Studies on the constituents of Aster scaber Thunb. III. Structures of scaberosides B7, B8 and B9, minor oleanolic acid glycosides isolated from the root.

Abstract

Three new oleanolic acid 3,28-O-bisdesmosides, scaberosides B7, B8 and B9, were isolated as minor saponins from the root of Aster scaber THUNB. (Compositae), and their structures were determined based on spectral and chemical evidence as follows. Scaberoside B7 is 3-O-beta-D-glucopyranosyluronic acid oleanolic acid 28-[O-beta-D-apiofuranosyl-(1----3)-[O-beta-D-xylopyranosyl-(1---- 4)-O-alpha-L-rhamnopyranosyl-(1----2)-alpha-L-arabinopyranosyl] ester, scaberoside B8, 3-O-beta-D-glucopyranosyl oleanolic acid 28-[O-beta-D-xylopyranosyl-(1----4)-O-alpha-L-rhamnopyranosyl-(1----2)-a lpha-L-arabinopyranosyl] ester, and scaberoside B9, 3-O-beta-D-glucopyranosyluronic acid oleanolic acid 28-[O-alpha-L-rhamnopyranosyl-(1----2)-[O-beta-D-xylopyranosyl-(1----6)] -beta-D-glucopyranosyl] ester. Scaberosides B7 and B9 were obtained as their methyl esters.