![]() The sodium channel is a membrane protein with a hydrophilic interior. They are fast-acting axonic excitotoxins, the toxic effects of which are mediated by preventing the closure of the voltage-gated sodium channels in axonal membranes. Pyrethroids, including cyhalothrin, disrupt the functioning of the nervous system in an organism. FMC has entered the market as a supplier of γ-cyhalothrin for use as a broad-spectrum insecticide under the brand name Scion. The patents covering the parent compound expired in most major markets in 2003. In 2000, the agrochemical business of ICI merged with that of Novartis to form Syngenta, which still manufactures and supplies λ-cyhalothrin. At that time, γ-cyhalothrin, ICI code number PP345, was not a feasible alternative product owing to the difficulty of manufacturing that isomer alone, especially if this involved recycling the "wrong" isomer of the Z-cis acid. The new product was first launched in nine countries in 1985 using the trademark Karate. ![]() ![]() This so-called "enantiomer pair", ICI code number PP321, could be used after a process for its economic production and purification was developed using crystallisation with recycling of the unwanted enantiomer pair. After further research and field tests, ICI chose to focus on λ-cyhalothrin, the mixture containing the single most active isomer together with its mirror image. The first was to make the development and sales of tefluthrin feasible and the second was to spur research directed at making compositions of cyhalothrin with fewer isomers in the sales product. The process work made available a relatively large supply of the Z-cis acid and hence allowed two further commercially important steps to be taken. This led to the initial commercialisation of cyhalothrin, under the trade name Grenade, but the resulting material was still a mixture of four isomers owing to the racemic nature of the Z-cis acid and because the alpha-cyano group was a 1:1 mixture of possible R and S configurations. The second breakthrough occurred when ICI process chemists developed a practical manufacturing process for the Z-cis acid, by controlling the stereochemistry of the cyclopropane ring in addition to that of the double bond. The resulting material was found to be more potent than cypermethrin, to which it is most closely related, but also with good activity against the spider mite Tetranychus urticae, which added to its attractiveness as a potential new product. The first breakthrough was made when a trifluoromethyl group was used to replace one of the chlorines in cypermethrin, especially when the double bond was in its Z form. ![]() For that reason, in the period 1974–1977, chemists there sought patentable analogues which might have advantages compared to the Rothamsted insecticides by having wider spectrum or greater cost-benefit. Also, it was clear to ICI's own researchers at Jealott's Hill that future competition in the marketplace might be difficult owing to the greater potency of deltamethrin compared to the other compounds. Imperial Chemical Industries (ICI) obtained licenses to permethrin and cypermethrin but their agreement with the NRDC did not allow worldwide sales. These compounds were subsequently licensed by the NRDC, as NRDC 143, 149 and 161 respectively, to companies which could then develop them for sale in defined territories. The latter is racemic and contains the (1R) and inactive (1S) isomers in equal amounts.īy 1974, a team of Rothamsted Research scientists had discovered three pyrethroids (MoA 3a), suitable for use in agriculture, namely permethrin, cypermethrin and deltamethrin. Γ-cyhalothrin (a single chiral isomer) is indeed twice as active as λ-cyhalothrin on a weight-for-weight basis. The active isomer of deltamethrin, (1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylic acid, has the same stereochemistry. All of the insecticidal activity is due to the proportion of absolute stereochemistry (1R) in the mixture. ![]() Both are cyanohydrin esters of cis-3-2,2-dimethylcyclopropanecarboxylic acid. Gamma-cyhalothrin and lambda-cyhalothrin are the active ingredients in the current commercial products based on cyhalothrin. λ-and γ-cyhalothrin are now used to control insects and spider mites in crops including cotton, cereals, potatoes and vegetables. Pyrethroids such as cyhalothrin are often preferred as an active ingredient in agricultural insecticides because they are more cost-effective and longer acting than natural pyrethrins. It is a pyrethroid, a class of synthetic insecticides that mimic the structure and properties of the naturally occurring insecticide pyrethrin which is present in the flowers of Chrysanthemum cinerariifolium. Cyhalothrin is the ISO common name for an organic compound that, in specific isomeric forms, is used as a pesticide. ![]()
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