The mass spectra of amino-acid and peptide derivatives. Part I. Benzyloxycarbonyl derivatives

Abstract

N-Benzyloxycarbonyl dipeptide alkyl esters give abundant molecular ions, which lose a benzyloxy-radical in addition to showing the well recognised cleavages of the peptide bonds and side-chains. Cleavage of the peptide bond gives important fragments of type PhCH₂·O·CO·[graphic omitted]H:CHR which then lose carbon dioxide with concomitant migration of the benzyl group. Some benzyloxycarbonyl amino-acid and dipeptide phenylthio-esters have also been examined: the peak of highest m/e in the spectra of these compounds corresponds to the acylium ion formed by loss of a phenylthio-radical. It is suggested that phenylthio-esters may find application in sequential analysis by mass spectrometry, in ‘triggering’ the stepwise elimination of amino-acid residues from the carboxy-end.