Synthesis and Biological Activity Evaluation of Benzoxazinone-Pyrimidinedione Hybrids as Potent Protoporphyrinogen IX Oxidase Inhibitor.

Protoporphyrinogen IX oxidase (PPO/Protox, E.C. 1.3.3.4) is recognized as one of the most important targets for herbicide discovery. In this study, we report our ongoing research efforts toward the discovery of novel PPO inhibitors. Specifically, we identified a highly potent new compound series containing a pyrimidinedione moiety and bearing a versatile building block-benzoxazinone scaffold. Systematic bioassays resulted in the discovery of compound , ethyl 4-(7-fluoro-6-(3-methyl-2,6-dioxo-4-(trifluoromethyl)-3,6-dihydropyrimidin-1(2)-yl)-3-oxo-2,3-dihydro-4-benzo[][1,4]oxazin-4-yl)butanoate, which exhibited broad-spectrum and excellent herbicidal activity at the dosage of 37.5 g a.i./ha through postemergence application. The inhibition constant () value of to PPO (PPO) was 14 nM, while to PPO (PPO), it was 44.8 μM, indicating a selective factor of 3200, making it the most selective PPO inhibitor to date. Moreover, molecular simulations further demonstrated the selectivity and the binding mechanism of to PPO and PPO. This study not only identifies a candidate that showed excellent bioactivity and high safety toward humans but also provides a paradigm for discovering PPO inhibitors with improved performance through molecular simulation and structure-guided optimization.