| dc.description.abstract | From the fruits of Bulbine abyssinica three new dimeric anthracene derivatives, (P)-8,9,10,80-tetrahydroxy-3,30-dimethyl[10,70-bianthracene]-1,4,90,100-tetraone (trivial name abyquinone A), (10R)-1,4,8,10,80-pentahydroxy-3,30-dimethyl-[10,70-bianthracene]-9,90,100(10H)-trione (trivial name abyquinone B), and (10R)-30,40-dihydro-1,4,8,30,80,90-hexahydroxy-3,30-dimethyl-[10,70-bianthracene]-9,10(10H,20H)-dione (trivial name abyquinone C) were isolated. Despite their structural differences, these three compounds are connected to each other by the apparently biomimetic conversion of abyquinone
C (a preanthraquinonylanthrone with two stereogenic centers) into
B (an anthraquinonylanthrone with one stereogenic center) and finally into A (an axially chiral bianthraquinone) under mild conditions, involving a highly efficient center-to-axis chirality transfer. In addition, the known anthraquinones islandicin and chrysophanol were identified. The structures were determined on the basis of spectroscopical evidences, chemical transformations, and quantum chemical CD calculations. | en |
