Preparative enantioselective synthesis of benzoins and (R)-2-hydroxy-1-phenylpropanone using benzaldehyde lyase

A detailed study of the reaction parameters on the enzymatic activity and stability of benzaldehyde lyase (BAL) catalysed carboligation is presented, like the influence of the cosolvent (DMSO), the role of the cofactor ThDP, the pH of the reaction medium, and the substrate ratio in the case of cross condensation. Surprisingly, an alkaline reaction medium of pH 9.5 accelerates the BAL-catalysed condensation significantly. Under these conditions several (R)-benzoins were formed with high productivity of 240 g L−1 d−1 and high enantioselectivities (93–99% ee). For the synthesis of (R)-2-hydroxy-1-phenyl-propanone (2-HPP) by coupling benzaldehyde and acetaldehyde space-time-yields of 36 g L−1 d−1 were obtained with a maximum 2-HPP concentration of 15–20 g L−1 (97% ee) in 10–15 h.