Diastereoselective synthesis of (R)-(alkyl)-beta-D-galactopyranoside by using beta-galactosidase (Aspergillus oryzae) in low-water media.

A beta-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 alpha-helical content of the native structure better than the lyophilized form. Use of this formulation of beta-galactosidase under low water conditions (temperature 55 degrees C, reaction time of 4 h) gave enantioselectivity, E > 1000 for the stereoselective synthesis of (R)-(1-phenylethyl)-beta-D-galactopyranoside, starting from racemic 1-phenylethanol and D-galactose. For racemic 2-octanol also, EPRP worked better. Under similar conditions, (R)-(2-octyl)-beta-D-galactopyranoside was formed with an enantioselectivity, E = 38.