Fast atom bombardment (FAB) and chemical ionization (CI) mass spectrometry of γ-carboxyglutamic acid, 5-substituted-4,4-dicarboxyprolines, and their monodecarboxy derivatives glutamic acid and 5-substituted-4-carboxyprolines

DL-γ-Carboxyglutamic acid (Gla) reacts easily and quantitatively with aldehydes to give the racemic diastereoisomers of 5-substituted-4,4-dicarboxyprolines. After heating at 100 °C for 30 minutes these amino acids lose a carboxyl group from C-γ of Gla and C-4 of the proline ring to give glutamic acid and the racemic diastereoisomers of cyclic analogs of glutamic acid respectively. This paper reports a study of the above-mentioned compounds by using FAB mass spectrometry in comparison with CI analysis. FAB turned out to be an adequate ionization technique for dealing with such nonvolatile and thermolabile amino acids, and may thus allow the development of a rapid and sensitive method for detecting γ-carboxyglutamic acid in urine and in other biological matrices in pathological cases (i.e., renal stones and blood serum).