A new fragmentation rearrangement of the N-terminal protected amino acids using ESI-MS/MS.

A novel fragmentation rearrangement reaction with a carboxyl oxygen negative charge migration was observed in the N-terminal protected amino acids including Fmoc-protected phosphoserine. phosphothroenine, and phosphotyrosine and their analogues using the electrospray ionization tandem mass spectrometry (ESI-MS/MS). The possible mechanism of a five-membered ring transition state was proposed and supported by the further experiments. It was found that the tendency of the rearrangement was determined by the blocking status of its C-terminal and the reaction was proved to be independent of the N-terminal and side-chain protecting groups of the amino acids.