RhlR antagonist 1 is a highly effective antagonist of the RhlR protein, showing an IC50 value of 26 μM. It exhibits selective antagonistic activity against RhlR, with minimal effect on LasR and PqsR. RhlR antagonist 1 strongly inhibits biofilm formation in both static and dynamic environments and reduces the production of virulence factors, such as rhamnolipid and pyocyanin, in P. aeruginosa. These characteristics make RhlR antagonist 1 a valuable tool for the development of molecules that modulate quorum sensing and control P. aeruginosa infections [1].