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Total Synthesis of the Xyloketal Natural Products and Alboatrin TOTAL SYNTHESIS OF THE XYLOKETAL NATURAL PRODUCTS AND ALBOATRIN Jeremy David Pettigrew Bachelor of Science (Co-op.), Simon Fraser University, 2001 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY In the Department of Chemistry O Jeremy David Pettigrew 2006 SIMON FRASER UNIVERSITY Summer 2006 All rights reserved. This work may not be reproduced in whole or in part, by photocopy or other means, without permission of the author. APPROVAL Name: Jeremy David Pettigrew Degree: Doctor of Philosophy Title of Thesis: Total Synthesis Of The Xyloketal Natural Products and Alboatrin Examining Committee: Chair: Dr. R.H. Hill (Professor) Dr. P.D. Wilson (Associate Professor) Senior Supervisor Dr. N.R. Branda (Professor) Committee Member Dr. D.B. Leznoff (Associate Professor) Committee Member Dr. R.A. Britton (Assistant Professor) Internal Examiner Dr. V.A. Snieckus (Professor) External Examiner Department of Chemistry Queen's University Date Approved: June 16,2006 UNIVERS~ISIMON FRASER Ibra ry DECLARATION OF PARTIAL COPYRIGHT LICENCE The author, whose copyright is declared on the title page of this work, has granted to Simon Fraser University the right to lend this thesis, project or extended essay to users of the Simon Fraser University Library, and to make partial or single copies only for such users or in response to a request from the library of any other university, or other educational institution, on its own behalf or for one of its users. The author has further granted permission to Simon Fraser University to keep or make a digital copy for use in its circulating collection, and, without changing the content, to translate the thesislproject or extended essays, if technically possible, to any medium or format for the purpose of preservation of the digital work. The author has further agreed that permission for multiple copying of this work for scholarly purposes may be granted by either the author or the Dean of Graduate Studies. It is understood that copying or publication of this work for financial gain shall not be allowed without the author's written permission. Permission for public performance, or limited permission for private scholarly use, of any multimedia materials forming part of this work, may have been granted by the author. This information may be found on the separately catalogued multimedia material and in the signed Partial Copyright Licence. The original Partial Copyright Licence attesting to these terms, and signed by this author, may be found in the original bound copy of this work, retained in the Simon Fraser University Archive. Simon Fraser University Library Burnaby, BC, Canada ABSTRACT The isolation and structural characterization of seven closely related natural products, the xyloketals, from a mangrove fungus of the Xylaria species have been reported recently by Lin and co-workers. Of these natural products, all of which incorporate identical chiral nonracemic 5,6-bicyclic acetal moieties, xyloketal A has a unique and aesthetically pleasing C3-symmetric molecular structure that was elucidated by detailed spectroscopic studies and by X-ray crystallography. Xyloketal A, B, C and D have also been shown to be potent inhibitors of acetylcholine esterase and so represent important lead compounds for the treatment of neurological diseases. In addition, xyloketal A, B and F have been shown to have L-calcium channel blocking activity. Thus, the total synthesis of these natural products, and structural analogues thereof, is of notable significance. Towards these ends, a series of novel synthetic routes to prepare these compounds were developed. The initial route, in which the key synthetic transformation involved an inverse electron demand hetero Diels-Alder reaction between appropriately substituted ortho-quinone methides and dihydrofurans, afforded (f)-, (+)- and (-)-xyloketal D. In addition, demethyl analogues of xyloketal A and D were prepared. However, the application of this synthetic route to prepare the more structurally complex xyloketals was unsuccessful. A second route, utilizing a phenylboronic acid-mediated condensation reaction as the key synthetic transformation, afforded a series of novel tris-2H-chromenes that represent structural analogues of the natural product xyloketal A. However, due to the instability of a key synthetic intermediate, the total synthesis of xyloketal A was not completed by this route. A third route was also investigated that featured a boron trifluoride diethyl etherate-promoted electrophilic aromatic substitution reaction as a key step. This synthetic route was used to complete total syntheses of xyloketal A, By D, E, F and G. Moreover, demethyl analogues of xyloketal A, ByC, D, E and G were also prepared. The