Antimicrobial resistance is considered as one of the major threats for the near future as the lack of effective treatments for various infections would cause more deaths than cancer by 2050. The development of new antibacterial drugs is considered as one of the cornerstones to tackle this problem. Aminoacyl-tRNA synthetases (aaRSs) are regarded as good targets to establish new therapies. Apart from being essential for cell viability, they are clinically validated. Indeed, mupirocin, an isoleucyl-tRNA synthetase (IleRS) inhibitor, is already commercially available as a topical treatment for MRSA infections. Unfortunately, resistance developed soon after its introduction on the market, hampering its clinical use. Therefore, there is an urgent need for new cellular targets or improved therapies. Follow-up research by Cubist Pharmaceuticals led to a series of selective and in vivo active aminoacyl-sulfamoyl aryltetrazole inhibitors targeting IleRS (e.g. CB 168).

Here, we describe the synthesis of new IleRS and TyrRS inhibitors based on the Cubist Pharmaceuticals compounds, whereby the central ribose was substituted for a tetrahydropyran ring. Various linkers were evaluated connecting the six-membered ring with the base-mimicking part of the synthesized analogues. Out of eight novel molecules, a three-atom spacer to the phenyltriazole moiety, which was established using azide-alkyne click chemistry, appeared to be the optimized linker to inhibit IleRS. However, 11 (K_i,app = 88 ± 5.3 nM) and 36a (K_i,app = 114 ± 13.5 nM) did not reach the same level of inhibitory activity as for the known high-affinity natural adenylate-intermediate analogue isoleucyl-sulfamoyl adenosine (IleSA, CB 138; K_i,app = 1.9 ± 4.0 nM) and CB 168, which exhibit a comparable inhibitory activity as the native ligand. Therefore, 11 was docked into the active site of IleRS using a known crystal structure of T. thermophilus in complex with mupirocin. Here, we observed the loss of the crucial 3′- and 4′- hydroxyl group interactions with the target enzyme compared to CB 168 and mupirocin, which we suggest to be the reason for the limited decrease in enzyme affinity. Despite the lack of antibacterial activity, we believe that structurally optimizing these novel analogues via a structure-based approach could ultimately result in aaRS inhibitors which would help to tackle the antibiotic resistance problem.

抗菌药物耐药性被认为是近期的主要威胁之一，因为到2050年，缺乏有效的各种感染治疗方法将比癌症引起更多的死亡。新抗菌药物的开发被认为是解决这一问题的基石之一。氨酰基-tRNA合成酶（aaRSs）被认为是建立新疗法的良好靶标。除了对细胞生存力至关重要以外，还经过了临床验证。实际上，莫匹罗星是一种异亮氨酰-tRNA合成酶（IleRS）抑制剂，已经可以作为MRSA感染的局部治疗方法在市场上买到。不幸的是，耐药性在投放市场后不久就发展起来，阻碍了其临床应用。因此，迫切需要新的细胞靶标或改进的疗法。靶向IleRS的体内活性氨基酰基氨磺酰基芳基四唑抑制剂（例如CB 168）。

在这里，我们描述了基于Cubist Pharmaceuticals化合物的新型IleRS和TyrRS抑制剂的合成，其中中心核糖取代了四氢吡喃环。评价了将六元环与合成类似物的模拟碱基的部分连接的各种接头。在八个新分子中，使用叠氮化物-炔烃点击化学法建立的苯基三唑部分的三个原子间隔基似乎是抑制IleRS的最佳连接子。然而，11（K _i，app  = 88±5.3 nM）和36a（K _i，app  = 114±13.5 nM）没有达到与已知的高亲和力天然腺苷酸中间体类似物异亮氨酰-相同的抑制活性水平。氨磺酰基腺苷（IleSA，CB 138; K_i，app  = 1.9±4.0 nM）和CB 168，它们具有与天然配体相当的抑制活性。因此，使用与莫匹罗星复合的嗜热毁丝霉的已知晶体结构，将11对接入IleRS的活性位点。在这里，我们观察到与CB 168和莫匹罗星相比，与目标酶的关键3'-和4'-羟基相互作用的丧失，我们认为这是酶亲和力有限降低的原因。尽管缺乏抗菌活性，我们认为通过基于结构的方法在结构上优化这些新型类似物最终可能会导致aaRS抑制剂的出现，这将有助于解决抗生素耐药性问题。