Re-exploration of phenolic compounds from natural waste rice husks: Combined synthesis of novel herbicide and evaluation of herbicidal activity

In a global context, weed management has emerged as a significant challenge in agricultural production, causing substantial economic losses annually. Consequently, the development of innovative and efficient herbicides is crucial. Natural products serve as important sources for discovering novel herbicides. Through chemical synthesis and structural modification of natural compounds, novel herbicides can be developed. Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) catalyzes the oxidation of protoporphyrinogen IX to protoporphyrin IX, a critical step in the biosynthesis of porphyrins. PPO inhibitors target protoporphyrinogen oxidase, inhibiting its activity and thereby blocking porphyrin biosynthesis, ultimately leading to plant death. In this research, protoporphyrinogen oxidase was targeted, and monomeric compounds were extracted from natural rice husks, followed by selective manipulation to design and synthesize 33 new compounds. Weed control assays (37.5–300 g ai/ha) showed that most of the new compounds exhibited significant herbicidal activity against dicot weeds, but less effectiveness against monocot weeds. In particular, compound I–c4 demonstrated excellent post-emergence herbicidal activity on six weed species, comparable to the commercial herbicide oxyfluorfen. Activity experiments showed that compound I–c4 significantly reduced PPO levels in weeds. Molecular docking results indicated that compound I–c4 effectively occupies the substrate pocket of PPO enzymes, demonstrating strong inhibitory effects on receptor protein activity. Thus, compound I–c4 shows promise as a novel PPO herbicide for effective weed control.