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Kwok, Wun Sang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 147-152). / Abstracts in English and Chinese. / Acknowledgment --- p.i / Table of Contents --- p.ii / Abstract --- p.iii / Abstract (Chinese Version) --- p.iv / Abbreviation --- p.v / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- General Background --- p.1 / Chapter 1.1.1 --- "1,3-Dipolar Cycloaddition" --- p.1 / Chapter 1.1.2 --- Structure of Preparation of Nitrile Oxide --- p.3 / Chapter 1.2 --- Intramolecular Nitrile Oxide Alkene Cyclization (INOC) --- p.7 / Chapter 1.2.1 --- INOC in Organic Synthesis --- p.7 / Chapter 1.2.2 --- Formation of Oximolactone as Unwanted Reaction in INOC --- p.10 / Chapter 1.2.3 --- Nitrile Oxide Alkene Cyclization with Free Hydroxyl Group --- p.11 / Chapter 1.3 --- Natural Occurring Gabosine --- p.14 / Chapter 1.3.1 --- "Structure, Biological Effect and Syntheses of Gabosines" --- p.14 / Chapter 1.3.2 --- Synthesis of Gabosine O and its 4-epimer --- p.17 / Chapter 1.4 --- Protected 6-dehydroxy-Pseudo-a-D-Talose --- p.21 / Chapter 1.4.1 --- Structures and Biological Effects of Valienamine and its Derivatives --- p.21 / Chapter 1.4.2 --- Structural and Biological Studies of Valienamine by Our Group --- p.23 / Chapter 2. --- Results and Discussion --- p.28 / Chapter 2.1 --- Studies on INOC of Sugar Derivatives with Free Hydroxyl Group(s) --- p.28 / Chapter 2.2 --- Enantiospecific Synthesis of 4-epi-Gabosine O --- p.47 / Chapter 2.3 --- Enantiospecific Synthesis of Gabosine O --- p.84 / Chapter 2.4 --- Synthesis of 6-Deoxy-Pseudo-a-D-Talose --- p.87 / Chapter 3. --- Conclusion --- p.95 / Chapter 4. --- Experimental --- p.100 / References --- p.147 / Appendix NMR spectra --- p.153

The lability of cobalt(III) in vitamin B12 is thought to come about as a function of its coordination environment. The thermodynamics and kinetics of ligand substitution reactions of vitamin B12a were compared to those of a synthetic, more electron rich, corrole-based biomimetic model. The feasibility of corrole synthesis was established with the synthesis of several corroles with different meso substituents. The biomimetic model was designed such that the central meso position bore a substituent with a terminal imidazole (referred to as the ‘tail’) which might act as an axial ligand for a coordinated cobalt ion while the remaining two meso positions bore water-solubilising glucose substituents. Unfortunately, the biomimetic model was water soluble below pH 4 only. This rendered the model unsuitable for the present study and these water solubilising groups were not incorporated into the final model. The model system used in this work is [10-(2-{[4-(1Himidazol-1-ylmethyl)benzoyl]amino}phenyl)-5,15-diphenylcorrolato]cobalt(III), referred to as DPTC-Co Intermediates of the ‘tail’ meso substituent were found to be polymorphic and five pairs of polymorphs were identified. Polymorphism arose from differences in weak termolecular forces and these differences were evaluated. The stability constants for the binding of various neutral N-, P- and S-donor ligands and anionic N-, S-, I- and C-donor ligands to both vitamin B12a and DPTC-Co were determined in a buffered 80:20 methanol:water solvent system. The more stable binding of neutral ligands to DPTC-Co and anionic ligands to vitamin B12a indicates that the interaction between the metal and an incoming ligand is indeed affected by the metal’s coordination environment. Cobalt(III) in DPTC-Co appeared to favour softer ligands while harder ligands were favoured by vitamin B12a. Kinetic studies showed that the coordination of cyanide to cobalt in vitamin B12a was faster than in DPTC-Co. The reaction between cyanide and vitamin B12a was found to be entropically driven while the reaction with DPTC-Co was enthalpically driven. This suggests that while the reaction between cyanide and vitamin B12a is faster, the reaction between cyanide and DPTC-Co is electronically more labile. The coordination environment of cobalt has been seen to significantly affect its chemistry. Coordination by the more electron rich corrole macrocycle led to a softer and more electronically labile metal then when coordinated by the corrin macrocycle of vitamin B12a.

