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-β-D-glucopyranosyluronic acid oleanolic acid 28-{O-β-D-apiofuranosyl-(1→3)-[O-β-D-xylopyranosyl-(1→4)]-O-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranosyl} ester, scaberoside B₈, 3-O-β-D-glucopyranosyl oleanolic acid 28-[O-β-D-xylopyranosyl-(1→4)-O-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranosyl] ester, and scaberoside B₉, 3-O-β-D-glucopyranosyluronic acid oleanolic acid 28-{O-α-L-rhamnopyranosyl-(1→2)-[O-β-D-xylopyranosyl-(1→6)-β-D-glucopyranosyl} ester. Scaberosides B₇ and B₉ were obtained as their methyl esters.