Nadifloxacin: Multimilligram Enantioresolution and Enantioselective Ecotoxicological Studies

Emerging contaminants are an increasing global concern, with antibiotics representing a notable case due to their continuous release and possible contribution to antimicrobial resistance. Fluoroquinolones (FQs) combine high stability, low biodegradability, and biological activity at trace levels, which result in persistence, ecotoxicity, and bioaccumulation in aquatic systems. Nadifloxacin (NAD) is a chiral FQ prescribed as a racemate for dermatological infections, but (S)-NAD is more potent than the racemate and 64 to 256 times more active than (R)-NAD against both Staphylococcus aureus and Propionibacterium acnes, as well as other gram-positive and gram-negative pathogens. Though the stereochemistry plays a decisive role in both pharmacological activity and environmental fate, the enantioselective ecotoxicological evaluation of NAD is of high importance. Thus, this work described the enantioseparation of NAD by chiral liquid chromatography (cLC) on a Lux amylose-1 column (4.6 mm I.D. × 250 mm L, particle size 5 μm) under normal-phase conditions. Optimized analytical conditions provided good chromatographic parameters (Rs = 5.92, α = 2.77, retention 6-10 min) and were successfully scaled up to semipreparative enantioseparation on a CHIRALPAK AD-H DAICEL column (10 mm I.D. × 250 mm L, particle size 5 μm), allowing the separation of both enantiomers in > 98% enantiomeric purity. The absolute configuration and the elution order of the enantiomers were determined by the agreement between the experimental and calculated data of electronic circular dichroism. The acute ecotoxicity of the NAD racemate and its enantiomers was evaluated using Daphnia magna as an aquatic model organism.