Chemical studies of necic acid analogues
- Authors: Guthrie-Strachan, Jeffry James
- Date: 1997
- Subjects: Organic acids , Chemistry, Organic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4425 , http://hdl.handle.net/10962/d1006909 , Organic acids , Chemistry, Organic
- Description: Various aldehydes have been reacted with methyl acrylate under Baylis-Hillman conditions, using DABCO as a catalyst, to afford a range of α-substituted acrylic esters containing an allylic hydroxy group. Selected Baylis-Hillman products have been brominated, hydrolysed and acetylated to afford substrates for the synthesis of necic acid analogues. The diastereo- and regioselectivity of nucleophilic attack, using sodium methylmercaptan, on the Baylis-Hillman products and selected brominated derivatives was investigated. The allylic hydroxy compounds favour conjugate addition with the generation of a new chiral centre, while the allylic bromo derivatives favour substitution (SN and SN') (S[subscript N] and S[subscript N]') with consequent loss of chirality. (E)-2-Isopropylcrotonic acid, a vital precursor in the synthesis of all stereoisomers of trachelanthic and viridifloric acid, was synthesised in an attempt to obtain the necic acid components required for total alkaloid synthesis of lycopsamine and its derivatives. This precursor and salicylic acid were then used to prepare esters of retronecine, a dihydroxy necine base obtained via extraction and consequent hydrolysis of retrorsine.
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Synthesis and conformational studies of indolizines
- Authors: George, Rosemary
- Date: 1994
- Subjects: Indole alkaloids -- Research , Organic compounds -- Synthesis , Chemistry, Organic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4367 , http://hdl.handle.net/10962/d1005032 , Indole alkaloids -- Research , Organic compounds -- Synthesis , Chemistry, Organic
- Description: The present investigation has involved a kinetic and mechanistic study of the thermal cyclization of 3-acetoxy-3-(2-pyridyl)-2-methylenepropanoate esters and related compounds to 2-substituted indolizines. Substrates for the kinetic study were prepared via the Baylis-Hillmann reaction of pyridine-2-carboxaldehydes with acrylate esters, acrylonitrile and methyl vinyl ketone. The resulting hydroxy compounds were then acetylated to afford the acetoxy derivatives, thermal cyclization of which gave the corresponding 2-substituted indolizines. The cyclization reactions was followed using 'H NMR spectroscopy and were shown to follow firstorder kinetics. The influence of the various substituents on the observed first-order rate constants has been examined and variable temperature studies have permitted evaluation of activation parameters for the formation of methyl indolizine-2-carboxylate and ethyl indolizine-2-carboxylate. An alternative route to 2-substituted indolizines via halogenated derivatives was explored and several halogenated 2-pyridyl derivatives were synthesised and their thermal cyclization to indolizines was attempted. Novel 5-methylindolizine-2-carboxamides were prepared as part of this investigation and dynamic NMR spectroscopy was used to study internal rotation about the amide N-CO bond in these compounds.
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Intersolid pyrotechnic reactions of silicon
- Authors: Rugunanan, Rajan Anil
- Date: 1992
- Subjects: Thermochemistry , Thermal analysis , Chemistry, Analytic , Chemistry, Organic , Silicon
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4527 , http://hdl.handle.net/10962/d1015571
- Description: A study of the role of different oxidants with silicon as the fuel in simple binary pyrotechnic compositions is reported. Several oxidants were examined, but only three (Sb₂0₃, Fe₂0₃ and Sn0₂) satisfied the restrictions that the combustion temperatures should be below the melting point of platinum/rhodium thermocouples (1760°C), that burning rates should not exceed the response of the thermocouples, and that burning should occur without significant mass-transport. A fourth oxidant, KN0₃, was selected on account of its low melting point and general importance as a pyrotechnic oxidant. The oxidation of silicon in the presence of either Sb₂0₃ or KN0₃ could be identified from thermal analysis curves. No thermal events were noted when Si/Sn0₂ and SiFe₂0₃ compositions were heated under similar conditions. The oxidation of Si powder in oxygen was also studied. All four binary systems sustained burning over a reasonably wide range of compositions. The range of burning rates measured (2 to 35 mm s⁻¹) depended on the oxidant used. Fe₂0₃ and Sb₂0₃ gave slow burning mixtures compared to Sn0₂ and to KN0₃ compositions with a high Si content. Burning rates generally increased with increasing specific surface area of silicon, but decreased in the presence of inert diluents and moisture. The burning rates of the Si/Fe₂0₃ and Si/Sn0₂ systems increased with increasing compaction of the samples. Kinetic parameters derived from the temperature proftles recorded during combustion were generally low (6 to 37 kJ mol⁻¹). This is in keeping with proposals that burning is diffusion controlled. The values of kinetic parameters derived from thermal analysis curves were considerably greater ( > 250 kJ mol⁻¹). Two other fuels, FeSi₇ and CaSi₂, gave similar thermal analysis curves when used instead of silicon. There were considerable differences in the burning rates for binary mixtures of these fuels compared to silicon. Ternary systems with two fuels or two oxidants showed that only limited interaction occurs during thermal analysis. The use of a second fuel or oxidant did, however, modify the burning behaviour considerably. Other techniques used in this study to probe the details of the reaction processes included bomb calorimetry, measurement of thermal conductivities, infrared spectroscopy, X-ray diffraction and scanning electron micoscropy.
