Discovery and Optimization of Thieno[2,3- <i>d</i> ]pyrimidine Inhibitors of NADH-Quinone Oxidoreductase (NuoD) as Medical Countermeasures against <i>Francisella tularensis</i>

<i>Francisella tularensis</i>, the etiological agent of tularemia, is a highly infectious Gram-negative bacterium that poses a significant threat as a potential biowarfare agent. Although antibiotic resistance is uncommon, the potential for widespread antibiotic use following a bioterrorism event, coupled with the risk of resistant strains engineered by malicious actors, has prompted the development of novel medical countermeasures with unique mechanisms of action that are not exploited by current therapies. High-throughput screening has identified a thieno[2,3-<i>d</i>]pyrimidine lead series exhibiting potent activity against <i>F. tularensis</i>. Through systematic structural modifications at various sites on the thienopyrimidine scaffold, the research team has enhanced antibacterial potency, minimized mammalian cell toxicity, and sought to improve aqueous solubility. Mechanism of action studies suggest that the molecular target is NuoD, the NADH quinone oxidoreductase subunit D. Further efforts will be required to improve metabolic stability prior to nomination of a clinical candidate. This research represents an initial step in the development of a narrow-spectrum antibiotic specifically designed to treat tularemia and safeguard public health against biowarfare threats.