Alkaline Degradation of Oligosaccharides Coupled with Matrix-Assisted Laser Desorption/Ionization Fourier Transform Mass Spectrometry:  A Method for Sequencing Oligosaccharides

A new technique for determining sequence and linkage information of underivatized oligosaccharides is developed using alkaline degradation and matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS). Alkaline degradation (also known as the “peeling” reaction) is a chemical degradation technique that only cleaves the glycosidic bond at the reducing end by β-elimination to yield a new reducing end. The reaction products are sampled directly with minimal cleanup and monitored by MALDI-FTMS to elucidate the oligosaccharide sequence. Linkage information is provided by cross-ring cleavage fragmentation of the new reducing ends, created by either MALDI source fragmentation or sustained off-resonance irradiation collision-induced dissociation. This method is illustrated by the successful sequence and linkage determination of neutral, branched, fucosylated, and sialylated oligosaccharides. Experiments on differently linked disaccharides are also performed to determine the specificity of the cross-ring cleavage reactions. The power of this technique is enhanced by the Fourier transform mass analyzer, which provides high-resolution, exact mass, and facile tandem mass spectrometry experiments of MALDI-produced ions.