Fragmentation behaviour ofN-acylamino-O-alkyl ester derivatives of an aliphatic tripeptide in negative ion mass spectrometry

Abstract

The N-acetyl-, N-trifluoroacetyl-, N-pentafluoropropioayl-and N-heptafluorobutylamino derivatives of the tripeptide valyl-alanyl-leucine have been synthesized in every combination with the carboxy derivatives O-methyl ester, O-(l-H,H)-trifluoroethyI ester, 041-H,H)-pentafluoropropyl ester and 041-H,H)-heptafluorobutyl ester. These 16 derivatives have been mass measured after negative ionization using a 10% CO,/Ar moderator gas mixture in an electron impact ion source of a VGZAB2F mass spectrometer. The fragmentation behaviour of the peptide derivatives have been studied by negative linked-scan, negative mass-analysed ion kinetic energy and charge inversion mass spectrometry. Mast detected sequence ions originate from N-terminal fragments. Recorded anion currents and linked-scan measurement have shown that fluoro residues at the C-terminus increase the intensities of sequence ions, whereas N-terminal perfhoroalkyl derivatives generate [M -HFI-and [M -2HFl-ions. The abundances of these fragment ions increase with increasing molecular weight of the N-terminal residues. The best sequence information with intense anion currents has been recorded with the peptide derivative Ntrifluoroacetylarnino-0-hepatafluorobutyl ester.