A Potent and Narrow-Spectrum Antibacterial against Clostridioides difficile Infection

Clostridioides difficile is an anaerobic Gram-positive bacterium that colonizes the gut of patients treated with broad-spectrum antibiotics. The normal gut microflora prevents C. difficile colonization; however, dysbiosis by treatment with broad-spectrum antibiotics causes recurrent C. difficile infection (CDI) in 25% of patients. There are no fully effective antibiotics for multiple recurrent CDIs. We report herein that oxadiazole antibiotics exhibit bactericidal activity against C. difficile vegetative cells. We screened a library of 75 oxadiazoles against C. difficile ATCC 43255. The findings from this collection served as the basis for the syntheses of an additional 58 analogs, which were tested against the same strain. We report a potent (MIC₅₀ = 0.5 μg/mL and MIC₉₀ = 1 μg/mL values for 101 C. difficile strains) and narrow-spectrum oxadiazole (3-(4-(cyclopentyloxy)phenyl)-5-(4-nitro-1H-imidazol-2-yl)-1,2,4-oxadiazole; compound 57), which is not active against common gut bacteria or other tested organisms. Compound 57 is selectively bactericidal against C. difficile and targets cell-wall synthesis.