Antioxidant xanthones from Swertia mussotii, a high altitude plant.

Four new xanthones, 3,5,6,8-tetrahydroxyxanthone-1-C-ß-D-glucoside (1), 7-hydroxy-3,4,8-trimethoxyxanthone-1-O-(ß-D-glucoside) (2), 6-hydroxy-3,5-dimethoxyxanthone-1-O-(ß-D-glucoside) (3), 3,4,7,8-tetramethoxyxanthone-1-O-(ß-D-glucoside) (4), together with twenty-one known xanthones (5-25) were isolated from the ethanol aqueous extract of Swertia mussotii. Their structures were elucidated via spectroscopic analyses. Oxygen radical absorbance capacity of all the isolated xanthones was systematically evaluated by ORAC(FL) assay. Results disclose that all the tested xanthones display moderate to excellent antioxidant activity, where 1 is the most active compound and 13 is the least one. A preliminary structure-activity relationship is also discussed.