The treacherous nature of tuberculosis (TB) combined with the ubiquitous presence of the drug-resistant (DR) forms pose this disease as a growing public health menace. Therefore, it is imperative to develop new chemotherapeutic agents with a novel mechanism of action to circumvent the cross-resistance problems. The unique architecture of the Mycobacterium tuberculosis (M. tb) outer envelope plays a predominant role in its pathogenesis, contributing to its intrinsic resistance against available therapeutic agents. The mycobacterial membrane protein large 3 (MmpL3), which is a key player in forging the M. tb rigid cell wall, represents an emerging target for TB drug development. Several indole-2-carboxamides were previously identified in our group as potent anti-TB agents that act as inhibitor of MmpL3 transporter protein. Despite their highly potent in vitro activities, the lingering Achilles heel of these indoleamides can be ascribed to their high lipophilicity as well as low water solubility. In this study, we report our attempt to improve the aqueous solubility of these indole-2-carboxamides while maintaining an adequate lipophilicity to allow effective M. tb cell wall penetration. A more polar adamantanol moiety was incorporated into the framework of several indole-2-carboxamides, whereupon the corresponding analogues were tested for their anti-TB activity against drug-sensitive (DS) M. tb H37Rv strain. Three adamantanol derivatives 8i, 8j and 8l showed nearly 2- and 4-fold higher activity (MIC = 1.32 – 2.89 µM) than ethambutol (MIC = 4.89 µM). Remarkably, the most potent adamantanol analogue 8j demonstrated high selectivity towards DS and DR M. tb strains over mammalian cells [IC₅₀ (Vero cells) ≥ 169 µM], evincing its lack of cytotoxicity. The top eight active compounds 8b, 8d, 8f, 8i, 8j, 8k, 8l and 10a retained their in vitro potency against DR M. tb strains and were docked into the MmpL3 active site. The most potent adamantanol/adamantane-based indoleamides 8j/8k displayed a two-fold surge in potency against extensively DR (XDR) M. tb strains with MIC values of 0.66 and 0.012 µM, respectively. The adamantanol-containing indole-2-carboxamides exhibited improved water solubility both in silico and experimentally, relative to the adamantane counterparts. Overall, the observed antimycobacterial and physicochemical profiles support the notion that adamantanol moiety is a suitable replacement to the adamantane scaffold within the series of indole-2-carboxamide-based MmpL3 inhibitors.

结核病 (TB) 的危险性质与普遍存在的耐药 (DR) 形式相结合，使这种疾病成为日益严重的公共卫生威胁。因此，开发具有新作用机制的新型化疗药物以规避交叉耐药性问题势在必行。结核分枝杆菌( M. tb ) 外膜的独特结构在其发病机制中起主要作用，有助于其对可用治疗剂的内在抗性。分枝杆菌膜蛋白大3（MmpL3），这是在锻造的关键角色的结核分枝杆菌刚性细胞壁，代表了结核病药物开发的一个新兴目标。之前在我们的小组中发现了几种 indole-2-carboxamides 作为有效的抗结核药物，可作为 MmpL3 转运蛋白的抑制剂。尽管它们在体外具有很强的活性，但这些吲哚酰胺的致命弱点可以归因于它们的高亲脂性和低水溶性。在这项研究中，我们报告了我们尝试提高这些 indole-2-carboxamides 的水溶性，同时保持足够的亲脂性以允许有效的结核分枝杆菌细胞壁渗透。将极性更强的金刚烷醇部分并入几种吲哚-2-甲酰胺的框架中，随后测试了相应类似物对药物敏感 (DS) 结核分枝杆菌的抗结核活性H37Rv 菌株。三种金刚烷醇衍生物8i、8j和8l 的活性（MIC = 1.32 – 2.89 µM）比乙胺丁醇（MIC = 4.89 µM）高出近 2 倍和 4 倍。值得注意的是，与哺乳动物细胞相比，最有效的金刚烷醇类似物8j对 DS 和 DR M. tb菌株表现出高选择性[IC ₅₀（Vero 细胞）≥ 169 µM]，证明其缺乏细胞毒性。8b , 8d , 8f , 8i , 8j , 8k , 8l和10a的前八种活性化合物保持了它们的体外抗 DR 效力。M. tb菌株并停靠在 MmpL3 活性位点。最有效的基于金刚烷醇/金刚烷的吲哚酰胺 8j / 8k对广泛 DR (XDR)结核分枝杆菌菌株的效力增加了两倍，MIC 值分别为 0.66 和 0.012 µM。相对于金刚烷对应物，含金刚烷醇的吲哚-2-甲酰胺在硅片和实验上均表现出改善的水溶性。总体而言，观察到的抗分枝杆菌和物理化学特征支持这样的观点，即在基于吲哚-2-甲酰胺的 MmpL3 抑制剂系列中，金刚烷醇部分是金刚烷支架的合适替代品。