Discovery, SAR, and putative mode of action of N‐benzyl‐2‐methoxybenzamides as potential bleaching herbicides

BACKGROUND Herbicides acting on biosynthesis of plant pigments have contributed greatly to weed control in recent years. In our previous studies, 2‐methoxybenzamides were discovered as a novel type of lead compound for the development of bleaching herbicides. RESULTS A total of 67 benzamide analogues were synthesized and evaluated for herbicidal activity. The structure–activity relationship (SAR) revealed that a methoxyl substitution at the 2‐position of the benzoyl moiety is essential for the herbicidal activity of benzamide derivatives, and introduction of small substituents at the meta‐ or para‐position of the benzylamine moiety is also beneficial. Compounds 4, 43 and 44 showed 100% inhibition against Abutilon theophrasti and Amaranthus retroflexus at an application rate of 150 g a.i. ha−1. CONCLUSION The relationship between the structure and herbicidal activity of 2‐methoxybenzamides was discussed intensively. Compounds 4, 43 and 44 may serve as novel candidates with a bleaching effect. © 2021 Society of Chemical Industry The herbicidal activity of N‐benzyl‐2‐methoxybenzamide was discovered using a random screening procedure. Sixty‐seven N‐benzyl‐2‐methoxybenzamides were synthesized and evaluated for herbicidal activity. Their structure–activity relationship was discussed thoroughly.