{"id":{"repo_id":"cape-town","oai_identifier":"oai:open.uct.ac.za:11427/16573"},"canonical_url":"https://search.dev.ndltd.org/etd/cape-town/oai:open.uct.ac.za:11427/16573","repository":{"repo_id":"cape-town","name":"University of Cape Town","base_url":"https://open.uct.ac.za/oai/request"},"display":{"title":"Studies on the use of peptide auxiliaries in the meso-desymmetrization of epoxides, and the kinetic resolution of secondary alcohols","abstract":"This thesis reports on the use of amino acids and peptides as chiral ligands/catalysts in two asymmetric processes: Meso-desymmetrization of an epoxide and the kinetic resolution of secondary alcohols. Chapter 1 comprises a literature review, which gives a general overview of methods of asymmetric synthesis, followed by an overview on the existing classes of asymmetric DMAP-type acyl-transfer catalysis as the major topic of the thesis. Chapter 2 describes the synthesis and evaluation of four peptide ligands used in combination with scandium(III) triflate for the meso-desymmetrization of cyclohexene oxide. Enantioselectivities were determined by chiral HPLC, and gave results of up to 41 % ee. Chapter 3 discusses the synthesis and characterisation of three clas ses of nucleophilic DMAP-type catalysts, in which various amino acid/peptide auxiliaries were attached either α, β, or γ-to the pyridine nitrogen. The peptides contained tryptophan, chosen to exploit a potential π - π stacking interaction with the acyl-pyridinium cation. Catalysts substituted at the α and γ positions gave no kinetic resolution for 1-(2-naphthyl)ethanol 121 ; however, a dipeptide (Leu-Trp)-containing catalyst 128 substituted at the β-position gave an s-v alue of 5.3. In order to improve the selectivity, 128 was derivatised at the C-terminal to form two tripeptide-containing catalysts, and acylated at the NH group of the indole ring (141). A range of secondary alcohols were tested and selectivity factors in creased to up to 10.7 . A series of second-generation catalysts were synthesised, but s-values did not improve. An NMR study was performed to reveal a possible conformational change during the stereoselective step. Computational modelling was performed using molecular mechanics (MMFF94) and quantum mechanics (B3LYP/6-31G, M06/6-31G*, ω B97X-D/6-31G) to determine a po ssible transition-state model, which indicated a π - cation interaction of the electron-rich indole ring of a tryptophan moiety with the electron-deficient pyridinium cation as a likely determinant of stereoselectivity.","abstract_html":"This thesis reports on the use of amino acids and peptides as chiral ligands/catalysts in two asymmetric processes: Meso-desymmetrization of an epoxide and the kinetic resolution of secondary alcohols. Chapter 1 comprises a literature review, which gives a general overview of methods of asymmetric synthesis, followed by an overview on the existing classes of asymmetric DMAP-type acyl-transfer catalysis as the major topic of the thesis. Chapter 2 describes the synthesis and evaluation of four peptide ligands used in combination with scandium(III) triflate for the meso-desymmetrization of cyclohexene oxide. Enantioselectivities were determined by chiral HPLC, and gave results of up to 41 % ee. Chapter 3 discusses the synthesis and characterisation of three clas ses of nucleophilic DMAP-type catalysts, in which various amino acid/peptide auxiliaries were attached either α, β, or γ-to the pyridine nitrogen. The peptides contained tryptophan, chosen to exploit a potential π - π stacking interaction with the acyl-pyridinium cation. Catalysts substituted at the α and γ positions gave no kinetic resolution for 1-(2-naphthyl)ethanol 121 ; however, a dipeptide (Leu-Trp)-containing catalyst 128 substituted at the β-position gave an s-v alue of 5.3. In order to improve the selectivity, 128 was derivatised at the C-terminal to form two tripeptide-containing catalysts, and acylated at the NH group of the indole ring (141). A range of secondary alcohols were tested and selectivity factors in creased to up to 10.7 . A series of second-generation catalysts were synthesised, but s-values did not improve. An NMR study was performed to reveal a possible conformational change during the stereoselective step. Computational modelling was performed using molecular mechanics (MMFF94) and quantum mechanics (B3LYP/6-31G, M06/6-31G*, ω B97X-D/6-31G) to determine a po ssible transition-state model, which indicated a π - cation interaction of the electron-rich indole ring of a tryptophan moiety with the electron-deficient pyridinium cation as a likely determinant of stereoselectivity.","abstract_has_math":false,"creators":["Cozett, Rudy Edgar"],"institution":"Department of Chemistry","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Hunter, Roger"],"committee_chairs":[],"committee_members":[],"year":2015,"date_issued":"2015","date_published":"2015","updated_at":"2026-07-22T22:22:43Z","subjects":[],"languages":["eng"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/11427/16573","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Hunter, Roger"]},{"key":"dc:creator","label":"Author","values":["Cozett, Rudy Edgar"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2016-01-26T12:06:47Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2016-01-26T12:06:47Z"]},{"key":"dc:date.issued","label":"Date","values":["2015"]},{"key":"dc:publisher.department","label":"Dc Publisher Department","values":["Department of Chemistry"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cape