published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

The neuroprotective effects of AF4, a flavonoid-enriched extract derived from the peel of Northern Spy apples (containing quercetin-3-O-glucoside, quercetin-3-O-galactoside, quercetin-3-O-rhamnoside, quercetin-3-O-rutinoside, epicatechin, and cyanidin-3-O-galactoside) were examined by assessing neuronal loss and motor impairment resulting from hypoxic-ischemic (HI) brain injury in adult C57BL/6 mice. Relative to vehicle treatment (water, 10mL/kg/day), oral administration of AF4 (50 mg/kg/day) for 3 days reduces HI-induced neuronal loss in the striatum and hippocampus, motor impairments, and reduces the ability of LPS to stimulate the production of TNF-alpha in whole blood. Pretreatment with AF4 (1 ug/mL) decreased the death of mouse primary cortical neurons subjected to oxygen glucose deprivation (12 hours) in comparison to vehicle (DMSO) or the same concentration of quercetin or its metabolites. Taken together these findings indicate that AF4 reduces HI-induced brain injury and motor deficits by increasing the resistance of vulnerable neurons to ischemic cell death and decreasing the production of inflammatory cytokines.

Kraussianone 1 and kraussianone 2 were previously isolated as active compounds from the roots of Eriosema kraussianum Meisn., a plant used for the treatment of male impotence and urinary complaints in KwaZulu-Natal. The objectives of this study were firstly, to develop a method for the analysis of metabolites from E. kraussianum and other Eriosema plants that are used for erectile dysfunction and secondly, to develop synthetic methods for kraussianone 1 and structurally related compounds. A reversed-phase HPLC-PDA method was developed for the analysis of the extracts of plants from different sources, two of which were authentic E. kraussianum collected from the Drakensberg and Pietermaritzburg. The roots of other Eriosema species called ubangalala and uqonsi in Isizulu were also analysed. These plants were bought from the local herbal traders. The extracts of the two E. kraussianum plants and one uqonsi sample showed a similar chemical profile, even though there were variations in the relative concentrations of the metabolites within each plant. In these three plants, kraussianone 1, the most active metabolite of E. kraussianum, occurred in relatively low quantities, whereas kraussianone 2 was one of the major constituents. The other commercial plants that were analysed contained different compounds from those found in E. kraussianum. The HPLC method developed herein facilitates rapid identification and relative quantification of metabolites from E. kraussianum. Strategies based on semi-synthesis and total synthesis were employed for the preparation of kraussianone 1. The semi-synthetic route was based on the transformation of the prenyl side chain of kraussianone 2 into a linear dimethylpyran scaffold fused to the A-ring. Two routes were investigated for the semi-synthesis of kraussianone 1 from kraussianone 2. In the first route, the dimethylchromene ring was to be prepared by the acid-catalysed cyclisation of the prenyl group of kraussianone 2, followed by dehydrogenation of the resulting dimethylchroman chromophore. This route was abandoned due to poor regioselectivity of the cyclisation reaction and the difficulty of oxidising the dimethylchroman scaffold on the phloroglucinol moiety into a dimethylchromene. The second strategy involved selective protection of the OH-2', followed by DDQ-mediated oxidative cyclisation of the prenyl group to OH-7. This was the most viable route and kraussianone 1 was prepared in an overall yield of 54% from kraussianone 2. The total synthesis of kraussianone 1, on the other hand, employed the Suzuki-Miyaura reaction for the construction of the isoflavone nucleus and the regioselective introduction of the dimethylpyran scaffolds to the A- and B-rings. The key precursors in this synthesis were 3-iodo-5,7-dimethoxymethoxychromone and a boronic acid coupling partner, 7- benzyloxy-2,2-dimethylchromene-6-boronic acid, already bearing the prerequisite chromene scaffold attached to the B-ring. The isoflavones genistein, 2-hydroxygenistein, eriosemaone D and a geranyl analogue of kraussianone 1 were prepared via the route developed for the total synthesis of kraussianone 1 by structural modifications of rings A and B. Furthermore, this synthetic approach was expanded to the synthesis of the coumarochromones lupinalbin A and lupinalbin H. The development of the feasible semi-synthetic and total synthetic routes described herein for kraussianone 1 is of importance for the production of material for an in depth study of the pharmacological activities and the structure-activity relationship studies of kraussianone 1 and related compounds. / Thesis (Ph.D.)-University of KwaZulu-Natal, 2011.

