Design, Synthesis and Antibacterial Studies of 1,3,4‐Oxadiazole‐Fluoroquinolone Hybrids and Their Molecular Docking Studies

Abstract A series of novel hybrids built on fluoroquinolone skeleton were synthesized by introducing 1,3,4‐oxadiazole derivatives to the C‐7 site of ciprofloxacin or norfloxacin. In vitro antibacterial evaluation showed that hybrids 4 b – d (5‐(hydroxyphenyl)‐1,3,4‐oxadiazol‐2‐yl substituted ciprofloxacin) were an increased activity against Staphylococcus aureus , with a minimum inhibitory concentration (MIC) of ≤0.125 μg/mL, four times superior to the parent drug. Hybrids 4 b – e ( 4 e , 5‐(4‐(trifluoromethyl) phenyl)‐1,3,4‐oxadiazol‐2‐yl substituted ciprofloxacin) also exhibited significant activity against methicillin‐resistant S. aureus (MRSA), resistant to the parent drug. All the hybrids demonstrated a bactericidal effect on standard bacteria with the MBC value not exceeding four times of their corresponding MIC values. In time‐killing assays, 4 c demonstrated a superior bactericidal action in eradicating S. aureus and E. coli within 2 h, respectively, equipotent to ciprofloxacin. In the molecular docking study, hybrids 4 c exhibited a high binding affinity for type IV topoisomerase with a minimum binding energy of −10.2 kcal/mol.