Enzymatic transglycosylation of ginsenoside Rg1 by rice seed α-glucosidase

Six α-monoglucosyl derivatives of ginsenoside Rg1 (G-Rg1) were synthesized by transglycosylation reaction of rice seed α-glucosidase in the reaction mixture containing maltose as a glucosyl donor and G-Rg1 as an acceptor. Their chemical structures were identified by spectroscopic analysis, and the effects of reaction time, pH, and glycosyl donors on transglycosylation reaction were investigated. The results showed that rice seed α-glucosidase transfers α-glucosyl group from maltose to G-Rg1 by forming either α-1,3 (α-nigerosyl)-, α-1,4 (α-maltosyl)-, or α-1,6 (α-isomaltosyl)-glucosidic linkages in β-glucose moieties linked at the C6- and C20-position of protopanaxatriol (PPT)-type aglycone. The optimum pH range for the transglycosylation reaction was between 5.0 and 6.0. Rice seed α-glucosidase acted on maltose, soluble starch, and PNP α-D-glucopyranoside as glycosyl donors, but not on glucose, sucrose, or trehalose. These α-monoglucosyl derivatives of G-Rg1 were easily hydrolyzed to G-Rg1 by rat small intestinal and liver α-glucosidase in vitro.