A growing interest in sustainable development has made efficient utilisation of starting materials and, if they occur, by-products become increasingly important. Vast amounts of by-products are generated by the forestry and food industry. Incineration for energy production is one way to make use of these by-products but some of them contain compounds that would have an increased value if they were extracted, so called “high value species”. The by-products are often very complex, so reliable methods for analysis of the high value species are required in the development of processes to utilise them. A wide range of compounds can be analysed using chromatographic separation coupled to mass spectrometry, making it a powerful tool in the evaluation of methods for extracting high value species from industry by-products. This thesis is based on four studies of potential high value species. In the first study, methods were developed to differentiate isobaric flavonoids and then use this knowledge to determine the identity of the flavonoids in three different plant extracts. In the second study, three different methods to extract betulin from birch bark were evaluated regarding extracted amount and purity of betulin. One of the methods was then investigated in industrial scale using a model approach. In the third study, the flavonoid contents of lovage were determined and other major extracted compounds were investigated by high performance liquid chromatography coupled to electrospray ionisation mass spectrometry. Gas chromatography and supercritical fluid chromatography were used to obtain complementary information about major components. In the fourth study, high resolution mass spectrometry utilising two different types of fragmentation was used with the purpose of overcoming the shortcomings of the methods developed in the first study. The results indicated that it would be possible to develop methods compatible with chromatographic separation for differentiating different types of isobaric substituents. The ability of performing sequential fragmentation was used to investigate some isobaric aglycones by creating spectral trees, and unique pathways were found for each of them.

No description available.

The primary aim of this project was to synthesize new heterocyclic dimers of isoflavones and flavones, and investigate various methodologies for their synthesis. The secondary aim of the project was to synthesize some flavonoid natural products. Dimeric systems were synthesized using various methodologies including acid catalyzed arylation of isoflavanols and flavanols, acid catalyzed dimerization of flavenes, oxidative dimerization, Sonogashira coupling, Ullmann coupling and Suzuki-Miyaura coupling reactions. The acid catalyzed arylation of isoflavanols was found to proceed in a very stereoselective fashion to give trans-4-arylisoflavans in good yield in a single step. However, related flavanols under similar conditions gave mixtures of cis and trans isomers of 4-arylflavans. Interestingly, it was found that appropriately substituted flavenes, upon treatment with acid undergo stereoselective rearrangement and dimerization to give benzopyranobenzopyrans in high yields. A rationale for the rearrangement is proposed and this dimerization was used for the stereoselective synthesis of the natural product dependensin. As part of the project, some polycyclic natural products such as octandrenolone, flemiculosin, 3-deoxy-MS-II and laxichalcone were also synthesized. Oxidative dimerization of activated isoflavones was found to be very regioselective, and novel isoflavone dimeric systems were synthesized. Related flavones however, failed to undergo dimerization under similar conditions. A probable explanation for high regioselectivity in the case of isoflavones and unreactivity of flavones has been presented. Phenol oxidative coupling was used for the one-step synthesis of another natural product kudzuisoflavone-A from daidzein. Sonogashira coupling was utilized for the synthesis of dimeric systems linked via an acetylic linker. A variety of soflavone isoflavone, flavone-flavone and isoflavone-flavone dimers were synthesized in "one-pot" by this methodology and in excellent yields. Although Ullmann coupling was found not to be suitable for the synthesis of isoflavone or flavone dimers, one-pot Suzuki-Miyaura methodology gave flavone dimers and various other heterocyclic dimers in good yields.

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: leaf 239-252.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 200-221) Also available in print.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (leaves 215-232). Also available in electronic version.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Includes bibliographical references (p. 188-194). Also available via the World Wide Web: http://www.lib.utexas.edu/etd/d/2006/williamsj92964/williamsj92964.pdf#page=3