Aminophenyl chalcones potentiating antibiotic activity and inhibiting bacterial efflux pump

•The APCHAL chalcone presented a synergistic effect with gentamicin.•When a chlorine radical was added to this structure (ACLOPHENYL), the synergistic effect was lost.•Docking studies have shown that the electronegativity of the chlorine impairs the ability to bind to the efflux pump. Chalcones and their derivatives are substances of great interest for medicinal chemistry due to their antibacterial activities. As the bacterial resistance to clinically available antibiotics has become a worldwide public health problem, it is essential to search for compounds capable of reverting the bacterial resistance. As a possibility, the chalcone class could be an interesting answer to this problem. The chalcones (2E)-1-(4′-aminophenyl)-3-(phenyl)‑prop-2-en-1-one (APCHAL), and (2E)-1-(4′-aminophenyl)-3-(4-chlorophenyl)‑prop-2-en-1-one (ACLOPHENYL) were synthesized by the Claisen-Schmidt condensation and characterized by 1H and 13C nuclear magnetic resonance (NMR), Fourier-transform infrared (FT-IR), and mass spectrometry (MS), In addition, microbiological tests were performed to investigate the antibacterial activity, modulatory potential, and efflux pump inhibition against Staphylococcus aureus (S. aureus) multi-resistant strains. Regarding the S. aureus Gram-positive model, the APCHAL presented synergism with gentamicin and antagonism with penicillin. APCHAL reduced the Minimum inhibitory concentration (MIC) of gentamicin by almost 70%. When comparing the effects of the antibiotic modifying activity of ACLOPHENYL and APCHAL, a loss of synergism is noted with gentamicin due to the addition of a chlorine to the substance structure. For Escherichia coli (E. coli) a total lack of effect, synergistic or antagonistic, was observed between ACLOPHENYL and the antibiotics. In the evaluation of inhibition of the efflux pump, both chalcones presented a synergistic effect with norfloxacin and ciprofloxacin against S. aureus, although the effect is much less pronounced with ACLOPHENYL. The effect of APCHAL is particularly notable against the K2068 (MepA overexpresser) strain, with synergistic effects with both ciprofloxacin and ethidium bromide. The docking results also show that both compounds bind to roughly the same region of the binding site of 1199B (NorA overexpresser), and that this region overlaps with the preferred binding region of norfloxacin. The APCHAL chalcone may contribute to the prevention or treatment of infectious diseases caused by multidrug-resistant S. aureu