Identification and Quantification of Related Impurities of a Novel Ketolide Antibiotic Nafithromycin

Nafithromycin (NFT, WCK 4873) is a novel antimicrobial drug being developed to treat infections caused by Gram-positive bacteria. It is a second-generation drug of the lactone ketolide class. A mass spectrometry-compatible reversed-phase liquid chromatographic method was developed to separate and identify the impurities in NFT. Forced degradation (FD) study ensured specificity of the method and revealed the probable degradation products. Seven process impurities and five degradation products were chromatographically resolved and identified based on the protonated molecule peak and product ions. Process impurities were synthesized and characterized for identity and purity. Separation was achieved on the XTerra C18 stationary phase using the binary gradient method. Mobile phase ‘A’ constituted of a mixture of an aqueous solution of ammonium acetate (pH 9.0), acetonitrile and methanol in the ratio of (48:27:25, v/v/v). Mobile phase ‘B’ constituted of an aqueous solution of ammonium acetate (pH 9.0) and acetonitrile in the ratio of (05:95, v/v). The method was validated for accurate and precise quantification of the impurities. The developed method was employed for quality control and stability studies of the NFT drug substance used for pre-clinical and clinical studies. Graphical Abstract