Structure-activity Relationship of Tetrazole Derivatives as Kynurenine Monooxygenase Inhibitors

Kynurenine monooxygenase (KMO) is a key enzyme involved in the degradation of tryptophan via the kynurenine pathway (KP). KMO has been implicated in various neurodegenerative and non-neurodegenerative disorders due to its role in regulating levels of several critical metabolites. Inhibition of KMO offers a promising therapeutic strategy. This dissertation focuses on the development of novel KMO inhibitors containing a tetrazole moiety and the investigation of their protein–ligand interactions with KMO. The tetrazole group is a well-established bioisosteric replacement for carboxylic acids. We designed and synthesized a series of tetrazole-containing derivatives and conducted structure–activity relationship (SAR) studies to optimize their potency. KMO crystals were obtained, and the protein structures complexed with our compounds were successfully solved. Additionally, we designed a substrate analog, 5-nitrokynurenine(5-Nkyn), which acts as an uncoupler of KMO activity. We explored the binding mechanisms of both competitive and uncoupling inhibitors. Furthermore, during the synthesis of 5-nitrokynurenine, we developed a novel aromatic nitration method using lithium nitrate under mild conditions. This method is effective for a wide range of deactivated aromatic substrates and heterocyclics and affords moderate to excellent yields. These collective findings provide a comprehensive framework for rational KMO inhibitor design and offer valuable insights for future therapeutic development targeting the kynurenine pathway.