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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.


Mingle, David, Shilabin, Abbas 05 April 2018 (has links)
SYNTHESIS OF PYRROLO[2,1-c] [1,4] BENZODIAZEPINE -11- HYDRAZINYL DEVRIVATIES AS A POTENTIAL ANTIMICROBIAL AGENT David Mingle and Abbas G. Shilabin Department of Chemistry, East Tennessee State University, Johnson City, TN 37614, USA ABSTRACT Pyrrolo [2,1-c] [1,4] benzodiazepine (PBD) is a class of natural products obtained from various actinomycetes which have both anti-tumor and antibiotic activities. They can bind to specific sequences of DNA that can trigger a biological response which is of pharmacological interest. PBD can also prevent cell division leading to death of the bacteria. This research focuses on the synthesis of novel PBD-11-hydrazinyl derivatives using a multi step synthesis. PBD-dilactam was initialy produced using isatoic anhydride and (S)-proline which was then converted to the PBD-thiolactam using Lawesson's reagent. Reaction of thiolactam with hydrazine in ethanol afforded PBD-11-hydrazinyl in good yield. Condensation of PBD-11-hydrazinyl with aldehydes possessing various substitutions was performed to generate (S,E)-11-[2-(phenylmethylene)hydrazono]-1,2,3,10,11,11a-hexahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepin-5-one. 1H-NMR , 13C-NMR , DEPT and GC-MS were used to characterize the products. Inhibition activity of the products were carried out using TEM-1 and p99 β-lactamases. Microbial activity will be conducted in collaboration with Natural Product Center at University of Mississippi on the final products.

Synthesis, Characterization and Biological Evaluation of novel (S, E)-11-[2-(arylmethylene)hydrazono] pyrrolo [2,1-c] [1,4] benzodiazepine derivatives.

Mingle, David, Shilabin, Abbas G, Dr 12 April 2019 (has links)
Pyrrolo [2,1-c] [1,4] benzodiazepine (PBD) is a class of natural products obtained from various actinomycetes which have both anti-tumor and antibiotic activities. They can bind to specific sequences of DNA that can trigger a biological response which is of pharmacological interest. PBD can also prevent cell division leading to death of the bacteria. This research focuses on the synthesis of novel 11-hydrazinyl PBD derivatives using a multi-step synthesis. PBD-dilactam was initially produced using isatoic anhydride and (L)-proline which was then converted to the PBD-thiolactam using Lawesson's reagent. Reaction of thiolactam with hydrazine in ethanol afforded PBD-11-hydrazinyl in good yield. Condensation of 11-hydrazinyl PBD with aldehydes possessing various substitutions was performed to generate (S, E)-11-[2-(phenylmethylene) hydrazono]-1,2,3,10,11,11a-hexahydro-5H benzo[e]pyrrolo[1,2-a] [1,4] diazepin-5-one. 1H-NMR, 13C-NMR, DEPT, IR, GC-MS and X-ray Crystallography were used to characterize the products. Inhibition activity of the products were carried out using TEM-1, AmpC and p99 β-lactamases. National cancer Institute tested some selected compounds on 60 NCI- cell lines

The Far Ultraviolet Photochemistry of Alkyl-Substituted Cyclobutenes

Clark, Brady Kenneth 12 1900 (has links)
<p>Electrocyclic reactions of ground and excited state hydrocarbons are well known. These transformations have helped to form a basis on which modern organic chemistry has been built on. For a variety of reasons, the photochemical transformations of one of the simplest systems, the cyclobutene system, are not well understood. This thesis attempts to provide the first thorough and systematic study of the excited state behaviour of cyclobutene in solution. The direct photochemistry of some simple, alkyl-substituted derivatives of cuclobutene is the main concern of the following chapters; the prime concern of the thesis is on the following chapters, the prime concern is on the stereochemistry of the photochemical electrocyclic ring opening process.</p> <p>Ten cyclobutene systems were synthesized with a view to delineating the path of formal electrocyclic ring opening, formal (O26+O2S) cycloreversion, and the possible role of intermediates in the photochemistry of these systems. These studies have revealed that, in general, photochemical ring opening of cyclebutenes with monochromatic far ultraviolet (185, 193, and 214nm) light sources in solution proceeds non-stereospecifically to yield mixtures of all the corresponding diene geometric isomers, These results appear to contradict orbital symmetry selection rules.</p> <p>Ultraviolet absorption spectra and the dependence of the photochemistry on excitation wavelength have been studies in hydrocarbon solution in order to investigate the possible involvement of two or more excited states in the direct photochemistry of these compounds. The direct photochemistry of these cyclobutene derivatives shows varying degrees of wavelength dependence throughout the series. In addition, far UV irradiations have been carried out in a hydrocarbon liquid at low temperatures, in order to study the dynamics of the formal electrocyclic ring opening process. These studies have shown that a slight barrier exists for the formally forbidden conrotatory process relative to the formally allowed disrotatory process.</p> <p>It is not possible to correlate these results within the framwork of the most recently calculated (ab initio) state correlation diagrams for the ground and excited state interconversions of butadiene and cyclobutene. The results of this thesis contradict the most recent ab initio calculations, which predict that the process should proceed stereospecifically in a disrotatory fashion for the π,π* excited state of cyclobutene, indicating possibly that the theoretical work does not adequately describe the excited state character of cyclobutene or at least the theoretical results for cyclobutene itself cannot extrapolated to substituted systems.</p> / Thesis / Doctor of Philosophy (PhD)


