Fast-Atom Bombardment Mass Spectrometry of Phosphonopeptides

Abstract

The fast-atom bombardment mass spectra of phosphonopeptides, having an α-aminoalkanephosphonic acid as the acid-terminal residue, have been recorded using a glycerol matrix and a primary beam of xenon atoms operating at 6–8 kV. The identities of selected ions were confirmed by exact mass measurements. All peptides gave characteristic pseudomolecular ions, [MH]⁺, which appeared as the base peak in many cases. Protonated dimers, [2M + H]⁺, higher clusters, and ions resulting from association with glycerol were also observed, particularly in the case of dipeptides. Fragmentation occurred mainly by the elimination of α-amino-carboxylic acid residues, via peptide bond cleavage with hydrogen transfer, and by elimination of phosphorous acid from the aminophosphonic moiety. In addition, evidence was seen in certain cases for amide-bond fission with formation of an acylium ion which subsequently lost carbon monoxide.

Key Words:

• Phosphonopeptides
• FAB mass spectrometry.