Chemical constituents of gentianaceae. Part 22. Structures of new 1,3,5-tri- and 1,3,5,6,7-penta-oxygenated xanthones of Canscora decussata Schult

Abstract

Two new xanthone glucosides and two free xanthones, isolated from Canscora decussata, have been identified as 1-glucosyloxy-3-hydroxy-5-methoxy-(1), 7-glucosyloxy-1,6-dihydroxy-3,5-dimethoxy-(2), 1.5.6-trihydroxy-3,7-dimethoxy-(4), and 1.5.7-tryhydroxy-3,6-dimethoxy-xanthone (7) on the basis of chemical transformations and spectral evidence. On the basis of reassessment of the spectroscopic data and additional chemical evidence, it has been shown that the pentaoxygenated xanthones previously reported to be 1,3,7-trihydroxy-5,6-dimethoxy-xanthone (‘Xanthone IV’) and 1,7-dihydroxy-3,5,6-trimethoxyxanthone (‘Xanthone XII’) are in fact 1,3,5-trihydroxy-6,7-dimethoxy-(9) and 1,5-dihydroxy-3,6,7-trimethoxy-xanthone (10), respectively. The stucture of 1,6,7-trihydroxy-3,5-dimethoxyxanthone (‘Xanthone XIII’) has been confirmed.