Synaptosides A and A1, triterpene glycosides from the sea cucumber Synapta maculata containing 3-O-methylglucuronic acid and their cytotoxic activity against tumor cells

Two novel triterpene holostane glycosides, synaptosides A (1) and A(1) (2), have been isolated from the Vietnamese sea cucumber Synapta maculata (Synaptida, Apodida). Their structures were elucidated by spectroscopic methods (NMR and MS) and chemical transformations. Glycosides I and 2 have rare branched pentasaccharide carbohydrate chains featuring a 3-O-methylglucuronic acid residue not previously reported in glycosides from sea cucumbers and a 6-O-sulfated glucose. Glycoside 2 has an oxo group at C-7 and a 8(9)-double bond. All these structural features are unknown in glycosides from sea cucumbers. Glycoside I has moderate cytotoxic activity (IC50 8.6 mu g/mL) and glycoside 2 is inactive against HeLa tumor cells.