Discovery of novel herbicidal cyclic keto‐enol derivatives containing a pyridazinone moiety and their structure–activity relationship studies on weeds

BACKGROUND: Acetyl-coenzyme A carboxylase (ACCase) is one of the most important enzymes involved in the biosynthesis of fatty acids in both plants and animals, and its inhibitors are widely used to control gramineous plants or sucking pests in crop fields. Phenyl-substituted cyclic keto-enols (CKEs) are known as a chemical class inhibiting ACCase, and several compounds are commercially available as herbicides or insecticides. RESULTS: We synthesized a new series of phenyl-substituted CKEs containing a pyridazinone moiety and examined the structure-activity relationship (SAR) based on herbicidal activity. We found that the methyl group at the 2 position of the pyridazinone ring significantly contributes to herbicidal efficacy. Similarly, we revealed that a methyl group at the 6 position of the pyridazinone ring is critical for exerting high herbicidal activity on both grass weeds and broadleaf weeds. Additionally, compounds with ethyl groups at the ortho position of the phenyl ring showed improved herbicidal activity, especially against grass weeds. The ACCase inhibition assay results showed good correlations with the SAR of the pot tests. Several optimized compounds, based on herbicidal activity, demonstrated high herbicidal efficacy against not only grass weeds but also broadleaf weeds, causing characteristic bleaching symptoms. CONCLUSION: Phenyl-substituted CKE derivatives containing a pyridazinone moiety have a broad weed control spectrum and likely possess multiple modes of action. These features make these compounds useful as tools for effectively controlling a variety of weeds, including resistant weeds.