Contortisiliosides A-G : Isolation of seven new triterpene bisdesmosides from Enterolobium contortisiliquum and their cytotoxic activity

Seven new bisdesmosidic triterpene saponins, with up to eight monosaccharides, which were given the trivial names contortisiliosides A–G (1–7), were isolated from Enterolobium contortisiliquum. The structures of the new saponins were determined on the basis of extensive spectroscopic and chromatographic analyses of both intact and acid-hydrolyzed compounds. The isolated saponins were evaluated for their cytotoxic activities against BAC1.2F5 mouse macrophages, EL-4 mouse lymphoma cells, and L-929 mouse fibroblasts. Whereas contortisiliosides A (1) and C (3) were moderately cytotoxic to both BAC1.2F5 macrophages and EL-4 cells, and contortisiliosides D–G (4–7) did not show any apparent cytotoxic activities against the three cell lines, contortisilioside B (2) exhibited selective cytotoxic activity against BAC1.2F5 mouse macrophages, with an IC50 value of 3.4 μM. The macrophage death caused by 2 was shown to be neither necrotic nor apoptosis-inducing based on the unique morphological change of the killed cells, whose cytosols were transformed into large vacuoles, and according to the TUNEL assay.