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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The development and evaluation of an individualized learning programme for the teaching of organic chemistry at form six level.

Hung Ip, Kit-lin, Margaret. January 1977 (has links)
Thesis--M. Phil., University of Hong Kong, 1978. / Copy 2 xerox copy of typescript. Typescript.
2

Origins of the structural theory in organic chemistry

Rocke, Alan J., January 1900 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Vita. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.
3

Synthesis and reactivity of organotantalum complexes containing nitrogen ligation

Fox, Peter Anthony, 1965- January 1996 (has links)
This work examines various aspects of hydrodenitrogenation catalysis. Various tetrahydroquinolinyl (THQ) and indolinyl (DHI) complexes of tantalum were synthesized including: Ta(THQ)ₓCl₅₋ₓ(x = 1 to 5), Ta(DHI) ₓCl₅₋ₓ(THF) (x = 1 and 2). In addition, THQ and DHI complexes containing aryloxide (OAr = 2,6-diisopropylphenoxide) and alkyl complexes were also synthesized: Ta(THQ)(OAr)Cl₃(OEt₂), Ta(THQ)₂(OAr)₂Cl, Ta(THQ)(OAr)R₃Cl (R = Me and Et), Ta(THQ)₂(OAr)₂R (R = Me and Et), Ta(DHI)(OAr)Cl₃(OEt₂), and Ta(DHI)₂(OAr)₂Cl. The effects of sulfur ligation versus oxygen ligation was examined by comparison of the crystal structures of Ta[η²(N,C)-2,4,6-tri-t-butylpyridinel](OAr)₂(OᵗBu) and Ta[η²(N,C)-2,4,6-tri-t-butylpyridine](OAr)₂(SᵗBu). The sulfur ligand donates less π density to the metal center, resulting in a longer Ta-C bond for the pyridine ligand. The arene complexes (η⁶C₆Me₆)Ta(OAr)(SAr')Cl and (η⁶-C₆Me₆)Ta(OAr)(SAr'')Cl were also synthesized. These arene-thiolate complexes do not appear to bind quinoline, unlike the oxygen analogs A number of Ta(η⁴-diene)(OAr)₃ complexes were synthesized (diene = butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-cyclohexadiene) and their reactivity with respect to nitriles examined. Nitriles typically insert into Ta(η⁴-isoprene)(OAr)₃ to form (ArO₃Ta(CH₂CHCMeCH₂CRN) which can then be thermally rearranged to (ArO) ₃Ta(=NCRCH₂CHCMeCH₂) (R = Me, Ph, ᵗBu). Similar reactivity is observed with butadiene and 2,3-dimethylbutadiene diene complexes. The Ta(η⁴-C₄H₆)(OAr)₃ complex is also capable of inserting two nitriles to form (ArO)₃Ta(NCRCH₂CHCHCH₂CRN), whereas Ta(η⁴-1,3-cyclohexadiene)(OAr)₃ only forms the bis-insertion product. Aspects of the formation of the above complexes with specific concentration on the tantalum-nitrogen interactions are presented.
4

Methods for Direct Carbon-Carbon Bond Formation and Their Application to Natural Product Synthesis

Zhou, Guoqiang January 2009 (has links)
<p>Direct carbon&mdashcarbon bond formation via soft enolization and in situ enolate formation provides a straightforward approach to certain key transformations of synthetic organic chemistry. Reactions are generally operationally simple and proceed under mild conditions using untreated, reagent&ndashgrade solvent open to the air. Using this direct approach as a basis, we have developed methods for the synthesis of β&ndashhydroxy thioesters, β&ndashketo thioesters, and 1,3&ndashdiketones, which are key intermediates for the synthesis of natural products, pharmaceuticals, and other biologically relevant compounds. In particular, we describe: 1) a direct aldol addition of simple thioesters, 2) a direct synthesis of 1,3&ndashdiketone compounds, 3) a direct crossed&ndashClaisen reaction, and 4) an <italic>anti<italic>&ndashselective four&ndashcomponent direct aldol cascade reaction.</p><p>Progress toward the total synthesis of apratoxin D is described. The key steps of the synthesis involve the asymmetric alkylation via chiral <italic>N<italic>&ndashamino cyclic carbamate (ACC) hydrazones, a new technology recently developed in our group.</p> / Dissertation
5

