Selective α-glucosylation of eugenol by α-glucosyl transfer enzyme of Xanthomonas campestris WU-9701

For one-step enzymatic synthesis of eugenyl α-glucoside as a promising pro-drug for a hair restorer and a derivative of spices, selective α-glucosylation of eugenol was carried out using the α-glucosyl transfer enzyme of Xanthomonas campestris WU-9701. When 130 μmol eugenol and crude enzyme showing 1.0 unit of α-glucosyl transfer activity were shaken in 2 ml of 10 mM H₃BO₃-NaOH-KCl buffer (pH 8.0) containing 1.2 M maltose as a glucosyl donor at 40°C, only one form of eugenyl glucoside was selectively obtained as a product and identified as eugenyl α-D-glucopyranoside (α-EG) by ¹³C-NMR, ¹H-NMR, and two-dimensional heteronuclear multiple-bond coherence analyses. In the reaction, no other glucosylated products such as maltotriose or eugenyl maltoside were detected in the reaction mixture. The reaction at 40°C for 48 h under the above conditions yielded 68 μmol α-EG in 2 ml suspension, and the maximum molar conversion yield based on the amount of eugenol supplied reached 52%.