<p>Bioactivity-guided fractionation was used to identify the most potent antioxidant and antimutagenic fractions contained in the methanol extract of unfermented rooibos (Aspalathus linearis), as well as the bioactive principles for the most potent antioxidant fractions. The aim of this thesis was to investigate whether the same flavonoids are responsible for both the potent antioxidant and antimutagenic properties of unfermented rooibos.</p>

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M. Med. Sc.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 38-50)

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (leaves 99-119). Also available in electronic version.

Thesis (Ph. D.)--West Virginia University, 1999. / Title from document title page. Document formatted into pages; contains x, 130 p. : ill. Vita. Includes abstract. Includes bibliographical references.

Thesis (M.Med.Sc.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 44-54).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 244-261).

Magister Scientiae - MSc / Bioactivity-guided fractionation was used to identify the most potent antioxidant and antimutagenic fractions contained in the methanol extract of unfermented rooibos (Aspalathus linearis), as well as the bioactive principles for the most potent antioxidant fractions. The aim of this thesis was to investigate whether the same flavonoids are responsible for both the potent antioxidant and antimutagenic properties of unfermented rooibos. / South Africa

Part I describes an investigation of the following electrophilic substitution reactions of 3-methylfuran. Acylation under Friedel-Crafts conditions yielded 3-methyl-2-acetylfuran (8) and 3-methyl-5-acetylfuran (9) in the ratio 65:35. Vilsmeier and Gatterman formylation procedures yielded 3-methylfurfural (10) and 3-methyl-5-furfural (11) in the same ratio, 93.5:6.5. Mercuration of 3-methylfuran yielded only the 2-mercuro derivative. Part II describes the isolation and structural elucidation of two major oxygen heterocyclic compounds C and D occurring in the leaves of Zeyhera tuberculosa Bur. et Verlot (Bignoniaceae). Compound C is assigned the structure 5,6,7,8-tetramethoxyflavone (25) on the basis of spectroscopic evidence. Compound D is shown to possess the structure 5,6,7-trimethoxyflavone (35). In this latter instance spectroscopic and chemical evidence could be obtained in support of the structural assignment. In particular, alkaline hydrolysis of D yielded 2,3,4-trimethoxy-6-hydroxyacetophenone (34), the identity of which was established by an unambiguous synthesis. In the synthesis of the acetophenone derivative (34), the key intermediate is 2,6-dimethoxyhydroquinone diacetate (31) which was subjected to Fries rearrangement conditions, followed by acid hydrolysis, to give 2,4-dimethoxy-3,6-dihydroxyacetophenone (33). Partial methylation of (33) yielded (34). / Science, Faculty of / Chemistry, Department of / Graduate

>Magister Scientiae - MSc / Flavonoids, one of the biggest classes of secondary metabolites, are found abundantly in nature in a broad range of fruits, vegetables and beverages such as tea, coffee, beer, wine and fruit drinks. Flavonoids have been reported to exert multiple biological functions as well as tremendous pharmacological activity, including anticancer activity, protection, antioxidant activity, cardiovascular protection, antibacterial, antifungal and antiviral activity. The antioxidant activity of flavones is reported to be associated with those bearing hydroxyl functions. In the present study, several reaction steps have been carried out to synthesize three sub classes of flavonoids namely; chalcones, dihydrochalcones and flavanones with various substituents attached. The first step involved protection of hydroxyl groups of acetophenone and benaldehyde as starting materials. Thereafter the Clasien Schmidt condensation reaction, under basic conditions, was performed to afford chalcone intermediates. Treatment of these chalcones with sodium acetate, under reflux, afforded flavanones as a single product in high yields. Thereafter all protecting groups where removed to yield the final products. All products and intermediates where purified by column chromatography and were characterized by Nuclear Magnetic Resonance Spectroscopy (NMR) (1H NMR and 13C NMR). An electrochemical analysis on all flavonoid compounds was performed by Cyclic Voltammetry (CV) and Square Wave Voltammetry (SWV) to give information on the accessible redox couples identified by their oxidation potentials. Oxidation potentials, which gave valuable information about reducing ability and hence the antioxidant activity, where used to compare all compounds. The antioxidant activity was observed to increase with the addition of hydroxyl groups on the B-ring. Compounds with a combination of hydroxyl groups on the A-ring and methoxy groups on the B-ring showed increased antioxidant activity when compared to those with only hydroxyl groups on the base structure. 2, 5, 4’-trihydroxy dihydrochalcone showed moderate antioxidant ability. However the 2, 5, 4’-trihydroxychalcone, containing the α, β unsaturated double bond, proved to have the greatest antioxidant ability.