Filter Dissertations and Theses By:
Synthesis of Heteroatom Containing Aromatic Conjugated Polymers Using Acyclic Diene Metathesis (ADMET)
Year of Dissertation:
This doctoral thesis describes the synthesis of heteroatom (B/Si/Ge/Sn) containing conjugated macromolecules via Acyclic Diene Metathesis (ADMET) polycondensation. The main objective was to obtain a library of macromolecules with unique optical properties based on different aromatic segments and heteroatoms. In chapter 2, the selective synthesis and characterization of a germanium containing macrocycle with two stilbene fluorophores is reported. The structure and size of the macrocycle were determined by 1H NMR, 13C NMR, GPC (polystyrene standards) and MALDI - TOF. The macrocycle features "all - trans" configuration at the vinylene bonds. The optical properties were studied by UV/Vis and fluorescence spectroscopy. The material emits in the blue region around 363 nm with a quantum efficiency of 0.4 relative to trans - stilbene. Theoretical calculations using B3LYP/6-31G** and Lanl2dz basis sets offered a better understanding of structural and electrooptical properties. They showed the presence of two important transitions in the absorption and the involvement of germanium orbital in the electronic conjugation with the stilbene segments. Chapter 3 outlines the extension of this aforementioned synthetic strategy to the group 14 element boron, in order to generate a new class of conjugated macromolecules - homopolymers based on boron (p2a, p2b) and co-polymers based on silicon and boron (p12a, p12b). The structures and these new systems were determined by 1H NMR, 13C NMR and correlation NMR spectroscopy. The molecular weights were determined by GPC using polystyrene standards. Both the homopolymers and copolymers have "all - trans" configuration around the internal vinylene bonds. The copolymers were found to be random. The optical properties showed that all the macromolecules absorbed in the range of 327 - 406 nm and emitted at 416 nm (p2a, p12a) and 494 nm (p12b). The quantum efficiencies of these macromolecules were in the range of 0.28 - 0.30. p12a was found to be a potential fluoride ion sensor with very high sensitivity due to a polymer co-operative effect. Two distinct emissions dominated the emission spectrum of p12b, investigation of which indicated possible intermolecular energy transfer. The thermal properties indicated higher stability of the copolymers compared to the homopolymers. Degradation of p12a followed a two-step process and p12b was found to be more stable than p12a. Chapter 4 of this thesis reports the synthesis of a library of homologous polymers based on Si, Ge, or Sn alternating with dithienylthiophene segments. The microstructures were analyzed by 1H NMR, 13C NMR and Correlation spectroscopy (HSQC, COSY). All the polymers p3a - c showed "all - trans" configuration at the vinylene bonds. The molecular weights were determined by GPC using polystyrene standards. No significant side products were observed under the ADMET conditions employed. Optical property analysis showed that the monomers were non-emissive whereas they absorb in the range of 263 - 264 nm. The polymers were highly fluorescent emitting in the range of 419 - 423nm. The quantum efficiencies were found to decrease from 0.18 to 0.11 from Si over Ge to Sn along with a small gradual blue shift of the emission maximum with the increase in size of the heteroatom. Thermogravimetric analysis indicated that Si based p3a showed the highest stability among the three homologous polymers. Chapter 5 is strongly related and involves alkyloxy homologous side - chain substituted systems. The microstructures of the macromolecular products were analyzed by 1H NMR, 13C NMR showing that these polymers also have an "all - trans" configuration around the vinylene bond. The molecular weights were determined by GPC using polystyrene standards. Alkyloxy substituted silicon containing stilbene polymers showed a strong red shift compared to their stilbene homologous without side chains, with an absorption maximum at 371 nm. The emission maximum was observed at 412 nm. The quantum yield was 0.50 - 0.52 indicating that, there is no photo - induced cis - trans isomerization.