Jeyakanthan, Ketharagowry January 2014 (has links)
<p>Three novel 1-aryl-1-(3-butenyl)germacyclopent-3-enes (26a, 26b and 26c) were synthesized and their photochemistry in hexane solution was studied by steady state and laser flash photolysis (LFP) methods. Steady state photolysis of 1-(3-butenyl)-3,4-dimethyl-1-phenylgermacyclopent-3- ene (26a) was found to proceed cleanly to afford the corresponding germylene derived product along with 2,3-dimethyl-1,3-butadiene (DMB) in the presence of acetic acid, methanol and isoprene, suggesting that free (3-butenyl)phenylgermylene (GeBuPh) is the primary photochemically generated species. However, we were unable to detect the germylene by laser flash photolysis with this compound, due to rapid “self –quenching” of the germylene by the precursor. The direct detection of the germylene in solution by laser flash photolysis requires the use of a more strongly absorbing derivative. Indeed, 3-butenylphenylgermylene (GeBuPh) was successfully detected directly by laser flash photolysis of 1-(3-butenyl)-3-methyl-1,4-diphenylgermacyclopent-3-ene (26b) in hexane solution, where it exhibits a UV-Vis absorption band centered at λmax= 490 nm and decays with second order kinetics on the microsecond timescale. In the absence of reactive substrates the decay of GeBuPh is accompanied by the growth of a second transient absorption, assigned to Ge2Bu2Ph2 (34) λmax = 420 nm; the assignment is based on a comparison to the laser flash photolysis of 1,3-dimethyl-1,4- diphenylgermacyclopent-3-ene (26d). Rate constants have been determined for reaction iv of the germylene with selected germylene substrates in order to evaluate the effects of intramolecular π-complexation on its reactivity. The results indicate that GeBuPh exhibits similar reactivity to GeMePh under otherwise identical experimental conditions, and thus show no significant indication of intramolecular π-complexation. With this in mind we have synthesized and studied 1-(3-butenyl)-3-methyl-4- phenyl-1-[3,5-bis(trifluoromethyl)phenyl]germacyclopent-3-ene (26c), which was designed to produce a more strongly electrophilic Ge(II) center in the corresponding germylene. The germylene 46 is detectable as a weakly absorbing transient species with λmax = 490 nm by laser flash photolysis of 26c in hexane solution. Generation of germylene 46 in the presence of THF leads to the formation of the corresponding Lewis acid base complex 48 at λmax = 330 nm. The reactivity of germylene 46 with selected substrates such as AcOH, THF and isoprene has been examined and the results compared to analogous data for the parent germylene GeBuPh. The forward rate constant for germylene 46 with acetic acid is slightly higher than that for GeBuPh, and no evidence for intramolecular complexation with the remote C=C bond could be obtained.</p> / Master of Science (MSc)

