Microwave-assisted desulfation of sulfated polysaccharides

Several sulfated polysaccharides were desulfated by heating their pyridinium salts dissolved in dimethyl sulfoxide in a microwave oven. The procedure was applied to different products like a λ-carrageenan, a partially cyclized μ/ν-carrageenan, an agar-like product like corallinan, a fucoidan and a chondroitin sulfate. When their pyridinium salts were generated in carefully chosen conditions, the desulfation proceeds smoothly after 1 min of heating, leading to a removal of 60–93% of the original sulfate present. Some depolymerization was found to occur, but its effect is moderate (yields of the recovered products are 64–89%), even for polysaccharides with labile bonds. An in situ methylation procedure was coupled with the microwave-aided desulfation method in order to facilitate the retrieval of structural data. Both spectroscopical and chemical studies showed that the integrity of the polysaccharides was not affected by this procedure (besides the loss of sulfate and the above-mentioned depolymerization).