Intelligent Nano/Microgels for Cell Scaffold and Drug Delivery System
Year of Dissertation:
Stimulus-responsive polymer microgels swell and shrink reversibly upon exposure to various environmental stimuli such as change in pH, temperature, ionic strength or magnetic fields. Therefore, they become ideal candidates for biomaterial applications. For this work, we focus on the several intelligent microgels and their application on two areas: the cell scaffold and the drug delivery system. As for the cell scaffold, it can be realized by colloidal supra-structure microgels, which constructed by the thermo-driven gelation of the colloidal dispersion of poly(N-isopropylacrylamide-co-acrylamide) poly(NIPAM-co-AAm) microgels (Chapter 3). Such microgels exhibit a reversible and continuous volume transition in water with volume phase transition temperature (VPTT) 35 oC and remain partially swollen and soft under physiological conditions. More importantly, the size of the microgel particles can affect the sol-to-gel phase transition of the microgel dispersions, alter the syneresis degree of the constructed colloidal supra-structures, and tailor the cytocompatibility. The constructed colloidal supra-structure can be regarded as a model system for a new class of cell scaffolds. As for drug delivery system, Chapter 4 and Chapter 5 focus on the development of biocompatible microgels-based systems for delivering a traditional anti cancer drug curcumin. These thermo-responsive core-shell structure microgels are constructed from oligo(ethylene glycol) as a hydrophilic shell and hydrophobic biocompatible materials as core, such as poly(2-vinylanisole) and poly(4-allylanisole). The rationally designed core chain networks can effectively store the hydrophobic curcumin drug molecules via hydrophobic interactions, thus provide high drug loading capacity; while thermo-sensitive nonlinear poly(ethylene glycol) (PEG) gel shell can trigger the drug release by local temperature change, offering sustained drug release profiles. In Chapter 5, additionally embedded of magnetic Fe3O4 nanoparticles enable such hybrid nanogels to delivery pharmaceuticals to a specific site of the body by applying a gradient magnetic field. Chapter 6 investigated a class of well-defined glucose-sensitive microgels as an insulin drug release carrier, obtained via polymerization of 4-vinylphenylboronic acid (VPBA), 2-(dimethylamino) ethyl acrylate (DMAEA), and andoligo(ethylene glycol)methyl ether methacrylate (MEO5MA). The presence of MEO5MA monomer could retard the glucose-sensitive network from swelling because the rapid hydrogen bonding between the glucose molecules and the ether oxygens of the MEO5MA is prior to the glucose binding to the PBA groups. Therefore, the set point of glucose sensitivity of microgels could be adjusted possibly and result in potential biomedical applications. Compared to the non-imprinted copolymer microgels, the glucose imprinting of the microgels can create and rigidly retain more binding sites complementary to the shape of the target glucose molecule in the crosslinked polymer network, thus improve the sensitivity and selectivity of the microgels in response to the glucose level change. Additionally, the introduction of fluorescent Ag nanoparticles (NPs) to the microgels can realize the integration of optical glucose detection and self-regulated insulin delivery into a single nano-object.
