Enzymatic synthesis of α-arbutin by α-anomer-selective glucosylation of hydroquinone using lyophilized cells of Xanthomonas campestris WU-9701

α-Arbutin, a useful cosmetic ingredient, was selectively synthesized by α-anomer-selective glucosylation of hydroquinone with maltose as a glucosyl donor using lyophilized cells of Xanthomonas campestris WU-9701 as a biocatalyst. When 45 mM hydroquinone and 120 mg of lyophilized cells showing 11 nkat of α-glucosyl transfer activity were shaken in 2 ml of 10 mM H₃BO₃-NaOH-KCl buffer (pH 7.5) containing 1.2 M maltose at 40°C, only one form of hydroquinone glucoside was selectively obtained as a product and identified as hydroquinone 1-O-α-D-glucopyranoside (α-arbutin) by ¹³C-NMR, ¹H-NMR and two-dimensional HMBC analysis. Although hydroquinone has two phenolic -OH groups at the para position in its structure, only one -OH group, but not both -OHs, was glucosylated and no other glucosylated products such as maltotriose were detected in the reaction mixture. The reaction at 40°C for 36 h under optimum conditions yielded 42 mM α-arbutin, and the maximum molar conversion yield based on the amount of hydroquinone supplied reached 93%.