STUDIES ON THE CONSTITUENTS OF ASTER-SCABER THUNB .2. STRUCTURES OF ECHINOCYSTIC ACID GLYCOSIDES ISOLATED FROM THE ROOT

Four new echinocystic acid 3,28-O-bisdesmosides, scaberosides A1, A2, A3 and A4, were isolated together with aster saponin Ha, aster saponin Hb and foetidissimoside A from the polar glycoside fraction of the root of Aster scaber THUNB. (Compositate) as their methyl esters, and their structures were determined based on spectral and chemical evidence. Scaberosides have a common prosapogenin, echinocystic acid 3-O-beta-D-glucopyranosiduronic acid, and differ in the structures of the ester-linked sugar moieties. Scaberoside A1 is a 28-[O-beta-D-apiofuranosyl-(1 --> 3)-O-alpha-L-rhamnopyranosyl-(1 --> 2)-alpha-L-arabinopyranosyl] ester, A2, a 28-[O-beta-D-xylopyranosyl-(1 --> 4)-O-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-xylopyranosyl] ester, A3, a 28-{O-beta-D-apiofuranosyl-(1 --> 3)-[O-beta-D-xylopyranosyl-(1 --> 4)-]-O-alpha-L-rhamnopyranosyl-(1 --> 2)-alpha-L-arabinopyranosyl} ester, and A4, a 28-{O-beta-D-xylopyranosyl-(1 --> 3)-[O-beta-D-xylopyranosyl-(1 --> 3)-O-beta-D-xylopyranosyl-(1 --> 4)-]-O-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-xylopyranosyl} ester of the prosapogenin.