Energy of the Quasi-free Electron in Atomic and Molecular Fluids
Year of Dissertation:
The ability to predict accurately the density dependent evolution of the conduction band energy of insulators has applications in the optimization of solvent choice and thermodynamic conditions for chemical reactions. However, directly investigating density dependent changes in the conduction band is experimentally difficult. Therefore, we have used field ionization of high-n dopant Rydberg states to determine the perturber induced shift of the dopant ionization energy Delta(ρP), where ρP is the perturber number density. Appropriate modeling allows the minimum of the conduction band energy V0(ρP) to be extracted from Delta(ρP). Field ionization requires the measurement of photoionization spectra of a dopant at two different electric field strengths. Thus, in this study, photoionization spectra of various dopants (i.e., CH3I, C2H5I, N,N-dimethylanaline, trimethylamine and triethylamine) were obtained under different electric field strengths in atomic (i.e., Ar, Kr, and Xe) and molecular (i.e., CH4, and C2H6) perturbers from low density to the density of the triple point liquid, at non-critical temperatures and on an isotherm near the perturber critical isotherm. At low perturber number density, a temperature dependence was observed in Delta(ρP), with |Delta(ρP)| increasing as the temperature decreases. This observation contradicts the prediction of the Fermi-Alekseev-Sobel'man model. Within the local Wigner-Seitz model developed by our group, the temperature behavior at low density arises from the ensemble average ion/perturber polarization energy P+(ρP and is caused by variations in the dopant/perturber radial distribution function. Moreover, a striking critical point effect in V0(ρP was observed in all of the perturbers investigated. This critical point effect is explained by the dramatic increase in the local density around a perturber particle near the critical point of the perturber. This local density increase, caused by an increase in the correlation length of the perturber, acts to confine the quasi-free electron, thereby increasing its kinetic energy. Various intermolecular potentials and integral methods necessary to calculate the radial distribution functions were studied and tested in order to achieve the best fit to the experimental Delta(ρP) in molecular perturbers.
Label-free Detection of Cancer Cells with Polysilicon Sensor Chips and Biomolecule-assisted Synthesis of Shape-controlled Nanoparticles
Year of Dissertation:
Constant effort has been made for the detection of cancer cells. Recently, ovarian and kidney cancer cell lines have been shown to have higher cellular elasticity as compared to normal cells assessed by monitoring the degree of deformation under hyposmotic pressure. This method has been modified and applied to various cases. In cancer cells, the oncogenic mutant p53 (mtp53) protein is present at high levels and contributes to tumor growth and metastasis. Herein the influence of mtp53 on the mechanical property of breast cancer cells was assessed by monitoring the swelling ratio of cells with time using the impedance measurements. The depletion of mtp53 led to decrease of impedance variation, which is corresponding to the lower elasticity. All results suggest that electric probing for the extent of the mtp53 expression of breast cancer cells may serve as a meaningful fingerprint for the cancer diagnostics, and this outcome will also have an important clinical implication for the development of mtp53-based targeting for tumor detection and treatment. Meanwhile, the samples containing a mixture of red blood cells and cancer cells were examined by impedemetric detection. The results suggest that the cancer cells need to be enriched before applying impedance measurements to the samples with high concentration of red blood cells. Thus, dielectrophoresis (DEP) provides as a solution by taking most red blood cells apart from the cancer cells, which is supported by taking most red blood cells apart from the cancer cells, which is supported by experimental data. The DEP system will be integrated with microfluidic channels for DEP analysis in future. Biomolecule-assisted synthesis of shape-controlled nanoparticles is the other part of this dissertation. One project refers to the PbSe nanocrystal growth with the aid of peptide. Pb-binding TAR-1 peptides (ISLLHST) were covalently conjugated on a peptide nanotube substrate and the precursors of PbSe were incubated at room temperature. This resulted in the growth of highly crystalline PbSe nanocubes on this biomimetic cylindrical substrate. The growth mechanism to generate nanocubes occurs via the directed self-assembly of nanoparticles and then nanoparticle fusion. The peptide conformation and the cylindrical peptide nanotube substrate play important roles in the mesoscopic crystallization of PbSe nanocubes. The conformational change of the TAR-1 peptide on the nanotubes due to the change in the buffer seems to be responsible for aggregating intermediate nanoparticles in different directions for the directed fusion and mesoscopic crystallization of PbSe into the different shapes. The other project is the directional growth of LiFePO4 nanoribbons using glutathione and PVP as capping agents. The structure, size and morphology were investigated by XRD, TEM, AFM, SEM. The HRTEM result suggests that the nanoribbons are growing along , which is highly possible to enhance the rate capability, achieving the better battery performance.
