Structure of polysaccharide from Polygonatum cyrtonema Hua and the antiherpetic activity of its hydrolyzed fragments.

A neutral polysaccharide named PD was isolated from the traditional Chinese medicinal herb, Polygonatum cyrtonema Hua. Five fragments were isolated by Bio-Gel P4 chromatography from hydrolysates of PD. Using assays of cytopathic effect inhibition, neutral red dye uptake and plaque forming inhibition, it was proved that the fragments with degree of polymerization (DP) of 4 and 5 were the shortest ones which retained the activity against herpes simplex virus type 2 (HSV-2) in vero cell culture. The structures of PD and one of its activity-retaining fragments, B3, were determined by permethylation followed with reductive cleavage, mass spectrometry and nuclear magnetic resonance spectrometry. It was shown that PD was a branched fructan with average DP of 28. There was one two-residue side chain composed of (2 --> 6)-linked beta-d-fructofuranosyl (Fruf) residues every three (2 --> 1)-linked beta-d-Fruf residues in the backbone of PD, whereas B3 was a mixture containing 1-kestose and neokestose series of oligosaccharides of DP 3-5 without branches.