Ring systems, neonicotinoids

From the lead structure 2-nitromethylene-tetrahydro-l,3-thiazine (6, nithiazine) [7, 8], resulting neonicotinoids [9] such as the open-chain compounds, e.g., nitenpyram (8), acetamiprid (9), dothianidin (12), dinotefuran (13) (Chapter 29.2.1), the five-membered ring systems, e.g., imidacloprid (7), thiacloprid (11) (Chapter 29.2.2), and the six-membered ring systems, e.g., thiamethoxam (10), AKD 1022 (14)... 

In general, all commercialized neonicotinoids can be divided into open-chain compounds (Chapter 29.2.1) and neonicotinoids having ring systems such as five-membered (Chapter 29.2.2) and six-membered compounds (Chapter 29.2.3) that differ in their molecular characteristics. The structural requirements for both neonicotinoids having open-chain stmctures and ring-system containing neonicotinoids consist of different segments Usted below (Fig. 29.2.1, Tables 29.2.1 and 29.2.2) [1, 2]. 

Fig. 29.2.1.1. Stable conformations of open-chain neonicotinoids (1,2), the five-membered ring system imidacloprid (11) and predicted properties of their binding site (Okazawa et al., 2000) [72].

On the other hand, the sterically forbidden regions beyond the imidazolidine 3-nitrogen atom of 11 is important for binding [72]. The area around the 6steric interactions were more important for open-chain neonicotinoids than ring systems. 

Two commercial neonicotinoids containing five-membered ring systems belong to this group, imidacloprid (1) and thiadoprid (9). 

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