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

Abstract

A series of 1,3,4(2H)-isoquinolinetriones have been found to be fastacting 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-l,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.which gives rise to the herbicidal activity of the isoquinolinetriones, and describe the results of a preliminary study designed to probe the structureactivity-property relationships within a series of compounds. EXPERIMENTAL METHODS Chemical synthesisThe three general methods used for the preparation of 1,3,4(2H)-isoquinolinetriones are outlined in Fig. 1.Method A involves the oxidation of a homophthalimide derivative to the corresponding isoquinolinetrione. This transformation has been conveniently carried out using a two-step one-pot procedure, in which the homophthalimide is first condensed with N,N-dimethyl-p-nitrosoaniline to give an intermediate imine which is then hydrolysed in situ by the addition of aqueous acid." Method B requires the 49 Pestic. Sci. 0031-613X/95/$09.00 0 1995 SCI. Printed in Great Britain 1,3,4(2H)-isoquinolinetrione herbicides~~~~~~ ~ ~ Average score across weed species, on a scale of 0-9 where 0 indicates no damage five days after treatment and 9 signifies Estimated from a half life of 3.8 min at 40°C. Estimated. Estimated from a measurement made at pH 6. Estimated from a measurement made at pH 5. complete kill (see Section 2.2).' Not measured; this compound could not be obtained >90% pure.

Herbicidal indolizine‐5,8‐diones: photosystem I redox mediators

“…The rate of oxygen uptake for each concentration was measured over a period of 60 s, during which time oxygen consumption was linear. The dose responses over a 20 µ M range were plotted using a curve‐fitting analysis programme to obtain values for 50% stimulation of oxygen consumption ( S 50 ) and V max as previously reported 6…”

“…The redox properties of compounds were studied in DMF at a platinium working electrode by cyclic voltammetry using the method previously reported 6, 23. Cathodic ( E pc ) and anodic ( E pa ) peak potentials were recorded for the 0 to −2 V range at voltage sweep rates of 0.02, 0.1 and 0.5 V s −1 versus a saturated calomel reference electrode.…”

“…Aqueous buffer solutions (10 m M ) for the pH 5–11 range were prepared from sodium acetate, sodium dihydrogen phosphate, disodium hydrogen phosphate or sodium carbonate adjusted with hydrochloric acid or sodium hydroxide. Compound stock solution (20 µl) was added to buffer solution (2 ml) at 25 or 40 °C in HPLC vials for direct measurement of compound loss versus time by HPLC, as previously reported 6. A similar procedure was used to investigate the reactivity of selected indolizinediones with glutathione (GSH, 5 m M ) at different pH values, full details of which have also been reported 30…”

“…The acetone was removed from the flask by rotary evaporation and the compound residue re‐dissolved in HPLC mobile phase (2 ml) prior to transfer to an HPLC vial for analysis against a standard solution of compound (16 µl stock solution in 2 ml of HPLC mobile phase). Full details of the HPLC method have been published 6, 30. The time for loss of the first 50% of deposit was read from a plot of compound remaining versus time and photostability reported as a T 50 value.…”

“…The synthetic accessibility and the redox and physical properties of quinones and related systems have made them attractive starting points for exploratory redox‐mediating herbicides 5–9. Indolizine‐5,8‐diones are a novel class of quinone‐like compounds which have been recently patented as herbicides 10.…”