Isolation, purification and structural characterization of a new water-soluble polysaccharide from Eremurus stenophyllus (boiss. & buhse) baker roots

A new water-soluble polysaccharide (ESPS-1), with the average molecular weight of 52.1 kDa and a specific optical rotation of +169.7° (c 1.0, H2O), was successfully isolated by warm-water extraction and then purified using DEAE-Cellulose and Sephadex G-100 columns from the roots of Eremurus stenophyllus. The results from chemical and instrumental tests including FT-IR, methylation and GC-MS analysis, periodate oxidation and Smith degradation, partial acid hydrolysis, and NMR spectroscopy (1H, 13C, 1H-1H COSY, HMQC and HMBC) demonstrated that ESPS-1 was a 2-O-acetylgalactan, composed of galactose, arabinose and mannose in a molar ratio of about 10:3:1, respectively. It has a backbone of (1 → 6)-α-d-galactopyranosyl residues, with branches at O-3 consisting of α-d-Manp-(1 → 3)-α-l-Araf-(1 → 3)-α-l-Araf-(1 → 3)-α-l-Araf-(1→. The acetyl groups are substituted at O-2 of (1 → 6)-linked Galp and the degree of acetylation was about 14%.