Sulfated polysaccharides from the red seaweed Georgiella confluens

The water-soluble polysaccharides from Georgiella confluens, collected in Antarctica, were fractionated with cetrimide. The complexed material was subjected to fractional solubilization in solutions of increasing sodium chloride concentration. The initially extracted polysaccharide and the major fraction isolated, soluble in 0.5 M NaCl, were studied. These are sulfated xylogalactans naturally rich in methylated sugar residues, comprising of 3,6-anhydro-2-O-methyl-L-galactose, 2-O-methyl-L-galactose and 6-O-methyl-D-galactose. Structural analysis was carried out by methylation, ethylation, desulfation-ethylation, desulfation-methylation, Smith degradation, 13C NMR spectroscopy and determination of the absolute configuration of monosaccharides by gas chromatography of diastereomeric derivatives produced by reductive amination. The results indicated the presence of an agaran backbone with an unusual substitution pattern: sulfation mainly at the 3-position of the alpha-L-galactose units and the presence of xylose side chains at the 4-position of the beta-D-galactose residues.