Glycolipids from Sponges: Isolation and Structure Elucidation

The systematic study of glycolipids from sponges is quite recent. Earlier investigators have probably been discouraged by the difficulty of obtain pure glycolipids, when the standard techniques for the isolation of natural products are used. In addition, up to the early 1990s structure elucidation of glycolipids required specific skills, being largely based on chemical degradation, in contrast with the spectroscopic techniques largely used for other classes of natural products. Actually, Porifera are one of the richest source of new glycolipids. Many glycosphingolipids (GSLs) from marine sponges have unique structures, such as the immunostimulating alpha-galactosyl-GSLs from Agelas species, the immunosuppressive plakoside A and B from Plakortis simplex, or ectyoceramide , a galactofuranosyl ceramide from Ectyoplasia ferox. In addition, marine sponges contain a number of atypical glycolipids, without counterpart among glycolipids from other phyla. For example, simplexides are glycosides of a very-long-chain secondary alcohol,whereas plaxyloside possesses a linear polyisoprenoid aglycon and a carbohydrate chain composed of six linearly arranged xylopyranose units. The communication will deal with the most recent results of our work on glycolipids. The techniques that have been developed in our laboratories for their efficient isolation and purification as well as those for their structure elucidation by 2D NMR, MS/MS spectroscopy, and submilligram chemical degradation will be also described.