An efficient strategy for the chemo-enzymatic synthesis of bufalin glycosides with improved water solubility and inhibition against Na+,K+-ATPase

In this study, bufalin was glycosylated by an efficient chemo-enzymatic strategy. Firstly, 2-chloro-4-nitrophenyl-1- O- b -D -glucoside (sugar donors) was obtained by chemical synthesis. Then the glycosylation of the bufalin was achieved with the synthesized sugar donor under the catalysis of two glycosyltransferase s (Loki and ASP). Finally, two glycosides, i.e. bufalin-3-O-b-D-glucopyranoside ( 3 ) and bufalin-3-O-[b-D-glucopyranosyl(1→2)-b-D-glucopyranoside)] ( 4 ), were obtained by preparative HPLC. Compared to our previously reported sole chemical (total yield 10% in four steps) or enzymatic methods (30%), our combined chemo-enzymatic strategy in this paper greatly improves the yields of monoglycoside (68%) and diglycoside (21%) and decreased the experimental cost (90%). Furthermore, we tested water solubility of these glycosides and found that the water solubilities of 3 and 4 were 13.1 and 53.7 times of bufalin, respectively. In addition, the inhibitory activity of these glycosides against Na + , K + -ATPase were evaluated. The mono-glycosylated compound 3 show more potent activity than bufalin, while the diglycosylated compound 4 was less potent.