Parkinson’s disease is an age-related neurodegenerative disorder. The major symptoms of Parkinson’s disease are closely linked to the pathology of the disease. The main pathology of Parkinson’s disease consists of the degeneration of neurons of the substantia nigra pars compacta (SNpc), which leads to reduced amounts of dopamine in the brain. One of the treatment strategies in Parkinson’s disease is to conserve dopamine by inhibiting the enzymes responsible for its catabolism. The monoamine oxidase (MAO) B isoform catalyses the oxidation of dopamine in the central nervous system and is therefore an important target for Parkinson’s disease treatment. Inhibition of MAO-B provides symptomatic relief for Parkinson’s disease patients by increasing endogenous dopamine levels as well as enhancing the levels of dopamine after administration of levodopa (L-dopa), the metabolic precursor of dopamine. Recent studies have shown that phthalide can be used as a scaffold for the design of reversible MAO inhibitors. Although phthalide is a weak MAO-B inhibitor, substitution on the C5 position of phthalide yields highly potent reversible MAO-B inhibitors. In the present study, sesamol and benzodioxane were used as scaffolds for the design of MAO inhibitors. The structures of sesamol and benzodioxane closely resemble that of phthalide, which suggests that these moieties may be useful for the design of MAO inhibitors. This study may be viewed as an exploratory study to discover new scaffolds for MAO inhibition. Since substitution at C5 of phthalide with a benzyloxy side chain yielded particularly potent MAO inhibitors, the sesamol and benzodioxane derivatives possessed the benzyloxy substituent in the analogous positions to C5 of phthalide. These were the C5 and C6 positions of sesamol and benzodioxane, respectively. The sesamol and benzodioxane derivatives were synthesised by reacting sesamol and 6- hydroxy-1,4-benzodioxane, respectively, with an appropriate alkyl bromide in the presence of potassium carbonate (K2CO3) in N,N-dimethylformamide (DMF). 6-Hydroxy-1,4- benzodioxane, in turn, was synthesised from 1,4-benzodioxan-6-carboxaldehyde. The structures of the compounds were verified with nuclear magnetic resonance (NMR) and mass spectrometry (MS) analyses, while the purities were estimated by high-pressure liquid chromatography (HPLC). Sixteen sesamol and benzodioxane derivatives were synthesised. To determine the inhibition potencies of the synthesised compounds the recombinant human MAO-A and MAO-B enzymes were used. The inhibition potencies were expressed as the corresponding IC50 values. The results showed that the sesamol and benzodioxane derivatives are highly potent and selective inhibitors of MAO-B and to a lesser extent MAOA. The most potent MAO-B inhibitor was 6-(3-bromobenzyloxy)-1,4-benzodioxane with an IC50 value of 0.045 μM. All compounds examined displayed selectivity for the MAO-B isoform over MAO-A. Generally the benzodioxane derivatives were found to be more potent inhibitors of human MAO-A and MAO-B than the sesamol derivatives. The reversibility and mode of MAO-B inhibition of a representative derivative, 6-(3- bromobenzyloxy)-1,4-benzodioxane, was examined by measuring the degree to which the enzyme activity recovers after dialysis of enzyme-inhibitor complexes, while Lineweaver- Burk plots were constructed to determine whether the mode of inhibition is competitive. Since MAO-B activity is completely recovered after dialysis of enzyme-inhibitor mixtures, it was concluded that 6-(3-bromobenzyloxy)-1,4-benzodioxane binds reversibly to the MAO-B enzyme. The Lineweaver-Burk plots constructed were linear and intersected on the y-axis. Therefore it may be concluded that 6-(3-bromobenzyloxy)-1,4-benzodioxane is a competitive MAO-B inhibitor. To conclude, the C6-substituted benzodioxane derivatives are potent, selective, reversible and competitive inhibitors of human MAO-B. These compounds are therefore promising leads for the future development of therapy for Parkinson’s disease. / MSc (Pharmaceutical Chemistry), North-West University, Potchefstroom Campus, 2015

