Quorum sensing in Pseudomonas aeruginosa: Design, synthesis and analysis of autoinducer analogs as antagonists for the quorum sensing pathway

Quorum sensing (QS) regulates production of virulence factors and maturation of biofilm in many bacteria, including Pseudomonas aeruginosa. The QS cascade is activated by the interaction of bacterial signaling molecules, called autoinducers (AIs), with their corresponding regulatory proteins.; Our initial studies with the library of AI analogs based on the P. aeruginosa AIs led to the identification of new structural analogs of homoserine lactone that agonize the QS system. However, the stereochemical requirements of these agonists remain to be determined. In the first part of this dissertation we report a series of studies to define the stereochemical preferences of the synthetic agonists. One of the key findings of this work is that the ring structure and the absolute and relative stereochemistry of the amide and hydroxyl groups dictate the agonist activity. This study aids in determining important structural and stereochemical characteristics necessary for interaction with the QS regulatory proteins, thus expanding our understanding about their microenvironment.; With the growing number of reports providing evidence for the involvement of rhl circuit in virulence, and our earlier study which pointed out the differences between the microenvironment of the two P. aeruginosa QS regulators LasR and RhlR directed us towards synthesizing and screening a library of C4-L-HSL analogs. This study led to the identification of novel structural scaffolds and pointed out to some requirements for an antagonist and contribution of hydrophobic factors, H-bonding interactions and steric factors. We believe that combination of antagonists for the las and rhl cascade would provide effective therapy for Pseudomonal infections.; Additionally, we carried out docking studies for the agonists from the study of enantiomers and C4 library antagonists to gain better understanding regarding the interaction of these derivatives with the regulatory proteins. It is hoped that these results would assist in rational design of antagonists.; In another part of this work synthetic tools were utilized to understand regulatory mechanisms in plant-associated bacteria such as B. glumae and P. fluorescens. In addition, the applicability of the C4 library derivatives was investigated in management of oral biofilms.