ABSTRACT
Bioassay-guided fractionation of a CH(2)Cl(2)-MeOH extract of the aerial parts of Albizia inundata resulted in the isolation of two new natural oleanane-type triterpene saponins {3-O-[α-L-arabinopyranosyl(1â6)]-2-acetamido-2-deoxy-ß-D-glucopyranosyl oleanolic acid (1) and 3-O-[α-L-arabinopyranosyl(1â2)-α-L-arabinopyranosyl(1â6)]-2-acetamido-2-deoxy-ß-D-glucopyranosyl acacic acid lactone (2)} along with seven known saponins {3-O-[α-L-arabinopyranosyl(1â6)]-2-acetamido-2-deoxy-ß-D-glucopyranosyl echinocystic acid (3), 3-O-[ß-D-xylopyranosyl (lâ2)-α-L-arabinopyranosyl(lâ6)]-2-acetamido-2-deoxy-ß-D-glucopyranosyl acacic acid lactone (concinnoside D) (4), 3-O-[ß-D-glucopyranosyl(lâ2)]-ß-D-glucopyranosyl oleanolic acid (5), 3-O-[α-L-arabinopyranosyl(1â2)-α-L-arabinopyranosyl(lâ6)]-ß-D-glucopyranosyl oleanolic acid (6), 3-O-[ß-D-xylopyranosyl(1â2)-α-L-arabinopyranosyl(lâ6)]-ß-D-glucopyranosyl oleanolic acid (7), 3-O-[α-L-arabinopyranosyl(lâ2)-α-L-arabinopyranosyl(1â6)-[ß-D-glucopyranosyl(lâ2)]-ß-D-glucopyranoside echinocystic acid (8), and 3-O-[ß-D-xylopyranosyl(lâ2)-α-L-arabinopyranosyl(1â6)-[ß-D-glucopyranosyl(lâ2)]-ß-D-glucopyranoside echinocystic acid (9)}. The structures of 1 and 2 were established on the basis of extensive 2D NMR ((1)H-(1)H COSY or DQF-COSY, HSQC, HMBC, TOCSY, and HSQC-TOCSY) spectroscopic, ESIMS, and chemical methods. Saponins 1, 3, 6, and 7 showed cytotoxicity against human head and neck squamous cells (JMAR, MDA1986) and melanoma cells (B16F10, SKMEL28) with IC(50) values in the range 1.8-12.4 µM, using the MTS assay.