Structural Analysis and Immuno-Stimulating Activity of an Acidic Polysaccharide from the Stems of Dendrobium nobile Lindl.

Dendrobium nobile Lindl., an epiphytic herb distributed in the Southeast Asia, is used as a tonic and antipyretic herbal medicine in China. In this study, a water-soluble acidic heteropolysaccharide, DNP-W4, containing mannose, glucose, galactose, xylose, rhamnose, and galacturonic acid, in the molar ratios of 1.0:4.9:2.5:0.5:1.0:0.9, was obtained from the stems of Dendrobium nobile Lindl. Using methylation analysis, partial acid hydrolysis, pectolyase treatment, NMR, and ESI-MS, the structure of DNP-W4 was elucidated. The obtained data indicated that DNP-W4 was a complex heteropolysaccharide and possessed a backbone composed of (1 -> 4)-linked beta-D-Glcp, (1 -> 6)-linked beta-D-Glcp, and (1 -> 6)-linked beta-D-Galp, with substitutes at O-4/6 of Glcp residues and O-3 of Galp. The branches of DNP-W4 were composed of terminal Manp, (1 -> 6)-linked beta-D-Manp, (1 -> 3)-linked beta-D-Glcp, beta-D-Glcp, beta-D-Galp, (1 -> 4)-linked alpha-D-GalAp, (1 -> 2)-linked alpha-L-Rhap, and Xylp. DNP-W4 had little immunological activities, but its derivatives had immuno-stimulating activities to some extent.