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

New N-benzoyl-l-homoserine lactone derivatives bearing a meta-fluorosulfonyl or a meta-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 meta- 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.