ABSTRACT
The earlier Indian chemists concentrated on the bitter principles of neem oil. Sen and Banerjee (1931) gave an account of these. Siddiqui (1942) isolated the crystalline bitter compound nimbin, and later developed a method for separation of these bitters (Siddiqui, 1945a,b,c). Mitra (1963) described all these activities in his book on neem. According to Govindachari (1992), after the work on nimbin, interest in neem constituents became dormant except for the isolation of two new compounds, vilasinin and vepenin. With the discovery of the activity of the neem compound that suppressed feeding in locusts (Butterworth and Morgan, 1968), the detailed chemistry of these received a new stimulus. Very exhaustive studies were undertaken, particularly on the known active compound azadirachtin (Figure 6). Some of the important publications in this direction were by Lavie et al. (1971), Connolly (1983), Kraus (1983), Kraus et al. (1985, 1987), Morgan and Mandava (1987), Siddiqui et al. (1988) and Balandrin et al. (1988). Rastogi and Mehrotra (1990, 1991, 1995) in the Compendium of Indian Medicinal Plants in three volumes gave various stages of this study. In their monographic account of neem, Koul et al. (1990), Nat et al. (1991), Tewari (1992) and Govindachari (1992) gave a brief summary of the salient points of research on the chemistry of neem. Schmutterer (1995) has also given the relevant account of compounds which gave promising pesticidal results. Broadly speaking, the following types of compounds have been reported.
