The natural antibiotic fosmidomycin acts via inhibition of 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR), an essential enzyme in the non-mevalonate pathway of isoprenoid biosynthesis. Fosmidomycin is active on Mycobacterium tuberculosis DXR (MtDXR), but it lacks antibacterial activity probably because of poor uptake. α-Aryl substituted fosmidomycin analogues have more favorable physicochemical properties and are also more active in inhibiting malaria parasite growth. We have solved crystal structures of MtDXR in complex with 3,4-dichlorophenyl substituted fosmidomycin analogues; these show important differences compared to our previously described forsmidomycin–DXR complex. Our best inhibitor has an IC50 = 0.15 μM on MtDXR but still lacked activity in a mycobacterial growth assay (MIC > 32 μg/mL). The combined results, however, provide insights into how DXR accommodates the new inhibitors and serve as an excellent starting point for the design of other novel and more potent inhibitors, particularly against pathogens where uptake is less of a problem, such as the malaria parasite.

Treatment of tuberculosis (TB) is impaired by the long duration and complexity of therapy and the rising incidence of drug resistance. There is an urgent need for new agents with improved efficacy, safety, and compatibility with combination chemotherapies. Oxazolidinones offer a potential new class of TB drugs, and linezolid-the only currently approved oxazolidinone-has proven highly effective against extensively drug-resistant (XDR) TB in experimental trials. However, widespread use of linezolid is prohibited by its significant toxicities. AZD5847, a novel oxazolidinone, demonstrates improved in vitro bactericidal activity against both extracellular and intracellular M. tuberculosis compared to that of linezolid. Killing kinetics in broth media and in macrophages indicate that the rate and extent of kill obtained with AZD5847 are superior to those obtained with linezolid. Moreover, the efficacy of AZD5847 was additive when tested along with a variety of conventional TB agents, indicating that AZD5847 may function well in combination therapies. AZD5847 appears to function similarly to linezolid through impairment of the mycobacterial 50S ribosomal subunit. Future studies should be undertaken to further characterize the pharmacodynamics and pharmacokinetics of AZD5847 in both in vitro and animal models as well is in human clinical trials.T uberculosis (TB), caused by Mycobacterium tuberculosis, continues to pose an enormous threat to global public health (1). In 2010, nearly 9 million people were infected with M. tuberculosis and 1.4 million died from the disease (1, 2). While the vast majority of cases of drug-sensitive TB are curable with appropriate drug therapy, rates of treatment success have stagnated due to the long duration and complexity of therapy and the rising incidence of drug resistance (1, 3, 4). Standard TB therapy alone involves four drugs taken for at least 6 months, and treatment for multidrugresistant (MDR) and extensively drug-resistant (XDR) TB requires administration of more toxic antibiotics-including at least one injectable-for durations of 1 to 2 years (5). Often, patients are coinfected with HIV, which further complicates treatment due to deleterious potential drug-drug interactions between TB medications and antiretrovirals (6). Despite the limitations of current treatment options, only one new class of TB drugs has been approved in the past 40 years (7). There is an urgent need for new TB drugs with greater efficacy, reduced toxicities, and improved compatibility with antiretrovirals.Recent evidence demonstrates that linezolid, the only member of the oxazolidinone class of antimicrobials currently on the market, has efficacy against MDR TB (8-11). The potential of linezolid for the treatment of TB is limited due to the incidence of serious adverse effects, including cytopenias, neuropathies, lactic acidosis, and rhabdomyolysis (12, 13). Risk increases with increasing dose and duration, which is particularly problematic, given the typical extended course of chemotherapy for TB. A numbe...

M. tuberculosis thymidylate kinase (Mtb TMK) has been shown in vitro to be an essential enzyme in DNA synthesis. In order to identify novel leads for Mtb TMK, we performed a high throughput biochemical screen and an NMR based fragment screen through which we discovered two novel classes of inhibitors, 3-cyanopyridones and 1,6-naphthyridin-2-ones, respectively. We describe three cyanopyridone subseries that arose during our hit to lead campaign, along with cocrystal structures of representatives with Mtb TMK. Structure aided optimization of the cyanopyridones led to single digit nanomolar inhibitors of Mtb TMK. Fragment based lead generation, augmented by crystal structures and the SAR from the cyanopyridones, enabled us to drive the potency of our 1,6-naphthyridin-2-one fragment hit from 500 μM to 200 nM while simultaneously improving the ligand efficiency. Cyanopyridone derivatives containing sulfoxides and sulfones showed cellular activity against M. tuberculosis. To the best of our knowledge, these compounds are the first reports of non-thymidine-like inhibitors of Mtb TMK.

Mycobacterium tuberculosis glutamine synthetase (MtGS) is a promising target for antituberculosis drug discovery. In a recent high-throughput screening study we identified several classes of MtGS inhibitors targeting the ATP-binding site. We now explore one of these classes, the 2-tert-butyl-4,5-diarylimidazoles, and present the design, synthesis, and X-ray crystallographic studies leading to the identification of MtGS inhibitors with submicromolar IC50 values and promising antituberculosis MIC values.

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