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Treatments with natural products rich in anti-oxidants have attracted remarkable interest in the cosmetic and pharmaceutical industry to combat oxidative stress and reverse the effects of ageing. Rooibos (Aspalathus linearis) is a South African fynbos plant, well-known for its strong anti-oxidant capacity and use in many cosmetic products. However, little published research exists on its potential as an anti-ageing treatment. The anti-ageing properties of fermented and green rooibos were investigated using an in vitro cell culture model designed to evaluate the involvement of mitochondrial dysfunction in the age related decline in preadipocyte function. Mitochondrial DNA (mtDNA) deficient preadipocytes, ρ0 3T3-L1preadipocytes, were generated following continuous long-term exposure to sub lethal concentrations of ethidium bromide (EtBr). Depletion of the mtDNA resulted in a significantly reduced mitochondrial membrane potential, rate of proliferation in culture, as well as an increased glucose utilization and lactate production. Treatment with the green rooibos (100 μg/mL) stimulated cell growth rates for both the wildtype and mutant cell lines. MtDNA depleted cells showed arrest in the G1 phase (48.8 ± 3.34%) compared to wildtype cells (44.6 ± 1.38%), which was significantly attenuated after treatment with green rooibos for mutant (42.0 ± 0.83%) and wildtype (36.5 ± 5.80%) treated cells. The results obtained for glucose utilization and lactate production, indicated a significant increase in glucose utilization along with a concomitant increase in lactate production after treatment with both green and fermented rooibos for wildtype and mutant cell lines. A significant improvement in mitochondrial membrane potential was also later observed after treatment with green and fermented rooibos on both the wildtype and mutant cell lines. The results obtained indicate that rooibos extracts, particularly the green rooibos, exhibit effects which preserve the functional capacity of preadipocytes exposed to ageing related insults, and indicate that rooibos could cause a metabolic shift in cells redirecting carbon flow away from mitochondrial metabolism, and towards lactate production and consequently, cells become resistant to mitochondrial dysfunction.

Macrocyclization is a synthetically challenging step in the total synthesis of natural products. The success of chemical approaches such as the Corey-Nicolaou, Yamaguchi and Keck macrolactonization is heavily based on the confirmation and stereochemistry of the substrate. While there have been some advances in computational modeling, it has been difficult to predict whether the above-mentioned reactions will work. We have begun characterizing polyketide thioesterase catalytic activity and substrate tolerance to find more efficient and dependable routes towards macrolactonization and macrolactamization.

Master of Science

Coinage metals such as copper, silver and gold have captivated mankind with their desirable qualities and social value. Recently, these metals have peaked the interests of scientists, where organic chemists have used them extensively in the homogenous catalysis of organic transformations. In our laboratory, we exploited their π-Lewis acidic properties to activate alkyne to induce intramolecular cyclization of nucleophilic enol ethers. We discovered that modulating the steric and electronic profiles of the ancillary ligand on the cationic metal complexes allowed for the regioselective control of such reactions. During the exploration of the substrate dependency of these transformations, we discovered that unsubstituted alkynes undergo a 6-endo-dig/acetalization/Prins reaction cascade in the presence of a silver salt such as [(BrettPhos)Ag(MeCN)]SbF6, resulting in the formation of highly strained polycycles. We have demonstrated that the formation of these products is initiated by a selective 6-endo-dig cyclization. Further mechanistic studies suggested that the reaction may occur through silver dual catalysis using deuterium-labelling experiments, however, single activation of the starting material would lead to the same product and thus both mechanisms were proposed. The further reactivity of these interesting polycyclic products was also explored. Total synthesis of natural products is often referred to as an art, as it defines the boundaries of organic chemistry. In our laboratory, we have always been interested in the challenge of ingeniously building architecturally complex molecules. With the development of optimized conditions for the selective formation of decaline cores from silylenol ethers, the application of this methodology to the synthesis of teucrin A was sought. Our synthetic approach is highlighted by a sequential Diels-Alder/6-endo-dig cyclization reaction to rapidly assemble the clerodane diterpenoid framework of the natural product. To that end, the synthesis of the target utilized a strategy featuring a Diels-Alder reaction between an exocyclic allene and a silyl enolether, which proceeded in 59% yield at 110°C with a diasteomer ratio of 3:1. Unfortunately, attempts to induce the [4+2] cycloaddition using Lewis acids that were vital to the proposed synthetic route led to either no conversion or hydrolysis of starting material. Since this key step proved challenging, alternative synthetic pathways are currently being investigated in our group. Since the elucidation of its molecular structure by Robinson in 1925, morphine has received tremendous attention from the synthetic community. Indeed, about 50 formal and total syntheses of morphinans have been reported since the original synthesis by Gate in 1952. Herein, the synthetic efforts achieving a 9-step formal synthesis of (±)-morphine from readily available starting materials such as o-vanillin is presented. This synthesis features the quick assembly of the phenanthrofuran framework of the natural product in only five steps. The tetracyclic intermediate was synthetized through the careful orchestration of a Diels-Alder/elimination/deprotection sequence as well as a telescopic Claisen rearrangement/Friedel-Crafts alkylation. Subsequent strategic functional group manipulations allowed us to reach the advanced compound in four more steps and thus intercepting a known intermediate, which required two additional chemical transformations to form morphine. Overall, the work presented in this thesis represents the development of innovative methods for the creative disconnection of natural products. These advancements promote the rapid assembly of molecular cores found in many bioactive molecules.

