The work embodied in the present thesis describes phytochemical investigations on the chemical constituents of azadirachta indica A. Juss.(neem) with reference to their insecticidal activity against Aedes aegypti and anopheles stephensi.
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 and steroids with particular reference of the tetranortriterpenoids is also included.
New constituents: Melianol(1) Desfurano-6 α –hydroxyazadiradione (2) Zeeshanol (4) 7 α- Senecioyl-(7-deacetyl)-23-O methylnimocinolide (6) 22,23- Dihydronmiocinoal (7) Zafaral (9) 23-O- Methlnimocinolide (10) Meliacinol (12) Desfuranodesacetylnimbin -17-one (14) Meliatetraone (16) 6 α-O-Acetyl-7 deacetylnimocinol (17) Meliacinanhydride(18) Meliatetraolenone (20) Unreported compound: Odoratone (22) Known constituents: Nimocinol Nimocinolide Isonimocinolide Meldenin Isomeldenin
Compounds 6,10 ,17 and nimocinol showed IGR effect on mosquitoes (Aedes ageyptiy ) and exhibited mortality on the 4th instar larvae with C50 2.14, 53.00, 21.00 and 83.00 ppm respectively. Compounds 2,7,20 and 22 were tested for their pesticidal activities against 4th instar larvae of anopheles stephensi, and exhibited toxicity with LC50 43.00, 60.00, 16.00 and 154.00 ppm respectively.
The structure elucidation of all the new and known compounds was carried out using spectroscopic techniques including 1D and 2D NMR such as 1H 13C NMR DEPT, HMQC, HMBC, COSY-45, NOESY, J-resolved as well as various modes of mass spectrometry, EI, CI, FD, FABS +ve and –ve; IR, and UV- Chemical transformations were also carried out in most of the cases to confirm the structures.
The biological activity of these constituents was determined against 4th instar larvae of Aedes aegypti and anopheles stephensi, whichever was available depending on their rearing season, by Dr. S.N.H Naqvi, Department of pharmacology, Baqai University, Karachi and Mr. Tariq Rajput department of Zoology , University of Karachi, Karachi.