Structural features of a pectic polysaccharide from the stems of Dendrobium nobile Lindl

Dendrobium nobile is commonly used as a Yin tonic for reinforcing body fluid and nourishing blood in Southeast Asia. In this paper, a pectic polysaccharide DNP-W5 was obtained from the stems of D. nobile. It contained mannose, glucose, galactose, xylose, rhamnose and galacturonic acid in molar ratios of 3.1:8.1:8.2:0.6:4.2:3.9. About 21% of the galacturonic acid existed as methyl ester and O-acetyl groups were approximately 6.9%. The structural analysis indicated that DNP-W5 possessed a backbone of a disaccharide of [→4)-α-GalAp-(1 → 2)-α-Rhap-(1→] with branches at O-4 of the Rhap and O-3 of the GalpA. The side chains consisted of galactosyl, mannosyl, glucosyl, and xylosyl residues. In vitro bioactive tests, DNP-W5 displayed remarkable immunoenhancing activities on T- and B-lymphocytes and its branches and acetyl groups are very important for the expression of the immunological activity.