Rational Design, Structural Optimization, Synthesis, Biological Assessment, and Theoretical Validation of Novel...

4-Hydroxyphenylpyruvate dioxygenase (HPPD; EC 1.13.11.27) is regarded as a critical target enzyme in herbicide discovery and rational design. In this study, a series of 3-aroylpyridine-2,4(1H,3H)-diones were designed as potential HPPD inhibitors by combining active-substructure splicing with the bioisosterism strategy. A total of 48 triketones (III-1-III-48) were synthesized by a one-pot procedure that included O/C-isomerization of enol acylates II-1-II-48, obtained in situ by O-acylation of pyridine-2,4(1H,3H)-diones Ia-Ii. Some triketones displayed good in vitro Arabidopsis thaliana HPPD (AtHPPD) inhibitory activity. Compound III-22 exhibited a potent inhibitory activity against AtHPPD (IC₅₀ = 0.210 μM), which was higher than that of reference compound mesotrione (IC₅₀ = 0.670 μM). Bioassay results revealed that compound III-22 exhibited herbicidal activity exceeding 90% against all examined weed species at a dosage of 200 g a.i./ha; meanwhile, no significant phytotoxicity was observed in wheat, corn, soybean, and peanut fields even when applied at 300 g a.i./ha. Molecular docking revealed that compound III-22 established a bidentate chelating interaction with Co²⁺ while forming π-π stacking interactions with residues Phe381 and Phe424. Molecular dynamics simulations further confirmed that compound III-22 could stably bind to the target protein AtHPPD. Density functional theory (DFT) calculations elucidated the structure-activity relationships and the greater electronic stability of compound III-22. The present work indicated that aroyl-substituted pyridinones can be used as promising HPPD-targeting inhibitors and herbicide candidates for sustainable weed management in the field.