Chemical Reactions and Self-assembly in Nano-confined Environments: the Development of New Catalytic Microcontact Printing Techniques and Multicomponent Inorganic Janus Particles

Shestopalov, Alexander A. January 2009 (has links)
<p>Modern patterning and fabrication techniques provide powerful opportunities for the preparation of micro- and nanostructured objects with applications in fields ranging from drug delivery and bioimaging to organic based electronic devices and real time biochemical sensors. In this thesis we report a systematic study focused on the development of new unconventional patterning and fabrication techniques with applications in the preparation of functional micro- and nanostructured devices.</p><p>Catalytic microcontact printing is a powerful technique that offers a simple and effective methodology for patterning chemically-functionalized surfaces with sub-100 nm accuracy. By avoiding diffusive mechanisms of pattern replication it effectively obviates the most significant limitation of traditional microcontact printing - lateral molecular ink diffusion. Moreover, catalytic microcontact printing significantly expands the diversity of patternable surfaces by using prefunctionalized substrates and gives rapid facile access to chemically discriminated surfaces that can be further functionalized with organic and biological molecules. We have developed several catalytic microcontact printing techniques that transfer pattern from an elastomeric stamp bearing an immobilized catalyst to a preformed functionalized self-assembled monolayer. By avoiding diffusive pattern transfer we were able to replicate features with sub-50 nm edge resolution. We also demonstrated that catalytic printing can be expanded to technologically important substrates not accessible through conventional soft lithography, by patterning reactive organic monolayers grafted to chemically passivated silicon.</p><p>The non-symmetric structure of Janus particles produces novel physical properties and unusual aggregation behavior that makes these materials attractive candidates for drug delivery and as nano-sensors and nano-probes, SERS and PEF imaging agents, small molecules carriers, and switchable devices. We have developed a new protocol for preparation of non-spherical inorganic Janus particles comprising metallic and semiconductor layers. The method allows for precise control over the composition, shape and size and permits fabrication of non-symmetrical particles, the opposite sides of which can be orthogonally functionalized using well-established organosilane and thiol chemistries.</p> / Dissertation
6

I.Total Syntheses and Biological Studies of Largazole and Brasilibactin A. II.Stereoselective Synthesis of 2,6-Cis- and 2,6-Trans-Piperidines through an Organocatalytic Aza-Michael Reaction.

Ying, Yongcheng January 2010 (has links)
<p>The dissertation focuses on three main projects which complement the studies towards the total syntheses of biologically active natural products as well as the development of stereoselective synthesis of 2,6-disubstituted piperidines. </p> <p>The first project introduced the first total synthesis of largazole, which is a marine natural product isolated from cyanobacterium of genus Symploca sp. in 2008. It consists of an unusual 16-membered macrocycle incorporating a 4-methylthiazoline linearly fused to a thiazole and an ester of 3-hydroxy-7-mercaptohept-4-enoic acid unit, part of which has been identified to be essential for the potent histone deacetylase (HDAC) inhibitory and consequently antiproliferative activities. Structure-activity relationship (SAR) studies suggest that thiol group generated by hydrolysis of the thioester moiety is the warhead and is critical for its HDAC inhibitory and antiproliferative activity. The biological evaluation of the analogues focusing on macrocycle and linker chain between sulfur atom and macrocycle suggests that the four-atom linker between the macrocycle and the octanoyl group in the side chain and the (S)-configuration at C17-position are critical to potent HDAC inhibitory activity of largazole. In contrast, the valine residue in the macrocycle can be replaced with alanine without compromising activity to a large extent. These SAR results would provide insights into structural requirements for HDAC inhibitory activity including the observed HDAC selectivity of largazole and help in the design of isoform-specific HDAC inhibitors based on largazole.</p> <p>The second project involved the synthesis of cytotoxic mycobactin-like siderophore-brasilibactin A and its unnatural diastereomers, which are then identified to unambiguously confirm that brasilibactin A possesses the 17S, 18R absolute stereochemistry at &#946;-hydroxy acid fragment. The convergent synthetic strategy has been applied to the synthesis of a more water-soluble analogue-Bbtan, iron-binding studies of which suggest brasilibactin A may play an important role in the iron-uptake mechanism in mycobacteria and related organisms. </p> <p>The third project elucidated a convergent stereoselective synthesis of 2,6-cis- and 2,6-trans-piperidines through a reagent-controlled organocatalytic aza-Michael reaction promoted by the gem-disubstituent effect introduced by 1,3-dithiane. The reaction was applicable to a broad range of substrates and proceeded with good stereoselectivities (up to 20:1 dr) and yields. The 1,3-dithiane group allowed for rapid access to substrates, promoted the intramolecular aza-Michael reaction via the gem-disubstituent effect, and improved the yield of the reaction. This synthetic method should be broadly applicable to the efficient synthesis of a diverse set of bioactive natural products with 2,6-disubstituted piperidines.</p> / Dissertation
7

