Stereoselective Reaction Mass Spectrometry with Cyclic α-Amino Acids

Stereoselective reaction mass spectrometry in the chemical ionization (isobutane) mode has been used to detect the absolute configuration of enantiomerically pure cyclic α-amino acids. Thus, an enantiomerically pure cyclic α-amino acid was allowed to react on a micromole level with both enantiomers of a chiral selector and the mass spectra were detected. The relative abundances of characteristic ions formed by the diastereoselective reaction between the α-amino acid and the chiral selector of the same configuration were much higher than those ions formed by the α-amino acid and the chiral selector of a different configuration. The absolute configuration of the α-amino acid may be predicted by careful examination of the two stereoselective reaction mass spectra of the α-amino acid measured with both, the chiral (R)-and (S)-selector respectively. Various (R)- and (S)-carboxylic acids and (R)- and (S)-α-phenylethyl amine have been used as chiral selectors.