作用机制导向的水杨酸合成酶MbtI抑制剂的设计、合成及其抗结核活性评估

Tuberculosis is caused by the bacterium known as Mycobacterium tuberculosis (Mtb) and is the second leading cause of infectious mortality after HIV-AIDS. The mycobactins, the small-molecule iron-chelators (siderophores) produced by Mtb, are responsible for obtaining iron from the human host, a process that is essential for the survival of Mtb. Inhibition of mycobactin biosynthesis is expected to block iron acquisition, representing a potential target to develop anti-tubercular agents with novel modes of action that is urgently needed for the treatment of resistant TB infections. Mtb salicylate synthase (MbtI) catalyses the first committed step in the biosynthesis of mycobactin. We propose to synthesize transitions-state inhibitors of MbtI. Our proposed synthesis is based on the stereocontrolled synthetic route to Bartlett inhibitor (inhibitor of homologous enzyme of MbtI), which enable structural modification at several important positions. Their anti-tubercular activities will be evaluated against a mutant strain of M. tuberculosis that enables conditional expression of MbtI. The correlation between anti-tubercular activity of inhibitors and MbtI expression level would provide support for the designed mechanism of action, which would be used to guide the generation of derivative compounds that will possess higher specificity and activity.

结核病是由结核杆菌感染引起的慢性传染病，是继艾滋病之后，在全世界由单一传染性病原体引起的最大杀手。结核杆菌利用铁载体从外界获取铁离子以维持生长和繁殖。抑制铁载体的生物合成从而阻断结核杆菌对铁的摄取是具有全新作用机制的抗结核病的潜在药靶，并有望对耐药性结核病产生作用。水杨酸合成酶MbtI参与铁载体合成的关键步骤，是抑制铁载体合成的理想药靶。本课题旨在模拟分支酸与MbtI酶反应的过渡态，设计、合成MbtI酶抑制剂。我们将改进Bartlett抑制剂（MbtI的同源酶抑制剂）的外消旋合成，不对称合成环己烯骨架，并且将在关键部位进行结构修饰，从而进一步明确这些部位的构效关系。同时，我们将采用MbtI酶表达可控的结核杆菌变异株，对抑制剂的药靶活性做出评估，判断抑制剂对MbtI酶的抑制是否和抗结核活性相关联，为设计高特异性、高灵敏度的抑制剂提供起点和依据。

结核杆菌利用铁载体Mycobactin从外界获取Fe3+离子以维持生长和繁殖。在项目执行的三年里，项目组成员紧密围绕阻断结核杆菌通过Mycobactin对人体宿主体内Fe3+的摄取来开展两个方面的研究工作：（1）在发展MbtI酶小分子抑制剂的策略中，项目组设计了两套不对称合成路线，分别合成5位为CH2和O连接的过渡态模拟类似物，并首次不对称合成了Bartlett抑制剂（分支酸利用酶家族中的最强抑制剂）。Bartlett抑制剂和其它类似物未显示出明显的靶向MbtI酶的抑制活性，说明分支酸利用酶家族酶之间存在细微但重要的结构差别。（2）在发展靶向铁载体Mycobactin的全合成疫苗策略中，项目组以肿瘤糖抗原STn作为模型，研究了内嵌NKT细胞激动剂的全合成疫苗设计策略。初步的免疫评价表明：该策略能够打破免疫耐受，迅速实现靶向抗原的IgM到IgG的抗体类型转换，产生高滴度的IgG抗体。该结果为结核杆菌疫苗以及其它疫苗的研制开拓新思路。项目执行期间在国际权威性期刊发表论文9篇，申请中国专利1项，培养硕士毕业生4人，1人获国家奖学金。