Faculty of Science

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    Open Access
    Studies in the Chemistry and Properties of 7, 8, 9, 10-Tetrahydro Pyrido (1, 2-A) Aquinoxalin-6-Ones
    (University of Lagos, 1989-04) Graham-Ode, E. A.
    This thesis reports the results of investigations into the chemistry and properties of the new heterotricycle: 7, 8, 9, 10-tetrahydropyrido (1, 2-a) aquinoxalin-6-one. The chemistry and properties of quinoxalines, pyrrolo (1,2-a) quinoxalines and pyrido (1,2-a) quinoxalines are reviewed. A re-investigation of the methods of synthesis of the title compound and some of its derivatives was undertaken. Condesation of pipecolinic acid with the appropriately substituted 1-fluoro-2-nitrobenzene in ethanol basified wih 10% sodium hydrogen carbonate solution followed by cyclization of the resulting N-(2 - nitrophenyl) piperdine-2- carboxylic and with alkaline sodium dithionite was developed as the optimum method. The 2-fluoro-and 3-methyl- derivatives of the heterotricycle were prepared in this manner. The sodium dithionite reductive cyclization method, however, proved ineffective when there was another reducible group in the acid adduct. In this case, selective hydrogen transfer reductive cyclization of the methyl ether of the carboxylic acid, via palladium on carbon, was the preferred method. The 3-nitro derivative of the heterotricycle was available only by this method. The reactions of 7, 8, 9, 10-tetrahydropyrido (1,2-a) quinoxalin-6-one with electrophilic reagents have been studied. The tetrahydropyioxalinone was found to be completely unreactive to some reagents and in several other instances, intractable mixtures of compounds were obtained. Nitration of the heterocycle was however achieved with a mixture of potassium nitrate and sulphuric acid, giving the 2-nitro compound. Attempted nitration with concentrated nitric acid alone, or in other solvents, gave ring-opened products, as the tricyclic skeleton is readily cleaved under these conditions. Bromination of the heterocycle was examined under four different conditions in order to delineate the role played by the amine and amide nitrogen atoms in directing electrophilic substitution into the aromatic ring. With one mole equivalent bromine in acetic acid and with bromine in bioling hydrobromic acid, two different monobromo derivatives were obtained. Mixtures of products were obtained, on the other hand, from the reactions of the heterocycle with N-bromosuccinimide in 50% sulphuric acid and also with excess bromine in acetic acid. 1H-NMR nuclear Overhauser enhancement studies involving the amide N-H of the 7,8,9,10-tetrahydropyrido (1,2-a) quinoxalin-6-ones have been used to fully assign for the first time, the aromatic proton signals of the pyrido (1,2-a)quinoxalin-6-ones as well as to unambiguously characterize the products of nitration with potassium nitrate/sulphuric acid and bromination with one mole equivalent bromine in glacial acetic acid as the 2-nitro-; and 3-bromo compounds respectively. Attempted N-alkylations of 7,8,9,10-tetrahydropyrido(1,2-a) quinoxalin-6-one by the conventional methods of reaction with an alkyl halide in the presence of a strong base such as sodium hydride or sodium methoxide were unsuccessful. A convenient and mild method of N-alkylation of the heterocyclic compounds via a phase transfer process was however developed. N-alkylation of the tetrahydropyridoquinoxalinones were accomplished in a solid-liquid two-phase system consisting of powdered sodium hydroxide/potassium carbonate suspended in benzene, in the presence of a catalytic amount of tetra-n-butylammonium hydrogen sulphate. Good yields of the relatively more soluble N-alkyl products were obtained. Several attempts at selective replacement of the 6-oxo group in the title compound with chlorine by reaction with phosphoryl chloride were unsuccessful and gave rise to a suspected polychlorinated compound. Products of attempted oxidation with manganese dioxide and alkaline potassium ferricyanide are described. Full assignments of the 1H and 13C-NMR resonance of the new heterocycle 7,8,9,10-tetrahydropyrido (1,2,-a) quinoxalin-6-one and some of its derivatives are reported for the first time. Unambiguous assignments were made by extensive NOE experiments in conjunction with the use of 2D one-bond and long rage 13C:1H chemical shift correlations. The replacement of hydrogen with deuterium has been known to produce shifts in the position of the neighbouring carbon-13 NMR signals. The magnitude of these effects has recently been shown to possess a stereochemical dependance. Exchange of the amide N-of the7,8,9,10-tetrahydropyrido (1,2-a) quinoxalin-6-ones with deuterium induces shifts in the carbon-13 resonances of the heterocycle. Evidence is presented in this work to show that the magnitude of the deuterium isotope effect on these carbon-13 NMR resonance bears a geometrical relationship to the N-H. Fungicide activity of the tetrahydropyridoquinoxalinones, their precursors and N-alkyl derivatives are also reported for the first time.
