda et al. and Colombo et al. That is, all pyranosides are acylated at the same terminus of the three secondary hydroxyl groups. If this specific hydroxyl group has the axial orientation then the regioselectivity is low. These results contribute to the prediction of the regioselectivity of the lipase-catalyzed acylation of glycopyranosides.

Notes

The sequence starts from the left side of the pyranose ring as drawn in scheme 2 in which E stands for equatorial and A stands for axial.