Photochemistry of cyclobutenes and related constrained s-cis dienes

Postigo, Alberto Jose 11 1900 (has links)
<p>This thesis is concerned with the development of a new qualitative model to explain the photochemistry of cyclobutene and 1,3-butadiene, in which the $\rm 2A\sb{g}{\to}1A\sb{g}$ decay channel of the van der Lugt-Oosterhoff mechanism does not actually correspond to a $\rm 2A\sb{g}$ avoided crossing pericyclic minimum. In fact, decay from the $\rm 2A\sb{g}$ excited state to the ground $\rm(1A\sb{g})$ state occurs at a conical intersection point (crossing between the excited state and ground state potential energy surfaces). The study described pertains to the photochemical ring opening of a series of alkyl-substituted bicyclic cyclobutenes (structure I), and the cis,trans isomerization of related constrained s-cis dienes (structure II). The high degree of disrotatory stereospecificity observed in the ring opening of I is not related to ring strain factors induced by the ancillary ring, but rather to the decreased flexibility in the isomeric 1,3-diene products or the rotational flexibility of the substituents on the cyclobutene double bond. These results strongly suggest that orbital symmetry selection rules are important in these reactions. The effects of constraining the C-C central bond in 1,3-dienes on the cis,trans photoisomerization process and motions around C=C bond in cyclobutene photochemical ring opening are two of the direct implications of the results obtained from these experiments.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) The results from the photochemical ring opening of alkyl-substituted monocyclic cyclobutenes provide evidence that orbital symmetry does play a significant role in the reaction, as indicated by the decrease in the quantum yields of ring opening upon syn-dimethyl substitution. In addition, the same results are exclusive of the presence of operative non-concerted pathways in the ring opening reaction. The energy requirements for the photochemical ring opening of cyclobutenes have been clearly established. Thus, the inability of 1-phenylcyclobutenes to undergo ring opening reactions has been found to be related to energetic considerations rather than polarizability of their excited states.</p> / Doctor of Philosophy (PhD)

Preparation, chemistry, and characterization of hypervalent organosulfur fluorides

Savoie, Paul R. 29 December 2015 (has links)
<p> Since the discovery of the pentafluorosulfanyl (SF<sub>5</sub>) group around the 1960s, progress in exploring the chemistry of aliphatic SF<sub> 5</sub>-containing compounds stagnated because of a lack of efficient synthetic methods. More recent developments in the preparations of SF<sub>5</sub>-containing compounds afforded easier access to these compounds, and sparked great interest in exploring their chemistry. Chapter 1 discusses the development of efficient methods used to prepare SF<sub>5</sub>-containing aliphatic compounds. </p><p> This dissertation investigates the combination of steric and polar effects of pentafluorosulfanylation on aliphatic molecules. Chapter 2 discusses the synthesis and chemistry of aliphatic aldehydes and aldimines containing the SF<sub>5</sub> group in the 2-position. The aldehydes undergo many of the common chemical transformations of aliphatic aldehydes, affording a variety of SF<sub>5</sub>-containing compounds. The large C&ndash;S bond dipole helps direct additions to the carbonyl group in a manner consistent with the Cornforth hypothesis, resulting in highly diastereoselective nucleophilic additions. Similarly, the synthesis of SF<sub>5</sub>-containing SF<sub>5</sub>&beta;-lactams by [2+2] cycloadditions of 2-pentafluorosulfanylaldimines with azidoketene proceeds with high diastereofacial selectivity. The SF<sub>5</sub> &beta;-lactams formed by this reaction may lead to a greater variety of diastereoselectively-prepared amino acid compounds for study in peptides, the preparation of new antibacterial compounds, and the design of novel SF<sub>5</sub> &beta;-lactamase inhibitors. </p><p> Chapter 3 discusses the structural studies of some synthesized pentafluorosulfanylated molecules to help further elucidate the steric and polar effects of pentafluorosulfanylation on aliphatic compounds. Coupling constant analyses determined the local molecular structure near the SF<sub>5</sub> group and revealed that the unexpected diastereotopic resonances in 1H NMR spectra were the result of partial insertion of a hydrogen atom between two equatorial fluorine atoms, thus &ldquo;locking&rdquo; the conformation of the alkyl chain near the SF<sub>5</sub> group. Computational experiments confirmed the experimentally-determined S&ndash;C&ndash;C&ndash;O dihedral angle of 85&deg; observed in the alcohols formed by nucleophilic addition to the aldehyde carbonyl group of 2-pentafluorosulfanyl aldehydes. Computation of the reaction profile for the [2+2] cycloaddition of 2-pentafluorosulfanylaldimines with azidoketene revealed a difference in the reaction barriers leading to the two diastereomeric pairs of products of about 4.1 kcal/mol. Formation of the 1,2-<i>lk,lk</i> products is favored over the formation of the other possible products.</p>

Development of synthetic methods to access key structural features of tetrapetalone A

