Tuberculosis continues to be the leading cause of death by a pathogen. The prolonged course of drug therapy necessary to cure Mycobacterium tuberculosis (Mtb) infections, and the continuing development of multiply drug resistant (MDR) and extremely drug resistant (XDR) strains of Mtb emphasize the ongoing need for new classes of antimycobacterials. Genomics together with biological studies have provided a number of new antibacterial targets. However, features unique to this bacillus - such as its slow rate of growth, its multiple growth states (including latency), and its nearly impenetrable cell wall make drug development challenging. One recently identified pathway unique to mycobacteria and some related actinomycetes is that of mycothiol biosynthesis and mycothiol-mediated detoxification, and mycothiol biosynthesis has been shown to be essential for growth of Mtb. This project seeks to design or discover inhibitors of mycothiol biosynthesis and detoxification, and to evaluate such inhibitors against Mtb. In addition to the chemistry efforts, this project requires substantial efforts in protein production and assay development. Progress in 2006 includes development of an M. smegmatisE.coli shuttle vector for expression of the essential biosynthetic enzyme MshC and large scale production of MshC for future screening efforts and structural studies. Synthetic efforts included construction of a series of substrate-mimic mycothiol analogs built upon a quinic acid-derived scaffold to yield pseudo-disaccharide azides in place of the natural substrate GlcN-Ins. Use of a polymer supported triphenyl phosphine reagent allowed near quantitative derivatization of the azide with commercially available acid chlorides to yield several low micromolar inhibitors of the detoxification enzyme mycothiol-S-conjugate amidase.
