Left-Hand Side Exploration of Novel Bacterial Topoisomerase Inhibitors to Improve Selectivity against hERG Binding

Structure–activity relationship (SAR) exploration on the left-hand side (LHS) of a novel class of bacterial topoisomerase inhibitors led to a significant improvement in the selectivity against hERG cardiac channel binding with concomitant potent antimycobacterial activity. Bulky polar substituents at the C-7 position of the naphthyridone ring did not disturb its positioning between two base pairs of DNA. Further optimization of the polar substituents on the LHS of the naphthyridone ring led to potent antimycobacterial activity (Mtb MIC = 0.06 μM) against <i>Mycobacterium tuberculosis</i> (Mtb). Additionally, this knowledge provided a robust SAR understanding to mitigate the hERG risk. This compound class inhibits Mtb DNA gyrase and retains its antimycobacterial activity against moxifloxacin-resistant strains of Mtb. Finally, we demonstrate <i>in vivo</i> proof of concept in an acute mouse model of TB following oral administration of compound <b>19</b>

Pyrazolopyrimidines Establish MurC as a Vulnerable Target in <i>Pseudomonas aeruginosa</i> and <i>Escherichia coli</i>

The bacterial peptidoglycan biosynthesis pathway provides multiple targets for antibacterials, as proven by the clinical success of β-lactam and glycopeptide classes of antibiotics. The Mur ligases play an essential role in the biosynthesis of the peptidoglycan building block, <i>N</i>-acetyl-muramic acid-pentapeptide. MurC, the first of four Mur ligases, ligates l-alanine to UDP-<i>N</i>-acetylmuramic acid, initiating the synthesis of pentapeptide precursor. Therefore, inhibiting the MurC enzyme should result in bacterial cell death. Herein, we report a novel class of pyrazolopyrimidines with subnanomolar potency against both <i>Escherichia coli</i> and <i>Pseudomonas aeruginosa</i> MurC enzymes, which demonstrates a concomitant bactericidal activity against efflux-deficient strains. Radio-labeled precursor incorporation showed these compounds selectively inhibited peptidoglycan biosynthesis, and genetic studies confirmed the target of pyrazolopyrimidines to be MurC. In the presence of permeability enhancers such as colistin, pyrazolopyrimidines exhibited low micromolar MIC against the wild-type bacteria, thereby, indicating permeability and efflux as major challenges for this chemical series. Our studies provide biochemical and genetic evidence to support the essentiality of MurC and serve to validate the attractiveness of target for antibacterial discovery

Novel N‑Linked Aminopiperidine-Based Gyrase Inhibitors with Improved hERG and in Vivo Efficacy against Mycobacterium tuberculosis

DNA gyrase is a clinically validated target for developing drugs against Mycobacterium tuberculosis (Mtb). Despite the promise of fluoroquinolones (FQs) as anti-tuberculosis drugs, the prevalence of pre-existing resistance to FQs is likely to restrict their clinical value. We describe a novel class of N-linked aminopiperidinyl alkyl quinolones and naphthyridones that kills Mtb by inhibiting the DNA gyrase activity. The mechanism of inhibition of DNA gyrase was distinct from the fluoroquinolones, as shown by their ability to inhibit the growth of fluoroquinolone-resistant Mtb. Biochemical studies demonstrated this class to exert its action via single-strand cleavage rather than double-strand cleavage, as seen with fluoroquinolones. The compounds are highly bactericidal against extracellular as well as intracellular Mtb. Lead optimization resulted in the identification of potent compounds with improved oral bioavailability and reduced cardiac ion channel liability. Compounds from this series are efficacious in various murine models of tuberculosis

Aminoazabenzimidazoles, a Novel Class of Orally Active Antimalarial Agents

Whole-cell high-throughput screening of the AstraZeneca compound library against the asexual blood stage of Plasmodium falciparum (<i>Pf</i>) led to the identification of amino imidazoles, a robust starting point for initiating a hit-to-lead medicinal chemistry effort. Structure–activity relationship studies followed by pharmacokinetics optimization resulted in the identification of <b>23</b> as an attractive lead with good oral bioavailability. Compound <b>23</b> was found to be efficacious (ED₉₀ of 28.6 mg·kg^–1) in the humanized P. falciparum mouse model of malaria (<i>Pf</i>/SCID model). Representative compounds displayed a moderate to fast killing profile that is comparable to that of chloroquine. This series demonstrates no cross-resistance against a panel of <i>Pf</i> strains with mutations to known antimalarial drugs, thereby suggesting a novel mechanism of action for this chemical class