Design, Synthesis, and Bioevaluation of Substituted Phenyl Isoxazole Analogues as Herbicide Safeners

Herbicide safeners enhance herbicide detoxification in crops without affecting target weed sensitivity. To enhance crop tolerance to the toxicity-related stress caused by the herbicide acetochlor (ACT), a new class of substituted phenyl isoxazole derivatives was designed by an intermediate derivatization method as herbicide safeners. Microwave-assisted synthesis was used to prepare the phenyl isoxazole analogues, and all of the structures were confirmed via IR, 1H NMR, 13C NMR, and HRMS. Compound I-1 was further characterized by X-ray diffraction analysis. Bioassay results showed that most of the obtained compounds provided varying degrees of safening against ACT-induced injury by increasing the corn growth recovery, glutathione content, and glutathione S-transferase activity. In particular, compound I-20 showed excellent safener activity against ACT toxicity, comparable to that of the commercial safener benoxacor. Gaussian calculations have been performed and the results indicated that the nucleophilic ability of compound I-20 is higher than that of benoxacor, thus the activity is higher than that of benoxacor. These findings demonstrate that phenyl isoxazole derivatives possess great potential for protective management in cornfields.