Weaver, Marisa Gail 18 February 2016 (has links)
<p>The tetracyclic natural product, tetrapetalone A has eluded chemists since its isolation in 2002. The complex structural features of this natural product provide a platform from which new synthetic methods can be developed. One approach to build tetrapetalone includes formation of a Nitrogen-Aryl bond. Despite the prevalence of this bond connection in natural and pharmaceutical compounds, previous methods to form Nitrogen-Aryl bonds were not applicable in our approach to the tetrapetalone A scaffold. To overcome this limitation and provide a different route to access compounds containing Nitrogen-Aryl bonds, we approached the problem with a different strategy. This divergent strategy relies upon distinct deprotonation conditions of a cyclic vinylogous amide to afford regioisomeric dienes. Each diene can then undergo a tandem Diels-Alder and retro-Diels-Alder sequence with a variety of acetylenic dienophiles to afford a range of multi-substituted aromatic products containing Nitrogen-Aryl bonds. The scope of this method and its application toward tetrapetalone A will be discussed. While investigating different synthetic approaches, our group also probed the reactivity of the tetramic acid C-5 position. When our group encountered limitations among the current methods to install vinyl groups at the C-5 position we turned to develop a more general vinylation strategy. Our progress toward a "vinylation reagent" is reported and future directions will be discussed.

An Umpolung Approach to the &#945;-Functionalization of Ketones and Aldehydes

Hatcher, John January 2011 (has links)
<p>The &#945;-alkylation of N-sulfonyl hydrazones via in situ-derived azoalkenes provides an umpolung approach to ketone &#945;-alkylation that has considerable potential with regard to catalysis and the direct incorporation of functionality not amenable to the use of enolate chemistry. Herein, the first Cu(I)-catalyzed addition of Grignard reagents to in situ-derived N-sulfonyl azoalkenes is described. This method is remarkable in its ability to deliver highly sterically hindered compounds that would be difficult or impossible to synthesize via traditional enolate chemistry, including those having up to three contiguous quaternary centers. This method is compatible with a wide variety of &#945;-halo tosylhydrazones, including cyclic and acyclic &#945;-halo tosylhydrazones as well as those derived from both ketones and aldehydes. Also, herein, the first asymmetric organocatalytic sulfenylation of in situ-derived nitrosoalkenes leading to chiral nonracemic &#945;-sulfenylated ketones is described. The transformation proceeds in an umpolung fashion, relative to enolate/azaenolate methods, and uses simple thiols, thereby obviating the need for elecrophilic sulfur reagents. Moreover, excellent ee's were obtained starting from a variety of &#945;-chloro oximes, including cyclic and acyclyic systems. Chiral nonracemic sulfur containing compounds are important both biologically, and in synthetic context through their use as chiral auxiliaries, ligands for metal catalysis, and organocatalysts. Also, herein, the addition of cuprates to &#945;,&#946;-epoxy tosylhydrazones is described. The transformation is operationally simple and efficient and has the unusual feature of giving high syn selectivity, which is opposite of that produced by a simple SN2-type epoxide opening reaction. This method compatible with &#945;,&#946;-epoxy tosylhydrazones with additional &#945;-substitution, which provides access to aldol-like products that would be impossible to make using traditional enolate chemistry. Moreover, this method is compatible with a wide variety of both cyclic and acyclic &#945;,&#946;-epoxy tosylhydrazones, and produces dr's of >20:1.</p> / Dissertation

Evaluation of a silica hydride-based undecynoic acid stationary phase for high performance liquid chromatography

Kozhikote, Veena Menon 11 February 2017 (has links)
<p> Undecynoic acid (UDA) attached to a silica hydride surface has been found to exhibit weak cationic exchange properties and an aqueous normal phase (ANP) type of retention. ANP is a mechanism similar to normal phase chromatographic retention, except for the use of a polar solvent such as water in the mobile phase. In ANP, the retention of a polar molecule is increased with a higher concentration of the non-polar mobile phase solvent (usually acetonitrile). Non-polar molecules exhibit retention behavior as in reverse phase (RP) chromatography. The goal of this research was to characterize the chromatographic retention pattern of an undecynoic based silica hydride column by studying various polar and nonpolar analytes. Also investigated were the effects of varying the buffer concentrations&mdash;formic acid and ammonium acetate and the effect of temperature on the retention of selected compounds. It has been established from the current work that a silica hydride based UDA column can be used for separation and analysis of nucleotides and nucleosides as well as phenolic acid components in pomegranate peel samples. A phenyl hydride column was additionally used to complete the study on the peel samples since the UDA column was not effective in separating isobaric compounds found in the peels. In conclusion, silica hydride based UDA column has been found to exhibit dual retention capabilities for polar and non-polar molecules.</p>

