Achiral Chromatography Offers a Cost-Effective Method for Separating Non-Racemic Mixtures of Enantiomers

Researchers at Rzeszow University of Technology in Poland have developed a new model for achiral chromatography (ACh) that can separate non-racemic mixtures of enantiomers. The model, described in the Journal of Chromatography A, assumes the formation of associates of chiral molecules due to homo and hetero-chiral interactions in the adsorbed phase (1). This process occurs due to the effect of self-disproportionation of enantiomers (SDE), which is already documented for a variety of chiral compounds.

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ACh is a separation technique used to separate racemic mixtures of enantiomers without using a chiral stationary phase. It is based on the phenomenon of SDE, which results in partial separation of enantiomeric mixtures. The SDE mechanism underlying adsorption of enantiomers on achiral surfaces is not fully understood, which limits its large-scale applications. However, recent research has developed a mechanistic model for the retention behavior of SDE-phoric compounds in silica-based ACh.

ACh offers a cost-effective alternative to chiral chromatography (CCh) and diastereoisomeric crystallization for separating enantiomers. CCh is often expensive on an industrial scale due to the high costs and limited mechanical stability of chiral stationary phases (CSPs). While diastereoisomeric crystallization can be economically attractive, it requires the use of suitable resolving agents to provide pure crystals of the target enantiomer, which can be problematic.

The researchers were able to verify the model's ability to reproduce band profiles for enantiomeric mixtures of three structurally different chiral compounds. This could have implications for large-scale separations, as the ability to accurately model SDE-phoric compounds could make ACh a viable option. The new model could pave the way for a more cost-effective method for separating enantiomers, which could be useful in pharmaceutical and chemical industries.

While ACh has limitations, such as a lower resolution power than CCh and sensitivity to experimental conditions, it offers an alternative for separating enantiomers. ACh could be used to separate mixtures that do not occur in crystalline form and for large-scale separation of chiral compounds. The new model offers a promising development for ACh, and further research could help to refine the technique for industrial use.

Reference

(1) Olbrycht, M.; Gumieniak, J.; Mruc, P.; Balawejder, M.; Piątkowski, W.; Antos, D. Separation of non-racemic mixtures of enantiomers by achiral chromatography. J. Chromatogr. A 2023, 1693, 463877. DOI: https://doi.org/10.1016/j.chroma.2023.463877