Polysaccharides from Caulerpa racemosa: Purification and structural features

To study the relationship between the structure and anti-viral activity of polysaccharides present in hot water extracted fraction (CrHWE) of the green seaweed Caulerpa racemosa we have purified the crude extract by anion exchange chromatography. A neutral glucan (F1) and an acidic heteroglycan sulfate (F3) containing arabinose, xylose and galactose residues were isolated. This neutral fraction (F1), which on partial hydrolysis produces a series of gluco-oligosaccharides having a degree of polymerization ranging from 3 to 18, is made up of α-(1 → 4)-linked glucose residues. The heteroglycan sulfate, a water-soluble polymer, has a molecular mass of 80 kDa. Glycosidic linkage and 13C NMR analysis of the native (F3) and desulfated (F3D) heteroglycan sulfate suggested that this polysaccharide is branched and contains, inter alia, (1 → 3)-linked galactose, terminal- and (1 → 4)-linked xylose, and (1 → 4)- and (1 → 3,4)-linked arabinose residues. Sulfate groups, when present, are located at C-3 of (1 → 4)-linked arabinose and C-6 of (1 → 3)-linked galactose units. Degradation of this polysaccharide with trifluoro acetic acid and structural analysis of the resulting fragments by gas liquid chromatography–mass spectrometry (GLC–MS) and matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS) indicate the presence of two series of oligosaccharides: (i) the first contains two to nine galactose residues and a sulfate group, and (ii) the other one contains an arabinose or xylose, one to eight galactose residues and one sulfate group.