Enzymatic Synthesis of Novel Glycyrrhizic Acid Glucosides Using a Promiscuous Bacillus Glycosyltransferase

Glycyrrhetinic acid (GA) and glycyrrhizin (GA-3-O-[beta-D-glucuronopyranosyl-(1 -> 2)-beta-D-glucuronopyranoside], GL) are the major bioactive components of Glycyrrhiza uralensis and possess multifarious notable biological activities. UDP-glycosyltransferase (UGT)-catalyzed glycosylation remarkably extends the structural and functional diversification of GA-glycoside derivatives. In this study, six glucosides (1-6) of GA and GL were synthesized using a Bacillus subtilis 168-originated flexible UDP-glycosyltransferase Bs-YjiC. Bs-YjiC could transfer a glucosyl moiety from UDP-glucose to the free C3 hydroxyl and/or C30 carboxyl groups of GA and GL and further elongate the C30 glucosyl chain via a beta-1-2-glycosidic bond. Glycosylation significantly increased the water solubility of these novel glucosides by 4-90 folds. In vitro assays showed that GA monoglucosides (1 and 2) showed stronger antiproliferative activity against human liver cancer cells HepG2 and breast cancer cells MCF-7 than that of GL and GL glucosides. These findings provide significant insights into the important role of promiscuous UGTs for the enzymatic synthesis of novel bioactive GA derivatives.