Design, synthesis, and antimycobacterial activity of novel ciprofloxacin derivatives

Tuberculosis is the deadliest infectious disease affecting humankind with a death toll of approximately 1.7 million people in 2016. The increasing prevalence of multidrug-resistant strains of the causative pathogen, Mycobacterium tuberculosis (Mtb) which results in reduced effectiveness of the current therapies, underscores the urgent need for the development of new antitubercular drugs. In the search for such drugs, we investigated two series of ciprofloxacin (CPX) derivatives (analogues and hybrids). We herein report the design, synthesis, and biological activity of these series against the human virulent Mtb H37Rv strain in vitro. The small propionyl analogue 11 (MIC₉₀ 1.6 μM; SI > 61) and the large cholesteryl hybrid 32 (MIC₉₀ 2.0 μM; SI > 6) were the most active derivatives, comparable to CPX (MIC₉₀ 1.8 μM). However, the slightly less active but non-cytotoxic para-fluorobenzyl hybrid 28 (MIC₉₀ 3.7 μM; SI 27) was more selective toward bacteria than 32. Thus, the CPX derivatives 11 and 28 were identified as preferred antitubercular hits for further investigation including distribution, metabolism and pharmacokinetic parameters determination and in vivo activity assessment in animal models.