SYNTHESIS OF NEW PORPHYRINOIDS FOR BIOMEDICAL AND MATERIALS APPLICATIONS
Year of Dissertation:
The facile synthesis of three non-hydrolysable thioglycosylated porphyrinoids is reported. Starting from meso perfluorophenylporphyrin (TPPF20), the non-hydrolysable thioglycosylated porphyrin (PGlc4), chlorin (CGlc4), isobacteriochlorin (IGlc4), and bacteriochlorin (BGlc4) can be made in 2-3 steps. The ability to append a wide range of targeting agents onto the perfluorophenyl moieties, the chemical stability, and the ability to fine-tune the photophysical properties of the chromophores make this a suitable platform for development of biochemical tags, diagnostics, or as photodynamic therapeutic agents. With reduction of one or two pyrrole double bonds, there is a red shift in the lowest energy absorption band and a significant increase in intensity. The fluorescence of these porphyrinoids is in the order PGlc4 = BGlc4 < CGlc4 4 and there is a corresponding decrease in the amount of triplet formed. Fluorescence micrographs of cells after treatment with these four porphyrinoids indicate they are taken up. The CGlc4 and IGlc4 may be dual function agents that can detect cancer by luminescence, and treat cancer by photodynamic therapy (PDT). Porphyrins appended with four rigid hydrogen bonding motifs on the meso positions were synthesized and self-assembled into a cofacial cage with four complementary bis- (decyl)melamine units in dry solvents, these hydrogen-bonded cages were analysed by diffusion-ordered spectroscopy (DOSY) in solution. The hydrocarbon chains on the melamine mediate the formation of nanofilms on surfaces as the solvent slowly evaporates. A water soluble zinc (II) phthalocyanine symmetrically appended with eight thioglucose units was synthesized from commercially available hexadecafluoro-phthalocyaninato zinc(II) by controlled nucleophilic substitution of the peripheral fluoro groups by thio-sugars. The photophysical properties and cancer cell uptake studies of this nonhydrolyzable thioglycosylated phthalocyanine are reported. The new compound has amphiphilic character, is chemically and photochemically stable, and can potentially be used as a photosensitizer in photodynamic therapy. A porphyrin bearing pyridyl groups at the meso positions was synthesized using 2,6-diacetamido-4-formylpyridine. A new method has been developed for the synthesis of the precursor aldehyde that avoid much of the problems associated with the earlier synthesis. With this porphyrin it is possible to build hetero-complementary rigid, multi-porphyrin supramolecular arrays via hydrogen bonds. For example, when using naphthalenediimide (NDI) units a checkerboard pattern is expected to be formed using this porphyrin as a donor and NDI as an acceptor where triple hydrogen bond is formed between the diimide and pyridyl units. Energy transfer can be studied through this hydrogen bonded supramolecular assembly. The synthesis of a triply bridged diporphyrin appended with six thioglucose units is reported. The electronic spectrum of this triply bridged porphyrin has enhanced intensity at low- energy wavelengths that reaches the near infrared region. The goal of this project is to create tumor targeting dyes that can be activated with red wavelengths of light that penetrate deeper into tissues. This new compound is amphiphilic in nature, chemically and photochemically stable, expected to have unusual photophysical and electrochemical properties, and can potentially be used as a photosensitizer in photodynamic therapy.
