Studies on the Constitutents of Aster scaber THUNB. II. Structures of Echinocystic Acid Glycosides Isolated from the Root

Abstract

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. (Compositae) as their methyl esters, and their structures were determined based on spectral and chemical evidence. Scaberosides have a common prosapogenin, echinocystic acid 3-O-β-D-glucopyranosiduronic acid, and differ in the structures of the ester-linked sugar moieties. Scaberoside A₁ is a 28-[O-β-D-apiofuranosyl-(1→3)-O-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranosyl] ester, A₂, a 28-[O-β-D-xylopyranosyl-(1→4)-O-α-L-rhamnopyranosyl-(1→2)-β-D-xylopyranosyl] ester, A₃, a 28-{O-β-D-apiofuranosyl-(1→3)-[O-β-D-xylopyranosyl-(1→4)-]-O-α-L-rhamnopyranosyl-(1→2)-β-D-xylopyranosyl]ester, A₄, 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)-β-D-xylopyranosyl} ester of the prosapogenin.