Synthesis and Evaluation of Thiazolidine Amide and N‐Thiazolyl Amide Fluoroquinolone Derivatives

In an effort to develop new fluoroquinolones, we synthesized eight compounds and tested them against a panel of bacteria. The design of these compounds was guided by the introduction of the isothiazoloquinolone motif. The three most active compounds in this series, 8–10 , demonstrated good antibacterial activity against methicillin‐sensitive Staphylococcus aureus and healthcare‐acquired methicillin‐resistant Staphylococcus aureus (MIC 0.62–6.3 µg/mL). Further, when these three active compounds were tested for their inhibitory effects on bacterial enzymes, compound 9 was the most effective agent exhibiting IC 50 values of 33.9 and 116.5 μM in the S. aureus deoxyribonucleic acid (DNA) gyrase supercoiling and topoisomerase IV decatenation assays, respectively.