Development of new synthetic inhibitors of \(Mycobacterium\) \(tuberculosis\) DprE2

DprE2 is an essential enzyme for \(Mycobacterium\) \(tuberculosis\) (M.tb); it is involved in the biosynthesis of decaprenyl monophosphoryl-D-arabinose, a central building block in the synthesis of key constituents of the mycobacterial cell wall. A hit-to-lead optimisation study of two DprE2 hits, discovered by GSK in a high-throughput, whole-cell phenotypic screen, is described. An indepth SAR study of these two hits highlighted the essentiality of the nitrofuran moiety in both structures for potency, and the need to retain the hydrazide moiety for DprE2 target engagement. These observations led us to propose that both hits function as prodrugs and are precursors of the bioactive metabolite(s). This hypothesis was confirmed in a recently developed DprE2 enzymatic assay, which revealed that both hits do not inhibit this enzyme. To probe this hypothesis further, the hits were shown to be substrates for a type I nitroreductase from \(E. coli.\) DprE 1 and Ddn are the only two enzymes that have been reported to bioactivate nitroaromatic drugs in M.tb; however, their involvement in the bioactivation of the DprE2 nitrofuran hits could be excluded. The selection of spontaneous resistant-mutants to the hits indicates the enzymes FGDl and FbiC are involved in mechanisms of resistance to the hits