Elucidation of the structure of a bioactive hydrophilic polysaccharide from Cordyceps sinensis by methylation analysis and NMR spectroscopy

The structure of a bioactive hydrophilic polysaccharide fraction from Cordyceps sinensis (CBHP) was studied using methylation analysis and 2D NMR spectroscopy. Monosaccharide composition analysis revealed that it consists mainly of glucose (95.19%) with trace amounts of mannose (0.91%) and galactose (0.61%). The results of methylation analysis indicated that α-1,4 linked Glcp is the main linkage type (65.7%), followed by t-Glcp (20.7%), 1,2,3,6-Glcp (4.1%), 1,2,4,6-Glcp (3.0%), 1,3,6-Glcp (2.0%), 1,4,6-Glcp (1.6%), and 1,2-Manp (1.9%) and 1,3-Galp (1.0%). Based on 1D and 2D NMR analysis, a preliminary structure is proposed: The backbone is composed of Glcp joined by 1 → 4 linkages and 1 → 3 linkages; the branching points are located at O-2 or O-6 of Glcp with α- terminal-d-Glcp as side chain. The trace amounts of 1,2-Manp and 1, 3-Galp linkages are probably located randomly in the side chains. A schematic structure is proposed as following: