Reaction intermediate analogues as bisubstrate inhibitors of pantothenate synthetase

Abstract

The biosynthesis of pantothenate, the core of coenzyme A (CoA), has been considered an attractive target for the development of antimicrobial agents since this pathway is essential in prokaryotes, but absent in mammals. Pantothenate synthetase, encoded by the gene panC, catalyzes the final condensation of pantoic acid with β–alanine to afford pantothenate via an intermediate pantoyl adenylate. We describe the synthesis and biochemical characterization of five PanC inhibitors that mimic the intermediate pantoyl adenylate. These inhibitors are competitive inhibitors with respect to pantoic acid and possess submicromolar to micromolar inhibition constants. The observed SAR is rationalized through molecular docking studies based on the reported co-crystal structure of 1a with PanC. Finally, whole cell activity is assessed against wild-type Mtb as well as a PanC knockdown strain where PanC is depleted to less than 5% of wild-type levels.

Validation of CoaBC as a Bactericidal Target in the Coenzyme A Pathway of Mycobacterium tuberculosis

“…35−37 These studies, together with the availability of crystal structures of a number of CoA pathway enzymes for use in structure-guided drug design, provided further support for investigating the CoA pathway as an attractive source of new TB drug targets, encouraging the development of inhibitors against various pathway enzymes. 9,13,38−41 However, despite resource-intensive efforts that led to the identification of potent inhibitors of Mtb PanC and PanK enzymes, these molecules failed to translate into lead compounds with significant whole-cell activity. 13,42,43 Using cKD mutants of Mtb as tools to assess target vulnerability and the target selectivity of small-molecule inhibitors in whole Mtb cells, we 21 and others 43 concluded that these failures might be explained, at least in part, by the relative invulnerability of Mtb to depletion of PanC and PanK.…”

The application of tetracyclineregulated gene expression systems in the validation of novel drug targets in Mycobacterium tuberculosis

“…In the target-based approach to TB drug discovery, compounds that inhibit the biochemical function of the target of interest are identified by high-throughput screening (HTS) of compound libraries or by structure-guided drug design ( Hung et al, 2009 ; Willand et al, 2009 ; Krieger et al, 2012 ). While this approach has yielded compounds with potent inhibitory activity against validated targets, the compounds frequently fail to display whole-cell activity against live bacilli ( Payne et al, 2007 ; Cole and Riccardi, 2011 ; Xu et al, 2014 ). This problem is commonly attributed to issues of permeation, metabolism, and efflux, all of which are likely exacerbated by the comparatively complex intracellular environment in which the drug-target interaction must occur in a cell-based assay.…”

Targeting adenylate-forming enzymes with designed sulfonyladenosine inhibitors

“…The first potent, selective inhibitors of pantothenate synthetase were developed by Abell and colleagues [130, 131], using acyl-AMS analogues (e.g., (2 RS )- 16.4 ) to mimic the pantoyl-AMP reaction intermediate ( 16.2 ), providing sub-μM inhibition of the enzymes from E. coli and Mycobacterium tuberculosis . Subsequently, Aldrich and colleagues [132] reported a stereoselective synthesis of (2 R )- 16.4 as well as additional analogues. Notably, all of these analogues were modified relative to the parent pantoyl-AMS inhibitor ( 16.5 ) to avoid lactonization of the pantoyl side chain.…”