Neem compounds

Advances in the chemistry of the neem tree Azadirachta indica A. Juss.) and other species of the Meliaceae have been rapid as a result of interest in the unique characteristics of their limonoids and other secondary metabolites. This is especially true for azadirachtin, the final compound in the biosynthetic scheme. The search for new, powerful, non-toxic insecticides has become a great priority for the pesticide industry, and azadirachtin is currently a leading candidate. Although recent reviews have been published 1-4), more precise information is rapidly being generated. In this chapter we will review present information on the chemical properties of neem compounds and specifically on the chemistry of azadirachtin and its use to control insect molt. 

Spectral Properties of Tetranortrite enes. and C-NMR data for some selected neem compounds are included in Tables 1-4. 

Another limonoid isolated from neem seeds and determined to be as potent as azadirachtin as an ecdysis inhibitor has been identified as 3-deacetylazadirachtinol (Figure 15) (57). Both compounds were lethal to 50% of the treated H. virescens larvae (EI5Q) at 0.8 ppm in artificial diet (Table VII). Structurally, there are two differences between the compounds. In 3-deacetylazadirachtinol, the C-ll-O-C-13 ether linkage of azadirachtin is reductively cleaved at the 11 position and the acetoxyl group at C-3 is hydrolyzed to a hydroxyl group. 

Affect only gram +ve bacteria. Medicated by other antiseptic herbal origin compounds (DETTOL, SAVLON, NEEM, MEDIMEX etc). 

Many triterpenes also have anti herbivore activity. In general, those which are highly oxygenated seem to be more active in this regard M). The role of cardiac glycosides, insects and their predators has been reviewed (91-94). A number of metabolically altered triterpenes from the Rutaceae, Meliaceae and Simaroubaceae are antifeedants. Extracts of neem tree seeds (Azadirachta indica. Meliaceae) were shown to be repellent to a number of insects when applied to various crop plants at low concentrations. The probable active compound is tetranortriter-pene, azadirachtin (9 ). This compound from the leaves and fruits... 

Other benefits of large numbers of analogs to plants may include slower evolution of tolerance or lower rates of metabolism of mixtures compared with that of single compounds in herbivorous insects. Feng and Isman (1995) investigated the possibility of adaptation in herbivores by repeated selection of peach aphid colonies with either pure azadirachtin or neem seed extracts containing a large number of limonoids. The colonies treated with azadirachtin soon showed evidence of tolerance of this pure compound, whereas no evidence of tolerance was... 

Neem extracts, pure constituents (i.e. azadirachtin) and formulated products showed positive results against Tetranichus mites [279-283]. Less polar extracts were considerably more toxic than polar ones or cold-pressed neem oil or commercial neem oil, and reduced the fecundity of the mites on treated plants and the survival of nymphs hatched from treated eggs application of pentane extract or neem oil in sublethal concentrations, caused growth disrupting effects on the nymphal stages and ovicidal effects. Quantification of the insecticidal substance azadirachtin in the extracts revealed that this compound was not the most active principle against the mites [284]. 

The powerful antifeedant and insecticide azadirachtin (213), from the neem tree (Azadirachta indica, Meliaceae), is a highly oxidized limonoid with rings A, B, and D intact.2 It is used as a benchmark against which all other antifeedants can be compared (vide infra). The total synthesis of azadirachtin has recently been achieved in 64 steps.96 This is very unlikely to provide a synthetic source of the compound, but it does allow SAR studies to find maximum activity, and opens up the field to possible simpler synthetics modelled on it. As yet, even slight modifications of the structure tend to decrease activity. Azadirachtin (213) has been available commercially, particularly in the United States, but at present the cost of the seeds and the isolation procedure inhibit its wider use. 

Limonoids are C2(, nortriterpenoids deriving from a C30 triterpene precursor. The best known limonoids are the Azadirachta indica (neem tree) antifeedant azadirachtin (C50L C40 C6 -C60(epoxide methylene cross-link) furan) and the Citrus species (Rutaceae) bitter antifeedant limonin (G50L G40 G6 G6 C50L(epoxide)-furan). Limonin gives a delayed bitter taste to Citrus fruit. The limonoids are typically bitter compounds with insect antifeedant activity... 

Neem seed oil possesses an unpleasant, garlicky-type odor, undoubtedly due to a number of sulfur compounds present. 

The neem tree, Azadirachta indica, is native to tropical Asia but has been planted widely in the warmer parts of Africa, Central and South America, and Asia. Extracts from neem seed kernels act as repellents, antifeedants, and growth disruptants. The main active principle in kernels is azadirachtin (AZ), a limonoid with a very complicated structure. A range of other compounds is also present. These neem substances can repel insects, prevent... 

The three metabolites assayed produced the same effect on the insect used that the control (a commercial extract of the neem tree, containing 2% of azadirachtin), although at higher concentrations. 20a-hydroxy-tingenone was the most active compound among the three assayed. Pristimerin shows also a high antifeedant activity together with molt effect suppression. 

Representatives of podocarpanes include podocarpinol in Podocarpus totara, and podocarpic acid, the dominant acidic constituent of podocarpus resin obtained from Javanese P. cupressina (Cupressaceae), as well as the bitter-tasting phenolic compounds nimbiol and nimbione. These are found in the bark and isolated from neem oil expressed from the seed-kernels of the Indian neem tree Azadirachta indica (Meliaceae). Extracts of this bark are added to some mouthwashes and skin creams neem oil is used as an agricultural insect repellant and antifeedant. 

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