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%).