Chemistry for gene silencing: 4'-modified and 2'-fluorinated nucleosides and oligonucleotides

Watts, Jonathan January 2008 (has links)
A series of studies on 2'-fluorinated and 4'-chalcogen-modified nucleic acids is described, mainly directed toward the development of better gene silencing therapeutics. NMR/MD and osmotic stressing were used to compare the structure and hydration of 10-bp 2'F-ANA:RNA, ANA:RNA and DNA:RNA duplexes. The 2'F-ANA and ANA strands both featured sugars that pucker in the east (O4'-endo) conformation, as previously observed for hairpin structures containing hybrid stems. Osmotic stressing suggested that the 2'F-ANA:RNA duplex liberated fewer molecules of water upon melting than did ANA:RNA, which may give the former an entropic advantage that contributes to its far greater thermal stability. The stability of 2'F-ANA to acid-mediated hydrolysis was compared to that of DNA and RNA. Several phosphodiester (PO) or phosphorothioate (PS) 2'F-ANA sequences were incubated at pH ~1.2, and virtually no cleavage was observed after 2 days. In contrast, rapid degradation was observed for DNA (t1/2 = minutes) and RNA (t1/2 = hours (PO) or days (PS)). The nuclease-catalyzed hydrolysis of 2'F-ANA was also explored in detail. One diastereomer of the PS-2'F-ANA linkage was much more vulnerable to enzymatic cleavage than the other, which is parallel to the properties observed for PS-DNA. We also show that the nuclease stability induced by 2'F-ANA depends on the oligonucleotide sequence. An improved synthesis of 2'-deoxy-2'-fluoro-5-methyl-4'-thioarabinouridine (4'S-FMAU) is described. Participation of the 3'-O-benzoyl protecting group in the thiosugar precursor influenced the stereochemistry of the N-glycosylation reaction in nonpolar solvents, permitting a higher beta/alpha ratio than previously observed for similar Lewis acid-catalyzed glycosylations. The nucleoside adopted a predominantly northern conformation, in contrast to 2'-deoxy-2'-fluoro-5-methylarabinouridine (FMAU), which adopts a predominantly southeast conform / On a fait une série d'études sur des acides nucléiques contenant un 2'-fluor et/ou un 4'-chalcogène. Ces études visent l'amélioration de thérapeutiques basées sur le silençage des gènes.On a utilisé la RMN/DM et le stressage osmotique pour comparer la structure et l'hydratation des duplex 2'F-AAN:ARN, AAN:ARN et ADN:ARN. Les sucres des brins de 2'F-AAN et d'AAN adoptent la forme O4'-endo (est), comme observé dans le passé. Le stressage osmotique a suggéré que la fusion du duplex 2'F AAN:ARN a libéré moins de molécules d'eau que celle du duplex AAN:ARN, ce qui pourrait donner à ce premier un avantage entropique qui contribue à sa stabilité beaucoup plus élevée. On a comparé la stabilité du 2'F-AAN envers l'hydrolyse par acide à celle de l'ADN et de l'ARN. Plusieurs oligonucléotides en PO ou PS ont été incubés à pH ~1.2, et il n'y avait pas de clivage pour le 2'F-AAN après deux jours. Par contre, on a observé une dégradation rapide pour l'ADN (t1/2 = minutes) et l'ARN (t1/2 = heures (PO) ou jours (PS)). On a exploré aussi l'hydrolyse du 2'F-AAN par nucléase en détail. Un diastéréoisomère de la liaison PS-2'F-AAN a été beaucoup plus vulnérable au clivage par l'enzyme que l'autre, ce qui est parallèle aux propriétés du PS-ADN. Nous démontrons aussi que la stabilité introduite par le 2'F-AAN dépend de la séquence de l'oligonucléotide.On décrit une synthèse améliorée du 2'-désoxy-2'-fluoro-5-méthyle-4'-thioarabinouridine (4'S-FMAU). Une participation par le groupe 3'-O-benzoyl influence la stéréochimie de la N-glycosylation dans des solvants non-polaires. Ceci a permis un plus haut rapport des produits beta/alpha que celui qui a été observé dans le passé pour des glycosylations semblables catalysés par acide Lewis. Le nucléoside adopte une forme nord, tandis que le 2'-désoxy-2'-fluoro-5-méthyle-arabinouridine (FMAU) adopte principalement une
8

