Separation of non-racemic mixtures of enantiomers by achiral chromatography

Abstract

The phenomenon of partial separation of enantiomeric mixtures in achiral chromatography (ACh) has already been documented for a wide variety of chiral compounds. It is attributed to the so-called effect of self-disproportionation of enantiomers (SDE). However, quantitative description of the SDE mechanism underlying adsorption of enantiomers on achiral surfaces is still incomplete, which hinders the application of that technique for large-scale separations. In this study, a mechanistic model for description of retention behavior of SDE-phoric compounds in silica-based ACh has been developed along with a procedure for fast determination of the model parameters. The model assumes formation of associates of chiral molecules, which occurs due to homo and hetero-chiral interactions in the adsorbed phase. The ability of the model to reproduce band profiles was verified for enantiomeric mixtures of three structurally different chiral compounds.

Keywords: Achiral chromatography; Enantiomer separation; Self-disproportionation; Thermodynamics.