Characterization of Isomeric Unsulfated Glycosaminoglycan Oligosaccharides by Mass Spectrometry/Mass Spectrometry

Both saturated and unsaturated forms of isomeric unsulfated glycosaminoglycan (GAG) oligosaccharides, i.e., tetrasaccharides of chondroitin (CH) and hyaluronan (HA), were analyzed by electrospray ionization mass spectrometry/mass spectrometry. Although the only structural difference between them was the hydroxyl group at the C-4 position in N-acetylhexosamine (GalNAc or GlcNAc, respectively), given the same m/z value of precursor ions, these isomers in both their saturated and unsaturated forms could be separated by careful examination of diagnostic fragment ions in their product ion mass spectra when the relative abundances of these fragment ions were considered. In addition, the product ion mass spectrum of the unsaturated HA tetrasaccharide was compared with its linkage isomer, N-acetylheparosan tetrasaccharide. In this case, the isomers were more easily differentiated by comparing their characteristic spectral patterns. By adopting this approach, systematic differentiation of isomeric unsulfated GAG oligosaccharides should be achieved by means of fragmentation. It should also contribute widely to GAG-related biochemical and medicinal research in the future.