1,3,4(2H)-isoquinolinetrione herbicides: Novel redox mediators of photosystem I

A series of 1,3,4(2H)-isoquinolinetriones have been found to be fast-acting post-emergence herbicides, producing symptoms of desiccation. These redox-active compounds are very potent stimulators of the light-dependent consumption of oxygen at photosystem I in isolated chloroplasts. Pulse radiolysis studies on 2-ethyl-1,3,4(2H)-isoquinolinetrione have shown it to have free-radical properties which could enhance the generation of superoxide radicals in plants. Electrochemical studies further support a redox mediator mode of action for the series. The compounds were found to be unstable towards hydrolysis, and this was considered to be a major factor limiting the overall herbicidal effects. Other parameters, related to uptake and/or translocation, which may limit the full expression of the herbicidal activity of certain compounds, are discussed.     

Synthesis and characterisation of some 4‐keto derivatives of 1,3,4(2H)‐isoquinolinetrione redox mediator herbicides

Derivatives of 2‐ethyl‐1,3,4(2H)‐isoquinolinetrione in which the 4‐keto group has been modified to (Z)‐oxime, (E)‐ and (Z)‐O‐methyl oxime, (Z)‐N,N‐dimethyl hydrazone, cyano‐imine and dicyanomethylene moieties have been prepared and evaluated as redox mediator herbicides. All of the compounds have the free‐radical properties required to function as redox mediators, as determined by cyclic voltammetry, though only the O‐methyl oximes, the N,N‐dimethyl hydrazone and the cyano‐imine have reduction potentials in the range required to stimulate the light‐dependent consumption of oxygen at photosystem I in isolated chloroplasts. The O‐methyl oximes and the cyano‐imine are fast‐acting post‐emergence herbicides, producing symptoms of rapid desiccation; the (E)‐O‐methyl oxime is the most active herbicide, being somewhat more potent than the parent isoquinolinetrione. Hydrolysis studies indicate that it is unlikely that any compound generates the parent isoquinolinetrione in vivo. Attempts to explain differences between in vitro and in vivo activities using hydrolytic stabilities and physical properties were unsuccessful, and it was concluded that these factors probably play a less significant role in moderating the herbicidal activity of isoquinolinetrione derivatives than originally thought. © 2000 Society of Chemical Industry     

1,3,4(2H)‐Isoquinolinetriones: evaluation of amino‐substituted derivatives as redox mediator herbicides

Amino‐substituted derivatives of 2‐ethyl‐1,3,4(2H)‐isoquinolinetrione have been prepared with the aim of enhancing their hydrolytic stabilities relative to other isoquinolinetriones, and hence potentially improving their herbicidal effects. 5‐Amino‐2‐ethyl‐1,3,4(2H)‐isoquinolinetrione has been shown to be 12 and 8 times more stable towards hydrolysis than the isomeric 7‐ and 8‐amino derivatives, respectively, and 120 times more stable than 2‐ethyl‐1,3,4(2H)‐isoquinolinetrione itself. Pulse radiolysis studies have shown 5‐amino‐2‐ethyl‐1,3,4(2H)‐isoquinolinetrione to have free‐radical properties which could enhance the generation of superoxide radicals in plants. The compound is a potent stimulator of the light‐dependent consumption of oxygen at photosystem I in isolated chloroplasts and also shows high activity in isolated leaf discs. Evidence is presented which indicates that the rate of foliar uptake is a major factor affecting herbicidal activity for this compound. © 2000 Society of Chemical Industry