Radical mediated dissection of oligosaccharides

Abstract

Radical chemistry continues to play an increasingly important role in tandem mass spectrometry based experiments on biomolecules. Oligosaccharides represent a very important class of target molecules that require structural characterization in terms of both monosaccharide identity and overall connectivity. Herein, two methods that generate radical oligosaccharides for subsequent activation are described. In one approach, a radical precursor is covalently attached to the oligosaccharide by reductive amination. Radicals can then be generated by homolytic bond cleavage of specific carbon–iodine bonds in protonated systems by either collisional activation or photodissociation. Subsequent activation of the radical species generates information rich spectra including numerous cross-ring fragments. Alternatively, noncovalent complexation with iodophthalic acid can be used to generate radical disaccharides by photoactivation. Subsequent radical transfer, loss of the radical precursor adduct, and collisional activation of the radical disaccharide results in characteristic glycosidic bond cleavage and cross-ring cleavage products that can easily distinguish isomeric species. Radical chemistry is demonstrated to have several advantages for the characterization of oligosaccharides relative to other approaches, including the identification of isomeric molecules of various sizes or analysis of various charge states.