Functionalizing arenes and heteroarenes has been an active area of research since the 19th century, due to the presence of these molecular structures in many industrially important sectors. A tremendous amount of research has been published in achieving these chemical transformations using stoichiometric reagents and transition metal-catalyzed reactions. However, challenges still remain. An alternative and comparable methodology to metal-catalyzed reactions to overcome the drawbacks will advance this particular area of research is desirable. Hypervalent iodine compounds offer a promising approach to metal-free arylation reactions. These mild, air and moisture stable compounds have showed significant success as non-toxic and metal-free reagents for the arylation reactions. In particular, unsymmetrical diaryliodonium salts offer functionalization of complex arene structure in an efficient and sustainable pathway. A base-mediated coupling reaction for the metal-free synthesis of alkyl-aryl ethers by using unsymmetrical diaryliodonium salts and aliphatic alcohols is described. This method shows broad substrate scope with respect to both of the coupling partners to produce industrially useful alkyl-aryl ethers in moderate to excellent yields. The reaction is operationally simple, proceeds at mild temperature, and is atom-economical. Sustainability and synthetic utility of this reaction is demonstrated by the use of unsymmetrical aryl(mesityl)iodonium salts as the arylating agents. A limitation of poor reactivity of electron rich unsymmetrical diaryliodonium salts was overcome by designing 2nd generation conditions and using trimethoxy benzene (TMP) as the auxiliary group. Additionally discovery and development of an efficient method to access highly functionalized arynes from unsymmetrical aryl(mesityl)iodonium tosylate salts is presented. The aryne intermediates are generated by ortho C-H deprotonation of aryl(mesityl)iodonium salt with an amide base and subsequently trapped in a cycloaddition reaction with furan in moderate to good yields. Selective iodonium moiety elimination is discussed and the effect of auxiliary and temperature to reduce the regioisomeric ratio is demonstrated. Finally, additional coupling partner including benzyl azide and aliphatic amines are presented to show further utility of this methodology. Also, mechanistic investigations leading to the moderate reactivity of some electron rich unsymmetrical diaryliodonium salts is discussed.

Diaryliodonium salts offer potential as novel reagents for arylation chemistry. An overall goal and successful outcome of this work has been to further understanding of diaryliodonium salt chemistry by developing practical methods that enable chemists more convenient access to these reagents, for the purpose of reaction development. To this end a robust and convenient preparation method has been developed and resulted in novel commercially available diaryliodonium salts. The remainder of the work described, has focused on understanding the parameters important to diaryliodonium mediated arylation and has resulted in a solid framework that multiple future development efforts can build upon. A strategy adopted throughout this work was to use multivariate methodologies such as Design of Experiments (DoE). Applicable chapters show the results of optimization studies that were carried out using DoE, during the course of this work. Additionally, the desire to further realize the potential that DoE has to offer inspired of a search for parameters to study fundamental reactivity. Chapter 2 details the development of a practical diaryliodonium salt synthesis that is convenient, facile, and economical. A detailed procedure is also included and was drafted to the requirements for publication in the journal Organic Synthesis. Finally, limitations and future directions of the method are discussed. Chapter 3 describes studies aimed at understanding the role of the counter anion; a very practical counter anion screening method is presented. Future directions are discussed and include detailed characterization of diaryliodonium salts by NMR. Chapter 3 also describes a practical, scalable, and rapid salt exchange method developed during this work. Chapter 4 describes the results obtained in studying an azidation reaction via solubility parameters. All Supporting Information, including characterization data and experimental details, are provided in Chapter 5.

This treatise studied two correlated important issues in atmospheric chemistry: real-time monitoring of ambient air and removal mechanisms of atmospheric hydrocarbons. An analytical system was designed for the purpose of identification and measurement of sub-ppb level hydrocarbons of different reactivities in air samples. This analytical system was then applied to a series of smog-chamber studies which simulated the removal of reactive hydrocarbons from the atmosphere by reaction with hydroxyl radicals. Six representative atmospheric hydrocarbons ( hexane, octane, toluene, m-xylene, a-xylene and mesitylene) were selected for these experiments. The experimental data indicated that the decay of atmospheric hydrocarbons under laboratory conditions is entirely due to reaction with hydroxyl radicals. The conclusion drawn from a time-resolved plume study that aromatic molecules decay much faster than could be accounted for solely by reaction with hydroxyl radicals was not verified; this indicates a difference between laboratory study and the study in the real atmosphere, and some physical factors besides chemical mechanism might take a more significant role in removing aromatics faster from the atmosphere.

Studies have shown that some canines have the ability to predict seizures in people with epilepsy, and that canines can be trained to recognize changes in humans before an epileptic seizure and make these predictions. It is not known with any certainty to what the canines are alerting. However, canines’ exceptional sense of smell and their ability to discriminate human scent is well established. Therefore, it is possible that the canines could be responding to an olfactory cue, such as the release of some volatile organic compounds (VOCs) prior to the onset of a seizure. Individuals release a wide array of VOCs, both odorous and non-odorous, from their bodies. The odorous VOCs collectively make up human scent and a number of these VOCs have been identified as biomarkers of different diseases. Evidence suggests that canines can perceive these biomarkers, leading to early detection of underlying physical ailments before individuals are aware of their own symptoms. The main purpose of this study was to use headspace solid phase microextraction (HS-SPME) with gas chromatography-mass spectrometry (GC-MS) to analyze hand odor, saliva and breath samples from epileptic with and without seizure activity to determine if the human scent profiles resulting from a seizure event differs from the scent profiles in the absence of seizure activity. the HS-SPME-GC-MS method was also used to analyze and compare hand odor, saliva and breath samples of healthy individuals and epilepsy patients to determine if the profiles can be differentiated. Comparison of the VOCs in each specimen from healthy individuals and epileptic patients revealed compounds that could be used as potential biomarkers to differentiate between healthy and epileptic individuals. Comparison of the VOCs in each specimen from epileptic patients with and without seizure activity revealed compounds that could be used as potential biomarkers for epileptic seizures. Finally, canine trials were used to verify that these compounds are indeed biomarkers.

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Bibliography: leaves 213-223.

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