De Novo Design and Synthesis of Novel Benzoxazinone Derivatives Targeting Dihydroxyacid Dehydratase

Dihydroxyacid dehydratase (DHAD), a key enzyme in the branched-chain amino acid (BCAA) synthesis pathway, is a promising herbicide target. Currently, no commercial herbicides target DHAD, and no inhibitors are in development. Structural analysis suggests that coordination with iron–sulfur clusters and hydrophobic interactions with Tyr215 and Phe181 are crucial for inhibitor binding. Based on this model, we designed and synthesised derivatives 4aa–4bb with a benzoxazinone ring. Compound 4bb effectively inhibited Arabidopsis seed germination at 50 μg/mL, reversible by BCAA supplementation. In vitro, 4bb showed a stronger binding affinity to DHAD ( K d = 83.18 μM) than AHAS ( K d = 132.70 μM). Compound 4bb exhibits minimal side effects on wheat seed germination at lower concentrations while ensuring high safety for rice at higher dosages during post-emergence treatment. Greenhouse tests revealed over 75% inhibition of broadleaf weeds such as Eclipta prostrata and Amaranthus retroflexus . The selectivity between crops and weeds is not due to species-specific DHAD differences. Safety assessments showed no significant toxicity to human cell lines and microorganisms. This study confirms DHAD as a viable herbicide target and offers a structural basis for optimising inhibitors, positioning 4bb as a lead compound for new herbicides.