Limonoids, bitter tetranortriterpene derivatives from a precursor with a 4,4,8-trimethyl-17-furanylsteroid skeleton (Fig. 2.3), are a class of secondary metabolites confined to the families of order Rutales and most of them are found in Meliaceae and Rutaceae [189]. Over 300 limonoids have been isolated to date and about one-third are generated from neem (Azadirachta indica) and Chinaberry (Melia azedarach) [190–192]. There are many proposed pathways for the biosynthesis of this type of furanoterpenoids. However, most of them are tentative as they are not supported by valid biosynthetic studies. Some studies have shown that limonoids isolated from plants belonging to the Meliaceae family are synthesized through terpenoids biosynthetic pathway [190–193]. Two chemically similar compounds, euphane and tirucallaneA derivative of gedunin (214), 6β-hydroxygedunin (215), previously only a synthetic compound, was recently also isolated from the Indian neem tree, A. indica, and was found to be an antifeedant toward the gram pod borer, H. armigera as well as against the Asian armyworm, with an EC50 of 24.1 ppm, and against S. litura at 21.5 ppm.97 Although not as active an antifeedant as azadirachtin it was more powerful than gedunin (214). Other non-azadirachtin limonoids from the Indian neem tree such asnimbocinol, salannin (216), and azadiradione (217) also seem to have antifeedant activity against these lepidopteran pests,98 but with an FI50 value at least 150 times higher than that of azadirachtin and five times more than that of 6β-hydroxygedunin