Fast Atom Bombardment Tandem Mass Spectrometry of Benzyloxycarbonyl-Protected Tetrapeptide Derivatives Containing Proline

Fragmentations of N-benzyloxycarbonyl-protected tetrapeptide ethyl esters containing L-proline and L-alanine in the gas phase were examined by the collisional-activated decomposition of the deprotonated molecule and the fragment ions produced by the cleavage of the tetrapeptide derivatives, in which changes in both the number and positions of the prolyl residues were observed, in negative-ion FAB-MS. The cleavage patterns of these ions in the collisional-activated decomposition mass spectra were observed to depend on the number and positions of prolyl residues in the peptide derivatives. These results indicate that the conformational difference in the tetrapeptide derivatives due to the existence of L-proline may be an important factor responsible for the fragmentations of peptide molecules in the gas phase.