Design, Synthesis, Structure–Activity Relationship, Molecular Docking, and Herbicidal Evaluation of 2-Cinnamoyl-3-Hydroxycyclohex-2-en-1-one Derivatives as Novel 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

Cinnamic acid, isolated from cinnamon bark, is a natural product with excellent bioactivity, and it effectively binds with cyclohexanedione to form novel 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors. According to the active sub-structure combination principle, a series of novel 3-hydroxy-2-cinnamoyl-2-en-1-one derivatives were designed and synthesized. The title compounds were characterized by infrared, ¹H NMR, ¹³C NMR, and HRMS. The in vitro inhibitory activity of AtHPPD verified that compound II-13 showed the most activity with a half-maximal inhibitory concentration (IC₅₀) value of 0.180 μM, which was superior to that of mesotrione (0.206 μM) in vitro. The preliminary herbicidal activity tests demonstrated that some compounds had good herbicidal activity especially compound II-13 at a concentration of 150 g ai/ha. The binding mode of AtHPPD through molecular docking indicated that two oxygens of compounds II-13 formed bidentate interactions with metal ions, and the benzene ring formed π-π accumulation effects with Phe-381 and Phe-424. The results of molecular dynamics simulations showed that compound II-13 exhibited a more stable binding ability with AtHPPD than mesotrione. This study provided insights into the development of natural and efficient herbicides in the future.