Innovative Chiral Column Boosts Enantioselective HPLC Separations

In a recent study, researchers demonstrated that a novel chiral stationary phase (CSP) could improve enantioselective high-performance liquid chromatography (HPLC). The research team successfully synthesized this new CSP by covalently bonding a [4+6]-type homochiral porous organic cage (POC), known as CC19-R to thiolated silica, utilizing a thiol-ene click reaction. The researchers’ efforts were published in the Journal of Chromatography A (1).

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CC19-R, which was synthesized through a Schiff-base reaction between 2-hydroxybenzene-1,3,5-tricarbaldehyde and (1R, 2R)-(-)-1,2-diaminocyclohexane, demonstrated enantioseparation capabilities (1). The CSP based on CC19-R was evaluated in both reversed phase HPLC (RP-HPLC) and normal phase HPLC (NP-HPLC) and successfully separated a diverse range of chiral compounds and pharmaceuticals, including alcohols, organic acids, ketones, diols, esters, and amines (1).

The team achieved the enantioseparation of 15 racemates in NP-HPLC and eleven racemates in RP-HPLC. Notably, several racemates, including 4-chlorobenzhydrol, cetirizine (in the form of dihydrochloride), 1,2-diphenyl-1,2-ethanediol, and 3-(benzyloxy)propane-1,2-diol, achieved exceptional resolution values of 3.66, 4.23, 6.50, and 3.50, respectively (1).

The new CSP exhibited improvements, successfully separating eight racemates in NP-HPLC and five racemates in RP-HPLC that were challenging on the NC1-R column. This revelation highlights the enhanced enantioselectivity and the significantly expanded separable range of chiral POC-type columns made possible by the CC19-R column (1).

Furthermore, the research team compared the performance of the CC19-R column with two commercial columns: Chiralpak AD-H (CSP: Amylose tris(3,5-dimethylphenylcarbamate)) and Chiralcel OD-H (CSP: Cellulose tris(3,5-dimethylphenylcarbamate)) (1). The CC19-R column was able to successfully separating racemates that the other columns struggled with.

The study also highlighted the stability and reproducibility of the CC19-R column. Even after undergoing multiple injections (100, 200, 300, and 400 times), the column demonstrated consistent performance, with a relative standard deviation (n = 5) for the retention time and resolution of less than 1.0% and 1.8%, respectively.

The research presents a pioneering approach in the world of chiral separations. The newly developed POC-based CSP, fabricated using CC19-R, demonstrated enantioseparation capabilities across a wide spectrum of compounds, outperforming both previous POC-based columns and commercial alternatives. With its potential for excellent resolution and straightforward synthesis methods, this CSP opens exciting prospects for chiral POC applications in HPLC racemic separation (1).

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Reference

(1) Liang, R.-X.; Zhang, Y.-P.; Zhang, J.-H.; Gong, Y.-N.; Huang, B.; Wang, B.-J.; Xie, S.-M.; Yuan, L.-M. Engineering thiol-ene click chemistry for the preparation of a chiral stationary phase based on a [4+6]-type homochiral porous organic cage for enantiomeric separation in normal-phase and reversed-phase high performance liquid chromatography. J. Chromatogr. A. 2023, 1711, 464444. DOI: 10.1016/j.chroma.2023.464444