M.Sc. (Chemistry) / Please refer to full text to view abstract

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Chamuvarinin (22) is a unique annoanceaeous acetogenin isolated from the roots of Senegalese medicinal plant Uvaria chamae by Laurens and co-workers in 2004. It displays highly potent cytotoxicity towards the cervical cancer cell lines (KB 3-1, IC₅₀= 0.8 nM). Structurally, chamuvarinin is the first reported acetogenin to contain an adjacently linked bis-THF-THP ring system spanning the C15-C28 carbon backbone. However, initial efforts to assign the relative and absolute configuration within this stereochemical array, on the basis of ¹H and ¹³C NMR analysis, provided only partial information pertaining to the relative configuration of C15-C19 region. As a consequence, 32 diastereomeric structural possibilities exist for the highly unusual structure of chamuvarinin; an unrealistic target for total synthesis. The synthesis of the central core tricyclic (BCD) intermediate represents the most challenging aspect in the entire synthesis, which in turn will aid ultimate structural proof. At the outset of the project the stereochemical configuration of C15-C28 (BCD) of chamuvarinin was uncertain and a library approach was proposed to enable structure elucidation (Scheme A-1). Chapter 2 and Chapter 3 detail the synthesis of possible diastereomers of the C9-C21 (51) and C22-C34 fragments (52). Chapter 4 details the intial strategy to couple the key diastereomeric fragments in a series of model studies. Chapter 5 describes the successful coupling strategy via an revised synthetic approach to reach the advanced C9-C34 intermediate 251 (Scheme A-2).

This work is an account of the phytochemical analysis of two genera, Vernonia and Vepris which are used as remedies for illness by the Kalenjin community of Kenya. Species of Vernonia are known to yield sesquiterpene lactones, which typify the genus whereas Vepris is rich in alkaloids and limonoids which have a wide range of biological activities. The species studied in this work were Vernonia auriculifera, Vernonia urticifolia, Vepris glomerata and Vepris uguenensis. Phytochemical studies revealed a range of compounds being present in the four species. From Vernonia, triterpenoids, a sesquiterpene amine, a carotenoid and a polyene were isolated. This was the first account of a sesquiterpene amine from a plant species and the first account of the novel polyene. The triterpenoids showed moderate antibacterial activity, with b-amyrin acetate and oleanolic acid being effective at decreasing adhesion of selected gram-negative and gram-positive bacteria. Lutein and urticifolene showed good antibacterial activity against Enterococcus feacium and Pseudomonas aeruginosa. In Vepris, a range of compounds were isolated, belonging to the furoquinoline alkaloids, coumarins, flavonoids, cinnamic acid derivatives, lignins, cinnamaldehydes, triterpenoids and limonoids. Five new compounds; a cinnamaldehyde derivative (glomeral), two flavonoids (veprisinol, uguenenprenol) and two A, D-seco-limonoids (uguenensene and uguenensone) were amongst the compounds isolated. Antibacterial studies showed that glomeral inhibited the growth of Staphylococcus aureus and Shigella dysentrieae at low concentrations (MIC of 2 μg mLˉ¹ and 0.4 μg mLˉ¹ respectively). Antioxidant assays of several compounds revealed that, veprisinol, isohaplopine-3,3’-dimethylallyl ether, uguenenprenol and 7-O-methylaromadenrin are good antioxidant agents. The limonoids isolated from Vepris uguenensis also make up an interesting biogenetic relationship. Structural elucidation was carried out by 1D and 2D NMR spectroscopy in conjuction with mass spectrometry, infrared, ultraviolet and circular dichroism analysis where applicable. Biological assays were carried out using standard methods at laboratories in the University of KwaZulu-Natal and Kenya Medical Research Institute (KEMRI-Nairobi). / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.

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Thèse (M.Ress.Renouv.) -- Université du Québec à Chicoutimi, 2003. / Bibliogr.: f. 116-131. Document électronique également accessible en format PDF. CaQCU

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2003. / Appendix consists of reprints and manuscripts of five papers co-authored with others. Includes bibliographical references. Also partially available online in PDF format; online version lacks appendix.

D.Phil. (Biochemistry) / This thesis concerns a study of the effect of isonitrosoacetophenone on plant metabolism. Three different systems were investigated; cultured tobacco and sorghum cells as well as Arabidopsis thaliana plants, and a metabolomic approach was followed. Unlike most scientific studies, metabolomics is a discipline which is not driven by a specific hypothesis, but rather by the obtained data to add scientific insights to the topic under investigation. As such, the current study lacks a definite overarching hypothesis, but specific objectives were outlined and answered in each experimental chapter. This thesis is therefore presented as a compilation of nine chapters in which experimental/research work is described in Chapter 3- 8. It is important to note that each chapter is presented in accordance with the guidelines for the respective journal in which the corresponding manuscript was published or submitted to.