Isolation and chemical characterization of a glucogalactomannan of the medicinal mushroom Cordyceps militaris

Cordyceps militaris dried fruiting bodies were extracted with 5% KOH solution. The extract was purified by freeze-thawing treatment, and dialysis (100 kDa), giving rise to a homogeneous polysaccharide (Mw 23,000 Da). Its monosaccharide composition was mannose (56.7%), galactose (34.5%), and glucose (8.8%). The anomeric configurations were determined by their coupling constants. A complex polysaccharide was identified by NMR and methylation analysis. The HSQC spectrum showed signals at δ 107.7/5.06 and 106.1/5.14; 105.9/5.12 relative to β-d-Galf, and O-2-substituted β-d-Galf units, respectively. The sign at δ 104.4/5.21 corresponded to α-d-Galf. Other signals corresponded to α-d-Manp O-6- and O-2-substituted (δ 100.2/4.94; 100.5/5.27; 100.6/5.23; 100.7/5.16), and α-d-Manp 2,6-di-O-substituted (from δ 99.3 to 99.9). The main linkages, confirmed by methylation analysis, showed the derivatives: 2,3,4-Me3-Manp (11.9%) and 3,4,6-Me3-Manp (28.6%). The branches were (1 → 6)-linked-α-d-Manp or (1 → 2)-linked-β-d-Galf, terminating with β-d-Galf, α-d-Galf, α-d-Galp, or α-d-Manp. 42.7% of the partially hydrolyzed product consisted of 3,4,6-Me3-Manp, suggesting a (1 → 2)-linked backbone.