Structural elucidation of an exopolysaccharide from mycelial fermentation of a Tolypocladium sp fungus isolated from wild Cordyceps sinensis

A novel polysaccharide designated EPS-1A with an average molecular weight around 40 kDa was fractionated and purified by anion-exchange and gel-filtration chromatography from the crude exopolysaccharide (EPS) isolated from fermentation broth of Cs-HK1, a Tolypocladium sp. fungus isolated from wild Cordyceps sinensis. The structural characteristics of EPS-1A were determined with various methods (e.g. GC, GC-MS, FT-IR,H-1 NMR and C-13 NMR) and through acid hydrolysis, methylation, periodate-oxidation and Smith degradation. The results suggested that EPS-1A was composed of glucose, mannose and galactose at 15.2:3.6:1.0 M ratio. EPS-1A was a slightly branched polysaccharide and its backbone was composed of (1 -> 6)-alpha-D-glucose residues (similar to 77%) and (1 -> 6)-alpha-D-mannose residues ( similar to 23%). Branching occurred at O-3 position of (1 -> 6)-alpha-D-mannose residues of the backbone with (1 -> 6)-alpha-D-mannose residues and (1 -> 6)-alpha-D-glucose residues, and terminated with beta-D-galactose residues. (C) 2009 Elsevier Ltd. All rights reserved.