Town"]},{"key":"dc:type","label":"Dc Type","values":["Doctoral Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["PhD"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["eng"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/11427/16573"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Includes bibliographical references"]},{"key":"dc:description.abstract","label":"Abstract","values":["This thesis reports on the use of amino acids and peptides as chiral ligands/catalysts in two asymmetric processes: Meso-desymmetrization of an epoxide and the kinetic resolution of secondary alcohols. Chapter 1 comprises a literature review, which gives a general overview of methods of asymmetric synthesis, followed by an overview on the existing classes of asymmetric DMAP-type acyl-transfer catalysis as the major topic of the thesis. Chapter 2 describes the synthesis and evaluation of four peptide ligands used in combination with scandium(III) triflate for the meso-desymmetrization of cyclohexene oxide. Enantioselectivities were determined by chiral HPLC, and gave results of up to 41 % ee. Chapter 3 discusses the synthesis and characterisation of three clas ses of nucleophilic DMAP-type catalysts, in which various amino acid/peptide auxiliaries were attached either α, β, or γ-to the pyridine nitrogen. The peptides contained tryptophan, chosen to exploit a potential π - π stacking interaction with the acyl-pyridinium cation. Catalysts substituted at the α and γ positions gave no kinetic resolution for 1-(2-naphthyl)ethanol 121 ; however, a dipeptide (Leu-Trp)-containing catalyst 128 substituted at the β-position gave an s-v alue of 5.3. In order to improve the selectivity, 128 was derivatised at the C-terminal to form two tripeptide-containing catalysts, and acylated at the NH group of the indole ring (141). A range of secondary alcohols were tested and selectivity factors in creased to up to 10.7 . A series of second-generation catalysts were synthesised, but s-values did not improve. An NMR study was performed to reveal a possible conformational change during the stereoselective step. Computational modelling was performed using molecular mechanics (MMFF94) and quantum mechanics (B3LYP/6-31G, M06/6-31G*, ω B97X-D/6-31G) to determine a po ssible transition-state model, which indicated a π - cation interaction of the electron-rich indole ring of a tryptophan moiety with the electron-deficient pyridinium cation as a likely determinant of stereoselectivity."]},{"key":"dc:title","label":"Title","values":["Studies on the use of peptide auxiliaries in the meso-desymmetrization of epoxides, and the kinetic resolution of secondary alcohols"]}]}],"canonical_facts":{"dc:contributor.advisor":["Hunter, Roger"],"dc:creator":["Cozett, Rudy Edgar"],"dc:date.accessioned":["2016-01-26T12:06:47Z"],"dc:date.available":["2016-01-26T12:06:47Z"],"dc:date.issued":["2015"],"dc:description":["Includes bibliographical references"],"dc:description.abstract":["This thesis reports on the use of amino acids and peptides as chiral ligands/catalysts in two asymmetric processes: Meso-desymmetrization of an epoxide and the kinetic resolution of secondary alcohols. Chapter 1 comprises a literature review, which gives a general overview of methods of asymmetric synthesis, followed by an overview on the existing classes of asymmetric DMAP-type acyl-transfer catalysis as the major topic of the thesis. Chapter 2 describes the synthesis and evaluation of four peptide ligands used in combination with scandium(III) triflate for the meso-desymmetrization of cyclohexene oxide. Enantioselectivities were determined by chiral HPLC, and gave results of up to 41 % ee. Chapter 3 discusses the synthesis and characterisation of three clas ses of nucleophilic DMAP-type catalysts, in which various amino acid/peptide auxiliaries were attached either α, β, or γ-to the pyridine nitrogen. The peptides contained tryptophan, chosen to exploit a potential π - π stacking interaction with the acyl-pyridinium cation. Catalysts substituted at the α and γ positions gave no kinetic resolution for 1-(2-naphthyl)ethanol 121 ; however, a dipeptide (Leu-Trp)-containing catalyst 128 substituted at the β-position gave an s-v alue of 5.3. In order to improve the selectivity, 128 was derivatised at the C-terminal to form two tripeptide-containing catalysts, and acylated at the NH group of the indole ring (141). A range of secondary alcohols were tested and selectivity factors in creased to up to 10.7 . A series of second-generation catalysts were synthesised, but s-values did not improve. An NMR study was performed to reveal a possible conformational change during the stereoselective step. Computational modelling was performed using molecular mechanics (MMFF94) and quantum mechanics (B3LYP/6-31G, M06/6-31G*, ω B97X-D/6-31G) to determine a po ssible transition-state model, which indicated a π - cation interaction of the electron-rich indole ring of a tryptophan moiety with the electron-deficient pyridinium cation as a likely determinant of stereoselectivity."],"dc:identifier.uri":["http://hdl.handle.net/11427/16573"],"dc:language.iso":["eng"],"dc:publisher.department":["Department of Chemistry"],"dc:publisher.institution":["University of Cape Town"],"dc:title":["Studies on the use of peptide auxiliaries in the meso-desymmetrization of epoxides, and the kinetic resolution of secondary alcohols"],"dc:type":["Doctoral Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["PhD"]},"updated_at":"2026-07-22T22:22:43Z"}