An acetylated galactomannoglucan from the stems of Dendrobium nobile Lindl

A water-soluble polysaccharide DNP-W2 composed of glucose, mannose, and galactose in the molar ratio of 6.1:2.9:2.0 had been isolated from the stems of Dendrobium nobile. Its molecular weight was 1.8 x 10(4) Da determined by HPGPC. Structural features of DNP-W2 were investigated by a combination of chemical and instrumental analysis, including FTIR, GC, GC-MS, periodate oxidation-Smith degradation, methylation analysis, partial acid hydrolysis, and NMR spectroscopy. The results showed that DNP-W2 is a 2-O-acetylgalactomannoglucan and has a backbone consisting of (1-->4)-linked beta-D-Glcp, (1-->6)-linked beta-D-Glcp, and (1-->4)-linked beta-D-Manp, with branches at O-6 of (1-->4)-linked beta-D-Glcp and beta-D-Manp. The branches are composed of alpha-D-Galp. The acetyl groups are substituted at O-2 of (1-->4)-linked Manp. Preliminary tests in vitro reveals that DNP-W2 can stimulate ConA- and LPS-induced T and B lymphocyte proliferation.