Synthesis and Antimicrobial Studies of New Antibacterial Azo-Compounds Active against Staphylococcus aureus and Listeria monocytogenes

Abstract

Some novel (phenyl-diazenyl)phenols (<b>4a</b>-<b>m</b>) were designed and synthesized to be evaluated for their antibacterial activity. Starting from an active previously-synthesized azobenzene chosen as lead compound, we introduced some modifications and optimization of the structure, in order to improve solubility and drug conveyance. Structures of all newly-synthesized compounds were confirmed by ¹H nuclear magnetic resonance (NMR), mass spectrometry, and UV-Vis spectroscopy. Antibacterial activity of the new compounds was tested with the dilution method against the bacteria strains <i>Listeria monocytogenes</i>, <i>Staphylococcus aureus</i>, <i>Escherichia coli</i>, and <i>Pseudomonas aeruginosa</i> PAO1. All the compounds were selectively active against Gram-positive bacteria. In particular, compounds <b>4d</b>, <b>4h</b>, and <b>4i</b> showed the highest activity against <i>S. aureus</i> and <i>Listeria monocytogenes</i>, reaching remarkable MIC₁₀₀ values of 4 μg/mL and 8 μg/mL. The relationship between antimicrobial activity and compound structure has suggested that the presence of hydroxyl groups seems to be essential for antimicrobial activity of phenolic compounds.