Structural characterization of chemically derivatized oligosaccharides by nanoflow electrospray ionization mass spectrometry

Oligosaccharides released from several glycoproteins were derivatized with either 4-aminobenzoic acid 2-(diethylamino)ethyl ester (ABDEAE) (Yoshino, IC; et al. Anal. Chem. 1995, 67, 4028-4031) or 2-aminopyridine. The resulting derivatives were analyzed on a nanoflow electrospray ionization (ESI) quadrupole-inlet time-of-flight mass spectrometer using the low-energy collision-induced dissociation technique. In the MS/MS spectra, the oxonium (b or internal series) and y series ions, which are derived from the multiply charged precursor ions, were predominant and were used for the structural readout, Some oxonium ions that were observed in the low-mass region, but that were not found in the PSD analyses (Mo, W.; et al. Anal. Chem. 1998, 70, 4520-4526), rendered a more detailed structural insight. The oxonium ions at m/z 512.2, which are derived from the fucosylated oligosaccharides of immunoglobulin Y and thyroglobulin, were observed, suggesting that fucosylation had occurred proximal to the outer nonreducing terminus. In addition, the data herein show that structural elucidation can be routinely achieved at a low sample concentration. For the case of ABDEAE derivatives, this can be achieved at the 50 fmol/mu L level and with the actual sample consumption at the attomole level using nanoflow ESI MS/MS.