A series of Schiff base peptide esters were examined by gas chromatography mass spectrometry. Electron impact induced elimination of aryl nitriles (ArCN) from Schiff bases , where R, R′ …are amino acid sidechains formed from aromatic aldehydes and peptide esters was shown to be associated with formation of C-terminal peptide fragments. Schiff base derivatives prepared from benzaldehyde and α-deuterobenzaldehyde with several peptide esters indicated that aryl nitrile elimination was accompanied by H(D) transfer to the α-C of the N-terminal amino acid residue. Of the many Schiff base peptide esters of different aldehydes studied, HCN elimination of the type observed in some nonpeptide Schiff bases could only be found among N-methyl pyrrolemethylidene derivatives.
