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 (171) and an acidic heteroglycan sulfate (F3) containing arabinose, xylose and galactose residues were isolated. This neutral fraction (F I), which on partial hydrolysis produces a series of gluco-oligosaccharides having a degree of polymerization ranging from 3 to 18, is made up of alpha-(l -> 4)-linked glucose residues. The heteroglycan sulfate, a water-soluble polymer, has a molecular mass of 80 kDa. Glycosidic linkage and C-13 NMR analysis of the native (H) 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. (c) 2006 Elsevier Ltd. All rights reserved.