Sea Cucumber Glycosides: Chemical Structures, Producing Species and Important Biological Properties
Four new triterpene glycosides, cucumariosides A(2)-5 (1), A(3)-2 (2), A(3)-3 (3), and isokoreoside A (4), along with the previously isolated koreoside A (5), have been found in the sea cucumber Cucumariaconicospermium. Glycoside 1 was isolated as a native substance, while glycosides 2-5 were identified through their desulfated derivatives. Their structures have been deduced by extensive spectral analysis (NMR and MS) and chemical evidence. All the glycosides contain the same branched pentasaccharide carbohydrate chain but differ in the number and positions of the sulfate groups. Glycoside 1 has one, glycosides 2 and 3 have two, and glycosides 4 and 5 have three sulfate groups. Glycosides 2-5 are non-holostane derivatives; their aglycons lack the 18(20)-lactone and are characterized by shortened side chains, which is a very rare feature among the sea cucumber glycosides.