Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 30 for “"Site-Selectivity"”.
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Electronic tuning of site selectivity and semisynthesis of C2'-deoxyamphotericin B
… with the sterol. Electronic tuning of site-selective acylation reactions was developed towards the synthesis of a C2’-deoxyAmB derivative. More electron-rich acyl donors create a less exothermic reaction in which the transition state is more product-like according to the Hammond …
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Enhancing chemoselectivity and predicting site-selectivity in manganese catalyzed C–H oxidation
… C–H oxidation has demonstrated that specific sites of oxidation can be preferentially targeted based on electronic, steric, and stereoelectronic selection rules. Additionally, the chemoselective oxidation of C–H bonds even in the presence of traditionally more oxidatively labile functional …
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Controlling Site-Selectivity in Palladium-Catalysed Cross-Coupling Reactions using Non-Covalent Interactions Between Ligand and Substrate
Controlling selectivity in chemical reactions is a fundamental challenge in organic synthesis. This thesis explores controlling the site-selectivity of palladium-catalysed cross-coupling reactions by using a non-covalent interaction between a ligand and substrate. A library of phosphine ligands …
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The development of palladium-catalyzed cross-coupling reactions of allylic silanolate salts with aromatic bromides
… gave lower, and in one case even reversed, site-selectivity. Electron-rich aromatic bromides reacted sluggishly under this protocol and led to lower product yields. The second protocol employed a sterically bulky phosphonium tetrafluoroborate salt (t-BuCy2PH+BF4−) and resulted in 73–94% …
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Control of selectivity in palladium-catalysed cross-coupling reactions using a sulfonated phosphine ligand
… are routinely used by enzymes to control selectivity of chemical reactions during biosynthesis. This prevalence in nature has inspired chemists to adapt these interactions to control selectivity in small molecule catalysis. This thesis describes efforts towards utilising non-covalent …
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Reactive Peptides for Site-Selective Cysteine and Lysine Bioconjugation
Achieving catalyst-free, site-selective modification of proteins in water is a significant challenge in chemical biology. Issues of residue specificity, site-selectivity, reagent stability, and reaction rate are pervasive. To address these challenges, we developed a matched peptide pair termed the …
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Manganese-catalyzed intermolecular benzylic C–H amination
… C—H amination reactions with high reactivity and selectivity are scarce. Achieving high levels of reactivity while maintaining excellent site-selectivity and functional group tolerance remains an important challenge for intermolecular C—H amination. We report a novel manganese …
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Studies in Asymmetric Catalysis: Lewis Base catalyzed/Lewis Acid Mediated Aldol Reactions of Ketone- and Amide Derived Nucleophiles
… These reactions provided high levels of gamma-site selectivity for a variety of substitution patterns on the dienyl unit. Both ketone- and morpholine amide-derived dienol ethers afforded excellent enantio- and diastereoselectivity in the addition to conjugated aldehydes. Although ketone-derived …
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Advances in Selectivity of the Suzuki-Miyaura and Hofmann-Löffler-Freytag Reactions
… proceed selectively in the presence of multiple sites of similar chemical reactivity has been a long-standing challenge. Cross-coupling and C–H functionalization processes have gathered significant attention over the past few decades as a result of their ability to rapidly generate molecular …
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The Application and Evolution of Chiral Ion-Paired Rhodium(II,II) Tetracarboxylate Catalysts for Enantioselective Nitrene Transfer
… Control over additional aspects including site-selectivity, chemoselectivity and diastereoselectivity were also shown. As a whole, the research described in this thesis aims to expand the scope of enantioselective nitrene transfer and demonstrate the power of a chiral ion-pairing strategy …
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Enantioselective nickel-catalyzed reductive coupling reactions of alkynes and aldehydes. Synthesis of amphidinolides T1 and T4 via catalytic, stereoselective macrocyclizations
… for ligand effects with respect to the regioselectivity and enantioselectivity of the coupling process. A class of P-chiral, ferrocenyl phosphines was designed, synthesized, and evaluated for efficacy. Ultimately, these phosphines were found to be the most effective chiral ligands for …
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Diffraction spectroscopy of metalloproteins
… diffractions. This process is referred to as site selectivity, it is unique to Diffraction Spectroscopy, and is achieved only when the sample is in crystal form. Through this work, a technique has been devised to site-separate two atoms of iron from within a protein, that builds on prior small …
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Nitrogen-Oxidants Enable Group-Transfer Reactions
… tertiary centers has been demonstrated with exquisite site selectivity. This investigation confirms the scientific insight that N-functionalized sulfamate esters enable complementary site selectivity to the previously known methods employing nitrogen-centered radicals. Additionally, this …
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Synthesis, study and application of silyl ketene imines in Lewis base catalyzed carbonyl addition
… unsaturated species occurred with excellent site selectivity and provide products with a 1,5-disposition of oxygen and nitrogen heteroatoms in moderate to excellent enantioselectivity. Finally, a new class of N-silyl oxyketene imines derived from protected cyanohydrins has been developed. …
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Enantioselective, Lewis base-catalyzed transformations: I. Polyene sulfenocyclization (preparative and mechanistic aspects) II. Sulfenofunctionalization of alkenyl boronates enabled by 1,2-boronate migration
… a superior solvent which dramatically improves site selectivity of thiiranium ion generation. A broad substrate scope is demonstrated, and the tricyclic products are isolated in good yield and enantioselectivity. Furthermore, a number of functional group interconversions (FGIs) of the resulting …
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Prey Selectivity by naticid gastropods from tertiary sediments of the United States coastal Plain
… In addition, earlier studies have demonstrated selectivity of drillhole siting and intraspecific prey size. This study focuses on prey selectivity by Oligocene naticid gastropods and is used to test Vermeij's (1987) hypothesis of escalation. The hypothesis of escalation states that biologic …
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The Application of sSPhos as a Chiral Ligand in Palladium-Catalysed Reactions: Arylative Dearomatisations, and Heteroarylative Cyclisations with Alkenes
… repurposed by the Phipps group, first to control site-selectivity in cross-coupling reactions, and then to control enantioselectivity in atroposelective Suzuki-Miyaura couplings. The work described in this thesis extends its use as a chiral ligand to new reaction types. In all cases, …
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Sortase as a Tool in Biotechnology and Medicine
… to generate new methods for the purification and site-selective modification of recombinant protein therapeutics. </p><p>We utilized native peptide ligation —a well-known function of sortase A— to attach a small molecule drug specifically to the carboxy-terminus of a recombinant protein. By …
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Synthesis of triplex-forming oligonucleotide conjugates of the anticancer drug temodal
… agents to specific gene sequences to maximise site-selectivity. In this work, polypyrimidine TFO conjugates of both drugs were synthesised and targeted to duplex DNA in an attempt to effect site-specific alkylation of guanine residues. Concurrently, in an attempt to enhance the triple helix …
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Exploring Potential Drug Target Sites In The Ribosome Using Cisplatin And Its Analogues
… thesis, two aspects of cisplatin, its preferred sites of interaction with RNA and its use as a chemical probe to gain accessibility information, were explored.</p> <p>To understand the site-selectivity of cisplatin with RNA, model RNA constructs and full-length 16S rRNA were employed. The binding …
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