There is an urgent need for new antibacterial drugs that are effective against infections caused by multidrug-resistant pathogens. Novel nonfluoroquinolone inhibitors of bacterial type II topoisomerases (DNA gyrase and topoisomerase IV) have the potential to become such drugs because they display potent antibacterial activity and exhibit no target-mediated cross-resistance with fluoroquinolones. Bacterial topoisomerase inhibitors that are built on a tetrahydropyran ring linked to a bicyclic aromatic moiety through a syn-diol linker show potent anti-Gram-positive activity, covering isolates with clinically relevant resistance phenotypes. For instance, analog 49c was found to be a dual DNA gyrase-topoisomerase IV inhibitor, with broad antibacterial activity and low propensity for spontaneous resistance development, but suffered from high hERG K(+) channel block. On the other hand, analog 49e displayed lower hERG K(+) channel block while retaining potent in vitro antibacterial activity and acceptable frequency for resistance development. Furthermore, analog 49e showed moderate clearance in rat and promising in vivo efficacy against Staphylococcus aureus in a murine infection model.

Novel antibacterial drugs that are effective against infections caused by multidrug resistant pathogens are urgently needed. In a previous report, we have shown that tetrahydropyran-based inhibitors of bacterial type II topoisomerases (DNA gyrase and topoisomerase IV) display potent antibacterial activity and exhibit no target-mediated cross-resistance with fluoroquinolones. During the course of our optimization program, lead compound 5 was deprioritized due to adverse findings in cardiovascular safety studies. In the effort of mitigating these findings and optimizing further the pharmacological profile of this class of compounds, we have identified a subseries of tetrahydropyran-based molecules that are potent DNA gyrase and topoisomerase IV inhibitors and display excellent antibacterial activity against Gram positive pathogens, including clinically relevant resistant isolates. One representative of this class, compound 32d, elicited only weak inhibition of hERG K(+) channels and hNaV1.5 Na(+) channels, and no effects were observed on cardiovascular parameters in anesthetized guinea pigs. In vivo efficacy in animal infection models has been demonstrated against Staphylococcus aureus and Streptococcus pneumoniae strains.

There is an urgent unmet medical need for novel antibiotics that are effective against a broad range of bacterial species, especially multidrug resistant ones. Tetrahydropyran-based inhibitors of bacterial type II topoisomerases (DNA gyrase and topoisomerase IV) display potent activity against Gram-positive pathogens and no target-mediated cross-resistance with fluoroquinolones. We report our research efforts aimed at expanding the antibacterial spectrum of this class of molecules toward difficult-to-treat Gram-negative pathogens. Physicochemical properties (polarity and basicity) were considered to guide the design process. Dibasic tetrahydropyran-based compounds such as 6 and 21 are potent inhibitors of both DNA gyrase and topoisomerase IV, displaying antibacterial activities against Gram-positive and Gram-negative pathogens (Staphylococcus aureus, Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii). Compounds 6 and 21 are efficacious in clinically relevant murine infection models.

Our strategy to combat resistant bacteria consisted of targeting the GyrB/ParE ATP-binding sites located on bacterial DNA gyrase and topoisomerase IV and not utilized by marketed antibiotics. Screening around the minimal ethyl urea binding motif led to the identification of isoquinoline ethyl urea 13 as a promising starting point for fragment evolution. The optimization was guided by structure-based design and focused on antibacterial activity in vitro and in vivo, culminating in the discovery of unprecedented substituents able to interact with conserved residues within the ATP-binding site. A detailed characterization of the lead compound highlighted the potential for treatment of the problematic fluoroquinolone-resistant MRSA, VRE, and S. pneumoniae, and the possibility to offer patients an intravenous-to-oral switch therapy was supported by the identification of a suitable prodrug concept. Eventually, hERG K-channel block was identified as the main limitation of this chemical series, and efforts toward its minimization are reported.

UDP-3-O-((R)-3-hydroxymyristoyl)-N-glucosamine deacetylase (LpxC) is as an attractive target for the discovery and development of novel antibacterial drugs to address the critical medical need created by multidrug resistant Gram-negative bacteria. By using a scaffold hopping approach on a known family of methylsulfone hydroxamate LpxC inhibitors, several hit series eliciting potent antibacterial activities against Enterobacteriaceae and Pseudomonas aeruginosa were identified. Subsequent hit-to-lead optimization, using cocrystal structures of inhibitors bound to Pseudomonas aeruginosa LpxC as guides, resulted in the discovery of multiple chemical series based on (i) isoindolin-1-ones, (ii) 4,5-dihydro-6H-thieno­[2,3-c]­pyrrol-6-ones, and (iii) 1,2-dihydro-3H-pyrrolo­[1,2-c]­imidazole-3-ones. Synthetic methods, antibacterial activities and relative binding affinities, as well as physicochemical properties that allowed compound prioritization are presented. Finally, in vivo properties of lead molecules which belong to the most promising pyrrolo-imidazolone series, such as 18d, are discussed.