Sulfated Triterpene Glycosides from the Saudi Red Sea Cucumber Holothuria atra with Antioxidant and Cytotoxic Activities

The bioactive constituents of sea cucumber Holothuria atra were investigated, and four sulfated holostan-type triterpene glycosides (1–4) along with other seven know metabolites were obtained. On the basis of the extensive NMR and ESI-MS data, the structures of triterpenoid saponins were assigned as a new compound echinoside B 12-O-methyl ether (1), and known echinoside B (2), 24-dehydroechinoside B (3), and holothurin B (4). The extract and isolated saponins displayed weak antioxidant DPPH radical scavenging activities, where echinoside B (2) showed the highest value at 26.41%. However, 24-dehydroechinoside B (3) showed mild antioxidant-reducing power activity (0.19 nm), compared to the synthetic antioxidant (BHT). Both compounds 2 and 3 exhibited moderate cytotoxic activity by reducing the viability of Ehrlich ascites carcinoma cells to 41.0% and 42.2%, respectively, compared to the drug control vincristine (95.2%).