Highly efficient and regioselective enzymatic synthesis of β-(1→3) galactosides in biosolvents

Abstract

A green synthesis for β-(1→3) galactosyldisaccharides that combines the use of a biodegradable biocatalyst, aqueous solutions, and solvent recycling (renewable and derived from biomass) has been developed. The use of biomass-derived solvents allows good catalytic activity in the synthesis of Gal-β-D-(1→3)GlcNAc and Gal-β-D-(1→)3GalNAc (99% and 95% yields respectively) with β-Gal-3-NTag β-galactosidase, preventing hydrolytic activity and with full regioselectivity. This represents a considerable improvement over the use of an aqueous buffer or conventional organic solvents. Furthermore, reaction scaling up and biosolvent recycling are feasible without losing catalytic action. In order to understand the role of these green solvents in the enzyme's synthetic behaviour, different structural studies were performed (fluorescence and molecular modelling) in the presence of some selected biosolvents to conclude that the presence of green biosolvents in the reaction media modifies the enzyme's tertiary structure allowing better substrate disposition in the active site, most probably due to solvation effects, explaining the behaviour observed.