Parkinson’s disease is an age-related neurodegenerative disorder. The major symptoms of Parkinson’s disease are closely linked to the pathology of the disease. The main pathology of Parkinson’s disease consists of the degeneration of neurons of the substantia nigra pars compacta (SNpc), which leads to reduced amounts of dopamine in the brain. One of the treatment strategies in Parkinson’s disease is to conserve dopamine by inhibiting the enzymes responsible for its catabolism. The monoamine oxidase (MAO) B isoform catalyses the oxidation of dopamine in the central nervous system and is therefore an important target for Parkinson’s disease treatment. Inhibition of MAO-B provides symptomatic relief for Parkinson’s disease patients by increasing endogenous dopamine levels as well as enhancing the levels of dopamine after administration of levodopa (L-dopa), the metabolic precursor of dopamine. Recent studies have shown that phthalide can be used as a scaffold for the design of reversible MAO inhibitors. Although phthalide is a weak MAO-B inhibitor, substitution on the C5 position of phthalide yields highly potent reversible MAO-B inhibitors. In the present study, sesamol and benzodioxane were used as scaffolds for the design of MAO inhibitors. The structures of sesamol and benzodioxane closely resemble that of phthalide, which suggests that these moieties may be useful for the design of MAO inhibitors. This study may be viewed as an exploratory study to discover new scaffolds for MAO inhibition. Since substitution at C5 of phthalide with a benzyloxy side chain yielded particularly potent MAO inhibitors, the sesamol and benzodioxane derivatives possessed the benzyloxy substituent in the analogous positions to C5 of phthalide. These were the C5 and C6 positions of sesamol and benzodioxane, respectively. The sesamol and benzodioxane derivatives were synthesised by reacting sesamol and 6- hydroxy-1,4-benzodioxane, respectively, with an appropriate alkyl bromide in the presence of potassium carbonate (K2CO3) in N,N-dimethylformamide (DMF). 6-Hydroxy-1,4- benzodioxane, in turn, was synthesised from 1,4-benzodioxan-6-carboxaldehyde. The structures of the compounds were verified with nuclear magnetic resonance (NMR) and mass spectrometry (MS) analyses, while the purities were estimated by high-pressure liquid chromatography (HPLC). Sixteen sesamol and benzodioxane derivatives were synthesised. To determine the inhibition potencies of the synthesised compounds the recombinant human MAO-A and MAO-B enzymes were used. The inhibition potencies were expressed as the corresponding IC50 values. The results showed that the sesamol and benzodioxane derivatives are highly potent and selective inhibitors of MAO-B and to a lesser extent MAOA. The most potent MAO-B inhibitor was 6-(3-bromobenzyloxy)-1,4-benzodioxane with an IC50 value of 0.045 μM. All compounds examined displayed selectivity for the MAO-B isoform over MAO-A. Generally the benzodioxane derivatives were found to be more potent inhibitors of human MAO-A and MAO-B than the sesamol derivatives. The reversibility and mode of MAO-B inhibition of a representative derivative, 6-(3- bromobenzyloxy)-1,4-benzodioxane, was examined by measuring the degree to which the enzyme activity recovers after dialysis of enzyme-inhibitor complexes, while Lineweaver- Burk plots were constructed to determine whether the mode of inhibition is competitive. Since MAO-B activity is completely recovered after dialysis of enzyme-inhibitor mixtures, it was concluded that 6-(3-bromobenzyloxy)-1,4-benzodioxane binds reversibly to the MAO-B enzyme. The Lineweaver-Burk plots constructed were linear and intersected on the y-axis. Therefore it may be concluded that 6-(3-bromobenzyloxy)-1,4-benzodioxane is a competitive MAO-B inhibitor. To conclude, the C6-substituted benzodioxane derivatives are potent, selective, reversible and competitive inhibitors of human MAO-B. These compounds are therefore promising leads for the future development of therapy for Parkinson’s disease. / MSc (Pharmaceutical Chemistry), North-West University, Potchefstroom Campus, 2015

