Xanthones from Swertia mussotii and Their alpha-Glycosidase Inhibitory Activities

Two new xanthones, 1,8-dihydroxy-3-methoxyxanthone 7-O-[��-L- rhamnopyranosyl(1 �� 2)-��-D-glucopyranoside] (1) and 1,8- dihydroxy-3-methoxyxanthone 7-O-[��-L-rhamnopyranosyl(1 �� 3)-��-L-rhamno-pyranosyl (1 �� 2)-��-D-xylopyranoside] (2), together with 26 known xanthones (3-28), were isolated from the aqueous ethanol extract of the traditional Chinese herb Swertia mussotii. Their structures were elucidated via spectroscopic analyses including 2D NMR. The inhibition of ��-glucosidase by the isolated xanthones was evaluated by an in vitro high-throughput screening assay. Our results indicated that 1,3,5,8- tetrahydroxyxanthone is the best inhibitor with an IC50 value of 5.33 �� 0.09 ��M, while the O-glycosylated xanthones were poor ��-glycosidase inhibitors. ? Georg Thieme Verlag KG Stuttgart �� New York.