Bismuth-mediated organometallic reactions in aqueous media

Lee, Yoon Joo, 1974- January 2003 (has links)
Recently, organometallic reactions in aqueous media have received considerable attention in organic synthesis because of environmental and economical concerns and synthetic efficiency. In this connection, the synthetic utility of environmentally benign non-toxic bismuth metal for aqueous organometallic reactions is investigated. Bismuth metal activated by ammonium hydrogen fluoride can efficiently reduce a wide variety of alpha-halocarbonyl compounds in aqueous media to provide the corresponding dehalogenated reduction products in excellent yields. Zinc fluoride is also found to be effective in activating bismuth to mediate the crossed aldol type reactions of diverse alpha-bromocarbonyl compounds with aldehydes in aqueous media to afford the corresponding beta-hydroxycarbonyl compounds in moderate to high yields. The scope of bismuth-mediated aqueous organometallic reactions is successfully extended to the Reformatsky type reactions. The factors that affect the reactivity of these reactions are examined and plausible reaction mechanisms are proposed.
9

Computer aided design for molecular inhibitors

Lee, Devin January 2010 (has links)
In-silico methods used to aid the development of therapeutic drugs have gained utility in the recent past and continue to grow in importance. Small molecule drugs for the use in the treatment of type 2 diabetes were designed using computational methods to probe the active site of Dipeptidyl Peptidase IV (DPP-IV) and were subsequently synthesized and tested in-vitro. A number of pseudodipeptides formed from derivatives of tryptophan and proline were synthesized. The effects of a tetrazole group on the pyrrolidine of proline were studied, as well as the effect of protecting groups on the activity on DPP-IV. Exploring the effects of rigidifying the active dipeptides was next explored by attempting to synthesize the analogous bicyclic structures. / In order to add to the knowledge in the realm of computation tools used for drug discovery, eight docking programs were used to screen a subset of a small molecule database, the Database of Useful Decoys (DUD). This study focused on the effects of protein flexibility, crystallographic waters and program/protein dependence on active compound identification accuracy. This knowledge gained on the efficacy of current docking programs in VS campaign on real world therapeutic targets will allow for more efficient drug design in the search for new therapeutic agents. / Les méthodes in-silico, utilisées pour faciliter le développement de composés thérapeutiques, ont dernièrement vu leur utilité croître en considérablement. Au cours de ce travail, une série de petites molécules visant le traitement du diabète de type 2 a été conçue en se servant de méthodes informatiques pour sonder le site actif de Dipeptidyl Peptidase IV (DPP-IV) et a, par la suite, été synthétisée et testée in-vitro. / Tout d'abord, de nombreux pseudo-dipeptides construits à partir de dérivés de tryptophane et proline ont été préparés. Les effets sur l'activité biologique d'un groupe tétrazole sur le groupe pyrrolidine de la proline ont été étudiés, ainsi que l'effet de la protection des groupes fonctionnels. L'étude de l'impact de la rigidification de ces dipeptides actives a ensuite été envisagée et une synthèse de structures bi-cycliques debutée. / Dans le but d'accroitre les connaissances sur les outils informatiques servant pour la découverte de médicaments, huit programmes d'amarrage ont été évalués sur une banque de données d'une petites molécules, "Database of Useful Decoys" (DUD). Nous nous sommes plus particulièrement intéressés à l'impact de la flexibilité des protéines, de l'eau cristallographique et du type de programme utilisé sur la fiabilité des résultats. Les données collectées au cours de cette étude va nous permettre de développer des programmes plus efficaces et par la suite permettre une meilleure fiabilité de ces programmes dans les campagnes de criblage virtuel futures qui auront pour but de trouver de nouveaux agents thérapeutiques.
10

