An investigation into the Curie-point pyrolysis mass spectrometry of glycyl dipeptides

Thirty-nine dipeptides with a fixed N- or C-terminal amino acid of glycine have been investigated by Curie-point pyrolysis-mass spectrometry. The non-fixed amino acid was varied among the 20 naturally occurring amino acids. Results indicate that the formation of diketopiperazines (DKPs) occurs as a thermal cyclization prior to electron ionization. The extent of cyclization to form DKPs was dependent on the substituent of each different amino acid attached to the backbone of the dipeptide. Three amino acids (aspartic acid, glutamic acid, and arginine) inhibited DKP formation. The factors affecting DKP formation, including size and the electronic nature of the substituent, are discussed.