[Preparation and chiral separation performance evaluation of a high performance liquid chromatography stationary phase based on a ［2+4］-type chiral porous organic cage Pim].

Porous organic cages （POCs） represent a class of emerging porous materials assembled from discrete three-dimensional cage-like molecules via intermolecular interactions. Owing to their good solubility and unique pore structures， they show great potential in gas adsorption， molecular recognition， separation， catalysis， and sensing. In this study， a phenolphthalein-based tetraaldehyde compound was synthesized via the Duff reaction using phenolphthalein as the substrate and trifluoroacetic acid （TFA） combined with hexamethylenetetramine （HMTA） as the formylation reagent. Subsequently， a ［2+4］-type chiral imine POC， Pim （C72H68N8O8）， was constructed by reacting the tetraaldehyde precursor with （1R，2R）-（-）-1，2-diaminocyclohexane via imine condensation. The synthesized Pim was functionalized with alkenyl groups using 5-bromo-1-pentene and then immobilized onto thiol-modified silica via thiol-ene click chemistry to afford a novel chiral stationary phase （CSP） for high performance liquid chromatography （HPLC）. The successful syntheses of tetraaldehyde compound， Pim， and CSP were characterized by nuclear magnetic resonance （NMR）， fourier transform infrared spectroscopy （FT-IR）， electrospray ionization mass spectrometry （ESI-MS）， thermogravimetric analysis （TGA）， and elemental analysis （EA）. The chiral separation performance of this CSP was evaluated under both normal-phase （NP） and reversed-phase （RP） HPLC separation modes. The results demonstrated that the CSP exhibits excellent chiral separation capabilities in both two separation modes. Under NP-HPLC conditions， ten racemates were resolved， including five with baseline separation. Under RP-HPLC conditions， nine racemates were resolved， of which eight achieved baseline separation. Furthermore， this CSP exhibits good chiral separation complementarity with two widely used commercial columns， Chiralpak AD-H and Chiralcel OD-H， showing the ability to resolve some chiral compounds that cannot be resolved or are poorly resolved by the two commercial columns. The effects of analyte injection mass and column temperature on chiral separation performance of the column were also investigated. Additionally， the prepared HPLC column exhibits good repeatability and stability. After hundreds of injections， no significant changes were observed in the retention times and resolutions compared to its initial performance， with relative standard deviations （RSDs， n=5） of ≤1.50% and ≤1.92%， respectively. Meanwhile， after the column was placed and stored for one month， its separation performance showed no significant change compared with that at the initial stage of column use， and the RSDs （n=3） of retention time and resolution were ≤1.88% and ≤2.26%， respectively. This study confirms that the chiral POC Pim is a promising material for HPLC chiral separation， providing significant theoretical and experimental support for the development of novel POC-based CSPs and holding great significance for expanding the POC-based CSPs.