環状イミド系除草剤の分子設計に関する研究

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Now that many biocidal types of herbicides are being phased out in the field of newer herbicides designs, because of phytotoxicological selectivity or environmental considerations, the photosynthesis inhibiting herbicides, which make up the group which we call inhibitors in photosynthetic electron transport, light-activated herbicides and so on, have come to dominate the herbicide molecular design. Cyclic imide herbicides belong to this diverse group of compounds and have a number of interesting features. For instance, both potency and phytotoxic selectivity vary over great extremes, all the way from the total herbicides to highly selective compounds which are almost safe to many useful plants. It is not at all difficult to synthesize an entirely new photosynthesis inhibitor, because there is a great deal of diversity of permitted attachments to the basic structure. The problem is to design compounds which are of modest price, excellent potency and appropriate safty to useful plants and the environment. To find out a solution to this problem in the molecular design of cyclic imide herbicides, the author has applied so-called biorational approaches in which we can systematically make use of information obtained from studies on phytotoxic actions, metabolism, absorption and translocation, mechanism of action, structure-activity relationships, agricultural application and others. The discovery of phytotoxic properties of N-aryl-3, 4, 5, 6-tetrahydrophthalimides (Ia) gave a new impetus to the subsequent research for the related imide types of herbicides (Ib, IIa-b & IIIa-d) which have been found as preemergence or early post-emergence herbicides. These herbicides shows phytotoxicity at low rate against many grassy and broadleaf weeds and are exceptionally phytotoxic to hairly galinsoga, common purslane and toothcup. Further biological and biochemical studies using higher plants, e.g. sawa millet, tobacco plants, pigment mutants of rice plants and mung bean, and unicellular green microalgae, Scenedesmus acutus, have revealed that these cyclic imide class of herbicides commonly indicate an apoplastic pattern of translocation in plants, a light-dependent bleaching action and a severe decrease of photosynthetic pigments caused by inhibition of the light-dependent 5-aminolevulinate formation step in chlorophyll biosynthesis and photooxidative destruction of plant pigments already formed. A closer look at the structure of the compounds (Ia-b, IIa-b & IIIa-d) shows a number of interesting features ; namely, alkylene ring (Moiety A), electron-donating moiety (Moiety B), imide structure (Moiety C) and aryl ring (Moiety D), all of which could be responsible for their herbicidal activity. Having such structural consideration in mind, all series of compounds were analyzed on the basis biological and biochemical data in order to obtain some ideas why these imide types of compounds exhibit so potent phytotoxic activity, and also to find out whether variation in their structures would be possible. In the context of the molecular design of cyclic imide herbicides, principle information has been obtained on the structural characteristics required for herbicidal activity and it suggests that a large number of cyclic imide types of compounds can be herbicidal. The incidence of this activity is extremely high amongst compounds whose structure conform to the following rule ; (1) C_1 and C_2 carbon atoms in the alkylene ring should form part of planer in Moieties A and B, (2) Moieties B and C should form a planer, (3) A : The p-substituent on benzene ring in Moiety D should have a proper size and direction for the activity, B : Introduction of a halogen atom (especially F or Cl) at o-position of the active p-substituted aryl derivatives does not reduce activity of the parents, C : Introduction of a carboxyl or an amino acid group as a m-substituent on benzene ring may enhance symplast uptake of the herbicidal molecules.
日本農薬学会の論文
1988-05-20

環状イミド系除草剤の分子設計に関する研究

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