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-alpha-L-rhamnopyranosyl-(1-->2)-[O-alpha-L-rhamnopyranosyl-(1-->3) ] - beta-D-xylopyranosyl] ester, Hb1, a 28-[O-beta-D-xylopyranosyl-(1-->4)-O-alpha-L-rhamnopyranosyl-(1-->2)- [O-alpha-L-rhamnopyranosyl-(1-->3)]-beta-D-xylopyranosyl] ester, Hb2, a 28-[O-beta-D-xylopyranosyl-(1-->3)-O-beta-D-xylopyranosyl-(1-->4)-O-alph a-L- rhamnopyranosyl-(1-->2)-[O-alpha-L-rhamnopyranosyl-(1-->3)]-beta-D- xylopyranosyl] ester, and Hc1, a 28-[O-beta-D-xylopyranosyl-(1-->3)-O-beta-D-xylopyranosyl-(1-->3)-[O-bet a- D-xylopyranosyl-(1-->4)]-O-alpha-L-rhamnopyranosyl-(1-->2)-[O-alpha-L- rhamnopyranosyl-(1-->3)]-beta-D-xylopyranosyl] ester of the prosapogenin.