Post-source decay fragmentation analyses of linkage isomers of Lewis-type oligosaccharides in curved-field reflectron matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: combined in-source decay/post-source decay experiments and relative ion abundance analysis.
Linkage isomers of Lewis(X) trisaccharide (Le(X)) and Lewis(a) trisaccharide (Le(a)) were distinguished by the post-source decay (PSD) fragment spectra obtained by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) without permethylation. Both Y- and Z-type fragmentations were observed at the C-3 position of N-acetylhexosamine. beta-Elimination at C-3 of the reducing-end N-acetylglucosamine in Le(X) formed a double bond, which conjugated to an N-acetyl group, making the chemical species stable. In contrast, the double bond formed in the reducing end glucose of 3-fucosyllactose was unstable owing to the lack of a conjugated system. Therefore, beta-elimination of N-acetylglucosamine occurred predominantly rather than that of hexose in MALDI-PSD fragmentation. The measurements of the PSD fragment mass spectra using pseudo precursor ions originating from in-source decay were useful for the analyses of the fragmentation mechanisms and for the assignments of the chemical species of the fragment ions. The combined in-source decay/post-source decay experiments revealed the formation of a double bond between C-2 and C-3 in N-acetylglucosamine of Le(X). Abundance analysis of the PSD ions indicated that the 1-3 glycosyl linkage cleaves more easily than does the 1-4 linkage in MALDI-PSD fragmentation. Ion abundance analyses were useful in estimating the degree of Y- and Z-type fragmentation at the C-3 position of hexose and N-acetylhexosamine. The analysis of the relative ion abundances was a powerful tool for the assignments of the chemical species of the PSD ions.
Yamagaki
T
T
Department of Chemistry, School of Science, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. yamagaki@chem.s.u-tokyo.ac.jp
Nakanishi
H
H
D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D007477:Ions; D007536:Isomerism; D007983:Lewis Blood Group Antigens; D016256:Lewis X Antigen; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000032:analysis* / Q000737:chemistry* / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D014312:Trisaccharides / Q000032:analysis / Q000737:chemistry / Q000378:metabolism
D007477:Ions; D007983:Lewis Blood Group Antigens; D016256:Lewis X Antigen; D009844:Oligosaccharides; D014312:Trisaccharides; C111125:lewis(a)-lewis(x)