Structure-Guided Discovery of Benzothiazinone-Triketone Hybrids as Novel Subnanomolar 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors.

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays a pivotal role in the tyrosine metabolism pathway and is regarded as an important herbicide target. Herein, we present a class of benzothiazinone-triketone hybrids as novel HPPD inhibitors designed by using a structure-based drug design (SBDD) strategy. The enzyme inhibitory assay revealed that most of the derivatives exhibited excellent inhibitory efficacy against Arabidopsis thaliana HPPD (AtHPPD). Furthermore, three cocrystal structures of compounds (8j, 8x, and 8z) in complex with AtHPPD (PDB ID: 8XQY, 8HXF, and 8X6A) were determined to guide the structural optimization process, resulting in the discovery of novel subnanomolar HPPD inhibitors. Finally, a picomolar inhibitor 8z with a Ki value of 226 pM against AtHPPD was discovered. It showed about 20-fold higher potency than mesotrione (Ki = 4.56 nM) and was regarded as the most potent HPPD inhibitor to date. These results demonstrate that the triketone-benzothiazinone hybrid is a potential scaffold for discovering new HPPD inhibitors.