O–N-Acyl migration in N-terminal serine-containing peptides: mass spectrometric elucidation and subsequent development of site-directed acylation protocols

The synthesis of a modified pentapeptide involving the palmitoylation of the hydroxyl group of a serine residue present at the N-terminal position is presented. An O–N-acyl shift was observed by LC/MS/MS, the two isobaric molecules exhibiting upon collisional activation dissociation (CAD) different fragmentation behaviours. The synthetic pathway was thereafter modified to control the palmitoylation site (O or N). The method was validated with another serine acylation (octanoylation). The evidenced mass spectrometric criteria could serve to decipher peptide post-translational modifications in proteomics.