Glycolipids from sponges. 11. Isocrasserides, novel glycolipids with a five-membered cyclitol widely distributed in marine sponges.

In addition to the previously reported crasserides (1a-m), marine sponges contain smaller amounts of the isomeric isocrasserides (3a-m). The structures of these new glycoglycerolipid analogues were determined by NMR analysis and chemical degradation. Crasserides and isocrasserides were present in all the species of marine sponges we analyzed and therefore appear to be characteristic of the phylum Porifera.