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.

: An HPLC-based assay system has been developed to measure the reactivity of agrochemicals with glutathione (GSH) with and without catalysis by glutathione transferases (GSTs). Metabolism-related parameters based on second-order related rate constants from non-enzymatic GSH and enzymatic GSH ] GST assays have been derived for use in structureÈactivity and structureÈreactivity relationship studies of exploratory agrochemicals. The versatility and sensitivity of the assay system has been established using a diverse range of agrochemicals and model compounds, e.g. 4-nitrobenzyl chloride, 1-chloro-2,4-dinitrobenzene, atrazine, acetochlor, Ñuorodifen, Ñuazifop-butyl, tridiphane, Ñuazinam, chlorothalonil and diazinon. For the enzymatic GSH ] GST assay, second-order related rate constants, ratioed to the assay standard, 4-nitrobenzyl chloride to provide a parameter independent of assay conditions, spanned Ðve orders of magnitude, Ñuazinam being the most reactive and atrazine the least. Within chemical classes signiÐcant variations in reactivity were observed, alachlor being c.15-fold more reactive than pretilachlor. Applications of this assay system based on comparative measures of reactivity across and within chemical classes are discussed.1998 Society of Chemical Industry ( Pestic. Sci., 54, 385È393 (1998)

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6,7-Disubstituted indolizine-5,8-diones showed activity as herbicides, giving rapid desiccation symptomology in whole-plant tests and bleaching in leaf-disc assays. In isolated chloroplasts, such compounds initiated rapid uptake of oxygen in Photosystem I. A redox mediator mode of action was further supported by electrochemical studies. Several compounds described had low photostability, high volatility, hydrolytic instability or reactivity with glutathione. The detrimental effects that these factors may have had on expression of herbicidal activity are discussed.

The tripeptide H-Val-Ala-Leu-OH and the N-Ac-tetrapeptide amide Ac-Thr-Lys-Trp-Phe-NH2, and their beta-peptidic counterparts H-beta(3)hVal-beta(3)hAla-beta(3)hLeu-OH and Ac-beta(3)hThr-(S)beta(2)hLys-beta(3)hTrp-beta(3)hPhe-NH2, respectively, have been injected into Heliothis virescens larvae and added to cell cultures of black mexican sweet maize. The body liquids of the larvae and the supernatant of the plant cell cultures were sampled 0, 2, 3, 6, 17, and/or 24 h after application and analyzed by LC/MS. While the two alpha-peptides were degraded rapidly in these environments, the concentration of the beta-peptides was found to decrease very slowly. Thus, ca. 60% of the original amount of the beta-tetrapeptide was detected in the liquids of the insect after 24 h. The plant cells did not seem to make use of the beta-peptides at all, whereas, the alpha-tripeptide completely disappeared from the supernatant after 3 h. Thus, we have demonstrated, for the first time, the high stability of beta-peptides against degradation and metabolism in an insect and a plant. Especially remarkable is the persistence of the beta-tetrapeptide with its functionalised and, thus, 'metabolisable' side chains of Thr, Lys, Trp, and Phe in the insect larvae, which are known to have a high level of activity of oxidizing enzymes. The results described here match those of ADME investigations with radioactively labeled beta-peptides in rats, where essentially complete stability has been observed, while environmental microorganisms have been found to biodegrade beta-peptides, albeit slowly. Possible implications of these findings for biomedical and pest-control applications are proposed.