Constituents of Holothuroideae, V. Isolation and Structure of Cerebrosides from the Sea Cucumber Pentacta australis

Four new cerebrosides, PA‐0‐1, PA‐0‐5, PA‐2‐5 and PA‐2‐6, were isolated from the two cerebroside mixtures, PA‐0 and PA‐2, obtained from the less polar fraction of the methanol extract of the sea cucumber Pentacta australis. The structures of these cerebrosides were determined on the basis of chemical and spectroscopic evidence. Another cerebroside, PA‐1‐4, isolated in a pure state from a different cerebroside mixture PA‐1, was found to be identical with the known glucocerebroside CE‐2c obtained from the related sea cucumber Cucumaria echinata of the same family. Reversed‐phase HPLC was effective in isolating these cerebrosides, showing the very close similarity of their structures. An analysis of the mass spectrum of the dimethyl disulfide derivatives of cerebrosides was also useful for the determination of the double‐bond position in the sea cucumber cerebroside. (Formula Presented.)