Xanthone Glycoside Constituents of Swertia kouitchensis with α-Glucosidase Inhibitory Activity

Ten new xanthone glycosides, kouitchensides A-J (1-10), and 11 known analogues were isolated from an n-butanol fraction of Swertia kouitchensis. The structures of these glycosides were determined on the basis of extensive spectroscopic data interpretation and comparison with data reported in the literature. In an in vitro test, compounds 2, 4, 5, 6, 11, 12, and 13 (IC50 values in the range 126 to 451 mu M) displayed more potent inhibitory effects against alpha-glucosidase activity than the positive control, acarbose (IC50 value of 627 mu M).