Structure-Aided Design of a LuxR-Type Quorum Sensing SuFEx-Based Potential Inhibitor: Covalent or Competitive Inhibition?

New <i>N</i>-benzoyl-l-homoserine lactone derivatives bearing a <i>meta</i>-fluorosulfonyl or a <i>meta</i>-methylsulfonyl group have been designed, synthesized and evaluated as quorum sensing (QS) inhibitors. Docking simulations involving the structure of several targeted LuxR-type receptors suggested that a sulfonyl substituent on the benzene ring can trigger interactions within the binding site, possibly consistent with either covalent SuFEx reaction targeting a tyrosine residue or competitive interaction with additional hydrogen bonding. Biological evaluation of the two <i>meta</i>- methyl or fluorosulfonyl-benzoyl acylhomoserine lactone (AHL) analogs as LuxR-regulated quorumsensing inhibitors showed a significant effect for the fluorosulfonyl derivative with an IC₅₀ value of 15 ± 2 µM, while the methylsulfonyl was found to be a weak inhibitor. The stability of the fluorosulfonyl derivative was confirmed by kinetic studies based on ¹⁹F NMR experiments. Investigations dedicated to defining the mechanism of action, either covalent or competitive, were achieved through experiments including inhibition assays without or with pre-incubation in the bacterial medium, and LC/MS analysis with the ExpR protein. The results strongly suggest that the type of inhibition is a competitive one.