NEW DIRECTIONS WITH TRIAZOLE AND BENZOTRIAZOLE CHEMISTRY: FROM NUCLEOSIDE MODIFICATION TO C-H BOND-ACTIVATION
Year of Dissertation:
Engineered peptide molecules are commonly synthesized by utilizing various peptide coupling reagents such as 1H-benzotriazol-1-yloxy-tris(dimethylamino)phosphonium hexafluorophosphate (BOP), 1H-benzotriazol-1-yl-4-methylbenzenesulfonate (Bt-OTs), 1-hydroxybenzotriazole (HOBt), etc. Their ready commercial availability, limited synthetic chemistry applications, and relatively high oxophilicity, prompted us to explore their applicability in new areas of organic synthesis. We have shown, for the first time, the application of BOP for the facile synthesis of C-6 azidopurine ribonucleosides and 2'-deoxyribonucleosides via the O6-(benzotriazol-1-yl) nucleoside derivatives. In organic solvents these azido nucleosides exhibit azidetetrazole equilibrium. The extent of azide and tetrazole tautomers in various organic solvents was studied, and relative amount of each tautomer in that solvent was determined. Subsequently, a detailed analysis of Cu-mediated azide-alkyne cycloaddition (CuAAC) leading to C-6 purine triazolyl nucleoside analogues was undertaken. Some of these nucleoside triazole derivatives showed moderate cytotoxic activity in human colon and ovarian cancer cell lines. In an attempt to alter the biological activity of these nucleoside triazole analogues, purine N-directed ruthenium-catalyzed C-H bond functionalization was evaluated. Here a serendipitous discovery of C(sp3)-H bond functionalization of N-methyl-2-pyrrolidone (NMP) was made. This result was developed into a C-H bond functionalization of NMP, and two cyclic, and a silyl ether using two 1,2,3-1H-benzotriazoles. Further, BOP and Bt-OTs reagents were applied to develop a new method for the dehydration of aldoximes to nitriles. This aldoxime dehydration method was utilized to develop one of the shortest and simplest routes towards the synthesis of an antiviral agent, 4'-cyano adenosine. Spurred by these findings, we investigated the reactivity of Bt-OTs towards various alcohols and probed the mechanism of reaction. These studies lead to the development of a new method for synthesis of benzotriazolylethers of alcohols. Also, for the first time we showed that -OBt anion could act as a leaving group from a benzylic sp3 hybridized carbon atom. This very important finding led to the utility of benzotriazolyl ethers of benzylic alcohols in a palladium-catalyzed C-C cross-coupling reactions.
Nano-device Fabrication from Quantum Dot Assembly
Year of Dissertation:
Colloidal semiconductor nanocrystals are highly photoluminescent crystalline nanoparticles (also termed as: quantum dots, QDs) with diameters ranging typically from 1 to 10 nm. For over a decade, quantum dots have been applied in various areas ranging from biological imaging, novel sensors to electroluminescence light-emitting diode (LED) due to their unique optical and electrical properties, such as broad excitation region, tunable size-dependant photoluminescence, high quantum yield, excellent chemical stability as compared to conventional organic dyes, and narrow emission peaks. We successfully designed and built two fluorescence resonant energy transfer (FRET) donor-acceptor assemblies between quantum dots. Each assembly was characterized by steady-state and time-resolved photoluminescence measurements at different donor-toacceptor ratios. Both photoluminescence quenching and decrease in the lifetime of donor quantum dots provided a concrete evidence of occurrence of FRET in each quantum dots pair assembly. Accompanied by the tunability of the emission energy of quantum dots in the broad visible region, our investigations on QD-QD FRET pairs present an attractive approach towards developing efficient light emitters and bio-sensors. Furthermore, we explored to build a novel microcavity by embedding one QD-QD between two distributed Bragg reflectors (DBRs). The spontaneous emission of QDs embedded inside a quasi one-dimensional microcavity should be further enhanced by FRET from the donor QD to the acceptor of QD. Bio-templating is a promising alternative method for semiconductor nanowire synthesis since it offers a variety of advantages such as low energy consumption for the synthesis and eases of template bionanotube preparation and CdS coating process. As a continued work, we exploited the direct nucleation and growth of CdS nanocrystals on the biomolecular nanowires without using the mineralization peptides. The whole synthesis process is completed in simple two steps without the uses of catalytic peptides or capping agents, commonly used for various nanoparticle synthesis. We also report a peptide molecule that self-assembles at the air-water interface and is capable of reducing gold ions and coordinating them to form triangular nanoplatelets and related structures. We show that we are able to control both morphology and crystallinity of gold nanoplatelets as a function of surface pressure.
