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2.16 Azadirachta Species
2.16.1 Ethnopharmacological Properties and Phytochemistry
Azadirachta indica A. Juss. (Fam. – Meliaceae) has long been known for its insecticidal properties. The neem plant tree has broad leaves, height up to 30 m, flowers, and fruits borne in axillary clusters. Both the bark and leaves contain less amount of azadirachtin, while seed kernels have higher concentration. The tree is now grown in most tropical and subtropical areas of the world for shade and for reforestation programs and in plantations for the production of compounds that have toxic, antifeedant, and repellent properties against insects (Mordue and Nisbet 2000). The neem tree has been used for medicinal properties since centuries all over the world to control various diseases. The plant species possesses immune stimulation, blood purification, anti-inflammation, antitumor, insect repulsion, and bactericidal and growth-disrupting properties (Butterworth and Morgan 1968; Biswas et al. 2002; Haque et al. 2006). The antifeedant and insecticidal activities of salannin, nimbin, and 6-deacetylnimbin were evaluated against Spodoptera litura, Pericallia ricini, and Oxya fuscovittata (Govindachari et al. 1996a, 2000). By preparative high-performance liquid chromatography (HPLC), the various azadirachtins (azadirachtins A, B, D, H, and I) were isolated and purified from neem oil (Govindachari et al. 1992, 1996b, 1997; Saxena and Kumar 2008). Azadirachtin is in industrial demand due to its eco-friendly, biodegradable, biopesticide nature (Jadeja et al. 2011). Azadirachtin, isolated from the A. indica, has generated wide academic and industrial applications in control of insects (Yamasaki et al. 1986). From the crude extract of leaves, the nimbin, nimbidin, nimbic acid, nimbidinin, and nimbinin have been identified (Vani et al. 2016).
A new tetranortriterpenoid, 13,14-desepoxyazadirachtin-A, has been isolated from neem kernel extract by preparative HPLC and its structure established by spectroscopic methods (Govindachari and Gopalakrishnan 1997). Azadirachtins A, B, and H demonstrated nematicidal and antifungal properties, but azadirachtin B showed maximum activity against Rotylenchulus reniformis. Similarly, azadirachtin H exhibited strongest antifungal activity against Rhizoctonia solani (Sharma et al. 2003). Nimbolide was isolated from A. indica and isonimbolide (isomer) was prepared by rearrangement reaction of nimbolide by using boron trifluoride etherate and tetrabutylammonium bromide (Solomon et al. 2005). The noncrystalline dihydro derivative was synthesized from nimbolide (Ekong 1967). The salannin, nimbin, and their other derivatives including salannolide, isosalannolide, nimbinolide, and isonimbinolide were isolated from A. indica (Akhila and Rani 1999). The meliacin was isolated and purified from the seeds of A. indica and its identity was confirmed by spectral data (Rojatkar and Nagasmpaki 1994). Besides these compounds, the other compounds such as azadirol, azadironolide, isoazadironolide, limocin A, limocin B, and limocinin were also isolated from A. indica (Siddiqui et al. 1986).
The gas chromatography–mass spectrometry (GC–MS) analysis revealed the presence of the γ-elemene, (2E)-3,7,11,15-tetramethyl-2-hexadecen-1-ol, methyl petroselinate, phytol, methyl isoheptadecanoate, hexadecamethylcyclooctasiloxane, butyl palmitate, 2,6,10,14-tetramethylheptadecane, nonadecane, isobutyl stearate, oxalic acid, 2-ethylhexyl tetradecyl ester, heptacosane, eicosane, 7-hexyl, heptacosane, 7-hexyl, and octacosane in hexane extract; (Z,E)-α-farnesene, 2E-3,7,11,15-tetramethyl-2-hexadecen-1-ol, hexahydrofarnesyl acetone, methyl 14-methylpentadecanoate, 9,12,15-octadecatrienoic acid, methyl phytol, 1-tridecene, and (9E,12E,15E)-9,12,15-octadecatrien-1-ol in ethyl acetate extract; (2E)-3,7,11,15-tetramethyl-2-hexadecen-1-ol (14.43%), linoleoyl chloride, methyl isoheptadecanoate, and nonacosane from chloroform extract; and levoglucosenone, benzaldehyde, 2-methyl, 2-methyl-5-ethylfuran, (2E)-3,7,11,15-tetramethyl-2-hexadecen-1-ol, and hentriacontane from butanol extract of Omani neem (Hossain et al. 2013).