PYROLYSIS OF ALANINE AND ALPHA-AMINOISOBUTYRIC-ACID - IDENTIFICATION OF LESS-VOLATILE PRODUCTS USING GAS-CHROMATOGRAPHY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY MASS-SPECTROMETRY

In addition to volatile low-molecular-weight decomposition compounds, alpha-aminoisobutyric acid (Aib) and alanine (Ala) pyrolysis at 500 de grees C under nitrogen atmosphere leads to less-volatile products resu lting from amino acid intermolecular condensation. The major pathway i s the formation of cyclic dipeptides piperazine-2,5-diones with the yi elds of 1% for Aib and 68% for Ala. To identify other pyrolysis produc ts, they have been extracted by chloroform and analyzed by means of th e coupled technique of gas chromatography/Fourier transform infrared s pectroscopy/mass spectrometry with auxiliary computer simulation of IR spectra and H-1 and C-13 nuclear magnetic resonance spectroscopy. In the case of Aib, the condensation has been also found to produce a lin ear dipeptide Aib-Aib, which undergoes further decarboxylation and the loss of H2NCH(CH3)(2) and hydroxyl moiety. Formation of small amounts of the bicyclic amidines hexahydroimidazo[1,2-a]pyrazine-3,6-diones v ia amino acid condensation has been detected as well. The presence of alpha-hydrogen atom in Ala residue facilitates dehydrogenation reactio ns for the related PD and bicyclic amidine, whereas in the case of Aib the dehydrogenated compounds have not been found. Further pathways of PD pyrolysis can lead to 4- and 5-membered lactams and hydantoins. (C ) 1998 Elsevier Science B.V. All rights reserved.