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.