Abstracts of Vol. 27 No. 3

Original Articles

Fungicidal Activities of 2-Methoxy-2-[2-(benzylideneamino-oxymethyl)phenyl]-N-methylacetamide Derivatives

A number of 2-methoxy-2-(2-substituted phenyl)-N-methylacetamide derivatives were synthesized and their fungicidal activities were examined. Studies on structure-activity relationships revealed strong fungicidal activity when a α-methylbenzylideneaminooxymethyl group was introduced at the 2-position of the benzene ring of the phenylacetamide moiety. Furthermore, introduction of halogen atom(s), methyl or ethyl group(s), or methoxy or difluoromethoxy group(s) to the 3- and/or 4-position of the benzene ring of the benzylidene moiety resulted in an increase in fungicidal activity. When the α-position of the benzylideneaminooxymethyl moiety was not substituted with a methyl group, the fungicidal activity was extremely weak. However, the introduction of a α-methylthio group to this moiety increased the activity against cucumber downy mildew. Among the compounds synthesized in this study, (E)-2-methoxy-N-methyl-2-[2-(α-methylthio-4-trifluoromethylbenzylideneaminooxymethyl)phenyl]acetamide and (E)-2-[2-(4-difluoromethoxy-α-methylthiobenzylideneaminooxymethyl)phenyl]-2-methoxy-N-methylacetamide were very active against cucumber downy mildew. The former compound was also effective in the control of potato late blight.

Key words: 2-(substituted benzylideneaminooxymethyl)phenylacetamide derivatives, fungicide, strobilurin analogue.

Synthesis of a New 1,2,4-Oxadiazol-5-one Derivative, KC10017, and Its Controlling Activity against Rice Blast Disease Caused by Magnaporthe grisea

Fungicidal characteristics of KC10017, an oxadiazole compound, were investigated in a greenhouse. KC10017 showed strong protective activity against rice blast. When KC10017 (0.5 μg/ml solution) was sprayed on leaves, rice blast was controlled almost completely. Its protective activity decreased temporally, reaching 54% of the control value at 14 days after treatment. Further, its curative and systemic effects were not significant even at 100 μg/ml, and KC10017 was not active against the causal fungus, Magnaporthe grisea. However, it inhibited the melanization of appressoria and mycelia in M. grisea. KC10017 is the first oxadiazole compound showing an inhibitory effect on the biosynthesis of melanin in M. grisea. It was further confirmed that the protective activity of KC10017 was counteracted by wound inoculation of M. grisea. These results suggest that a compound with characteristics like KC10017 has potential as a new fungicide for rice blast.

Key words: melanin biosynthesis inhibitor, KC10017, an oxadiazole compound, rice blast.

Aerobic Aquatic Metabolism of Fenitrothion and Its Oxon Analog in Water-Sediment Systems

The aerobic aquatic metabolism of fenitrothion and its oxon was studied in French lake and Japanese pond water-sediment to estimate their behavior in the natural aquatic environment. The effect of aeration on the metabolic profiles of fenitrothion was examined by either passing air over the surface or gently bubbling the water phase. Almost the same metabolic profiles were obtained under both conditions but the partition profiles of radioactivity between the aqueous and sediment phases differed slightly. There was no significant difference in the metabolism of fenitrothion between French and Japanese sediments. Fenitrothion mainly underwent cleavage of the P-O-aryl linkage to form the corresponding phenol and reduction of the nitro group followed by the subsequent acetylation of the amino group. The oxidative desulfuration of fenitrothion to form the oxon was a minor route. The increase in phenol and 14CO2 with less reductive transformation under the bubbling of water with air was likely to originate at least in part from less anaerobicity. The oxon derivative of fenitrothion rapidly underwent cleavage of the P-O-aryl linkage to form the phenol in the water-sediment system.

Key words: biodegradation, fenitrothion, water sediment system, reduction, nitro group, ester hydrolysis, oxidative desulfuration.

