Structure and antioxidant activity study of sulfated acetamido-polysaccharide from Radix Hedysari

A new sulfated acetamido-heteropolysaccharide, HPS4-2A, was obtained by aqueous extraction followed by precipitation with ethanol and fractionation with DEAE column chromatography from Radix Hedysari. It was composed of rhamnose, arabinose, glucose, galactose and 2-acetamido-2-deoxy-d-galactose in the molar ratio of 10.09%:25.90%:25.90%:25.0%:12.30%. Elemental analysis indicated that HPS4-2A was a sulfated polysaccharide containing small amount of sulfate groups (1.87%). Partial acid hydrolysis, GC, GC–MS, 1D and 2D NMR spectroscopy analysis of the HPS4-2A revealed a predominance of glucose, galactose and 2-acetamido-2-deoxy-d-galactose linked in a highly-branched structure. The molecular weight of HPS4-2A was determined by HPSEC and HPSEC-MALLS. AFM study indicated that HPS4-2A took a highly branched conformation, which in consistent with the result studied by SEC-MALLS. Structural features of HPS4-2A were also investigated by SEM and TEM. Antioxidant assays demonstrated that HPS4-2A possessed of strong DPPH and hydroxyl radicals scavenging activities, suggesting that HPS4-2A could potentially be used as natural antioxidant.