Structural characterization of an α-1, 6-linked galactomannan from natural Cordyceps sinensis

An alpha-1, 6-linked galactomannan was isolated and purified from natural Cordyceps sinensis. The fine structure analysis of this polysaccharide was elucidated based on partial acid hydrolysis, monosaccharide composition, methylation and 1D/2D nuclear magnetic resonance (NMR) spectroscopy. Monosaccharide composition analysis revealed that this polysaccharide was mainly composed of galactose (68.65%), glucose (6.65%) and mannose (24.02%). However, after partial acid hydrolysis the percentages of galactose, glucose and mannose were changed to 3.96%, 13.82% and 82.22%, respectively. The molecular weight of this polysaccharide was 7207. Methylation and NMR analysis revealed that this galactomannan had a highly branched structure, mainly consisted of a mannan skeleton and galactofuranosyl chains. The structure of galactofuranosyl part was formed by alternating (1 -> 5)-lined beta-Galf and (1 -> 6)-liked beta-Galf or a single (1 -> 6)-liked b-Galf, attaching to the O-2 and O-4 of the mannose chain, and terminated at beta-T-Galf. The mannan core was revealed by analyzing the partial acid hydrolysate of the galactomannan and the structure was composed of (1 -> 6)-linked alpha-Manp backbone, with substituted at C-2 by short chains of 2-substituted Manp or Galf branches. (C) 2017 Published by Elsevier Ltd.