Nicotinoids and neonicotinoids

Besides an electron-withdrawing heterocyclic ring, they have a nitro-methylene, nitroimine, or cyanoimine group that can distinguish the insect receptor from the vertebrate nicotinic acetylcholine receptor (Tomizawa et al., 1995a, 1995b Yamamoto et al., 1995). 

The neonicotinoids many favorable properties may be summarized in these points  

The neonicotinoids were mainly developed in Japan, but imidacloprid is sold by the German company Bayer AG. 

Name Rat (Male) Oral LD50 (mg/kg) NOEL Rat (2 years) (mg/kg in food) Toxicity Class (WHO) Daphnia EC50 (mg/kg) Application Rates (g/ha) 

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Yamamoto, L, Yabuta, G., Tomizawa, M., Saito, T., Miyamoto, T., and Kagabu, S. 1995. Molecular mechanism for selective toxicity of nicotinoids and neonicotinoids. 

Matsuo H, Tomizawa M, Yamamoto 1 (1998) Structure-activity relationships of acychc nicotinoids and neonicotinoids for insect nicotinic acetylcholine receptor/ion channel complex. Arch Insect Biochem Physiol 37 17-23... 

Many pesticides are not as novel as they may seem. Some, such as the pyre-throid and neonicotinoid insecticides, are modeled on natural insecticides. Synthetic pyrethroids are related to the natural pyrethrins (see Chapter 12), whereas the neo-nicotinoids share structural features with nicotine. In both cases, the synthetic compounds have the same mode of action as the natural products they resemble. Also, the synthetic pyrethroids are subject to similar mechanisms of metabolic detoxication as natural pyrethrins (Chapter 12). More widely, many detoxication mechanisms are relatively nonspecific, operating against a wide range of compounds that... 

At a more subtle level, behavioral disturbances may make it more difficult for animals to find food. Pyrethroids, carbamates, OPs, and neonicotinoids can disturb the foraging activity of bees (Thompson 2003). Interestingly, effects have been shown upon the wagtail dance of bees, and this disrupts communication between individuals as to the location of nectar-bearing plants. Also, the neonicotinoid imidacloprid has been shown to adversely affect conditioned responses such as proboscis extension of honeybees (Guez et al. 2001). Nicotinoids can disturb the functioning of cholinergic synapses, which are involved in the operation of the proboscis reflex as... 

Figure 4 Moiecuiar modeis of binding subsites in the Drosophila or vertebrate nicotinic acetyichoiine-reguiated receptors. (Reprinted with permission from Tomizawa etal. (2003) The neonicotinoid eiectronegative pharmacophore piays the cruciai roie in the high affinity and seiectivity for the Drosophila nicotinic receptor An anomaiy for the nicotinoid cation-pi interaction modei. Biochemistry 42 7819-7827 American Chemicai Society.)...

Fig. 29.1.4. Comparison between electro-physiological and binding potencies of different neonicotinoids (6-9) and nicotinoids. Electrophysiological data were obtained from neurone cell bodies isolated from the CNS of H. virescens. pECsoS (= -log M) correspond to the half-...

Maienfisch P, Brandi F, Kobel W, RindUsbacher A, Senn R (1999). CGA 293 343 a novel, broad-spectrum neonicotinoid insecticide. In Yamamoto I, Casida JE (eds) Nicotinoid insecticides and the nicotinic acetylcholine receptor. Springer, Tokyo, pp 177-209 Majumdar DN (1952) Alkaloidal constituents of Withania somnifera. Curr Sci 21 46 Majumdar DN (1955) Withania somnifera. II. Alkaloidal constituents and their chemical characterization. Ind J Pharm 17 158-61... 

Another biological target for many insecticides is the nervous system of the insect because this can result in selective toxicity. The neonicotinoids, in group 4, work by this mechanism and act on insect nicotinic acetylcholine receptors (nACtiR). Nicotine, the namesake of the nACtiR has been used for pest control since the century [33], However nicotine is hazardous to people and has limited effectiveness as an insecticide. Nicotine and its analog epibatidine, isolated from a tropical poisonous frog, exist mainly in the pro-tonated form at physiological pH. They are examples of the nicotinoid family and are toxic to mammals. 

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