Oxidative generation of reactive iminium-intermediates: A powerful strategy for C-H bond functionalization

Baslé, Olivier January 2010 (has links)
This thesis is an investigation on the generation and reactivity of carbocations adjacent to a trisubstituted nitrogen atom (iminium). / In the first part of this thesis, a copper-catalyzed oxidative alkylation of sp3 C-H bond adjacent to a nitrogen atom is described. This environmentally respectful process used molecular oxygen as oxidant and water as solvent. / In the second part of the thesis, an aerobic sp3 C-H bond phosphonation reaction is presented. This process catalyzed by copper(I) bromide using dialkylphosphites as nucleophiles offered direct C-P bond formation via direct oxidative coupling of C-H and P-H bonds. / In the third part of the thesis, a copper-catalyzed sp3 C-H bond arylation with boronic acids in absence of directing group is described. The oxidative arylation reaction provided easy access to biologically active tetrahydroisoquinoline derivatives and can either use peroxide or molecular oxygen as oxidant. / In the last part of the thesis, the aerobic and electrochemical Cross-Dehydrogenative-Coupling in ionic liquids is presented. Ionic liquids have demonstrated high efficiency when applied as solvent and electrolyte solvent for the oxidative nitro-Mannich carbon-carbon bond formation. / Cette thèse est une investigation sur la génération et la réactivité de carbocations adjacents à un atome d'azote trisubstitué (iminium). / Dans la première partie de cette thèse, une alkylation d'une liaison sp3 C-H adjacente à un atome d'azote catalysée au cuivre est décrite. Ce procédé respectueux de l'environnement utilisa l'oxygène comme oxydant et l'eau comme solvant. / Dans la deuxième partie de cette thèse, une réaction aérobique de phosphonation de liaison sp3 C-H est présentée. Ce procédé catalysé par un sel de bromure de cuivre(I) et utilisant des bis-alkylphosphites comme nucléophiles permit la synthèse directe de liaisons C-P via le couplage oxydant de liaisons carbone-hydrogène et phosphore-hydrogène. / Dans la troisième partie de cette thèse, une réaction d'arylation de liaison sp3 C-H, catalysée par le cuivre, avec des acides boroniques en absence de groupement directeur est décrite. Cette réaction d'arylation, utilisant soit un peroxyde soit l'oxygène comme oxydant, donna des dérivés de la tétrahydroisoquinoline biologiquement actifs. / Dans la dernière partie de cette thèse, le couplage croisé déshydrogénant aérobique et électrochimique en liquides ioniques est présenté. Les liquides ioniques ont démontré une grande efficacité pour la formation de liaisons C-C (nitro-Mannich oxydante) lors de leurs utilisations comme solvant et solvant électrolyte.

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