Studies on the Constituents of Aster scaber THUNB, IV. Structures of Four New Echinocystic Acid Glycosides Isolated from the Herb

Abstract

Four new echinocystic acid 3, 28-O-bisdesmosides, scaberosides Ha, Hb₁, Hb₂ and Hc₁, were isolated as their methyl esters from the ground part of Aster scaber THUNB. (Compositae) along with foetidissimoside A and scaberoside A₂, and their structures were determined based on spectral and chemical evidence. These glycosides have a common prosapogenin structure, echinocystic acid-3-O-glucopyranosiduronic acid, and differ in the structures of the 28-O-linked sugar moieties.Scaberoside Ha₁ is a 28-[O-α-L-rhamnopyranosyl-(1→2)-[O-α-L-rhamnopyranosyl-(1→3)]-β-D-xylopyranosyl] ester, Hb₁, a 28-[O-β-D-xylopyranosyl-(1→4)-O-α-L-rhamnopyranosyl-(1→2)-[O-α-L-rhamnopyranosyl-(1→3)-β-D-xylopyranosyl] ester, Hb₂, a 28-[O-β-D-xylopyranosyl-(1→3)-O-β-D-xylopyranosyl-(1→4)-O-α-L-rhamnopyranosyl-(1→2)-[O-α-L-rhamnopyranosyl-(1→3)-β-D-xylopyranosyl] ester, and Hc₁, a 28-[O-β-D-xylopyranosyl-(1→3)-O-β-D-xylopyranosyl-(1→3)-[O-β-D-xylopyranosyl-(1→4)-O-α-L-rhamnopyranosyl-(1→2)-[O-α-L-rhamnopyranosyl-(1→3)]-β-D-xylopyranosyl] ester of the prosapogenin.