Synthesis and Characterization of Unsymmetrical Perylene Derivatives and PDI Oligomers
Year of Dissertation:
Abstract Synthesis and Characterization of Unsymmetrical Perylene Derivatives and PDI Oligomers By Runkun Sun Adviser: Professor Shi Jin Since the discovery of high fluorescent property of perylene tetracarboxylic diimide (PDI) derivatives in 1959, more and more researchers' attention has been attracted to related fields. Ever since, many kinds of PDI derives has been synthesized and characterized. And many special properties of PDI derivatives also has been found, such as strong absorbance ability, special redox property and self assembly induced by π-π interaction etc. All these properties endow PDI derivatives wide applications in photovoltaic field and semi-conducting materials area. At the same time, those important applications also encourage researchers to do more exploration on the synthesis and characterization of PDI derivatives. As one of those researchers, my thesis also mainly focused on developing new synthetic methods and characterization of novel PDI derivatives. In Chapter 1, the history of perylene, PDI derivatives and PDI oligomers are introduced. Their corresponding properties and applications also are introduced. Furthermore, the synthetic methods for different kinds of PDI derivatives, both advantages and disadvantages, are discussed thoroughly. In Chapter 2, with the investigation of known reactions which were used to prepare the key intermediate, perylene monoimide monoanhydride, a new synthetic method was developed. The key intermediate could be prepared with high yield conveniently. With the key intermediate, several unsymmetric PDI derivatives were prepared with decent yield. The optical property of one unsymmetric PDI was studied. In Chapter 3, the synthesis of peryelene diester monoanhydride (PEA) and perylene monoimide monoanhydride (PIA) was discussed. We discovered a new way to prepare PEA and PEI. Several PEA and PEI with complex structure were prepared with decent yield. The first unsymmetric PEA was synthesized. In Chapter 4, the synthesis of several perylene oligomers was discussed. Base on our experience gained in the Chapter 3 and our investigation of Langhals' strategy, a new mechanism to grow perylene oligomers was developed by us. With our strategy, the key intermediate, perylene dimer dianhydride, could be obtained with high yield. Starting from this intermediate, a few perylene oligomers were obtained. The extraordinary absorption ability of PDI Oligomers was studied.
SYNTHESIS OF OLIGO(P-PHENYLENE VINYLENE)S AND FUNCTIONALIZATION OF SI(100) AND/OR SI(111) SURFACES WITH OLIGO(P-PHENYLENE VINYLENE)S
Year of Dissertation:
This doctoral thesis focuses firstly on the step-wise synthesis of a library of rigid-rod-type conjugated difunctional oligo(p-phenylene vinylene)s (OPVs) with varying chain lengths of the main chain and side chain substitution, i.e., monomer, dimer, and trimer units with chain end - terminal alcohol, aldehyde, vinyl, and alkyne functionality. All oligomers are soluble and show trans configuration at the internal vinylene bonds. The solublizing side-chains are of the alkyloxy type, i.e. heptyloxy (-OC7H15), butyloxy (-OC4H9), and methyloxy (-OCH3). All OPVs were characterized by means of ATR-FTIR, 1H-NMR (200 or 600 MHz) and 13C-NMR (50 or 150 MHz), 2D-NMR (HMBC and HSQC experiments), and optical spectroscopy. In subsequent steps, the OPVs were used as "building blocks". One application involved using a Cu(1)-catalyzed [3+2] Huisgen "click" cycloaddition to connect biotin ligands to both ends of the OPV, using spacer chains of varying length, consisting of oligo(ethylene glycol). Combining the valuable electro-optical properties of conjugated organic molecules with the biological recognition capability of biotin, the latter can be placed at variable distances via choosing an appropriate length of the