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Biomimetic Cascade Reactions Towards the Synthesis of Ciguatoxin Farhan Ramez Bou Hamdan

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Biomimetic Cascade Reactions Towards the Synthesis of Ciguatoxin Farhan Ramez Bou Hamdan Florida State University Libraries Electronic Theses, Treatises and Dissertations The Graduate School 2007 Biomimetic Cascade Reactions Towards the Synthesis of Ciguatoxin Farhan Ramez Bou Hamdan Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] THE FLORIDA STATE UNIVERSITY COLLEGE OF ARTS AND SCIENCES BIOMIMETIC CASCADE REACTIONS TOWARDS THE SYNTHESIS OF CIGUATOXIN By FARHAN RAMEZ BOU HAMDAN A Dissertation submitted to the Department of Chemistry and BioChemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree Awarded Spring Semester, 2007 The members of the committee approve the dissertation of Farhan R. Bou Hamdan on November 9, 2006. Robert A. Holton Professor Directing Dissertation Laura L. Keller Outside Committee Member Martin A. Schwartz Committee Member Marie E. Krafft Committee Member Timothy M. Logan Committee Member The Office of Graduate Studies has verified and approved the above named committee members. ii In Memory of my late father, Ramez Bou Hamdan, whose love, kindness, and encouragment touched the lives of many. To him I dedicate this dissertation. iii ACKNOWLEDGEMENTS There are so many people who have helped and supported me during my time here at Florida State University. I am so grateful and indebted to all. I would like to express my special thanks and appreciation to Professor Robert A. Holton for all his continued guidance, support and encouragement thoughout the course of my studies at FSU. In addition, I would like to thank all of Holton’s research group members, both present and past, for their help, friendship and understanding. In particular, I would like to thank Dr. Alexander Batch who helped me get started in the lab, and Dr. Virginie Maggiotti for the tremendous help I have received from her during the preparation of this manuscript. Also, I would like to extend my thanks to all the staff and faculty at the FSU Department of Chemistry and Biochemistry for their appreciated advice and assistance. Special thanks go to Dr. Mariappan Manoharan for his help in performing the theoretical calculations. Moreover, I would like to thank the chemistry department at FSU and the MDS Research Foundation for their financial support. Finally, I wish to express my sincere thanks to my family for their unconditional support, care and love. iv TABLE OF CONTENTS LIST OF TABLES ...........................................................................................vii LIST OF FIGURES ..........................................................................................ix LIST OF SCHEMES .........................................................................................x LIST OF ABREVIATIONS ............................................................................xii ABSTRACT ...................................................................................................xvii CHAPTER I. INTRODUCTION ......................................................................1 Historical Aspects............................................................................................................................. 1 Ciguatera Fish Poisoning ................................................................................................................. 2 Ciguatoxins ....................................................................................................................................... 4 Synthetic Efforts ............................................................................................................................... 8 CHAPTER II. MODEL STUDIES..................................................................14 Background ..................................................................................................................................... 14 New Applications of the Electrophile-Induced Cascade Cyclizations........................................ 16 Electrophilic Cyclization of the Model Epoxy-Alcohols............................................................. 23 I. Preliminary studies..................................................................................................... 23 A) Structure determination...................................................................................... 23 B) Cyclization studies on model 23........................................................................ 25 C) Cascade vs. stepwise?......................................................................................... 28 II. Studies on model 24 ................................................................................................... 29 A) Structure determination...................................................................................... 29 B) Cyclization studies.............................................................................................. 30 III. Studies on models 25 to 28 ........................................................................................ 34 IV. Conclusion .................................................................................................................. 36 CHAPTER III. SYNTHETIC STUDIES TOWARDS CIGUATOXIN.........38 Previous Synthetic Efforts Towards the HIJ Rings of the Ciguatoxins ...................................... 38 I. Hirama’s approach ..................................................................................................... 39 II. Isobe’s approach......................................................................................................... 40 III. Sasaki’s approach ....................................................................................................... 40 IV. Fujiwara’s approach ................................................................................................... 41 Retrosynthetic Analysis.................................................................................................................. 42 Total Synthesis................................................................................................................................ 45 v I. Synthesis of alkyl iodide 86....................................................................................... 45 II. Synthesis of vinyl iodide 87B and 87A .................................................................... 47 III. Synthesis of the cascade cyclization substrates 88 and 85 ...................................... 49 IV. Electrophile promoted cyclizations of 88 and 85 ..................................................... 52 V. Construction of the H ring ......................................................................................... 56 CHAPTER IV. EXPERIMENTAL.................................................................60 Preparation of the Model Epoxy Alcohols.................................................................................... 61 Electrophilic Cascade Cyclizations of the Model Epoxy Alcohols............................................. 88 Synthetic Studies Towards the Ciguatoxins................................................................................110 APPENDIX ....................................................................................................147 REFERENCES ..............................................................................................314 BIOGRAPHICAL SKETCH.........................................................................322 vi LIST OF TABLES Table 1. Effect of the solvent polarity on the regioselectivity of the cascade reaction....................16 Table 2. Preliminary studies on the efficiency of the cascade process in the synthesis of [6,8] trans-fused polyethers ...........................................................................................................25 Table 3. Solvent effect on the efficiency of the cascade process in the synthesis of [6,8] trans- fused polyether.......................................................................................................................26 Table 4. Effect of HFIP on the reactivity of electrophiles in the synthesis of [6,8] trans-fused polyethers (1) .........................................................................................................................26 Table 5. Effect of HFIP on the reactivity of electrophiles in the synthesis of [6,8] trans-fused polyethers (2) .........................................................................................................................27 Table 6. Effect of the electrophile structure on the outcome of the cascade reaction in the synthesis of [6,8] trans-fused polyethers. ............................................................................ 28 Table 7. Cascade epoxy-alcohol cyclizations on model 24 ...............................................................31 Table 8. Effect of the nucleophilicity of the alcohol on the cyclization of model 24......................32 Table 9. Effect of the temperature on the cyclization of model 24 ...................................................33 Table 10. Effect of the temperature on the cyclization of model 24 using a solvent mixture...........33 Table 11. Effect of mercury electrophilic source on the cyclization of 25.........................................36 Table 12. Effect of the incorporation of the alcohol in a cyclic moiety on the activation energy of the acid-catalyzed cyclization of γ,δ-epoxyalcohols. ..........................................................44 Table 13. Optimization
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