Structural analysis of immunostimulating sulfated polysaccharides from Ulva pertusa

Sulfated polysaccharides were extracted from Ulva pertusa and fractionated to obtain the most immunostimulating fraction (F₂). The glycosidic linkages of the polysaccharides in the fraction F₂ 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 F₂ 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.