Chiral resolution of RS-ofloxacin through a novel diastereomeric cocrystal formation with L-glutamic acid by evaporative crystallization and quantification with capillary electrophoresis

Abstract

Chiral drugs often exhibit significant differences in pharmacological activity between their enantiomers, highlighting the importance of effective chiral separation to enhance therapeutic efficacy and safety. Despite advances in this field, efficient methods for enantiomer separation remain a critical demand, especially for drugs like RS-Ofloxacin (RS-OFX), a chiral fluoroquinolone antibiotic. For RS-OFX, the S-enantiomer exhibits significantly higher potency—approximately 8 to 128 times greater—than the racemic mixture. This highlights the need to accurately separate the enantiomers. This study presents a new cocrystallization-based method for the precise and economical chiral separation of RS-OFX using amino acids by utilizing the formation of diastereomeric cocrystals. L-Glutamic acid (L-Glu) was identified as an appropriate coformer during the screening of potential coformers; consequently, diastereomeric cocrystals of R-OFX:L-Glu and S-OFX:L-Glu were successfully obtained. Melting point data, Fourier-Transform Infrared Spectroscopy (FTIR), and Powder X-Ray Diffraction (PXRD) analyses all confirmed the existence of a new solid state, revealing significant modifications in the crystal structure indicative of cocrystal formation. Capillary electrophoresis (CE) was employed to quickly identify the most suitable solvent mixture for the separation of the diastereomeric pair. The diastereomeric cocrystals exhibited distinct solubility profiles in various solvent mixtures, allowing effective chiral separation through fractional crystallization in methanol:chloroform (50:50, v/v) mixture, yielding 61.82 % enantiomeric excess (ee) of the more active S-OFX:L-Glu. The results of this study suggest that the chiral resolution of racemic APIs through diastereomeric cocrystal formation with amino acids has the potential for scalability and adaptability in other APIs. This approach has the potential to be a valuable tool for the pharmaceutical industry in improving the efficiency of producing enantiopure pharmaceuticals.