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Cyclic Enediynes and Enyne-Allenes Containing Additional CYCLIC ENEDIYNES AND ENYNE-ALLENES CONTAINING ADDITIONAL FUNCTIONALITIES: ACHIEVING CONTROL OF THE MECHANISM AND REACTIVITY by NATALIA G. ZHEGALOVA (Under the Direction of Vladimir V. Popik) ABSTRACT Natural enediyne antibiotics are perhaps the most potent natural anticancer agents. Their extreme cytotoxicity is attributed to the ability of either (Z)-3-ene-1,5-diyne or (Z)-1,2,4- heptatrien-6-yne fragment to undergo cyclization producing a reactive 1,4-biradical. Enediynes undergo Bergman cyclization, while enyne-allenes undergo Myers-Saito cycloaromatization. These reactions cause simultaneous cleavage of both strands of duplex DNA. Unfortunately, low selectivity, poor thermal stability, and high general toxicity of naturally occurring enediynes, as well as designed compounds, prevent their wide use in clinical practice thus far. The goal of this work was to investigate the mechanism, the kinetics, and the triggering mode of the Bergman and Myers-Saito cyclizations in order to achieve control over the enediyne and enyne-allene activity. We have developed and synthesized 10- (3.1a, 4.1–4.6) and 11- (3.1b) membered cyclic enediynes with conjugated exo-double bond at the acetylenic termini of the (Z)-3-ene-1,5-diyne fragment. Kinetic studies and deuterium-labeling experiments confirmed our hypothesis that keto-endiynes (3.1a and b) undergo Bergman cycloaromatization via rate determining enolization, followed by cyclization of enol into 1,4-biradical. It was also found that electron-donating substituents at the β-position, with respect to the one of acetylenic termini of enediynes, increase the rate of cyclization, while electron-withdrawing groups have an opposite effect. The cyclization step is the rate determining step in these reactions. In order to achieve spatial and temporal control over the action of enediynes, we also developed compounds that are thermally stable, but their action can be triggered photochemically. The reactive allenes (5.3 and 6.4) and enyne-allene (6.10) compounds were proposed. The allene 5.3 was generated by UV irradiation of a thermally stable precursor (5.1) in which an aldehyde group was protected with a photoremovable protecting group as an acetal moiety. Reactive allene 6.4 and cyclic enyne-allene 6.10 were generated from acyclic 2-diazo- 1,3- dicarbonyl compounds by the photochemical Wolff reaction. Allene 6.4 and enyne-allene 6.10 readily add nucleophiles to the electron-poor double bond; 6.10 presumably undergoes fast Myers-Saito cyclization in non-nucleophilic solutions. INDEX WORDS: Enediynes, Enyne-allenes, Wolff rearrangement, Bergman cyclization, Myers-Saito cyclization, Diazo-compounds CYCLIC ENEDIYNES AND ENYNE-ALLENES CONTAINING ADDITIONAL FUNCTIONALITIES: ACHIEVING CONTROL OF THE MECHANISM AND REACTIVITY by NATALIA ZHEGALOVA M.S., Saint-Petersburg State University, Russia, 2004 A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY ATHENS, GEORGIA 2011 © 2011 Natalia G. Zhegalova All Rights Reserved CYCLIC ENEDIYNES AND ENYNE-ALLENES CONTAINING ADDITIONAL FUNCTIONALITIES: ACHIEVING CONTROL OF THE MECHANISM AND REACTIVITY by NATALIA ZHEGALOVA Major Professor: Vladimir V. Popik Committee: George F. Majetich Robert S. Phillips Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia May 2011 ACKNOWLEDGEMENTS I am heartily thankful to those who made this dissertation possible. First of all I would like to say thanks to my Mother who gave me the moral support I required. I owe my deepest gratitude to my advisor, Dr. Vladimir Popik, whose encouragement, supervision and support from the preliminary to the concluding level enabled me to develop an understanding of the subject. I am also thankful to my committee members for their valuable advices and members of Dr. Popik's research group for fruitful discussions and helpful suggestions. I also would like to make a special reference to Dr. Gregori Karpov who shared his professional experience with me during my first years as a graduate student. Lastly, I offer my regards to all of my friends who supported me in any respect during the completion of my dissertation. iv TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ........................................................................................................... iv LIST OF TABLES ....................................................................................................................... viii LIST OF FIGURES ....................................................................................................................... ix CHAPTER 1 LITERATURE REVIEW ..............................................................................................1 1.1 Introduction ........................................................................................................1 1.2 Enediyne Anticancer Antibiotics. Mechanism of Action ..................................1 1.3 Factors Affecting the Rate of Bergman Cyclization ........................................11 1.4 Conclusions and Goals of the Project ..............................................................41 1.5 References ........................................................................................................42 2 NON-CONJUGATED TEN-MEMBERED ENEDIYNE PRECURSORS: ATTEMPTED SYNTHESIS .......................................................................................48 2.1 Attempted Synthesis of 8-Diazo-12-ethyl-12-methoxy-5,6,10,11-tetradehydro- 7,8,9,12-tetrahydrobenzo[10]annulene-7,9-dione ..................................................48 2.2 Conclusions ......................................................................................................56 2.3 Experimental Section .......................................................................................57 2.4 References ........................................................................................................79 v 3 CONJUGATED TEN-MEMBERED CARBOCYCLIC MODEL ENEDIYNES WITH AN EXO-CARBONYL GROUP IN THEIR CORE: SYNTHESIS, THERMOCHEMISTRY AND KINETICS .................................................................82 3.1 Synthesis and Cyclization of 5,6,11,12-Tetradehydro-7,8,9,10-tetrahydro- benzo[10]annulene-7-one and 5,6,12,13-Tetradehydro-8,9,10,11-tetrahydro-7H- benzo[11]annulene-7-one ......................................................................................82 3.2 Kinetic Studies of the Cycloaromatization Reaction of Enediynes 3.1a and 3.1b ........................................................................................................................86 3.3 Conclusions ......................................................................................................94 3.4 Experimental Section .......................................................................................95 3.5 References ......................................................................................................106 4 INFLUENCE OF SUBSTITUENTS’ ELECTRONIC EFFECTS ON THE RATE OF BERGMAN CYCLIZATION IN SERIES OF METHYLIDENE DERIVATIVES OF 10-MEMBERED CYCLIC ENEDIYNES ................................................................108 4.1 Synthesis, Thermo-Chemistry and Kinetic Studies of Methylidene-Derivatives of 10-Membered Cyclic Enediynes .....................................................................108 4.2 Conclusions ....................................................................................................119 4.3 Experimental Section .....................................................................................120 4.4 References ......................................................................................................132 5 PHOTOCHEMICAL GENERATION OF ALENES: 4-PHENYLBUTA-2,3- DIENAL .....................................................................................................................134 5.1 Synthesis and Photolysis of Allene-Aldehyde Precursor 2-(2-(3-Phenylprop-2- yn-1-yl)-1,3-dioxolan-4-yl)cyclohexa-2,5-diene-1,4-dione .................................134 vi 5.2 Conclusions and Future Directions ................................................................141 5.3 Experimental Section .....................................................................................142 5.4 References ......................................................................................................151 6 PHOTOCHEMICAL GENERATION OF ALLENES AND ENYNE-ALLENES FROM DIAZO-DICARBONYL COMPOUNDS .....................................................152 6.1 Synthesis of Ethyl 2-Diazo-3-oxo-5-phenylpent-4-ynoate and Ethyl 2-Diazo- 5-(2-(3-hydroxyprop-1-yn-1-yl)phenyl)-3-oxopent-4-ynoate .............................152 6.2 Photochemical Studies of Ethyl 2-Diazo-3-oxo-5-phenylpent-4-ynoate and Ethyl 2-Diazo-5-(2-(3-hydroxyprop-1-yn-1-yl)phenyl)-3-oxopent-4-ynoate .....157 6.3 Conclusions and Further Directions...............................................................161 6.4 Experimental Section .....................................................................................162 6.5 References ......................................................................................................169 APPENDICES A TABLE OF ABBREVIATIONS ..............................................................................171 B 1H AND 13C NMR SPECTRA OF COMPOUNDS ..................................................172 vii LIST OF TABLES Page
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