Abstract A series of imidazo[1,2-a]pyridinyl-chalcones (5a–k) have been synthesized by claisen chimdt condensation between 3–acetyl-2-methylimidazo[1,2-a]pyridine (3) and various benzaldehydes (4a–k). The structures of all the synthesized compounds have been confirmed by 1H NMR, 13C NMR and mass spectral data. The antibacterial activities of these synthesized compounds were tested against sensible and clinical strains of Gram-positive and Gram-negative bacteria, using commercially available antibiotics, Azithromycin, Cefotaxim and Ciprofloxacin as reference drugs. The antibiogram showed that the clinical strains used were either intermediate or resistant to the antibiotics tested. The range of minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) was 200 – 3.125 μg /mL against ATCC and clinical strains. With MICs values of 6.25 μg / mL and 3.125μg / mL, compound 5h was found to be the most potent of all, respectively against clinical and reference strains of Gram-positive bacterium (S. aureus). Structure activity relationship studies revealed that the presence of electron-withdrawing substituent or of bulkier group at phenyl ring is favorable to low bactericidal activities and a shrinking of the spectrum of action toward P. aeruginosa. On the contrary, the presence of an electron donor substituent on the same nucleus is closely related to the broadening of the spectrum of activity against Gram-positive and Gram-negative bacteria, including the drug-resistant species of E. coli.
Keyword: imidazo[1,2-a]pyridine; chalcones, ; Antibacterial, S. aureus, , P. aeruginosa, E. coli.