Mesotrione Conjugation Strategies to Create Proherbicides with Reduced Soil Mobility

Proherbicides increase the utilization efficiency of herbicides by reducing their off-site movement and premature degradation. Mesotrione is a prevalent herbicide used to control weeds in maize crops, but it is susceptible to degradation and leaching in soil. We report the synthesis of hydrolytically reversible conjugates of mesotrione and detail the unique reactivity of its β-triketone moiety. Three proherbicides were created through phenyl thioether, ethyl thioether, or phenyl ester linkages to mesotrione. The derivatives demonstrated controlled release of mesotrione in aqueous conditions with nearly quantitative release in acidic pH within 24 days for both thioether derivatives and 100 min for the phenyl ester derivative. Moreover, all three conjugates reduced the mobility of mesotrione in acidic soil. Specifically, both thioethers demonstrated nominal mobility and release of mesotrione in soil. For the phenyl ester derivative, after approximately 100 mL of water leached, only 40% mesotrione was released from the soil column, compared to 80% observed in the free herbicide control. Finally, the phenyl ester conjugate exhibited improved pre-emergent herbicidal activity against a common weed, Chenopodium album, at a low application concentration of 50 g AI ha^–1. At 50 g AI ha^–1, the proherbicide demonstrated 31.4 ± 12.1% efficacy against C. album while free mesotrione controlled only 10.0 ± 5.3%. Overall, this study demonstrates the potential to increase mesotrione’s utilization efficiency by creating proherbicide derivatives.