A. Studies In The Allylic Substitution Chemistry Of Copper Hydride B. Stereoselective Silylcupration Of Conjugated Alkynes In Micellar Media C. Palladium-Catalyzed Synthesis Of 1,3-Butadienes and [3]-[6]Dendralenes D. Synthesis Of Small Molecule Underwater Adhesives Inspired By Mussels

Linstadt, Roscoe T. H. 27 April 2017 (has links)
<p> Copper hydride (CuH) has been shown to enable a number of selective 1,2- and 1,4-reductions when complexed with the appropriate ligand, yet the allylic substitution chemistry of CuH has been much less studied. This dissertation describes the further study of CuH to perform sequential reductions on Morita-Baylis-Hillman (MBH) adducts. Specifically: I) Selectivity in the SN2&rsquo; reduction of MBH adducts was shown to be highly dependant on the nature of the ligand used. II) The reaction of MBH alcohols was shown to involve an initial dehydrogenative silylation with PMHS, where both the oligomeric nature and electronics of the initially formed trialkoxysilyl ether intermediate are important in determining both the observed stereoselectivity, and efficiency of the substitution. III) MBH ketones could be employed in tandem SN2&rsquo;/1,2-reduction sequences to arrive at stereodefined allylic alcohols with central chirality. </p><p> Vinylsilanes are versatile intermediates in organic synthesis owing to numerous methods for their transformation into other functional groups that proceed with high stereoretention. While there are numerous methods to synthesize stereodefined vinylsilanes from alkynes, many existing methods require the use of highly reactive moisture intolerant reagents and harsh reaction conditions, features that limit the functionality that can be accommodated. Even fewer of these existing methods are conducted under environmentally responsible conditions. The use of Suginome&rsquo;s reagent as a moisture tolerant source of nucleophilic silicon, small catalytic quantities of a simple copper(I) salt, and an aqueous solution of TPGS-750-M as an environmentally benign nonionic surfactant, is described herein as a highly effective combination of reagents that allows for the stereoselective silylcupration of conjugated alkynes giving access to a variety of (<i>E</i>)-&beta;-silyl-substituted carbonyl derivatives under environmentally responsible conditions. </p><p> This dissertation also describes the application of substituted allenoates as electrophilic butadienyl coupling partners under palladium catalysis in aqueous micellar media. The substituted allenoates could then be transformed by the methods developed herein into a variety of 2-substituted butadienes, where the methods were then extended to provide entry into a variety of substituted [3]-[6]dendralenes. Specifically: I) Application of an additive based screen allowed for evaluation of functional group tolerance in the Pd-catalyzed coupling of substituted allenoates with boronic acids. II) Curiosity driven investigations to identify boron based sp3 coupling reagents compatible with the conditions of micellar catalysis led to the identification of OBBD alkylborinate reagents as stable and isolable coupling reagents, which was the applied to the synthesis of 2-alkyl 1,3-butadienes. III) An analogous vinylallenyl coupling partner that functions formally as an electrophilic [3]dendralene synthon was proposed, and a number of synthetic routes were examined to access this molecule. Optimization of the synthetic route allowed for access to multigram quantities of this material, where it was applied to the synthesis of variously substituted [3]-[6]dendralenes. </p><p> Efforts to understand the marine mussels mechanism of strong wet adhesion has been a subject of intense scientific investigation. Analysis of the peptide sequence of mfp-5, a mussel foot protein most correlated with interactions at the interface, revealed a high proportion of charged, hydrophobic, and catechol containing residues. Described in this dissertation is the synthesis of small molecule underwater adhesives by incorporation of these key features of mfp-5. These newly designed molecules formed adhesive bilayers underwater, and were shown to replicate and even exceed mfp-5&rsquo;s strong wet adhesive energy, while also being orders of magnitude smaller than both the native mussel proteins or existing biomimetic adhesive platforms. By systematically varying key portions of these small molecular adhesives, the adhesive bilayers could be transformed into molecularly uniform monolayers which were applied to the nanofabrication of organic electronic devices.</p>

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