Isolation, chemical investigation and antiviral activity of polysaccharides from Gracilaria corticata (Gracilariaceae, Rhodophyta).

Polysaccharides were sequentially extracted from the agarophyte Gracilaria corticata. Chemical analysis combined with infrared spectroscopy showed that the cold water extracted material consists mainly of a high molecular weight sulfated galactan. Most of the sulfate groups are alkali labile and are located at C-4 of the 1,3-linked D-galactose units and C-6 of the 1,4-linked L-galactose residues. The autoclaved extracts contain agar type polysaccharide having a high pyruvate content and a variable degree of methylation, but were contaminated with floridean starch. 1H-NMR studies indicate that methoxyl groups, when present, occur at C-6 of the 1,3-linked D-galactose units and C-2 of the 1,4-linked L-galactose residues of agar polymer. Bioassays showed that a high molecular weight galactan sulfate, exhibited selective antiviral activity against herpes simplex virus types 1 and 2, likely due to an inhibition of the initial virus attachment to the host cell.