LC-MS analysis of oligosaccharides

HexNAc 203.0794 3 N-Acetyl-galactose (GalNAc), N-Acetyl-glucose (GlcNAc) 

The structural complexity of oligosaccharides goes far beyond that of proteins and nucleotides [1-4], Because with nucleotides or amino acids only hnear chains with just one linkage type are formed, a tetramer of nucleotides or amino acids with four different monomeric subunits can have only 24 different stractures, while in excess of 10,000 different stractures are possible for a tetrasaccharide. The various stereochemical centres, the anomeric centre, the multiple linkage types, and the ability to form branched stractures all contribute to this structural diversity. 

A monomeric sugar unit has several structural characteristics  

Although the theoretical number of possible oligosaccharide stractures is very high, only a limited number of these actually occur in biological systems. 

An important step in the characterization of oligosaccharides may be the compositional analysis with respect to the type of monomeric units present. This is mostly done using methylation of the monomers after methanolysis or hydrolysis of the oligosaccharides and subsequent GC-MS analysis [5]. Permethylation of intact oligosaccharides can also be applied prior to ESl-MS analysis, in most cases using dimethylsulfoxide/NaOH and methyliodide [6]. The number of methyl substituents added to each sugar unit in an oligosaccharide is indicated in Table 20.1. 

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