Synthetic Agents for the Derivatization of N-Acyl Homoserine Lactones

Quorum sensing is a process of chemical communication in bacteria that enables bacteria to coordinate group function, including unified gene expression. As the quorum sensing mechanism is in part responsible for the virulent activity of many bacteria, inhibiting the communication pathway has the potential to lead to the development of novel antibiotics. The central focus of this dissertation is the investigation of strategies for chemically activating and modifying N-acyl homoserine lactones (AHLs), the agent of chemical communication in gram-negative bacteria. Probing the inherent reactivity of the AHLs is critical to understanding their evolved function while uncovering novel modes of inhibition and tools for chemical biology. Initial studies began by utilizing small molecule thiourea and guanidine-based catalysts for accelerating ring-opening reactions of the AHL by amines. The supramolecular catalysts achieved ten and sixty-five fold increases in reaction rate, respectively, for the addition of piperidine to the characteristic α-amino-γ-butyrolactone moiety. This demonstrated the susceptibility of the chemical messengers to be activated for nucleophilic attack through appropriate arrangement of hydrogen bond donors and acceptors. Further studies on the derivatization of the AHLs continued with the development of a hydrazine-mediated transamidation reaction under aqueous conditions. Experimental evidence supports the progression of the reaction via a condensation at the α-carbon of the chemical messenger, followed by an intramolecular cyclization to cleave the AHL at the amide bond. The reaction is operable at physiological pH and is specific for the 3-oxo-AHL in the presence of other AHLs. To rapidly identify a scaffold of non-covalent interactions to increase rate of the transamidation reaction, a reactive tagging assay was developed for high-throughput screening of hydrazine-containing peptide libraries. Combinatorial libraries were synthesized with designer Boc-protected hydrazines and screened against the AHL. Colorimetric hit development was achieved through a strained-cyclooctyne functionalized dye selecting peptides that react most readily with the chemical messenger. First generation library hits were resynthesized and screened for biofilm and quorum sensing inhibition. Further library development and screening holds the potential to identify peptides sequences and structures with the greatest propensity for rapidly functionalizing the 3-oxo-AHL.Doctor of Philosoph