Studies on Fragmentation Pathways of N-Ethoxy (phenyl) phosphoryl Amino Acids by Electrospray Ionization Tandem Mass Spectrometry1

The positive and negative ESI-MS/MS spectra of N-ethoxy(phenyl) phosphoryl amino acids (EPP-AA) were investigated by electrospray ionization (ESI) ion trap mass spectrometry. The fragmentation pathways of [M + Na]+ and [M − H]− ions are proposed and rationalized. The observation may have some potential applications in the interpretation of the MS/MS spectra of novel N-phosphoryl compounds. The complexity of MS/MS spectra of EPP-AA [M + Na]+ ions is decreased compared with that of N-dialkyloxyphosphoryl amino acid. Therefore, the new phosphonamidate method may be considered one of the superior methods that can be used in sequencing peptides and proteins extensively.