Oligosaccharides were covalently labeled with pyrenemethylamine in high yield. HPLC separation on C18 reverse-phase and HILIC regular phase, quantification, and off-line detection by Matrix-Assisted Laser Desorption/Ionization (MALDI) Time-of-Flight (TOF) mass spectrometry was demonstrated with excellent sensitivity. The labeling procedure was robust, reproducible, uniform across multiple glycan structures, fast (5 minutes), and the labeled glycans were separated in HPLC runs of &lt; 20 minutes. Unlike the more traditional aminobenzamide (AB) label, the pyrene-labeled glycans showed better chromatographic separation. A new MALDI mass spectral precursor ion for fragmentation studies was observed. The pyrenemethylene moiety was easily lost from the protonated molecule due to 2,5-dihydroxybenzoic acid matrix-promoted redox elimination. The resulting high-energy glycosyl ammonium ion provided excellent fragmentation efficiency (Y-ions), which covered almost the entire structure of several oligosaccharides at the low picomol level. In addition, due to favorable HOMO-LUMO energy gaps relative to the MALDI-laser energy, a photodimerization product of the pyrenemethylene moiety was observed. A fragmentation mechanism is proposed.

Photoionization of pyrenemethylamine-labeled oligosaccharides: A new MALDI-TOF precursor ion-type for efficient fragmentation

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