Chemical constituents of the gentianaceae. Part XII. Structure of the pentaoxygenated xanthones of Canscora decussata schult

Abstract

The oxygenation pattern of the major pentaoxygenated xanthones of Canscora decussata is shown by synthesis and reassessment of spectrsocopic evidence, to be 1,3,5,6,7- and not 1,3,6,7,8- as previously reported. The structures of three of these xanthones are revised to 1-hydroxy-3,5,6,7-tetramethoxy-1,7-dihydroxy-3,5,6-trimethoxy-, and 1,6,7-trihydroxy-3,5-dimethoxy-xanthone, and that of a new xanthone is shown to be 1,3,7-trihydroxy-5,6-dimethoxyxanthone. The presence of minor amounts of 1,3,6,7,8-oxygenated xanthones has also been established.