Regioselective Acylation of Ginsenosides by Novozyme 435 to Generate Molecular Diversity

Abstract

AbstractGinsenosides are major bioactive constituents of ginseng (Panax spp.; Araliaceae), a traditional Chinese medicinal herb. In order to increase the molecular diversity and broaden the potential usage of ginsenosides, ginsenosides Rd (1), Rg3 (2), (20R)‐Rg3 (3), Rh2 (4), Re (5), Rh1 (8), Rg2 (9), gypenoside XVII (6), and pseudoginsenoside F11 (7) were regioselectively acylated with vinyl acetate, catalyzed by Novozyme 435 (lipase B from Candida antarctica), in organic solvents to afford different mono‐acetyl ginsenosides. Ginsenoside Rd (1) was also acylated with vinyl decanoate or vinyl cinnamate to generate 1b and 1c, respectively. Acylation of glucosylated ginsenosides (1–4, 6, 8) occurred at the primary 6‐OH function of the terminal glucose (Glc) moiety of the sugar at C(3) or C(20) of the dammarane‐type aglycone. In contrast, ginsenosides 5, 7, and 9, containing mixed sugar moieties, resulted in acylation of both the rhamnose (Rha) and the glucose (Glc) moieties. In the case of ginsenoside Re (5) and pseudoginsenoside F11 (7), acylation at the secondary 4‐OH function of the terminal Rha moiety, attached at C(3) of the aglycone, is preferred. The structures of all acylated products were determined by extensive MALDI‐TOF‐MS and NMR analyses.