The uncontrolled spread of drug-resistant tuberculosis (DR-TB) clinical cases necessitates the urgent discovery of newer chemotypes with novel mechanisms of action. Here, we report the chemical synthesis of rationally designed novel transition-state analogues (TSAs) by targeting the cyclization (Cy) domain of phenyloxazoline synthase (MbtB), a key enzyme of the conditionally essential siderophore biosynthesis pathway. Following bio-assay-guided evaluation of TSA analogues preferentially in iron-deprived and iron-rich media to understand target preferentiality against a panel of pathogenic and non-pathogenic mycobacteria strains, we identified a hit, i.e., TSA-5. Molecular docking, dynamics, and MMPBSA calculations enabled us to comprehend TSA-5’s stable binding at the active site pocket of MbtB_Cy and the results imply that the MbtB_Cy binding pocket has a strong affinity for electron-withdrawing functional groups and contributes to stable polar interactions between enzyme and ligand. Furthermore, enhanced intracellular killing efficacy (8 μg/mL) of TSA-5 against Mycobacterium aurum in infected macrophages is noted in comparison to moderate in vitro antimycobacterial efficacy (64 μg/mL) against M. aurum. TSA-5 also demonstrates whole-cell efflux pump inhibitory activity against Mycobacterium smegmatis. Identification of TSA-5 by focusing on the modular MbtB_Cy domain paves the way for accelerating novel anti-TB antibiotic discoveries.

中文翻译：

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合理设计的新型苯恶唑啉合酶抑制剂：化学合成和生物学评价，加速新型抗分枝杆菌抗生素的发现


耐药结核病（DR-TB）临床病例的不受控制的传播需要迫切发现具有新作用机制的新化学型。在这里，我们报告了通过靶向苯基恶唑啉合酶（MbtB）的环化（Cy）结构域，合理设计的新型过渡态类似物（TSA）的化学合成，苯基恶唑啉合酶（MbtB）是条件必需的铁载体生物合成途径的关键酶。在生物测定指导下优先在缺铁和富铁培养基中评估 TSA 类似物，以了解针对一组致病性和非致病性分枝杆菌菌株的靶标优先性，我们发现了一个热门产品，即 TSA-5。分子对接、动力学和 MMPBSA 计算使我们能够理解 TSA-5 在 MbtB_Cy 活性位点袋上的稳定结合，结果表明 MbtB_Cy 结合袋对吸电子官能团具有很强的亲和力，有助于稳定的极性相互作用。酶和配体。此外，与针对金黄色分枝杆菌的中等体外抗分枝杆菌功效（64 μg/mL）相比，TSA-5 对受感染的巨噬细胞中的金分枝杆菌具有增强的细胞内杀伤功效（8 μg/mL）。 TSA-5 还表现出针对耻垢分枝杆菌的全细胞外排泵抑制活性。通过关注模块化 MbtB_Cy 结构域来鉴定 TSA-5 为加速新型抗结核抗生素的发现铺平了道路。