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.