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""Of molecules and men"" : inaugural lecture delivered at Rhodes University
- Authors: Kaye, Perry T
- Date: 1989
- Subjects: Biochemistry , Chemistry, Organic , Chemistry
- Language: English
- Type: Text
- Identifier: vital:643 , http://hdl.handle.net/10962/d1020712 , ISBN 0868101842
- Description: Inaugural lecture delivered at Rhodes University , Rhodes University Libraries (Digitisation)
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Adventures in natural product chemistry : inaugural lecture delivered at Rhodes University
- Authors: Rivett, Douglas E A
- Date: 1981
- Subjects: Natural products , Chemistry, Organic
- Language: English
- Type: Text
- Identifier: vital:660 , http://hdl.handle.net/10962/d1020729 , ISBN 0868100706
- Description: Inaugural lecture delivered at Rhodes University , Rhodes University Libraries (Digitisation)
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The effects of organic perturbants on the structure of soluble collagen
- Authors: Hart, Geoffrey Joseph
- Date: 1971
- Subjects: Chemistry, Organic , Collagen
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3846 , http://hdl.handle.net/10962/d1012157 , Chemistry, Organic , Collagen
- Description: Organic solvents were used in the present study as a means of investigating the non-covalent interactions involved in the maintenance and pertubation of the three-dimensional structure of the collagen macromolecule in solution. The two main types of non-covalent interaction under consideration are hydrogen bond formation and hydrophobic effects. Elucidation of the relative importance of these factors in the maintenance of the solution structure of proteins is an area of intensive investigation and fundamental significance to biochemistry as a whole. During the past decade, considerable progress has been made towards a clearer understanding of the forces involved, and a number of different theoretical and experimental approaches have emerged. Until about 1960, hydrogen bonding was widely believed to be the dominant non-covalent interaction responsible for the maintenance of secondary and tertiary structure in many proteins. Subsequently, an increasingly important role for apolar (hydrophobic) effects was suggested by a number of authors, and at present there is no satisfactorily definitive interpretation of the available experimental evidence. The current work is based on a comparison of the effects of organic solvents on widely different substrates, namely collagen, cellulose, and the chromatographic reference material, catechin. The chromatographic mobility of catechin on cellulose may be regarded as a phenomenon which is mediated entirely by polar interaction mechanisms. The effects of various organic perturbants and of changing solvent/water ratios are readily interpreted on this basis. In the collagenous systems, however, certain results appear to require the introduction of concepts other than those relating exclusively to polar bonding affinities. The experimental evidence shows that there are cases where the enhancement of the polar interaction potential of solvent/water mixtures, in relation to catechin-cellulose systems, is accompanied by an apparent reduction of polar interaction potential of the same solvent/water mixtures with respect to soluble collagen. The anomaly outlined above will be discussed in terms of two fundamentally different theoretical assumptions. In the first of these, the mechanism of perturbant action in collagenous systems is regarded as essentially similar to that governing catechin-cellulose affinity patterns. Thus, interaction processes are all treated as polar phenomena, in which direct hydrophobic destabilization of the collagen triple helix plays no part. In an attempt to explain the effects of perturbants in both collagen and cellulose-containing systems in terms of the above assumption, two hypotheses are examined involving (1) direct polar interaction between perturbant molecules and functional groups of the protein; (2.) the possibility of an enhanced polar interaction potential of water molecules, due to lowering of the environmental dielectric constant when organic solvents are added to the systems. Within the other broad conceptual division, collagen and cellulose substrates are considered to respond in fundamentally different ways to the action of organic perturbants. As before, cellulose-catechin-solvent interactions are treated as entirely polar phenomena, and perturbant effects interpreted in terms of mechanisms such as direct solvation of the substrate, and the enhanced hydrogen bonding activity of water molecules. In contrast, perturbant lyotropic action with respect to soluble collagen i s viewed as the manifestation of a major contribution by hydrophobic interaction processes to macromolecular stability. Thus, solvents that competitively reduce the assumed entropic contribution to the stability of the collagen triple helix, are seen as potential destabilizers of the native state of the protein and inhibitors of the regeneration of co-operative structures during renaturation. Both of the above approaches are critically assessed in the light of the present work and the dominant trends apparent in the recent literature.
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