Structural characterization of a 2-O-acetylglucomannan from Dendrobium officinale stem

A heteropolysaccharide obtained from an aqueous extract of dried stem of Dendrobium officinale Kimura and Migo by anion-exchange chromatography and gel-permeation chromatography, was investigated by chemical techniques and NMR spectroscopy, and is demonstrated to be a 2-O-acetylglucomannan, composed of mannose, glucose, and arabinose in 40.2:8.4:1 molar ratios. It has a backbone of (1→4)-linked β-D-mannopyranosyl residues and β-D-glucopyranosyl residues, with branches at O-6 consisting of terminal and (1→3)-linked Manp, (1→3)-linked Glcp, and a small proportion of arabinofuranosyl residues at the terminal position. The acetyl groups are substituted at O-2 of (1→4)-linked Manp and Glcp. The main repeating unit of the polysaccharides is reported.