Structural analysis of isomeric chondroitin sulfate oligosaccharides using regioselective 6-O-desulfation method and tandem mass spectrometry

• We developed a strategy to delineate the sulfation pattern of chondroitin sulfate.
• Regioselective 6-O-desulfation method has high specificity for 6-O-sulfated group.
• The strategy was successfully applied to shark cartilage chondroitin sulfate D.
• 12 sulfated tetrasaccharides could be successfully characterized.

A strategy based on a regioselective 6-O-desulfation reaction and negative ion electrospray ionization tandem mass spectrometry (ESI-MS(n)) was developed for the structural delineation of isomeric chondroitin sulfate oligosaccharides. Product ions resulting from the glycosidic cleavage provided information about the number of sulfate groups in each sugar residue. After the regioselective 6-O-desulfation reaction, the number of sulfate groups on each residue was obtained using a tandem mass spectrometry analysis of the reaction product. The sulfation pattern could be obtained based on the product ions of analytes before and after the desulfation reaction. The strategy was demonstrated using a series of tetrasaccharides prepared from shark cartilage chondroitin sulfate D. Among the 12 identified tetrasaccharides, six structures had not been reported before.

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