Synthesis and Antibacterial Evaluation of 3,5-Diaryl-1,2,4-oxadiazole Derivatives

This manuscript reports the synthesis of twenty 3,5-diaryl-1,2,4-oxadiazole derivatives, nine of which are novel compounds. The amidoxime reaction with acyl chlorides obtained from substituted benzoic acids was used. All compounds were tested against five standard (American Type Culture Collection (ATCC)) bacteria: Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, Proteus mirabilis and Staphylococcus aureus. Screening assays were carried out using agar-diffusion technique, in which 100 µM heterocyclic compounds solutions (20% dimethylsulfoxide/water) were employed. The minimum inhibitory concentrations (MIC) of the active compounds were determined by serial dilutions at decreasing concentrations in microtiter plates. The nitrated derivatives gave the best test results, where MIC = 60 µM (E. coli) was the lowest value found for an ortho-nitrated derivative. The activity of these compounds possibly involves a mechanism via free radicals. S. aureus and P. aeruginosa were resistant to all compounds.