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I. an Improved Procedure for Alkene Ozonolysis. II. Exploring a New Structural Paradigm for Peroxide Antimalarials

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I. an Improved Procedure for Alkene Ozonolysis. II. Exploring a New Structural Paradigm for Peroxide Antimalarials University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Student Research Projects, Dissertations, and Theses - Chemistry Department Chemistry, Department of 2011 I. An Improved Procedure for Alkene Ozonolysis. II. Exploring a New Structural Paradigm for Peroxide Antimalarials. Charles Edward Schiaffo University of Nebraska-Lincoln Follow this and additional works at: https://digitalcommons.unl.edu/chemistrydiss Part of the Organic Chemistry Commons Schiaffo, Charles Edward, "I. An Improved Procedure for Alkene Ozonolysis. II. Exploring a New Structural Paradigm for Peroxide Antimalarials." (2011). Student Research Projects, Dissertations, and Theses - Chemistry Department. 23. https://digitalcommons.unl.edu/chemistrydiss/23 This Article is brought to you for free and open access by the Chemistry, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Student Research Projects, Dissertations, and Theses - Chemistry Department by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. I. An Improved Procedure for Alkene Ozonolysis. II. Exploring a New Structural Paradigm for Peroxide Antimalarials. By Charles E. Schiaffo A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy Major: Chemistry Under the Supervision of Professor Patrick H. Dussault Lincoln, Nebraska June, 2011 I. An Improved Procedure for Alkene Ozonolysis. II. Exploring a New Structural Paradigm for Peroxide Antimalarials. Charles E. Schiaffo, Ph.D. University of Nebraska-Lincoln, 2011 Advisor: Patrick H. Dussault The use of ozone for the transformation of alkenes to carbonyls has been well established. The reaction of ozone with alkenes in this fashion generates either a 1,2,4- trioxolane (ozonide) or a hydroperoxyacetal, either of which must undergo a separate reduction step to provide the desired carbonyl compound. There is considerable interest in being able to perform a reductive ozonolysis to directly provide the carbonyl. Previous reports from the Dussault lab have shown that amine N-oxides are able to perform a reductive ozonolysis. In the course of efforts to expand this reaction to other oxyanions it was realized that water was also able to efficiently perform a net reductive ozonolysis via nucleophilic capture of the carbonyl oxide. This transformation was investigated for a variety of substrates and was shown to offer a useful alternative to conventional ozonolysis conditions. Malaria is a global health epidemic that affects between 300-500 million people annually, with the most deadly strain being P. falciparum. The current treatment for malaria is artemisinin combination therapy, but the development of artemisinin-resistant strains of malaria has spurred the need for the development of new treatments. 1,2,4- Trioxolanes exhibit high efficacy against malaria, but concerns remain about their thermal and serum stability. Our analysis of the likely mechanism of action of ozonides guided our development of structurally related 3-alkoxy-1,2-dioxolanes as a potential treatment for malaria. This class of compounds has shown to possess high levels of activity against P. falciparum in vitro. The synthesis of these dioxolanes required the development of new synthetic routes, which will be discussed in detail, as will efforts to optimize the activity of 3-alkoxy-1,2-dioxolanes. In addition, the synthesis and evaluation of 1,2,4-trioxepanes as potential antimalarials was explored. In the course of our investigation into the synthesis of 3-alkoxy-1,2-dioxolanes, we found Re (VII) oxide to be an effective catalyst for the transetherification of 3-alkoxy- 1,2-dioxolanes. Re (VII) oxide was briefly explored as a catalyst for allylation or etherification reactions that involve stabilized carbocations as intermediates. iii Acknowledgements First, I would like to thank my advisor, Professor Patrick Dussault for his help and guidance. I am grateful for all the time he spent helping me and his patience. I believe that he has helped me become a better scientist. I would like to thank the members of my committee: Prof. Takacs, Prof. Du, Prof. Nickerson, Prof. Redepenning, and Prof. Choe. I am indebted to the help that Joe Dumais and Sara Basiaga provided on the NMR and the other small instruments. Without the help of Sergio Wittlin and Matthias Rottman, who performed the antimalarial screening, and Tony Lloyd, from EHS who helped with the shipments, I would have no biological data and I thank them. I also thank Prof. Jonathan Vennerstrom and Yuxiang Dong at the University of Nebraska-Medical Center for there guidance on medicinal chemistry. I would like to thank Chris Schwartz, Chunping Xu, Roman Schepin, and Prasanta Ghorai for helping me during my first year. I thank Brad Johnson for challenging me and for the lively white board discussions that we would have. I am also grateful for all of the current group members who have helped me. I am fortunate for having parents who have been supportive of me through this journey. They never doubted me and provided encouragement at all the right times. Finally, I would like to thank my fiancée Van Nguyen Mai for her help, support, and guidance. She has been a true pillar of stability for me during this journey. iv Chapter 1: Improved procedure for alkene ozonolysis ..................................................1 Section 1.............................................................................................................................2 Section 1.1 Mechanism of ozonolysis .............................................................................2 Section 1.2 Issues with O3 in synthesis............................................................................3 Section 1.3 Reductive ozonolysis using N-Oxides..........................................................4 Section 1.4 Reductive ozonolysis using water.................................................................5 Section 2.............................................................................................................................6 Section 2.1 Rationale ......................................................................................................6 Section 2.2 Initial phase transfer studies..........................................................................7 Section 2.3 Anhydrous tetrabutyl ammonium salts .........................................................8 Section 2.4 Water as a trap ..............................................................................................9 Section 2.5 Substrate scope............................................................................................13 Section 2.6 Conclusions.................................................................................................15 Section 2.7 Experimentals .............................................................................................15 Section 3 References........................................................................................................25 Chapter 2: 3-Alkoxy-1,2-dioxolanes as potential antimalarials ................................28 Section 1...........................................................................................................................29 Section 1.1 Malaria ........................................................................................................29 Section 1.2 Antimalarial treatments...............................................................................30 Section 1.3 Artemisinin as a treatment for malaria........................................................31 Section 1.4 Mechanism of Fe-mediated artemisinin degradation..................................31 Section 1.5 Artemisinin mechanism of action against malaria......................................33 Section 1.6 Vennerstrom’s ozonides..............................................................................34 v Section 1.7 Rationale for 3-alkoxy-1,2-dioxolanes .......................................................36 Section 2.............................................................................................................................38 Section 2.1 Previous synthesis of 1,2-dioxolanes..........................................................38 Singlet oxygen .........................................................................................................38 DePuy ring expansion..............................................................................................40 Thermolysis..............................................................................................................41 Conjugate addition to α-β-unsaturated carbonyls ....................................................42 Ozonolysis of enol ethers.........................................................................................42 Radical cyclization...................................................................................................43 Electrophilic cyclization ..........................................................................................45 Section 2.2 Reactions of 1,2-dioxolan-3-ols and 3-alkoxy-1,2-dioxolanes...................47 Acid-mediated etherification ...................................................................................47 Base-mediated etherification ...................................................................................48
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