Mathematical Model of the Uptake of Non-Ionized Pesticides by Edible Root of Root Crops

A plant uptake model was developed to estimate the residual amount of non-ionized pesticides in the edible roots of root crops. An examination of the route of uptake of furametpyr (log Kow=2.36) and pyriproxyfen (log Kow=5.37) suggested that the more lipophilic of the two pesticides, pyriproxyfen, was mainly adsorbed by the root peel and incorporated by diffusion into the root core. On the other hand, the less lipophilic pesticide, furametpyr, was mainly taken up via the transpiration stream into the core through the root hairs. Based on the results, a mathematical model for the uptake of a pesticide into edible roots was developed based on the following route; (1) incorporation into the root core via the transpiration stream through the root hairs, (2) adsorption by the root peel, and (3) diffusion from the peel to the root core. To test the model, residual amounts of furametpyr and pyriproxyfen were analyzed and compared to those predicted when the pesticides were treated at one-tenth of the concentration in the model construction. Ratios of predicted to measured residual concentrations were 1.01‐1.38 and ?0.75‐1.28 for furametpyr and pyriproxyfen, respectively, showing the effectiveness of the model as a predictive tool.

Key words: plant uptake model, pesticide, root crop, furametpyr, pyriproxyfen.

Synthesis of Alkylene-Tethered Bis-Imidacloprid Derivatives as Highly Insecticidal and Nerve-Exciting Agents with Potent Affinity to [3H]Imidacloprid-Binding Sites on Nicotinic Acetylcholine Receptor

Bivalent molecules of bis-imidacloprid with 2‐10 alkylene tethers as well as tethers containing an ethenylene, ethynylene, phenylene and oxide joint were prepared. These dimeric chloronicotinyl molecules were highly insecticidal against American cockroaches on injection at 2‐30 nanomolar doses. The minimum lethal dose of the most potent hexamethylene derivative was close to that of imidacloprid, and the potency was augmented up to about thirty-five-fold following pretreatment with metabolic inhibitors, while the binding affinity to [3H]imidacloprid-binding sites on the nicotinic acetylcholine receptor was weaker than that of imidacloprid by a factor of 160. The hexamethylene derivative elicited impulses in cockroach central nerves with an initial excitation and subsequent block at a potency comparable to imidacloprid.

Key words: neonicotinoid insecticides, imidacloprid, American cockroach, insecticidal activity, nerve-excitatory activity, alkylene-tethered bis-imidacloprid.

Synthesis and Fungicidal Activity of α-Cyanoacetamide Derivatives: Discovery of a New Rice Blast Fungicide, Diclocymet (S-2900)

In order to search for a new systemic rice blast fungicide, a number of N-benzyl-α-cyanoacetamide derivatives and related compounds were prepared and their preventive activity against rice blast, Magnaporthe grisea was examined both in a foliar spray test and in a soil drench test. Several N-[1-(substituted-phenyl)ethyl]- 2-cyano-3,3-dimethyl-butanamides and -2-pentenamides showed high activity in both tests. Among them, (RS)-2-cyano-N-[(R)-1-(2,4-dichlorophenyl)ethyl]-3,3-dimethylbutyramide (diclocymet, S-2900) was selected as a practical new systemic rice blast fungicide, which shows potent fungicidal activity with little crop injury.

Key words: rice blast fungicide, systemic activity, α-cyanoacetamide derivatives, stereoisomer, diclocymet, S-2900.

Insecticidal and Neuroblocking Activities of Thiacloprid and Its Acyclic Analogues and Their Related Cyanoguanidine Derivatives

Acyclic analogues of thiacloprid and related cyanoguanidine derivatives were prepared. Their insecticidal activity against the American cockroach was determined by the injection method with or without metabolic inhibitor(s). Thiacloprid along with two cyanoguanidine analogues showed the highest insecticidal potency without the inhibitors, which was one twentieth that of imidacloprid. Metabolic inhibitors increased the activity by a factor of up to 100 for sulfur-containing compounds including thiacloprid, while the effect for the cyanoguanidine derivatives was much smaller. Most of the test compounds elicited impulses in cockroach central nerves with an initial excitation and subsequent block. Thiacloprid and its acyclic analogue were on a par with imidacloprid for blocking potency. As the blocking activity increases, the insecticidal activity measured with the metabolic inhibitors tends to strengthen.

