The present thesis describes phytochemical investigations on the chemical constituents of the flowers of Azadirachta indica A. Juss (neem) with reference to their biological activities including insecticidal activity against Anopheles stephensi, a carrier of malarial parasite, anti-bacterial activity, anti-oxidant activity and anti-mycobacterium activity.
The introduction of the thesis gives a review of the earlier contributions made in the chemistry and pharmacology of this tree, as well as a brief account of the present work. A brief review of biosynthesis of triterpenoids with particular reference to the tetranortriterpenoids and flavanoids is also included.
In the first working, the fresh flowers of Azadirachta indica were extracted with n-hexane \It room temperature and the extract after removal of the solvent, was fractionated through solvent separation, followed by various chromatographic techniques such as vacuum liquid chromatography, column chromatography, and thin and thick layer chromatography. Five pure constituents were ultimately obtained and characterized through spectral studies as azadirone (I), trichilinone acctate (2), epoxyazadiradione (3), nimbaflavone (4) and azadiradione (5).
In another working, the flowers were extracted with methanol and the crude methanolic extract was fractionated, followed by various chromatographic techniques such as vacuum liquid chromatography, column chromatography, HPLC and thin and thick layer chromatography. Eleven pure constituents were ultimately obtained and characterized through spectral studies and chemical transformations namely O-methylazadironolide (6), diepoxyazadirol (7), 3'-prenylnaringenin (8), flowerone (9), l-hydroxy-2-(p-hydroxyphenyl)ethane (10), β-D-glucoside of β.sitosterol (11), flowerin (12), isoazadironolide (13), azharone (14) and azadironolide (15) along with 1.
Besides these, several other constituents have been identified in the non-polar and less polar fractions using GC-FID and GC-MS. These compounds include five sesquiterpenes, three aromatics, twenty-two fatty acids (or their methyl esters), three steroids and eight hydrocarbons.
In the third working, the essential oil of flowers was collected through steam distillation, in which seven compounds were identified using GC-FID and GC-MS, which include two sesquiterpenes and five hydrocarbons.
Altogether fifty-six compounds are reported in the present thesis, fifteen of which were isolated in a pure state and their structures elucidated, whereas forty-one compounds were identified through GC-FID and GC-MS including twenty-five constituents identified for the first time from this source. Out of fifteen compounds isolated five are new (6, 7, 9, 12 and 14), three (2., 8 and 10) are reported for the first time from any part of neem, five (1, 3, 5, 13 and 15) are isolated for the first time from the flowers whereas two compounds (4 and 11) were earlier reported from the !lowers (lac. cit).
The structures of the new compounds have been elucidated through spectroscopic methods including UV, IR, MS, 1H-NMR and 13C-NMR, 2D-NMR experiments (J-Resolved, COSY-45°, NOESY, HMQC, HMBC, BB and DEPT) and chemical transformations. The known compounds have been identified through comparison of their physical and spectral data with those reported for the corresponding compounds in literature.
The biological activity of the different fractions of the extract and pure compounds was determined against 4th instar larvae of Anopheles stephensi, by Dr. S.N.H. Naqvi and Dr. Tariq Rajput, Department of Zoology, University of Karachi, Karachi. The anti-bacterial activity of different fractions was tested against Gram-positive and Gram-negative bacteria by Dr. Aqeel Ahamad and Miss Saira Kamal Khan Department of Microbiology, University of Karachi, Karachi. The anti-oxidant activity of flavanoids was determined by Dr. Ashana Oar and Dr. Sabra Naqvi of H.E.J Research Institute of Chemistry, University of Karachi, Karachi. The anti-mycobaclerium activity was tested by Dr. Cecil D. Kwong of Southern Research Institute, Brimingham, Alabama U.S.A, under TAACF program.