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 gro up has been modified to (Z)-oxime, (E)- and (Z)-O-methyl oxime, (Z)-N,N-dim ethyl hydrazone, cyano-imine and dicyanomethylene moieties have been prepar ed and evaluated as redox mediator herbicides. All of the compounds have th e free-radical properties required to function as redox mediators, as deter mined by cyclic voltammetry, though only the O-methyl oximes, the N,N-dimet hyl hydrazone and the cyanoimine have reduction potentials in the range req uired to stimulate the light-dependent consumption of oxygen at photosystem I in isolated chloroplasts. The O-methyl oximes and the cyano-imine are fa st-acting post-emergence herbicides, producing symptoms of rapid desiccatio n; the (E)-O-methyl oxime is the most active herbicide, being somewhat more potent than the parent isoquinolinetrione. Hydrolysis studies indicate tha t it is unlikely that any compound generates the parent isoquinolinetrione in vivo. Attempts to explain differences between in vitro and in vivo activ ities using hydrolytic stabilities and physical properties were unsuccessfu l, and it was concluded that these factors probably play a less significant role in moderating the herbicidal activity of isoquinolinetrione derivativ es than originally thought. (C) 2000 Society of Chemical Industry.