Highly selective nitroxyl radical-mediated oxidation of primary alcohol groups in water-soluble glucans

With catalytic amounts of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and hypochlorite/bromide as the regenerating oxidant in water, primary alcohol groups in glucans and derivatives thereof were rapidly and completely oxidised. For pyranosides, selectivity was higher than 95% and no side products could be detected with 1H and 13C NMR or with high-performance anion-exchange chromatography (HPAEC). The optimum pH for the reaction was between 10 and 11. The oxidation was found to be first order in TEMPO and Br−. The oxidation method can be applied to determine the amount of primary alcohol groups in water-soluble glucans; for pullulan, a proportion of 70% and for dextran, a proportion of 3% primary alcohol groups was found.