Quinine as a highly responsive chiral sensor for the 1 H and 19 F NMR enantiodiscrimination of N -trifluoroacetyl amino acids with free carboxyl functions.

Hydrogen-bond accepting and enantiodiscriminating abilities of quinine (Qui) have been exploited in the enantiodiscrimination of N -trifluoroacetyl (TFA) derivatives of amino acids by nuclear magnetic resonance (NMR) spectroscopy. 1 H and 19 F NMR resonances of derivatives of alanine, valine, leucine, norvaline, phenylalanine, phenylglycine, methionine, glutamic acid, proline, and tryptophan were well differentiated employing CDCl 3 and/or C 6 D 6 as solvent, with Qui acting in some cases not only as enantiodiscriminating agent, but also as solubility promoter. For derivatives soluble in both solvents, the best results were obtained in benzene-d6, with very high nonequivalence values, which were detectable not only starting from very low equimolar concentrations of 0.1 mM, but also in the presence of sub-stoichiometric amounts of Qui. The quality of enantiodifferentiation has been also evaluated by means of the enantioresolution quotient E . The method has been applied to the detection and quantification of mixtures of amino acid derivatives by single point measurements.