PREPARATION AND DESORPTION MASS-SPECTROMETRY OF PERMETHYL AND PERACETYL DERIVATIVES OF OLIGOSACCHARIDES

This chapter discusses preparation and desorption mass spectrometry of permethyl and peracetyl derivatives of oligosaccharides. The methods described in this chapter are applicable to all types of oligosaccharide and oligosaccharide conjugates including glycopeptides and glycolipids. Although many of these substances can be analyzed by desorption mass spectrometry without prior derivatization, the permethyl and peracetyl derivatives offer the following advantages: (i) higher sensitivity, (ii) applicability to impure samples (e.g., those contaminated with salts and proteins), (iii) reliable and well-defined fragmentation allowing unambiguous sequencing, and (iv) fragmentation data can frequently be obtained from high-molecular weight samples (5000-20,000) that are difficult or impossible to analyze as native compounds. Partial methanolysis of a permethylated sample using fast atom bombardment (FAB) MS to monitor the reaction provides valuable sequence information including branching patterns. During partial methanolysis, the permethylated sample is gradually degraded by hydrolysis of the glycosidic linkages. Methylglycosides (or perdeuteromethylglycosides if deuterated methanol is used in the reaction) are produced at released reducing termini, while each released glycosidic oxygen becomes a free hydroxyl group. © 1990, Elsevier Inc. All rights reserved.