New tetraoxygenated xanthones of Canscora decussata

From the alcoholic extract of Canscora decussata Schult (Gentianaceae), the previously unreported 1,3,6,7-tetrahydroxyxanthone (I), 1,3,5,6-tetrahydroxyxanthone-C₂-glucoside (II), and 1,5,6-trihydroxy-3-methoxyxanthone (III), have been isolated and identified. The structures of these xanthones have been established by chemical transformations, synthesis (in case of III), and spectral (UV, IR, PMR, MS) evidence. II and III have not been encountered before in nature, while I is reported for the first time in this genus. The significance of mass spectral fragmentation in the structural elucidation of oxygenated xanthones is discussed.