Enantioseparation of proton pump inhibitors using multimodal chiral cation exchangers

The growing demand for enantioselective pharmaceutical analysis has prompted the development of novel chiral stationary phases (CSPs) tailored for high-performance liquid chromatography (HPLC). More recently, particular attention has been paid to multimodal (mixed-mode) stationary phases, which combine several interaction principles and broaden the applicability of the CSP. In this study, multimodal CSPs based on N-(3,5-dinitrobenzoyl)-tyrosine derivatives, featuring both donor-acceptor and ion-exchange/ion-pairing functionalities, were applied for the enantioseparation of omeprazole, pantoprazole, and lansoprazole, widely used proton pump inhibitors. Two in-house-developed CSPs were evaluated under multiple chromatographic modes, using polar-organic (PO), polar-organic-water (POW), and normal-phase (NP) mobile-phase conditions. PO and POW modes were selected as optimal due to their MS compatibility and sustainable solvent composition. The effect of mobile-phase composition, including MeCN/MeOH ratio and acidic/basic additives, on retention and enantioselectivity was systematically studied. The optimized method enabled the direct analysis of omeprazole enantiomers in a commercial tablet formulation using LC-MS. In parallel, molecular dynamics (MD) simulations were employed to investigate the mechanistic basis of chiral recognition at the molecular level. Key interaction energies and conformational behaviors were analyzed, supporting the experimentally observed enantioselectivity trends and providing insight into the spatial arrangement of the chiral selector-analyte associates. These findings highlight the potential of tyrosine-based multimodal CSPs for robust enantioselective analysis of PPI-type drugs under UV and MS-compatible conditions.