hydrophilic spacer, which also serves to regulate the binding capabilities of the two terminal biotin units. To demonstrate this binding potential, networks were formed with streptavidin-coated quantum dots. The synthetic conditions are presented, together with representative optimizations of the key reactions. The organic compounds were analyzed by means of ATR-FTIR, 1H-NMR (200 or 600 MHz), 13C-NMR (50 or 150 MHz), 2D-NMR (HMBC and HMQC experiments), MS (ESI or MALDI-TOF), and optical spectroscopy. Networks were imaged with TEM. Another application involved templated grafting of the rigid-rod-type OPVs to flat surfaces of Si(100) and Si(111) via covalent Si(100)/Si(111)-O-C or Si(100)/Si(111)-C bonds. OPVs with terminal hydroxide (-OH), aldehyde (-CHO), alkyne (-CCH), and vinyl (-CH=CH2) functionalities were used. One approach involved the reaction of -OH, -CHO, and -CH=CH2 functional OPVs with Si(100)/Si(111)-H and/or Si(100)/Si(111)-Cl functionalized surfaces. Subsequent reaction of the resulting Si(100)/Si(111)-OPV-CH2OH surfaces with p-tolyl isocyanate produced urethane containing monolayers in a "click like" approach. The monolayers were characterized by means of XPS, ATR-FTIR, AFM, and confocal fluorescence laser scanning microscopy (CFLSM). A second approach involved synthesizing Si(100)/Si(111)-OCH2CH2N3 functional surfaces from the Si(100)/Si(111)-H and/or Si(100)/Si(111)-Cl with HOCH2CH2N3, then using a "click reaction" to attach -CCH functional (alkyne) OPV to the surface-bound N3. The resulting monolayers were characterized by means of XPS, ATR-FTIR, AFM, and CFLSM. A third approach involved the synthesis of Si(111)-OCH2CH2OH functional surfaces from Si(111)-H and/or Si(111)-Cl with HOCH2CH2OH, and then using a "click like" reaction between the Si(111)-OCH2CH2OH functionalized surfaces and 1,4-phenylene diisocyanate (OCN-Ph-NCO) to afford Si(111)-U-Ph-NCO surfaces. Subsequent reaction of these with the -OH functional OPVs produced urethane containing OPV monolayers. The latter were characterized by means of XPS, ATR-FTIR, AFM, and CFLSM. The combined results presented in this thesis represent a further major advance in the controlled functionalization of Si-surfaces and herald a variety of potential applications that use such a combination of inorganic and organic semiconductors.
SYNTHESES OF ENEDIYNERIBOFURANOSIDES
Year of Dissertation:
Enediynes are natural bacterial products isolated in the 1980s. They are characterized by nine- or 10-memberd rings containing two triple bonds separated by a double bond. These molecules have powerful antitumor activity. The enediyne moiety, which is often referred as "war head", undergoes Bergman cyclization to form a highly reactive 1,4-benzenoid diradical. These radicals cleave the DNA strand by hydrogen abstraction. Calicheamicin, esperamicin, dynemicin, and neocarzinostatin are some natural enediynes which are biologically active against Gram-positive and Gram-negative bacteria, Leukemia P388, Murine tumors P388, B16, Melanoma B16, and Tumor cells including L1210. Despite of their biological activity, the usefulness of natural enediynes as therapeutic agents have been limited due to their poor selectivity for the cancer cells. The structural complexity of the natural compounds also makes their synthesis cumbersome. So the quest for developing synthetic analogs by incorporating enediyne functional group on various substrates has been developed. Carbohydrate based enediynes have rarely been reported as templates for enediyne molecules. Careful study of the structures and biological activity of natural enediynes reveals that the carbohydrate part of these molecules plays a crucial role in the selectivity. So the goal of this research attempt is to design unique reaction schemes to synthesis a new class of enediynes on carbohydrate substrate such as ribose which are expected to have better selectivity for the target cell.