application of the electrophilic aromatic substitution reaction towards the total synthesis of the structurally related and biologically active natural product alboatrin was also investigated. This led to the first asymmetric total synthesis of this natural product as well as a demethyl analogue. To Nicolette and my parents, Carol and Alan. "Chance favours the prepared mind" Louis Pasteur, 1854 ACKNOWLEDGEMENTS My senior supervisor, Dr. Peter Wilson, is thanked for his advice, guidance and mentorship over the course of my doctoral studies. I am extremely grateful to Dr. Wilson for the training I received during my time as a member of his research group. The other members of my supervisor committee, Dr. Neil Branda and Dr. Daniel Leznoff, are thanked for their suggestions and encouragement throughout my studies. Mr. Michael Katz and Dr. Kimberly Jantunen (Simon Fraser University) are thanked for obtaining the data and solving the X-ray crystal structures found in this thesis. Mr. Jason Bexrud is thanked for his preliminary investigations of the Diels-Alder reactions that are discussed in Chapter 2. Dr. Rebecca Freeman is thanked for her assistance in making the racemic and optically active dihydrofurans that are described in Chapter 2. Mr. Simon So is thanked for his preliminary investigations of the phenylboronic acid-mediated reactions that are discussed in Chapter 3. Dr. Jean-Jacques Cadieux is thanked for the preparation of some of the aldehydes that are discussed in Chapter 3. Professor Yongcheng Lin (Zongshan University) is thanked for providing 'H and 13c NMR spectra of the xyloketals for comparison purposes. Professor Krohn (University of Paderborn) is thanked for checking the melting point of xyloketal D. My past and present lab colleagues (Dr. Jean-Jacques Cadieux, Mr. Patrick Chen, Dr. Rebecca Freeman, Dr. Hongjuan Hu, Dr. Summon Koul, Mr. Jason Lamontagne, Dr. Michael Lyle, Mr. Darren McMurtrie, Dr. Arun Narine, Dr. Peggy Paduraru and Mr. Brendan Whelan) are thanked for their friendship and helpful discussions over the years. vii The technical assistance of Dr. David McGillivray (University of Victoria, HRMS), Mrs. Marcy Tracey (NMR), Dr. Andrew Lewis (NMR), Mr. Greg Owen (MS), Mr. Philip Ferreira (MS), Mr. Simon Wong (MS) and Mr. Mickey Yang (CHN microanalysis) is gratefully acknowledged. Finally, Simon Fraser University (Special Entrance Scholavship and President's Ph. D. Research Stipend) and the Natural Sciences and Engineering Research Council of Canada (PGS-A and PGS-D) are thanked for their financial support. .. Vlll TABLE OF CONTENTS .. Approval ............................................................................................................................ 11 ... Abstract .............................................................................................................................111 Dedication ...........................................................................................................................v Quotation ..........................................................................................................................vi .. Acknowledgements ......................................................................................................... vii Table of Contents ............................................................................................................. ix List of Figures ...............................................................................................................xvi List of Schemes .............................................................................................................xvlll ... ... List of Tables ................................................................................................................ xxul List of Abbreviations ...................................................................................................xxiv 1 Introduction to the Xyloketal Natural Products and Alboatrin .................................1 1.1 Thesis Introduction ................................................................................................1 1.2 The Xyloketal Natural Products ............................................................................ 1 1.2.1 Isolation and Structural Characterization of the Xyloketal Natural Products ..........................................................................................................1 1.2.2 X-Ray Crystal Structures of the Xyloketals ...................................................4 1.3 Biological Properties of the Xyloketal Natural Products ......................................5 1.3.1 Acetylcholine Esterase Inhibition ..................................................................5 1.3.2 L-Calcium Channel Inhibition
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