Discovery of Novel N-Phenylpyrazole Derivatives as Protoporphyrinogen IX Oxidase Inhibitors.

Protoporphyrinogen oxidase (PPO) is one of the major targets for herbicide discovery. N-Phenylpyrazole derivatives bearing ester, oxime, and isoxazoline moieties were synthesized via isomerization, derivatization and cyclization. Bioassays showed C34 potently inhibited Nicotiana tabacum PPO (NtPPO) (Ki = 15.6 nM), with superior activity to fluazolate (Ki = 18.3 nM). Compound C34 showed excellent postemergence herbicidal efficacy to fluazolate at 37.5 g a.i./ha and broader-spectrum herbicidal activity than fluazolate at 75-150 g a.i./ha. Meanwhile, C34 produced only 10-20% injury in peanut and cotton at 75-150 g a.i./ha, outperforming fluazolate (peanut: 30-70%, soybean: 40-70%). Molecular docking demonstrated C34 forms more hydrogen bonds with Arg98 than fluazolate, and molecular dynamics simulations confirmed its stable binding to NtPPO. Density functional theory calculations revealed that C34 exhibits high chemical reactivity and favorable electronic chemical potential. These findings indicate C34 is a promising lead for novel PPO inhibitor development.