The discovery of thiamethoxam: a second-generation neonicotinoid
2001
Maienfisch, P. | Huerlimann, H. | Rindlisbacher, A. | Gsell, L. | Dettwiler, H. | Haettenschwiler, J. | Sieger, E. | Walti, M.
Neonicotinoids represent a novel and distinct chemical class of insecticides with remarkable chemical and biological properties. In 1985, a research programme was started in this field, in which novel nitroimino heterocycles were designed, prepared and assayed for insecticidal activity. The methodology for the synthesis of 2-nitroimino-hexahydro-1,3,5-triazines, 4-nitroimino-1,3,5-oxadiazinanes and 4-nitroimino-1,3,5-thiadiazinanes is outlined. Bioassays demonstrated that 3-(6-chloropyridin-3-ylmethyl)-4 -nitroimino-1,3,5-oxadiazinane exhibited better insecticidal activity than the corresponding 2-nitroimino-hexahydro-1,3,5-triazine and 4-nitroimino-1,3,5-thiadiazinane. In most tests, this compound was equally or only slightly less active than imidacloprid. A series of structural modifications on this lead structure revealed that replacement of the 6-chloro-3-pyridyl group by a 2-chloro-5-thiazolyl moiety resulted in a strong increase of activity against chewing insects, whereas the introduction of a methyl group as pharmacophore substituent increased activity against sucking pests. The combination of these two favourable modifications led to thiamethoxam (CGA 293 343). Thiamethoxam is the first commercially available second-generation neonicotinoid and belongs to the thianicotinyl sub- class. It is marketed under the trademarks Actara for foliar and soil treatment and Cruiser for seed treatment. The compound has broad-spectrum insecticidal activity and offers excellent control of a wide variety of commercially important pests in many crops. Low use rates, flexible application methods, excellent efficacy and the favourable safety profile make this new insecticide well-suited for modern integrated pest management programmes in many cropping systems.
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