Rhizochalins C and D from the Sponge Rhizochalina incrustata. A Rare threo-Sphingolipid and a Facile Method for Determination of the Carbonyl Position in a,o-Bifunctionalized Ketosphingolipids

摘要

Rhizochalins C and D (1, 2), new representatives of two-headed glycosphingolipids, were isolated from the sponge Rhizochalina incrustata. Rhizochalin D is an unexpected C_(29) homologue of the canonical C_(28) dimeric sphingolipid structures. Their structures including absolute configurations were established using spectroscopic data, micromolar-scale Baeyer-Villiger oxidation, and LCMS interpretation of the products. Application of the latter method leads to a revision of the structure of oceanapiside and placement of the keto group at C-18 rather than C-11.