Electrospray ionization mass spectrometry of 1-phenyl-3-methyl-5-pyrazolone derivatives of neutral and N-acetylated oligosaccharides

Derivatization using 1-phenyl-3-methyl-5-pyrazolone (PMP) was selected amon g a number of reported methods for labeling carbohydrates, since it gives a quantitative yield, proceeds through a rapid reaction and involves a simpl e clean-up procedure. Moreover, PMP derivatives provide an increase in sens itivity with ultraviolet and mass spectrometric detection relative to nativ e neutral sugars. Sensitivity studies were carried out using a standard oli gosaccharide, tetraglucose. One of the aims of these studies was to determi ne the minimum amounts of PMP-tetraglucose necessary to generate informativ e full-scan electrospray ionization (ESI) mass spectra and collision-induce d dissociation tandem mass spectra. Another aim was to characterize the fra gmentation pattern of PMP derivatives. Quantitative and qualitative studies were also carried out with a typical N-linked oligosaccharide obtained com mercially. The PMP-labeled compound underwent directed cleavages which prod uced fragments containing the reducing end. The native N-linked sugar yield ed fragments corresponding to cleavages from both ends of the molecule. Und er the same ESI conditions, the N-linked oligosaccharide exhibited more lab ility, or tendency to fragment, than neutral tetraglucose, in both the deri vatized and native forms. Also, PMP labeling was shown to enhance sensitivi ty in the case of a neutral oligosaccharide, i.e. tetraglucose, whereas the labeling of an N-acetylated oligosaccharide, NGA3, did not yield a noticea ble improvement in sensitivity. Copyright (C) 1999 John Wiley & Sons, Ltd.