Cytotoxic Oleanane-Type Saponins from the Leaves of Albizia anthelmintica <scp>Brongn.</scp>

Two new oleanane-type saponins: β-d-xylopyranosyl-(1 → 4)-6-deoxy-α-l-mannopyranosyl-(1 → 2)-1-O-{(3β)-28-oxo-3-[(2-O-β-d-xylopyranosyl-β-d-glucopyranosyl)oxy]olean-12-en-28-yl}-β-d-glucopyranose (1) and 1-O-[(3β)-28-oxo-3-{[β-d-xylopyranosyl-(1 → 2)-α-l-arabinopyranosyl-(1 → 6)-2-acetamido-2-deoxy-β-d-glucopyranosyl]oxy}olean-12-en-28-yl]β-d-glucopyranose (2), along with two known saponins: (3β)-3-[(β-d-Glucopyranosyl-(1 → 2)-β-d-glucopyranosyl)oxy]olean-12-en-28-oic acid (3) and (3β)-3-{[α-l-arabinopyranosyl-(1 → 6)-[β-d-glucopyranosyl-(1 → 2)]-β-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: 1 H- and 13 C-NMR, HSQC, HMBC and 1 H,1 H-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 3.60μm. Whereas, compound 1 showed the most potent cytotoxic effect with an IC50 value of 4.75μm on HCT-116 cells.