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Studies on the Synthesis and Biosynthesis Of STUDIES ON THE SYNTHESIS AND BIOSYNTHESIS OF INDOLE ALKALOIDS BY GEORGE BOHN FULLER B.A. (cum laude) , Macalester College, 1969 M.Sc, The University of California, Berkeley, 19 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of CHEMISTRY We accept this thesis as conforming to the required standard /-) THE UNIVERSITY OF BRITISH COLUMBIA July, 1974 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Depa rtment The University of British Columbia Vancouver 8, Canada ABSTRACT Part A of this thesis provides a resume1 of the synthesis of various radioactively labelled forms of secodine C76) and provides an evaluation of these compounds, as well as some radioactively labelled forms of tryptophan C25), as precursors in the Biosynthesis of apparicine (81), uleine C83), guatam- buine (90) , and olivacine (88) in Aspidosperma australe. Only apparicine (81) could be shown to incorporate these precursors to a significant extent. Degradation of apparicine (81) from Aspidosperma pyricollum provided evidence for the intact incorporation of the secodine system. Part B discusses the synthesis of 16-epi-stemmadenine (161), which provides an entry into the stemmadenine system with, radioactive labels at key positions in the molecule. The synthesis involved the degradation of strychnine (29) to Wieland-Gumlich aldehyde (130) by a previously established sequence of reactions. Initial conversion of Wieland-Gumlich aldehyde to nor^fluorocurarine (134) succeeded by a previously described route, although some study was necessary for determin• ing the conditions by which the Oppenauer oxidation of 2B,16a- cur-19-en-17-ol (137) could selectively yield either 23,16a-cur- 19-en-17-al (133) or nor-fluorocurarine (134). When nor-fluoro- curarine (134) could not be converted to the desired stemmadenine system, Wieland^GxunlictL aldehyde was converted to methyl 18- hydroxy^2&,16a-cur-19-en-17^oate (156) by a previously established procedure. Conversion of this compound to methyl 2 6/, 16a-cur-19- en-17-^oate 0.571 was accomplished by successive treatment with, hydrogen bromide and zinc in acetic acid. The ester 157 was converted to its- N Ca I *s£ o rmy-1 derivative 158 by reaction with methyl formate and sodium hydride. Treatment of this product with dry formaldehyde and sodium hydride in dimethyl sulfoxide led to the formation of the unexpected but nevertheless useful tetrahydrooxazine derivative 159. Hydrolysis of the tetrahydrooxazine moiety was accomplished with methanolic hydrogen chloride, resulting in the isolation of 2g,16g-carbo- methoxy-cur-19-en-17-ol (160) . Oxidation of compound 160 with lead tetraacetate followed immediately by treatment with sodium borohydride in methanolic acetic acid provided 16-epi-stemmaden- ine C161). Hydride reduction of the C-16 ester function in 161 and authentic stemmadenine (6a) led to the same diol 175 thereby providing the required interrelationship between the synthetic and natural compounds. This sequence also established the previously unknown configuration of stemmadenine (6a) about C-16 and provided an obvious pathway for the synthesis of stemmadenine via the saturated aldehyde 133. Also discussed in Part B is the lead tetraacetate oxidation of the ester 157 to akuammicine (66), representing the first total synthesis of that compound. Part C discusses the synthesis of 16-epi-stemmadenine (161) labelled with tritium in the aromatic ring. Simultaneous 3 administration of this material and stemmadenine-Car- H) (6a) to separate portions of A., pyricolluro root sections established that, while the latter was incorporated into apparicine (81), - iv - no incorporation could be detected in the. case of the former. y — TABLE OF CONTENTS Page TITLE PAGE . i ABSTRACT ii TABLE OF CONTENTS V LIST OF FIGURES vi LIST OF TABLES ix ACKNOWLEDGEMENTS x INTRODUCTION 1 DISCUSSION 35 PART A 35 PART B 57 PART C 10 7 EXPERIMENTAL 108 SECTION A 112 SECTION B 116 SECTION C 135 BIBLIOGRAPHY 136 - yi - LIST OF FIGURES Figure Page 1 Some Representative Indole Alkaloids 2 2 The Biosynthesis of Anthranilic Acid C21) 5 3 The Biosynthesis of Tryptophan (25) from Anthranilic Acid (21) 6 4 The Barger-Hahn-Robinson-Woodward Postulate for Indole Alkaloid Biosynthesis 8 5a The Wenkert Prephenate Postulate for Indole Alkaloid Biosynthesis 9 5b The Thomas Monoterpene Postulate for Indole Alkaloid Biosynthesis 9 6a The Leete Acetate-Malonate