Development of new ulvan-like polymer by regioselective oxidation of gellan exopolysaccharide using TEMPO reagent

The produced, purified and deacylated gellan exopolysaccharide was subjected to regiospecific oxidation at C6 with NaOCl in the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and NaBr in aqueous solution at pH 10. As with other polysaccharides, a high selectivity of oxidation was observed. The high performance anion-exchange chromatography (HPAEC) and 13C NMR analysis of the TEMPO-oxidized products was used to confirm that the C6 primary hydroxyl groups of deacylated gellan were completely converted to carboxylate groups. Thus, after the addition of 7.5 mmol of NaClO per gram of polysaccharide, a new and original water-soluble rhamnoglucuronan polymer was obtained quantitatively with homogeneous chemical structures. This original carbohydrate might find use as surrogates of ulvan, a sulfated cell-wall polysaccharides extracted from green seaweeds (Ulva species), in pharmaceutical and medical areas.