The unusual hydrogen-deuterium exchange of α-carbon protons in N-substituted glycine-containing peptides

Hydrogens connected to -carbon (-C) of amino acid residues are usually resistant to hydrogen-deuterium exchange (HDX) unless reaction conditions promote racemization. Although N-methylglycine (sarcosine) residue has been found in biologically active peptide such as cyclosporine, to the best of our knowledge, the HDX of -C protons of this residue was not explored yet. Here, we presented a new and efficient methodology of -C deuteration in sarcosine residues under basic aqueous conditions. The deuterons, introduced at -C atom, do not undergo back-exchange in acidic aqueous solution. The electrospray ionization-MS and MS/MS experiments on proposed model peptides confirmed the HDX at -C and revealed the unexpected hydrogen scrambling in sarcosine-containing peptides. Although the observed HDX of -C protons is only successful in N-acylglycine when the amide possesses a certain degree of alkylation, it offers a new approach to the analysis of sarcosine-containing peptides such as cyclosporine. Copyright (c) 2014 John Wiley & Sons, Ltd.