MALDI-TOF and ESI-MS analysis of oligosaccharides labeled with a new multifunctional oligosaccharide tag

A new multifunctional oligosaccharide label with a 1 degree amino-group was synthesized and characterized. The oligosaccharide label was introduced into several neutral oligosaccharides by reductive amination, and the derivatives were analyzed by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) and by electrospray ionization (ESI) mass spectrometry. It was demonstrated that the labeling reaction was satisfactory, and that as little as 50 pmol of starting material could be efficiently labeled with minimal loss to side reactions. A mixture of high-mannose N-glycans released from ribonuclease B was labeled. The label did not appear to interfere with structural characterization of the oligosaccharides by mass spectrometry. N-quaternization of the labeled oligosaccharides resulted in significantly increased sensitivity of detection with as little as 100 fmol on the probe detected. Deuterium coding of labeled oligosaccharide mixtures and relative abundance of mixture components was investigated. A protocol for the chromatographic separation of mixtures of labeled oligosaccharides by HPLC was developed and is reported here.