Key words: chloronicotinyl insecticide, thiacloprid, imidacloprid, American cockroach, insecticidal activity, neuroblocking activity.


Mode of Action of Herbicidal N-Benzyl-4-chloro-N-isobutyl-2-pentenamides

Key words: N-benzyl-4-chloro-N-isobutyl-2-pentenamides, phytotoxic mechanism of action, protox inhibition, ethane formation, photosynthetic pigments degrees.

An Efficient Assay of Bacillus thuringiensis Formulations by Low-Vacuum SEM Freeze Drying

Key words: Bacillus thuringiensis, BT formulation, quality check, low-vacuum SEM.

Technical Report

Model of the Uptake of Pesticides by Plant

The government agencies for pesticide registration in USA and EU are now adopting a tiered approach to evaluate pesticides. In this system, they are beginning to allocate important roles to computer simulation models as a screening tool, in order to handle the vast number of pesticides waiting to be registered or re-registered. To date, a number of plant uptake models for pesticides have been published, although no plant uptake model is in practical use in risk assessment for regulatory purpose. Recently, EU authorities reported the usage of the PlantX model developed by Trapp et al. in the European Union System for Evaluation of Substances (EUSES). With this as a foothold, it is well predicted that the increasing demand for more accurate plant uptake models will evolve in the future. The basic concept adopted in these models is the partition-based theory which expresses translocation and distribution of the pesticides via changes in the equilibrium of concentration between different phases or adjacent compartments. This review will summarize the foundation of the partition theory including fugacity as well as applications to these models.


Biodegradation of Synthetic Compounds and Agro-Chemicals by Soil Microorganisms in Field Soils

Key words: bioremediation, dehalo-respiration, anaerobic bacteria, paddy field, microbial ecology.

Optically Active Substances and Living Organisms―What Has Been Clarified by Synthetic Chemistry ?―

Recent development in the studies on the relationships between optically active bioregulators and organisms is reviewed with emphasis on the role of synthetic chemistry to provide pure enantiomers. The power of modern analytical methods was illustrated by determination of the absolute configuration of plakoside A, an immunosuppressive glycosphingolipid. Case studies on limatulone (a marine triterpene with antifeedant activity) and stigmolone (a microbial pheromone) revealed that bioregulators are not always enantiomerically pure. Diverse stereochemistry-bioactivity relationships among pheromones including japonilure, olean and sulcatol are discussed to show the importance of enantiomerism in exhibiting bioactivity.

Key words: absolute configuration, enantioselective synthesis, pheromones, plakoside A, stereochemistry-bioactivity relationships.

Strategies for the Use of Natural Products for Weed Management

Natural products have not been utilized as extensively for weed management as they have been for insect and plant pathogen management, but there are several notable successes such as glufosinate and the natural product-derived triketone herbicides. The two fundamental approaches to the use of natural products for weed management are: 1) as a herbicide or a lead for a synthetic herbicide and 2) use in allelopathic crops or cover crops. New technologies, such as molecular biology, provide tools for expanding the use of natural products in weed management. Strategies for implementation of these approaches are discussed, along with examples.

Key words: allelochemical, allelopathy, herbicide, natural products, phytotoxin, weed management.

Chlorophyll Fluorescence as a Probe for Determination of Inhibition Sites in Photosynthetic Electron Transport by Novel Inhibitors

Key words: chlorophyll fluorescence, inhibition site, photosynthetic electron transport.


Electrophysiological Study of the Mechanism of Action of Insecticides Activity on Ion Channels

Key words: GABA receptor, nACh receptor, fipronil, picrotoxinin, anisatin, patch clamp, ion channel.

Thermodynamic Estimation of Vapor Pressures for Carbamate Pesticides

Key words: carbamates, estimation of vapor pressure, modified Watson method.


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