Cytotoxic Oleanane-Type Saponins from the Leaves of Albizia anthelmintica BRONGN.

Two new oleanane-type saponins: beta-D-xylopyranosyl-(1 -> 4)-6-deoxy-alpha-L-mannopyranosyl-(1 -> 2)-1-O-{(3 beta)-28-oxo-3-[(2-O-beta-D-xylopyranosyl-beta-D-glucopyranosyl)oxy]olean-12-en-28-yl}-beta-D-glucopyranose (1) and 1-O-[(3 beta)-28-oxo-3-{[ beta-D-xylopyranosyl-(1 -> 2)-alpha-L-arabinopyranosyl-(1 -> 6)-2-acetamido-2-deoxy-beta-D-glucopyranosyl]oxy} olean-12-en-28-yl]-beta- D-glucopyranose (2), along with two known saponins: (3 beta)-3-[(beta-D-Glucopyranosyl-(1 -> 2)-beta-D-glucopyranosyl)oxy]olean-12-en-28-oic acid (3) and (3 beta)-3-{[alpha-L-arabinopyranosyl-(1 -> 6)-[beta-D-glucopyranosyl-(1 -> 2)]-beta-D-glucopyranosyl] oxy} olean-12-en-28-oic acid (4) were isolated from the acetone-insoluble fraction obtained from the 80% aqueous MeOH extract of Albizia anthelmintica BRONGN. leaves. Their structures were identified using different NMR experiments including: H-1- and C-13-NMR, HSQC, HMBC and H-1, H-1-COSY, together with HR-ESI-MS/MS, as well as by acid hydrolysis. The four isolated saponins and the fractions of the extract exhibited cytotoxic activity against HepG-2 and HCT-116 cell lines. Compound 2 showed the most potent cytotoxic activity among the other tested compounds against the HepG2 cell line with an IC50 value of 3.60 mu M. Whereas, compound 1 showed the most potent cytotoxic effect with an IC50 value of 4.75 mu M on HCT-116 cells.