The design, synthesis, and evaluation of N-acylated homoserine lactone analogs that modulate quorum sensing in gram-negative bacteria

Bacteria are capable of “communicating” their local population densities via a process termed quorum sensing (QS). Once they reach sufficiently high cell densities, bacteria alter gene expression levels to initiate a diverse range of group behaviors. Over the past four decades, both chemists and biologists have been actively investigating QS in order to gain further insights into its mechanism and role in host/bacteria interactions. Gram-negative bacteria use N-acylated L-homoserine lactones (AHLs), in conjunction with their cognate LuxR-type receptors, as their primary signaling circuit for QS. The focus of this thesis was to design, synthesize, and characterize synthetic ligands capable of intercepting AHL-mediated QS.;To start, a library of AHLs was designed using the X-ray crystal structure of TraR from Agrobacterium tumefaciens as a guide. An efficient, solid-phase synthetic route to native and non-native AHLs was developed and applied to construct the library. Evaluation of these compounds in reporter gene assays revealed several inhibitors of TraR in A. tumefaciens and LasR in Pseudomonas aeruginosa. The LasR inhibitors were also shown to strongly inhibit P. aeruginosa biofilm growth.;N-Phenylacetanoyl-L-homoserine lactones (PHLs) were amongst the most active QS modulators in our initial work. We synthesized a second-generation library of PHLs, and found that many of these compounds were capable of either inhibiting or, in some cases, strongly inducing LuxR in Vibrio fischeri. These studies revealed one of the first super-activators of QS, 3-nitro PHL.;Based on these results, we synthesized a larger, ∼90 compound collection of non-native AHLs and evaluated these compounds for QS modulation in A. tumefaciens, P. aeruginosa, and V. fischeri. This study represented the first comparative analysis of AHLs across multiple species, and revealed some of the most potent synthetic antagonists and agonists of AHL-mediated QS reported to date. Moreover, several of these ligands exhibited activity in all three species, while other ligands were only active in one or two species. Overall, this thesis demonstrates the vital role that organic chemistry can play in creating molecular tools to study and attenuate bacterial QS.