Bioactive Saponins and Glycosides. VI. Elatosides A and B, Potent Inhibitors of Ethanol Absorption, from the Bark of Aralia elata SEEM.(Araliaceae) : The Structure-Requirement in Oleanolic Acid Glucuronide-Saponins for the Inhibitory Activity

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Potent inhibitors of ethanol absorption, elatosides A and B, were isolated from the bark of Aralia elata SEEM. through bioassay-guided separation together with elatosides C and D and four known oleanolic acid glucuronide-saponins, spinasaponin A, spinasaponin A 28-O-glucoside, and stipuleanosides R₁ and R₂. The structures of elatosides A, B, C, and D were determined on the basis of chemical and physicochemical evidence as oleanolic acid 3-O-{[β-D-xylopyranosyl (1→2)][β-D-galactopyranosyl (1→3)]}-β-D-glucopyranosiduronic acid, oleanolic acid 3-O-{[β-D-galactopyranosyl (1→2)] [β-D-galactopyranosyl (1→3)]}-β-D-glucopyranosiduronic acid, and their 28-O-glucopyranosyl esters, respectively.The inhibitory effect of various oleanolic acid 3, 28-O-bisdesmosides, oleanolic acid 3-O-monodesmosides, and oleanolic acid on ethanol absorption was examined and it was found that the 3-O-glucuronide moiety and the 28-carboxyl group in oleanolic acid glucuronide-saponin were required to exert the inhibitory activity.