Magister Pharmaceuticae - MPharm / The growing resistance of Methicillin-Resistant Staphylococcus aureus (MRSA) to currently prescribed drugs has resulted in the failure of prevention and treatment of different infections caused by the superbug. Therefore, to keep pace with the resistance, there is a pressing need for novel antimicrobial agents, especially from non-conventional sources. Several natural products (NPs) have displayed varying in vitro activities against the pathogen but few of these natural compounds have been studied for their prospects to be potential antimicrobial drug candidates. This may be due to the high cost, tedious, and time-consuming process of conducting the important preclinical tests on these compounds. Hence, there is a need for cost-effective strategies for mining the available data on these natural compounds. This would help to get the knowledge that may guide rational prioritization of “likely to succeed” natural compounds to be developed into potential antimicrobial drug candidates.

<p> β-Lactones are present in a number of biologically interesting natural products. They also have inherent reactivity due to their strained ring system and act as important synthetic intermediates. In this current work, we focus on the development of an efficient stereoselective route for the synthesis of β-lactones. A Tandem Evans-type Aldol Lactonization (TEAL) method was developed and various di- and tri-substituted β-lactones were successfully synthesized in a one pot process, using the lithium enolates of N-acetyl- (2-8) and N-propionyl- (2-20) thiazolidine-2-thione and a variety of ketones with moderate to good yields. Substitution of these N-acyl thiazolidine-2-thiones with chiral N-acetyl and N-propionyl thiazolidine-2-thiones (2-41 and 2-42 respectively) produced β-lactones with good enantioselectivity (up to 83% e.e.) and also showed an improvement of diastereoselectivity indicating the potential of the developed method. </p> / Thesis / Master of Science (MSc)

Mass spectrometry was used in conjunction with numerous 1-D and 2-D NMR techniques to determine the structures, devoid of stereochemistry, of five different compounds isolated from the extracts of Eunicea succinea, Eunicea tourneforti, and an unidentified species isolated from the Eunicea genus by Professor Meledath Govindan, of the University of the Virgin Islands. Three of the compounds were then identified as the known compounds eunicin, 12,13-bisepieupalmerin, and 7(S),8(S)-epoxy-1(S),11(R)-dolabella-3E,12(18) -dien-13-one by comparison of their spectroscopic data and optical rotations with those published in the literature. Optical rotations could not be measured accurately for the other two compounds because of small sample sizes; therefore, another method had to be found to elucidate the stereochemistry of these two structures. To solve this problem, molecular modeling and NOESY were employed. Comparison of the NOESY interactions to the thermodynamically available conformations of several possible stereoisomers, calculated by molecular modeling, proved to be a useful technique. One of the remaining two structures was identified as the known stereoisomer euniolide. The stereochemistry of the one remaining structure could not be assigned because sample size was not large enough to obtain a clean NOESY spectra. Finally, based on published synthetic work by Corey and Kania, the absolute stereochemistry of the dolabellane was revised to 7(R),8(R)-epoxy-1(R),11(S)- dolabella-3E,12(18)-dien-13-one. / Master of Science

As part of the continuing work of the International Cooperative Biodiversity Group (ICBG), plant extracts were received from Madagascar. The extracts were screened for cytotoxicity using the A2780 human ovarian cancer cell line bioassay. The crude extract of Casearia nigrescens was fractionated and yielded five known compounds and one new compound that were cytotoxic. Mass spectrometry and 1D and 2D NMR techniques were used to determine the structure of the isolated compounds. The dichloromethane fraction of Casearia nigrescens was weakly active in the A2780 human ovarian cancer cell line bioassay. Further separation of the dichloromethane fraction resulted in the isolation of five known compounds (casearlucin A, caseamenbrol A, rel-18(S),19(R)-diacetoxy-18,19-epoxy-6(R)-hydroxy-2(S)-(2ξ-methylbutanoyloxy)-5(R),8(S),9(S),10(R)-cleroda-3,13(16),14-triene, casearlucin B, and rel-18(S),19(R)-diacetoxy-18,19-epoxy-2(S)-(2ξ-ethylbutanoyloxy)-5(R),8(S),9(S),10(R)-cleroda-3,13(16),14-triene) and one new compound (casearlucin L). Based on the available literature this was the first investigation of the natural products of Casearia nigrescens. The structure of the known compounds was determined by comparison of the NMR, MS, optical rotation, UV, and IR data with the data found in the literature. The structure of casearlucin L was determined by NMR data and comparison with the NMR data for similar known compounds. / Master of Science

Yes / A bidirectional synthesis of the originally proposed structures for the natural products elatenyne and a chloroenyne from Laurencia majuscula is described along with a reassessment of the structures of the halogenated enynes based upon a 13C NMR chemical shift/structure correlation / EPSRC