Design, Synthesis and In Vitro Studies of 3-Amidocoumarins as Novel Antibiofilm Agents

Pseudomonas aeruginosa, a life-threatening bacteria listed as a priority pathogen by World Health Organization WHO, is known to cause severe nosocomial infections and fatality in immunocompromised individuals through its quorum sensing (QS) mediated biofilm formation. P. aeruginosa’s antibiotic-resistant biofilms are highly challenging to the existing antibiotic treatment options. There is an urgent clinical need to develop novel alternative therapeutic molecules such as antibiofilm and antiquorum sensing agents to counter the emergence of an unprecedented pace of antibiotic resistance of pathogens. In this context, a library of seventy 3-amidocoumarin derivatives was designed, and docking studies were performed against the P. aeruginosa LasR receptor using AutoDock 4.0. Based on docking results, a final series of sixteen 3-amidocoumarin derivatives (4a–p) were synthesized and evaluated for antibiofilm activity in vitro. Eight compounds significantly inhibited the formation of P. aeruginosa PAO1 biofilm. Compounds 4f, 4l and 4o showed maximum % inhibition in antibiotic-resistant P. aeruginosa PAO1 biofilm formation in the range of 80% to 86%. Further, the structure–activity relationship (SAR) studies revealed that the presence of electron-donating and bromo substituents at benzamido and coumarin moieties, respectively, effectively enhances the antibiofilm activity. In addition, the binding interactions between the synthesized compounds and active sites of the LasR QS receptor (Protein Data Bank Code: 2uv0) in P. aeruginosa were also investigated by molecular docking. The high binding affinities indicate that these compounds might be suitable for development into potent inhibitors of QS and biofilm disruptors.