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    Open Access
    Biosystematic studies in the genus euphorbia L. in Nigeria
    (School of Postgraduate Studies, 2015) Faboyede, A.O.
    Euphorbia L. is a genus of the family Euphorbiaceae. Some of the species are culturally, economically and medicinally valuable. The taxonomy of the genus was re-evaluated using classical and experimental approaches to unravel the complex inter-relationships and problems of identification existing within the genus. Herbarium studies, natural population sampling, ecological observation, experimental cultivation, morphological and anatomical characterization were some of the study approaches. A total of thirty species, four of which are new to literature in Nigeria were circumscribed. Although there were various growth habits observed, species were found as herbs, trees and shrubs. Some species possess distinct leaves while others had ephemeral leaves. Cyathium was found to be a unique feature of the genus. It was also observed that the leaves, inflorescences, fruits and stems of most herbaceous species were covered by dense, woolly, soft- matted tomentose hairs which occur singly as multicellular hairs. The inflorescences occurred either singly, in a group of three or four or as a bunch of flowers (sessile or stalked). Each flower has one or more glands attached to it. The over-all appearances of the stem provided useful taxonomic data. All taxa studied have simple, monad, tri-colporate pollen grains with radial symmetry. The anti-clinal wall patterns of the leaf epidermis were wavy, undulate or straight. Stomata was either epistomatic or hypo-stomatic.Scanning Electron Microscopy revealed surface ornamentations on the abaxial surface of Euphorbia hirta. Epicuticular wax was present and granular in all taxa except the abaxial surface of Euphorbia glomerifera. The cuticle was either smooth, ridge or striated. Also, trichomes were either present or absent; where present, they were of acicular or fili-form types which were non-glandular (either uni-serrated or multi-serrated). All the species studied have uniform venation patterns that were pinnate with a single primary vein serving as the origin for the higher order venation and craspedodromous with secondary veins terminating at the margin. These were either semi-craspedodromous or mixed-craspedodromous. The cross section of the stems revealed that they were circular in outline. Variable chromosome numbers were recorded. Therefore, based on the results obtained, the Nigerian Euphorbia were separated into eight groups i. e: (a) Woody shrubs with spines (b) Succulent shrubs without spines and with deciduous leaves (c) Succulent or cacti form shrub or tree with spines and deciduous leaves (d) poorly understood un-branched geo-phyte (with tuberous root) (e) Dwarf perennial herbs (f) Erect annual herbs (g) Semi erect herbs or shrubs with stems and leaves that have indumenta and (h) Woody shrubs without spines. Systematics descriptions of all the taxa have been provided while dichotomous key for identifying all species has also been produced. This work has helped to solve some of the problems of misidentifications and synonymy in the genus Euphorbia.
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    Open Access
    Studies on viruses isolated from leaf vegetables in Lagos with reference to Celosia Argentea and cucurbita Moschata
    (School of Postgraduate Studies, University of Lagos, Akoka, 1993-04) Owolabi, A.T
    Monthly surveysfor the occurence and distribution of viruses of leafy vegetables were carried out in four commercial vegetable farms at Amuwo odofin, Abule Ado, Tejuosho and Oko Oba in Lagos in order to isolate and identify priviously unreported viruses in Nigeria.
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    Open Access
    A new composite multiderivative linear multistep methods for solving stiff initial value problems
    (School of Postgraduate Studies, University of Lagos, Akoka, 1994-12) Okunuga, S.A
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    Open Access
    Some aspects of the biology of the African Walnut (Tetracarpidium conophorum mullarg) hutch & Dalz)
    (School of Postgraduate Studies of the University of Lagos, Akoka, 1993-01) Oluwole, S.O.
    The difference in the current rates of increase in population (3.4t per annum) and food production reinforces the need to step up food production in order to meet the demands of the people. Although attempts are being made to reverse the trend.