二氢叶酸还原酶（mt-DHFR）是结核分枝杆菌（M.tb）叶酸代谢途径中重要节点，阻断该靶点，将导致M.tb无胸腺嘧啶死亡。目前临床主要抗结核药物仅有对氨基水杨酸（PAS）为mt-DHFR抑制剂前药，但易引起严重的胃肠道疾病，且其耐药结核菌株已出现，因此亟需研发新型mt-DHFR选择性抑制剂。我们前期报道了以1,3-二氨基-7H-吡咯并[3,2-f]喹唑啉为母核的mt-DHFR抑制剂，其体外活性与PAS相当，且具有全新结构骨架，此发现将极大拓展该靶点抑制剂的化学空间。近期，我们合成了一系列该类抑制剂，显著提高了其体外活性并兼具较好的选择性。本项目将在前期基础上，拟采用多种药物设计技术对该类分子进行结构优化，旨在提高其选择性、体内外活性和成药性，以期发现2-3个先导结构，此外通过深入研究先导结构与靶点的相互作用，解析其分子作用机理。本项目的顺利开展，将为发现新型抗结核药物奠定坚实的基础。

Dihydrofolate reductase (mt-DHFR) of Mycobacterium tuberculosis (M.tb) is an important enzyme in the folate metabolize pathway. By blocking this target, it will lead M.tb to the thymineless death. Currently p-aminosalicylic acid (PAS) is the only one in the first and second line anti-tuberculosis drugs, and it functions as the prodrug of mt-DHFR inhibitor. However, as PAS causes serious gastrointestinal diseases, and the PAS resistant M.tb strains have been developed, it is urgent to develop novel mt-DHFR selective inhibitors. In our previous publications, we reported a chemical compound with the core of 1,3-diamino-7H-pyrrolo[3,2-f]quinazoline as the mt-DHFR inhibitor. The M,tb inhibition ability of this hit compound is in the same level of PAS, and it contains a novel chemical structure, which will significantly expand the chemical space of mt-DHFR inhibitors. More recently, we have designed and synthesized a series of compounds, which are analogs of the previous hit compound, and they show strong anti M.tb effects with a reasonable selectivity against human DHFR in vitro. In the current project, based on our previous work, the lead optimization will be performed to improve the activity and selectivity of the hit compounds both in vitro and in vivo, and the pharmaceutical properties will be optimized at the mean time to make them more drug like, by using computer aided drug design and chemical synthesis. Through the study, we are aiming to obtain 2-3 drug-like leading compounds, and the biological mechanism of these compounds will be studied by analyzing the ligand-protein interactions. We believe that the successful development of the current project will build a solid foundation for the discovery of novel anti-TB drugs.