Bidesmosidic Oleanane Saponins from Xerospermum noronhianum

Three new oleanane-type triterpenoid saponins, 3-O-(alpha-L-rhamnopyranosyl(1 -> 2)-beta-D-fucopyranosyl)-28-O-{[alpha-L-rhamnopyranosyl(1 -> 2)][beta-D-fucopyranosyl(1 -> 6)]- beta-D-glucopyranosyl) oleanolic acid (1), 3-O-[alpha-L-rhamnopyranosyl(1 -> 3)-beta-D-fucopyranosylj-28-O-[alpha-L-rhamnopyranosyl(1 -> 4)-beta-D-glucopyranosyl] oleanolic acid (2), and 3-O-{alpha-L-rhamnopyranosyl(1 -> 2)-[3',4'-diacetoxy-beta-D-fucopyranosyl]}-28-O-[alpha-L-rhamnopyranosyl(1 -> 2)-beta-D-glucopyranosyl] oleanolic acid (3) have been isolated from the stems of Xerospermum noronhianum. The structures of the saponins were determined as a series of bidesmosidic oleanane saponins based on spectral evidence. The anticholinesterase activity of the saponins 1-3 was also evaluated.