Separation of Ofloxacin and Its Six Related Substances Enantiomers by Chiral Ligand-Exchange Chromatography

Enhanced antibacterial activity of levofloxacin/hydroxypropyl-β-cyclodextrin inclusion complex: In vitro and in vivo evaluation

Levofloxacin is the levo-enantiomer of ofloxacin (a fluoroquinolone class of antibacterial drug). Cyclodextrins (CDs) including hydroxypropyl-β-cyclodextrin (HPβCD) are generally used as a chiral selector for the enantioseparation of some drugs including levofloxacin or as a drug/food nanocarrier for the efficacy improvement of many pharmaceuticals. We hypothesized that the cyclodextrin inclusion is potentially able to further improve the antibacterial activity of levofloxacin. To test this hypothesis, the levofloxacin/HPβCD inclusion complex was prepared by the freeze-drying method and characterized by phase solubility diagram, differential scanning calorimetry (DSC), X-ray diffractometry (XRD), UV-Vis spectrophotometer, and ¹H NMR spectroscopy, confirming the successful HPβCD inclusion of levofloxacin. The in vitro antibacterial effects of HPβCD, levofloxacin, and the levofloxacin/HPβCD inclusion complex against four different bacterial strains in liquid media and on agar plates were determined/compared (an MIC₉₀ of 0.5-1.0 μg/mL for the inclusion complex compared with that of 1.0-2.0 μg/mL for free levofloxacin in liquid). Moreover, the in vivo antibacterial effects of levofloxacin and levofloxacin/HPβCD inclusion complex were tested by using a skin scald model in mice infected with Staphylococcus aureus, and decreased amounts of both bacteria and leukocytes were detected in scalded skin after the inclusion complex treatment. The data revealed that the levofloxacin/HPβCD inclusion complex had an enhanced antibacterial activity compared with free levofloxacin. It implies that cyclodextrins (e.g. HPβCD) may have a beneficial role when using as a chiral selector or as a drug nanocarrier for levofloxacin and that the levofloxacin/HPβCD inclusion complex has the potential of being developed into a pharmaceutical for antibacterial therapies.

Cellulose tris-(3,5-dimethyl phenyl carbamate) as a chiral stationary phase for enantiomeric determination of ofloxacin enantiomers and molecular docking study on the chiral separation mechanism

The higher the BE value, the harder the enantiomer was to elute, which was in agreement with the enantiomer elution order.

Enantioseparation of ofloxacin and its four related substances with ligand exchange-micellar electrokinetic chromatography using copper(II)-L-isoleucine complex as chiral selector

A ligand-exchange micellar electrokinetic capillary electrophoresis system with copper(II)-L-isoleucine complexes as the chiral selector incorporated in micelles of sodium dodecyl sulfate (SDS) was developed for the enantioseparation of ofloxacin and its four related substances (impurities A, C, E, and F). The effects of important parameters affecting separation such as buffer pH, SDS concentration, chiral selector concentration, and organic additive were investigated in detail. Under optimum experimental conditions, enantioseparation of ofloxacin, impurities A, C, E, and F enantiomers was accomplished with resolutions of 4.28, 2.83, 3.40, 3.58, and 2.46, respectively. Further, simultaneous separation of impurities A, C, E, and F enantiomers was achieved using 10 mmol/L NH₄ OAc as the running buffer containing 4 mmol/L copper sulfate,20 mmol/L L-isoleucine, 20 mmol/L SDS, and 5% methanol at pH 8.5. To the best of our knowledge, the simultaneous enantioseparation of four impurities of ofloxacin has not been reported previously.

Use of various β-cyclodextrin derivatives as chiral selectors for the enantiomeric separation of ofloxacin and its five related substances by capillary electrophoresis

A capillary electrophoretic method for the enantioseparation of ofloxacin and its five related substances (potential impurities, indicated as impurities B-F) was developed using β-cyclodextrin derivatives as chiral selectors. To our knowledge, there are no previous studies about using capillary electrophoresis for the separation of impurities B-D. Six β-cyclodextrin derivatives including cationic (piperidine- and cyclohexylamine-), neutral (dimethyl- and hydroxypropyl-), and anionic (carboxymethyl- and sulfated-) β-cyclodextrin derivatives were tested and operational parameters such as buffer pH and concentration of β-cyclodextrin derivatives were investigated. The best resolutions were all obtained with anionic β-cyclodextrin derivatives: ofloxacin, impurities C-F could be best resolved with carboxymethyl-β-cyclodextrin at satisfactory resolutions of 8.27, 9.98, 5.92, 8.49 and 6.78, respectively, while for impurity B, a particularly impressive resolution value, up to 21.38, was observed using sulfated-β-cyclodextrin. The enhancement of enantioseparation observed for the tested analytes using anionic β-cyclodextrin derivatives might be due to some favorable interaction between selectors and analytes. Given the fact that the selection of chiral selector depends on the structures of analytes, with the help of structural similarities and differences of the analytes, the structure-separation relationship was further discussed.