Direct chiral resolution of underivatized amino acids on a stationary phase dynamically modified with the ion-exchanger N(τ) -decyl-L-spinacine

Abstract

Increasing attention has been devoted in the last decades to chiral chromatography, principally to high-performance liquid chromatography techniques using a chiral stationary phase. Many chiral high-performance liquid chromatography columns are commercially available, but, unfortunately, they are most often rather expensive. A cheap alternative to the commercial chiral columns is the dynamic-coating procedure of a standard achiral stationary phase with a chiral selector containing both a chiral domain and a chain or a group able to tightly (but noncovalently) bind the achiral support. This is the case of N(τ) -decyl-l-spinacine, already successfully employed to dynamically cover a reversed-phase column to separate racemic mixtures of amino acids through the ligand-exchange mechanism. In the present work, the same chiral selector is employed to separate racemic mixtures of amino acids and oligopeptides, in the absence of metal ions: no coordination complex is formed, but only electrostatic and weak nonbonding interactions between the chiral phase and the analytes are responsible for the observed enantioselectivity. The new method is simpler than the previous one, very effective in the case of aromatic amino acids and oligopeptides and also suitable for preparative purposes.

Keywords: Amino acid enantiomers; Chiral separation; Dynamic column coating; Oligopeptides; Spinacine.