Discovery of Novel -Isoxazolinylphenyltriazinones as Promising Protoporphyrinogen IX Oxidase Inhibitors.

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) is a promising target for herbicide discovery. Search for new compounds with novel chemotypes is a key objective for agrochemists. Here, we describe the discovery and systematic SAR-based structure optimization of novel -isoxazolinylphenyltriazinones - as PPO inhibitors. The herbicidal activity and PPO (PPO) inhibitory activity were explored in detail. A number of the new synthetic compounds displayed strong PPO inhibitory activity with values in the nanomolar range. Some compounds exhibited excellent and broad-spectrum weed control at the rate of 9.375-37.5 g ai/ha by postemergence application and showed improved monocotyledonous weed control compared to saflufenacil. Most promisingly, ethyl 3-(2-chloro-5-(3,5-dimethyl-2,6-dioxo-4-thioxo-1,3,5-triazinan-1-yl)-4-fluorophenyl)-5-methyl-4,5-dihydroisoxazole-5-carboxylate, , with a value of 4.9 nM, displayed over 2- and 6-fold higher potency than saflufenacil ( = 10 nM) and trifludimoxazin ( = 31 nM), respectively. Moreover, showed excellent and broad-spectrum weed control against 32 kinds of weeds at 37.5-75 g ai/ha. Rice exhibited relative tolerance to at 150 g ai/ha by postemergence application, indicating that could be a potential herbicide candidate for weed control in paddy fields.