Study On Chemistry Of Neem And Its Bioactive Constituents

The neem tree, Azadirachta indica A. Juss, is a tropical plant that is well known for itspesticidal properties. Many studies have demonstrated that its seed contains abountconstituents which have biological activity, among this, tetranortriterpenoids are considered tobe the most important active principle due to their various effects on insects, and has gainedconsiderable attentions. In this paper many kinds of constituentes were isolated, purified andidentificated, and main studies were about the chemical and utilization oftetranortriterpenoids.Volatile constituents from freshly crushed neem seeds kernels were abtained by steamdistillation, and analyzed by means of GC-MS. A total of 16 compounds were identified,fifteen of them are sulfur-containing compounds. The volatile constituents can be grouped asaliphatic disulfides, trisulfides, tetrasulfides and thiaheterocycles. These sulfer-containingcompounds account for 89.63% of the total volatiles in the distilled oils of neem seeds kernels.Two new thiaheterocycles were being reported in neem seeds kernels for the fist times.10 compounds were isolated form the ethanolic extract of the neem seed kernels, 9 ofthem are identified to be tetranortriterpenoid. Neem extract were analyzed by means of LC-MS,17 compounds were separaed and 14 tetranortriterpenoids in it, and they are: azadirachtin I,azadirachtin H, azadirachtin D, azadiraehtin A, azadirachtin B, nimbinolide, salanninolide,isosalanninolide, Desacetylnimbin, Desacetylsalannin, nimbanal, nimbin, salannin and salannolacetate.neem oil also is the major commercially important products derived from the neem tree.Neem oil yield is sometimes as high as 50 percent of the weight of the kernel, It was analyzedby GC-MS to study the fatty acid composition. 8 fatty acids palmcitic acid, margaric acid,stearic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, behenic acid, wereidentified. Among them, unsaturated acid is the 64.38% of the total fatty acid. palmcitic acidand behenic acid were being founded in neem seeds kernels for the fist times. Fractionation ofthe dichloromethne extract of the neem oil has resulted in the isolation of one new estersderivatives named 2-Octadecanoic acid-4-Palmitic acid-2,4-Pentanediyl ester. Its structure isdeduced on the basis of spectroscopic evidence.A simple HPLC analysis method for quantitative determination of azadirachtin A was estsblished. The RSD of the method is 0.76%(n=5), and the rate of recovery is 100.31%, thelimit of detection for azadirchtin A is 300ng. On this base, method for extract and enrichmentof azadirachtin A were studied, such as: multi-solvent partition, solvent precipitation, clayadsorption, silica gel chromatography, Florisil chromatography and C18 chromatography.The photo-stabilization of azadirachtin A was examined when exposed to ultraviolet lightin the presence of some natural absorbers and some synthetical absorbers, azadirachtin Aextract solutions with and without UV light absorbers in methanol were applied onto surface ofglass slides. In certain intervals, the remaining concentration of azadirachtin A was analysed byHPLC. Using first order kinetic equation the dissipation half-life values (DT₅₀) for degradationof azadirachtin A under ultraviolet radiation were obtained. It indicated that the addition ofFerulic acid, Gallic acid, Rutin provided moderate degree of photo-stabilization to azadirachtinA, and addition of Aloin provided the best photo-stabilization of azadirachtin A among thesenatural UV absorbers studied. It was found to be able to stablize azadirachtin to high levels upto two times. And the addition of4-aminobenzoic, 2,4-dihydrobenzophenone,4,4'-dihydrobenzophenone and phenylsalicylate were able to stablize azadirachtin to 3,2.6, 1.4and 1.3times.The photo-stabilization of another two tetranortriterpenoid nimbin and salannin werestudies, nimbin and salannin are rapidly photo-oxidized under UV irritation and O₂atomosphere, under laboratory conditions, to two isomeric hydroxybutenolide products.nimbin is converted to nimbinolide and isonimbinolide, and salannin is correspondinglyconverted to salanninolide and isosalarminolide.Method to preparing cyclodextrin-azadirachtin complexes(microcapsule)was studied, andthe inclusion complexation behavior of azadirachtin withβ-cyclodextrin has beeninvestigated. The results show that the water solubility and photo-stabilization of azadirachtinA was obviously increased after resulting inclusion complex withβ-cyclodextrin. Thesatisfactory high thermal stability of the cyclodextrin microcapsule will be potentially usefulfor their application as insecticide products.