Structure and biological action of cladolosides B1, B2, C, C1, C2 and D, six new triterpene glycosides from the sea cucumber Cladolabes schmeltzii.

Six new nonsulfated triterpene glycosides, cladolosides B1 (1), B2 (2), C (3), C1 (4), C2 (5) and D (6) and known holotoxin A1 (7) have been isolated from the tropical Indo-West Pacific sea cucumber Cladolabes schmeltzii (Cladolabinae, Sclerodactylidae, Dendrochirotida). Structures of the glycosides were elucidated by 2D NMR spectroscopy and mass-spectrometry. Glycosides 1 and 2 have pentasaccharide branched carbohydrate moieties and differ from each other by the aglycone structures. Compounds 3-6 are hexaosides; 3-5 contain identical carbohydrate moieties with two terminal 3-O-methylglucose residues and glucose as the fifth sugar unit and differ from each other in the structures of their aglycones. Cladoloside D (6) has a new variant of carbohydrate chain with xylose and glucose residues as fifth and sixth monosaccharides, correspondingly. All of the substances demonstrated rather strong cytotoxic and hemolytic effects.