N-(2-diethylamino)ethyl-4-aminobenzamide derivative for high sensitivity mass spectrometric detection and structure determination of N-linked carbohydrates

N-Linked glycans were derivatised by reductive amination using N-(2-diethylamino)ethyl-4-aminobenzamide (DEAEAB, procainamide) and examined by electrospray mass spectrometry. This derivative ionised primarily by protonation of the tertiary amine group and attachment of an alkali metal to give M + H + X](2+) ions which were much more abundant that doubly charged ions from glycans derivatised with other aromatic amines. Fragmentation of these ions depended on the nature of the alkali metal (X). Lithium and sodium adducts fragmented to give prominent ions produced by cleavages within the DEAEAB derivative whereas the other adducts produced more abundant ions from fragmentation of the carbohydrate. Elimination of a sugar fragment, usually by cleavage adjacent to GlcNAc or sialic acid, together with a hydrogen atom, produced the most abundant singly charged fragment ions. These ions then formally fragmented by glycosidic cleavages. Potassium, rubidium and caesium adducts produced abundant losses of the alkali metal, but the resulting ions appeared not to undergo extensive fragmentation. Most fragment ions from all of the adducts were singly charged, the remainder being doubly charged. Although the spectra of the M + X + H](2+) ions were not as informative as those from the singly charged ions from other derivatives, they, nevertheless, provided much valuable information on the structure of these glycans.