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.
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