Structural analysis of immunostimulating sulfated polysaccharides from Ulva pertusa.

Sulfated polysaccharides were extracted from Ulva pertusa and fractionated to obtain the most immunostimulating fraction (F(2)). The glycosidic linkages of the polysaccharides in the fraction F(2) were determined using GC-MS and 2D-NMR spectroscopy after chemical modifications, including reduction and desulfation under various conditions. Methanol was used as a sulfate acceptor for the removal of sulfates from the polysaccharides. When desulfation was carried out at 120°C, the sulfates were removed upto 90.1% from the F(2) fraction without considerable backbone degradation. The GC-MS analysis as well as NMR spectra revealed that the backbone of the polysaccharides was mainly composed of α-(1→4)-L-rhamnopyranosyl, β-(1→4)-D-glucuronosyl, β-(1→2)-L-rhamnopyranosyl, and β-(1→4)-D-xylopyranosyl residues with branches at O-2 position of rhamnose. The sulfate groups were mostly found on glucuronic acid at O-3 position.