Development Of New Chemotherapeutics For Tuberculosis

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Currently this project focusses on four key areas: (1) the chemical synthesis of derivatives of a natural product that targets an enzyme involved in the biosynthesis of the mycobacterial cell wall called thiolactomycin, and (2) the chemical synthesis of analogs of nitroimidazoles such as PA-824, (3) the synthesis and evaluation of inhibitors of synthesis of the mycobacterial siderophore, Mycobactin, and (4) the synthesis and evaluation of substrates for, and inhibitors of, transpeptidases that are responsible for remodeling the TB cell envelope. Project (1) targets mycolic acids which are complex alpha-branched, beta-hydroxy fatty acids that are unique to mycobacteria which are heavily modified by a variety of functional groups. Mycolic acids are biosynthetically produced through an extension of normal fatty acid metabolism. In mycobacteria this is initiated by a "eukaryotic"-like Type I fatty acid synthase, a large multifunctional enzyme that produces primarily short-chain (16-24 carbons) fatty acids that are then substrates for a second fatty acid synthase system that is more typically associated with bacteria. This Type II system appears to be the molecular target for isoniazid as well as other inhibitors such as triclosan. Thiolactomycin is a low molecular weight natural product isolated from a soil Nocardia species that specifically inhibits one component of the bacterial Type II fatty acid synthase system. Although it is a modest inhibitor against most bacteria it has shown in vivo activity in various experimental infections of animals. Following on our structural studies of TLM in which we determined the co-crystal structure of two of our semisynthetic analogs with the homologous enzyme from E. coli we have been working with our collaborators at Stoneybrook to map active-site distances using an approach involving looking for interligand Nuclear Overhauser effects. We have synthesized several potential novel ligands and have been successful at observing such distance-dependent effect which are being used to improve the binding affinity of the lead molecule for the emzyme target. In Project (2) we are synthesizing analogs of nitroimiadazooxazines and nitroimidazooxazoles related to PA-824. PA-824 is currently in Phase II studies in humans for the treatment of tuberculosis. Working with scientists at the Novartis Institute for Tropical Diseases, TBRS scientists have synthesized and characterized a large collection of analogs of these compounds and are advancing these through preclinical studies. In Project (3) we are evaluating approaches to the inhibition of the biosynthesis of the iron-acquiring siderophore of Mycobacterium tuberculosis, Mycobactin. In collaboration with scientists at the Unvieristy of Minnesota's Center for Drug Design we are testing inhibitors of one of the earliest biosynthetic steps in this biosynthetic pathway. Targetting iron acquisition builds upon a strong historical interest in TBRS in understanding the biosynthesis of this molecule which is required for bacterial growth during infection. In project (4) we are exploring the biological role of a unique family of L,D-transpeptidases that are thought to contribute to the inherent beta-lactam resistance of TB. By a combination of biochemical and chemical studies we have established the function of two of the five members of this family and we have synthesized a panel of inhibitors and substrates in the hopes of both elucidating the underlying biology/enzymology as well as developing proof of concept molecules for a TB-specific family of penicillin-like compounds.