Structural elucidation of a novel mannogalactan isolated from the fruiting bodies of Pleurotus geesteranus

A novel water-soluble polysaccharide named PGPB-1, with a molecular weight of 1.3 × 104 Da as determined by high-performance liquid chromatography (HPLC), was isolated from the fruiting bodies of Pleurotus geesteranus by boiling water as well as DEAE-Sepharose Fast Flow and High-Resolution Sephacryl S-300. On the bases of compositional analysis, methylation analysis and NMR spectroscopy (1H NMR, 13C NMR, 2D-COSY, TOCSY, HMQC, HMBC and NOESY spectra) analysis, the structural elucidation of PGPB-1 consisted of a α-d-(1 → 6)-galactopyranan and a α-d-3-O-Me-d-galactosyl unit backbone with a α-d-Mannosyl unit on O-2 of the 2,6-di-O-substituted-d-galactosyl units. The repeating unit of the polysaccharide was established as: also contains a minor proportion of 6-linked-d-Glcp.