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 the desulfation was carried out at 120 degrees C, the sulfates were removed up to 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 alpha-(1 -> 4)-L-rhamnopyranosyl, beta-(1 -> 4)-D-glucuronosyl, beta-(1 -> 2)-L-rhamnopyranosyl and beta-(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. (C) 2012 Elsevier Ltd. All rights reserved.