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Applications of Nuclear Magnetic Resonance Spectroscopy APPLICATIONS OF NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY IN ORGANIC AND BIOLOGICAL CHEMISTRY Submitted in fulfilment of the degree of Doctor of Philosophy University of Stirling ABSTRACT Monocyclic derivatives of hydroxylamlnes were synthesised to Investigate their conformations and conformational rate processes. Derivatives of l,4,2-oxathlazlne(l-oxa-4-thla-2-azacyclohexane) were prepared, their conformational equilibria Investigated and their rates of nitrogen and ring Inversion measured. N-carbethoxy-l-oxa-2-azacyclo- octane was prepared and reduced to N—methyl—l-oxa-2-azacyclooctane, whose nitrogen inversion rate was. measured. N-carbethoxy-5,5-dlmethyl-l-oxa- 2-azacyclooctane and N-carbethoxy-6,6-dlmethyl-l-oxa-2-azacyclononane were also prepared. Treatment of these compounds led to the formation of N-carbethoxy-2-(amlnohydroxy)-3,3- dlmethylhexane and N-carbethoxy-2- (amlnohydroxy)-4,4-dimethylheptane respectively Instead of the N-methyl derivatives. Other attempts to make the N-methyl derivatives also failed. 23 An investigation of aqueous lanthanide shift reagents for Na 39 and K was undertaken. The best combinations were found with tripolyphosphate as the ligand In combination with Dysprosium or 23 Terbium. Isotropic hyperflne shifts of up to ca 40 ppm ( Na) and ca 39 13 ppm ( K) are reported. The shift reagents were used to Investigate intracellular Na^ and in cellular systems. A 39 quantitation of Intracellular K In human erythrocytes Is reported. The use of these shift reagents in combination with large unilamellar vesicles of egg-yolk phosphatidylcholine is demonstrated to be a viable technique for measuring ionophore mediated membrane transport of Na^ and K***. The monensln mediated transport of Na*^ was studied and shown to be first order In monensln. The transport was Inhibited by the substrate Itself, In a concentration dependent manner. Two related [15]-crown-5 derivatives were also investigated. The result indicated that anionic lonophoraa are more efficient In membrane transport than neutral ionophores. ACKNOWLEDGEMENTS I wish tc thank my supervisor. Dr F G Riddell, for his Invaluable patience, guidance and encouragement throughout the past three years. I also take this opportunity to express my thanks to the members of the Chemistry Department for their Interest and helpful suggestions during my period of studies at Stirling. I must also thank the technical staff of the department for being supportive and to Mr G Castle for'supplying me with much needed glassware and valuable reagents. I would also like to thank Dr P Brophy, Dr M North and Dr N J Dlx of the Biological Sciences Department for their assistance In the preparation of the cellular systems Investigated In this work. Dr Brophy has also to be thanked for his generous donation of egg—yolk phosphatidylcholine, guidance in the preparation of large unilamellar vesicles and numerous helpful discussions. My thanks are also due to Mr Dance for the recording of mass spectral data, Mr f Forrest for the electron microscopy work. Dr I Sadler and Dr D Reed of the SERC Regional NMR Service of University of Edinburgh for time and assistance with the Bruker WF360 spectrometer and SERC for some nmr financial support. Especial thanks Is due to Mrs P Brown for painstakingly and efficiently typing this manuscript. Finally, I wish to express my sincere gratitude to my mother for her encouragement and I dedicate this thesis to the memory of my late father. Chain Singh Hayer (1926-1982). SECTION I APPLICATION OF NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY IN ORGANIC CHEMISTRY CHAPTER 1: CONFORMATIONAL ANALYSIS OF SIX-MEMBERED AND LARGER RING HYDROXYLAMINE DERIVATIVES Page Introduction Conformation Directing Forces Nitrogen Inversion The Conformations of Hydroxylamine Derivatives 1.4.1 Acyclic Compounds 1.4.2 Cyclic Derivatives a. Three-membered Rings b. Four-membered Rings c. Flve-membered Rings d. Slx-membered Rings (i) Tetrahydro-1.2-Oxazlne 13 • (il) Tetrahydro-1,4,2-Dloxazlne 16 (111) Tetrahydro-1,2,4-Oxadlazlne 17 (iv) Tetrahydro-1,2,5-Oxadlazlne 17 e. Seven-membered Rings 18 1.5 Elght-membered Rings 20 1.6 Nlne-membered Rings 21 1.7 Conclusion 22 CHAPTER 2 ; RESULTS, ANALYSIS AND DISCUSSION OF SYNTHESES, H and ^^C NUCLEAR MAGNETIC RESONANCE SPECTRA AND CONFORMATION EQUILIBRIA OF HYDROXYLAMINE DERIVATIVES 2.1 Synthesis of Hydroxylamine Derivatives 2.1.1 l-Oxa-4-Thla-2-Azacyclohexanes 2.1.2 Eight- and Nlne-membered Hydroxylamine Derivatives a. Bromlnatlon of a- or 3-substltuted dimethyl dlols b. Baeyer Villlger Oxidation c. Reactions of N-Hydroxyurethane with Dlbromldes d. Reduction of the N-Carbethoxy Group e. Acid Hydrolysis of the N-Carbethoxy Group f. Base Hydrolysis of the N-Carbethoxy Group 2.1.3 Conclusion 2.2 Nuclear Magnetic Resonance Spectroscopy In Conformational Analysis 2 .2.1 Introduction 2.2.2 ■‘H1.. Nuclear Magnetic Resonance Spectroscopy a. Proton-Proton Coupling b. Llneshape Analysis 13 2.2.3 C Nuclear Magnetic Resonance Spectroscopy 2.2.4 Conclusion 1 13 