Design, synthesis and biological evaluation of N ‐phenylphthalimide derivatives as potential protoporphyrinogen IX oxidase inhibitors

Abstract BACKGROUND Protoporphyrinogen IX oxidase (PPO, EC 1.3.3.4) is an important target for the development of highly efficient and environmentally friendly herbicides. Unfortunately, conventional N ‐phenylphthalimide‐derived PPO inhibitors are often plagued by limited herbicidal spectra and unsatisfactory crop selectivity. Therefore, a series of novel and highly active broad‐spectrum N ‐phenylphthalimide herbicidal inhibitors were designed and synthesized via the introduction of amide and isoindolinone moieties. RESULTS Based on the active substructure splicing strategy, a series of N ‐phenylphthalimide derivatives were synthesized. Among them, compound C4 showed a strong inhibitory effect on Nicotiana tabacum PPO ( Nt PPO) with an inhibition constant ( K i = 38.1 n m ), which was superior to Flumiclorac‐pentyl ( K i = 46.3 nM) and Flumioxazin ( K i = 52.0 n m ). Glasshouse assays indicated that compound C4 showed excellent herbicidal activity against six weed species at 150 g a.i. ha −1 and exhibited higher safety on seven crops. Target validation demonstrated that compound C4 could completely inhibit the growth of the ΔhemG‐ Escherichia coli strain complemented with Arabidopsis thaliana PPO (∆hemG‐ At PPO) at 100 μ m . Computer simulation results showed that compound C4 could not only form strong hydrogen‐bonds with Arg98 (2.9 Å) and alkyl–π interactions with the Gly65, Phe439, and Trp435 residues of Nt PPO, but also possessed excellent chemical reactivity, good electrostatic field characteristics, and high polarity. CONCLUSION Studies have shown that the N ‐phenylphthalimide derivative C4 , containing amide and isoindolinone structural moieties, can serve as a potential PPO inhibitor. © 2026 Society of Chemical Industry.