|Keywords (Extracted from title, table of contents and abstract of thesis)
zadirachta indica a. juss, naeem, houseflies, mosquitoes, pesticide, anopheles stephensi, terpenoids, terpenes, prenylogues, squalenes, a. indica
The present studies have been undertaken on the ethanolic extract of fresh fruit coatings of Azadirachta indica A. Juss, (Neen) following a bioassay guided isolation in the light of our observation that (i) the coatings extract exhibited a larger degree of efficacy on houseflies and mosquitoes as compared to that of seeds and (ii) azadirachtin, the most potent naturally occurring pesticide found in neem is not present in the extract of coatings in any detectable amounts.
The pesticidal activity guided isolation against 4th instar larvae of mosquito, Anopheles stephensi (Orangi Town wild strain), a carrier of malarial parasite, led to the isolation of sixteen triterpenoids, including six new and ten known compounds as listed below. Two of the new constituents, namely meliacinin and azadironic acid represent the skeleton of biogenetic interest. Twelve of these were investigated for the aforementioned biological activity.
Beside these, several other constituents have also been identified (listed below) from the non-polar and less polar fractions showing considerable pesticidal activities. These compounds including sixteen hydrocarbons, one monoterpene, one sesquiterpene, three aromatics, three benzopyranoids and tree fatty acide esters were identified using GC-FID and GC-MS. Their identifies were also supported by other spectroscopic techniques.
Hydrolysis of the major component of neem i.e. azadiradione (2), was attempted under Zemplin conditions to deacetylate C-7 and relate the pesticidal activity with the structure. Fair amounts of required products (44) was obtained along with another product (45). Their pesticidal activity was also performed to extend the structure pesticidal activity relationship.
The structures of the new compounds have been elucidated through sophisticated modern spectroscopic methods including UV, IR, MS, 1H-NMR and 13C-NMR, 2D-NMR experiments 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.
Altogehter forty-five compounds are reported in the present thesis, sixteen of which were isolated and teir structures elucidated, whereas twenty-seven compounds were identified through GC-FID and GC-MS. Two analogues were obtained through hydrolysis of Azadirdione. The isolated compounds included six newa,b,c and ten previously reported constituents. The compounds identified through GC, included eight compounds, identified for the first time from fruit coatings, which are marked with the superscript ‘f and fifteen compounds hitherto unreported from any part of neem prior to these studies, which are marked with the superscript ‘g’. The LC50 against An. Stephensi of isolated compounds and of the fractions subjected to GC is given in parenthesis.c,d,e A discussion of the presticidal activity with reference to chemical structures has also been made.