Diastereoselective synthesis of (R)-(alkyl)-β-d-galactopyranoside by using β-galactosidase (Aspergillus oryzae) in low-water media

A β-galactosidase (from Aspergillus oryzae) preparation viz. EPRP (enzyme precipitated and rinsed with propanol), obtained by the removal of bulk water by precipitation with n-propanol, showed higher biological activity than the lyophilized powder. FT-IR study confirmed that EPRP had retained the α-helical content of the native structure better than the lyophilized form. Use of this formulation of β-galactosidase under low water conditions (temperature 55 °C, reaction time of 4 h) gave enantioselectivity, E > 1000 for the stereoselective synthesis of (R)-(1-phenylethyl)-β-d-galactopyranoside, starting from racemic 1-phenylethanol and d-galactose. For racemic 2-octanol also, EPRP worked better. Under similar conditions, (R)-(2-octyl)-β-d-galactopyranoside was formed with an enantioselectivity, E = 38.