N‐benzyl‐2‐methoxy‐5‐propargyloxybenzoamides, a new type of bleaching herbicides targeting the biosynthesis pathway of plastoquinone

Abstract BACKGROUND Previously, the herbicidal activity of N ‐benzyl‐2‐methoxybenzamides was discovered during a random screening program in our laboratory. The chemicals resulted in bleaching effect of newly grown leaves by interfering with the biosynthesis of β ‐carotene in plant. RESULTS A total of 28 benzamides were synthesized and subjected for the evaluation of herbicidal activity. Structure–activity relationship (SAR) showed that introducing propargyloxy group at 5‐position of benzoyl‐benzene ring and fluorine or methyl group at 3‐ or 4‐position of benzyl‐benzene ring is beneficial for the activity. Post‐emergence herbicidal activities of compounds 406 and 412 were comparable to those of mesotrione and diflufenican. Studies on MOA showed that 406 decreased the level of both β ‐carotene and plastoquinone (PQ) in treated plants. The bleaching effect in green alga caused by 406 could be reversed by supplying exogenous homogentisic acid (HGA), the precursor of plastoquinone. CONCLUSION N ‐benzyl‐2‐methoxy‐5‐propargyloxybenzoamides were discovered as new candidates for bleaching herbicides. Preliminary investigation on mechanism of action (MOA) showed that the title compounds might indirectly interfere with carotenoid biosynthesis by blocking the production of PQ. © 2023 Society of Chemical Industry.