Design, synthesis, and evaluation of potential inhibitors of the tryptophan biosynthesis pathway

The development of bacterial antibiotic resistance is an ever increasing problem in the pharmaceutical world in need of a solution. New classes of antibiotic compounds that employ different mechanisms for inhibiting bacterial reproduction are essential in helping combat this observed rise in resistance. The enzymes that are involved in amino acid biosynthesis represent a promising group of potential targets in the development of novel antibacterial compounds. Specifically, compounds that inhibit the enzymes within the tryptophan biosynthesis pathway are of interest. Tryptophan is an essential amino acid that cannot be synthesized natively in humans but is produced through biosynthetic pathways in bacteria and plants. Many of the enzymes in the tryptophan biosynthesis pathway contain no human homologues. This makes the tryptophan biosynthesis pathway ideal for investigation of potential inhibitors of enzymes required for survival of potentially harmful bacteria.;This work focuses on designing and producing inhibitors which target the fourth step of the tryptophan biosynthesis pathway, in which 1-( o-carboxyphenylamino)-1-deoxyribulose 5-phosphate (CdRP) is converted to indole-3-glycerol phosphate (IGP) via indole-3-glycerol phosphate synthase (IGPS). Using CdRP crystal structures and docking studies previously completed by Hennig, the binding pocket in the active site was identified and the essential amino acid residues in the conversion of CdRP to IGP discovered. CdRP fragment screening showed that mimics of the sugar moiety possessed high affinity for the active site, while anilines exhibited effective enzymatic inhibition. A first generation library of molecules was therefore designed to contain a simple amine linkage between the substituted arene and sugar chains of CdRP. Using information gathered from the synthesis of the first generation library, a second generation library of compounds was designed to allow rapid access to the desired library of compounds while maintaining the key substituents needed for active site binding. Compounds within this library were designed to prevent either the decarboxylation or irreversible indole ring formation in the conversion of CdRP to IGP. The synthetic approach used in an attempt to achieve this revolved around the inclusion of isoxazoline compounds with varying substituents. These compounds were afforded via 1,3-dipolar cycloaddition chemistry. The complete synthesis and design of a second generation library of potential inhibitors and associated results from in vitro screening studies are presented.