Enantioseparation of α-amino acids by means of Cinchona alkaloids as selectors in chiral ligand-exchange chromatography

A conventional nonchiral column was used for the enantioseparation of several racemic α-amino acids (native and derivatized) through the use of Cinchona alkaloids as chiral selectors along with Cu(II) ions in chiral ligand-exchange chromatography. The mobile phase composition (i.e., the organic modifier content and pH) was studied in order to modulate retention and enantioselectivity. Good enantioseparation of many amino acids was obtained using equimolar amounts of Cu(II) and either cinchonidine, quinine or quinidine as chiral selectors in the mobile phase. The molecular geometry of the diastereomeric complexes formed was modeled and energetic differences between both compounds were calculated by methods based on semi-empirical force-field. Good correlations were obtained between experimental enantioselectivity factors and calculated energetic differences.