Novel Rearrangement of Small Peptides in Electrospray Ionization Tandem Mass Spectrometry

Electrospray ionization mass spectrometry (ESI-MS) is a powerful method for sequencing peptides. A novel fragmentation pattern with the loss of a neutral fragment of 45 Da was observed with the dipeptides, tripeptides,tetrapeptides and pentapeptides containing phenylalanine or histidine residues. A novel rearrangement reaction with the extrusion of a formamide piece was studied and the rearrangement mechanism was proposed and confirmed by deuterium labeling experiments with ESI-MS^n and high-resolution mass spectrometry. These findings are potentially helpful in identifying the specific sequence pattern in the peptide sequencing.