This thesis is divided into six parts, all centered around the development of dynamic (i.e., reversibly interacting) systems of molecules and their applications in dynamic combinatorial chemistry (DCC) and organic synthesis. Part one offers a general introduction, as well as a more detailed description of DCC, being the central concept of this thesis. Part two explores the potential of the nitroaldol reaction as a tool for constructing dynamic systems, employing benzaldehyde derivatives and nitroalkanes. This reaction is then applied in part three where a dynamic nitroaldol system is resolved by lipase-catalyzed transacylation, selecting two out of 16 components. In part four, reaction and crystallization driven DCC protocols are developed and demonstrated. The discovery of unexpected crystalline properties of certain pyridine β-nitroalcohols is used to resolve a dynamic system and further expanded into asynthetic procedure. Furthermore, a previously unexplored tandem nitroaldol-iminolactone rearrangement reaction between 2-cyanobenzaldehyde and primarynitroalkanes is used for the resolution of dynamic systems. It is also coupled with diastereoselective crystallization to demonstrate the possibility to combine several selection processes. The mechanism of this reaction is investigated and a synthetic protocol is developed for asymmetric synthesis of 3-substituted isoindolinones. Part five continues the exploration of tandem reactions by combining dynamic hemithioacetal or cyanohydrin formation with intramolecular cyclization to synthesize a wide range of 3-functionalized phthalides. Finally, part six deals with the construction of a laboratory experiment to facilitate the introduction of DCC in undergraduate chemistry education. The experiment is based on previous work in our group and features an acetylcholinesterase-catalyzed resolution of a dynamic transthioacylation system. / QC 20100628

Activation of mammalian stress responsive pathways by plant secondary metabolites may contribute to the protection against certain chronic diseases afforded by fruit and vegetable consumption. This work focuses on the identification of plant compounds that activate the stress-responsive enzyme quinone reductase (QR) by stabilizing the transcription factor NF-E2 related factor-2 (Nrf2). Screening methanolic extracts of plants from Western Canada for QR induction in a mouse hepatoma cell line (Hepa-1c1c7) led to the identification of twenty-one extracts capable of doubling the activity of QR. Bioassay-guided fractionation of six extracts led to the identification of novel classes of compounds with QR-inducing activity including fatty-acid derived polyacetylenes, phthalides, and cannabinoids. Studies using low molecular weight thiols and the recombinantly expressed protein Keap1, the principal negative regulator of Nrf2, supported a mechanism of QR activation involving covalent modification of Keap1 cysteines for the polyacetylenes and phthalides. Analysis of transcriptional changes in response to treatment with a panel of QR-inducing compounds provided strong support for Nrf2 activation by the polyacetylene (3S,8S)-falcarindiol and the isothiocyanate (R)-sulforaphane and weaker support for the compounds (3R,8S)-falcarindiol, 6-isovaleryl-umbelliferone (6-IVU) and (Z)-ligustilide. Additionally, transcript level analyses supported a role for the aryl-hydrocarbon receptor in QR-activation by (3R,8S)-falcarindiol, (Z)-ligustilide, (R)-sulforaphane, 6-IVU and cannabidiol and suggested that treatment with polyacetylenes with a (3R)-configuration, (Z)-ligustilide and 6-IVU causes substantial changes in the expression of genes associated with lipid homeostasis and energy metabolism. As a whole, this work provides evidence that compounds that activate QR (and Nrf2) are widely distributed in the Canadian flora. However, of these QR activators, few are active at concentrations that are expected to be achieved through dietary consumption. Nevertheless, the most exceptional compounds isolated in this work, the compounds (3S,8S)-falcarindiol and epoxyfalcarindiol are highly potent and appear to be or are expected to be specific for activating Nrf2 and thus warrant attention with respect to dietary implications and as drug candidate leads.