Structural investigation of a novel heteropolysaccharide from the fruiting bodies of Boletus edulis

A novel water-soluble heteropolysaccharide, BEPF1, was isolated from the fruiting bodies of Boletus edulis with boiling water extraction and purified by Sephacryl S-300, with a molecular weight of 1.08 × 104 Da. Sugar composition of BEPF1 showed that it was composed of l-fucose, d-mannose, d-glucose and d-galactose in the ratio of 0.21:0.23:1.17:1.00. Methylation analysis together with 1H, 13C and 2D NMR spectroscopy established that BEPF1 was consisted of α-d-(1 → 6)-galactopyranan backbone with a terminal of α-l-fucosyl unit on O-2 of the 2-d-(2 → 6)-galactosyl units, β-d-(1 → 6)-4-O-Me-glucopyranan and β-d-(1 → 6)-glucopyranan backbone with a terminal β-d-glucosyl unit and it also contained a minor of 2,6-β-d-Mannopyranan residues.