2.3 The H and C Nuclear Magnetic Resonance Spectra and 43 Conformational Equilibria of Hydroxylamine Derivatives: Results, Analysis and Discussion 2.3.1 Introduction 43 2.3.2 l-Oxa-4-Thla-2-Azacyclohexanes a. Spectral Assignments b. Coupling Constants c. Conformational Equilibria Page 2.3.3 N-Methyl-l-Oxa-2-Azacyclooctane a. Spectral Assignments 52 b. Conformational Equilibria 52 2.3.4 Conclusion 53 CHAPTER 3: EXPERIMENTAL 3.1 General Notes 56 3.2 Synthesis of l-Oxa-4-Thla-2-Azacyclohexanes 57 3.3 Synthesis of N-Methyl-l-Oxa-2-Azacyclooctane 75 3.4 Synthesis of N-Carbethoxy-5,5-Dlmethyl-l-Oxa-2-Azacyclooctane 80 3.5 Synthesis of N-Carbethoxy-6,6-Dlmethyl-l-Oxa-2-Azacyclononane 87 REFERENCES 1.2.3 Membrane Transport a) Passive Diffusion b) Facilitated Diffusion (1) Protein Carriers (11) Non-Protein Carriers - lonophores c) Active Transport 1.3 Paramagnetic Lanthanide Shift Reagents in Nuclear Magnetic Resonance Spectroscopy 1.3.1 Induced Shifts and Complex Formation Equilibria 1.3.2 Chemical Shifts in Paramagnetic Lanthanide Complexes 1.3.3 Nuclear Relaxation in Lanthanide Complexes l.A ConclusIon CHAPTER 2; DISCUSSION 23 39 2.1 Shift Reagents for Na and K NMR. 2.1.1 Introduction 2.1.2 Discussion of Results 2.1.3 Conclusion 2.2 ^ Na NMR Studies of Ion Transport across the Membrane of Large Unilamellar Phosphatldychollne Vesicles. 2.1.1 Introduction 2.1.2 Discussion of Monensln Mediated Transport 2.2.3 Discussion of Crown-ether Mediated Transport 2.2.4 Conclusion CHAPTER 3 : EXPERIMENTAL 3.1 General Notes 180 CHAPTER 1 1.1 INTRODUCTION What Is conformational analysis? The fundamental tenet of conformational analysis, as suggested by Barton and Cookson,^ Is that the chemical and physical properties of organic molecules depend not only on their gross structure and stereochemistry but also on the conformations they prefer to adopt. The origins of conformation analysis, which Is considered as one of the most Important branches of stereochemistry, may be found in the work of Sachse. ’ He was the first to suggest that cyclohexane could exist in two possible arrangements, free from angle strain, and which were later named chair and boat conformations. Sachse's theories were confirmed by the work of HUckel on els and trans decalins and later by the work of Hassel on X-ray and electron diffraction of substituted cyclohexanes, and’ by the work of Pltzer^ on the shape and thermodjmamlc properties of cyclohexane derivatives. However, the actual start of conformational analysis may be considered to be the classical paper of Barton^ in 1950, which Introduced the concept of conformational analysis and pointed out some basic relationship between conformation and chemical reactivity. What then are conformations? This question Is best answered by placing the term "conformation” in the context of stereochemistry as a whole. The most adequate definition of what constitutes a conformation Is that given by Riddell.® It states that, "Conformations are stereoisomers that can be interconverted either by rotation about bonds of order approximately one, with any concomitant small distortions of bond lengths and angles, or by Inversion at a three-coordinate centre In the molecule, or by pseudorotation on phosphorus. This definition allows us Co CreaC conformations In Che same light as stereoisomers - as an assembly of molecules occupying a potential energy minimum. Those 9 10 forms of molecules which do not have a finite existence, ’ and in fact correspond to transition states, for example eclipsed ethane, do not fall under the definition. The above definition Includes not only conformational inter- conversions based on bond rotation, but also those which Involve ring or nitrogen inversion, and applies equally to allcycllc and heterocyclic 11-13 compounds 1.2 CONFORMATION DIRECTING FORCES The conformations of molecules, and the shapes and magnitudes of the barriers separating these conformations, depend on several factors. In six-membered ring systems the preferred conformation is commonly determined by the following factors: i) Torsional forces li) Non-bonded interactions ill) Bond-stretching iv) Bond-angle deformation v) Electrostatic interactions Vi) Solvent effects vil) Hydrogen bonding viii) Resonance effects Considerable effort has been put into devising functions which 14-19 describe the way molecular energy varies with headings (l)-(lv). Although functions are available for electrostatic interactions, they are mainly useful for qualitative rather than quantitative interpretation. Progress is being made on the evaluation of solvent effects on conformational equilibria. However, attempts at estimations of hydrogen bonding and resonance effects are at present strictly enlightened guesses, although some molecular orbital (MO) calculations on hydrogen bonding have been successful The discussion which follows is an attempt to give a general picture of the way in which molecular energy changes with geometry. The torsional strain is the 1,2-lnteractlon between non-bonded atoms or groups which arises in less energetically favourable conformations.
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