Hypothesis for Indole Alkaloid Biosynthesis 14 6b The Hendrickson Polyketide Modification 14 7 The Early Stages of Indole Alkaloid Biosynthesis as Proven by Experiment 16 8 The Postulated Derivation of Corynanthe Alkaloids from Vincoside (54) 19 9 The Wenkert (A) and Scott (B) Postulates for the Biosynthesis of Strychnos Alkaloids 21 10 The Wenkert Postulate for the Biosynthesis of Iboga and Aspidosperma Alkaloids 22 11 The Postulated Derivation of Aspidosperma and Iboga Alkaloids from Intermediate 75 26 12 The Wenkert Postulate for the Biosynthesis of Uleine (83) ' 29 13 The Djerassi Postulate for the Biosynthesis of Apparicine (81) 29 14 The Results of Incorporation of Various Possible Intermediates into Apparicine (81) and Uleine (83) 33 - yii - Figure Page 15 The Potier-Janot Postulate for the Biosynthe• sis of Non-tryptamine Alkaloids 34 16 The Conversion of Olivacine (88) to Guatam- buine (90) 37 17 The Ozonolytic Degradation of Apparicine (81)... 39 18 The Synthesis of Secodine-(Ar-3H) and (14COOCH^) (76) 7. 40 19 The Synthesis of Secodine-(19-3H) (76) 44 20 The Synthesis of 1-(31-pyridyl)-ethane-(1-3H) (116) 45 21 The Proposed Relationships of Secodine (76) to Stemmadenine (6) in Indole Alkaloid Biosynthe• sis 49 22 The Correlation of Akuammicine (66) and Stemm• adenine (6) via Preakuammicine (2) 58 23 The Attempted Synthesis of 19, 20-Dihydrostemm- adenine 60 24 The Degradation of Strychnine (29) to Wieland- Gumlich Aldehyde 61 25 A Summary of Some Known Reactions in the Wieland-Gumlich Aldehyde Series 64 2 6 The Boekelheide Mechanism for the Oppenauer Oxidation of 133 to 134 66 27 The Routes Considered for the Conversion of Nor-fluorocurarine (134) to Stemmadenine (6).... 68 2 8 The Nuclear Magnetic Resonance Spectrum of Nor- f luorocurarine (134) 72 29 The Reaction of 16-epi-WGA with HCN 73 30 The Reactions of Nor-fluorocurarine (134) with Cyclohexylamine, Pyrrolidine and Morpholine 75 31 The Synthesis of 16-epi-stemmadenine (161) from WGA (130) 78 yiii - Figure Page 32 The Proposed Mass Spectral Fragmentation of the Methyl Cur-19-en-17-oate System 80 33 Two Possible Routes to Stemmadenine (6) from Methyl 23,16a-cur-19-en-17-oate 0-57) 82 34 The Possible Condensation of Formaldehyde with Methyl 23 ,16a-cur-19-en-17-oate (157) 83 35 The Nuclear Magnetic Resonance Spectrum of the Carbomethoxy Tetrahydrooxazine 159 87 36 The Reversible Formation of the Model Tetrahydro• oxazine (166) 86 37 The Nuclear Magnetic Resonance Spectrum of the Model Tetrahydrooxazine (166) 89 38 The Proposed Mechanism for the Formation of the Carbomethoxy Tetrahydrooxazine 159 93 39 The Edwards and Smith Mechanism for the Zinc and Sulfuric Acid Reduction of Akuammicine (66) 96 4 0 The Nuclear Magnetic Resonance Spectrum of Akuammicine (66) 97 41 The Proposed Mechanism for the Formation of Indole Ester 141a 98 42 The Nuclear Magnetic Resonance Spectrum of the Indole Ester 141a 99 43 The Nuclear Magnetic Resonance Spectrum of the Indole Ester 141b 99 44 The Reduction of Natural and Synthetic Stemmaden• ine Systems to the Diol 175 103 4 5 The Infrared Spectra of Authentic and Synthetic Diol 175 104 46 The Nuclear Magnetic Resonance Spectra of Authentic and Synthetic Diol 175 105 47 The Proposed Route for the Synthesis of Stemm• adenine (6a) 106 - ix - LIST OF TABLES Table Page 1 Results of Incorporation of Secodine (76) into Apparicine (81) 47 2 Specific Activities Associated with the Experi• ments in Table 1 48 3 Specific Activities Associated with the Ozonoly- tic Degradation of Apparicine (81) in Experiments 2 and 5 50 4 The Various Compounds Fed to A. australe 52 5 Incorporation Results Associated with Table 3.... 53 6 Effects of Different Reaction Conditions on the Oppenauer Oxidation of the Alcohol 137 66 7 Summary of Results of the Investigations into Anion Formation at C-16 of the N-formyl ester (158) 85 8 A Summary of Pertinent Nuclear Magnetic Reson• ance Chemical Shifts for Compounds 156-159 91 9 Comparison of NMR Data of Natural and Synthetic Stemmadenine Systems 102 10 The Stemmadenine Systems Administered to A. pyricollum 106 11 Incorporation Results Associated with Table 10... 107 - X - ACKNOWLEDGEMENTS I would like to express xny appreciation to Professor James P. Kutney for his guidance and encouragement, and the generous contributions of his time which were provided throughout the course of this work. I would also like to express my gratitude to my wife, whose unfailing support, confidence, and understanding during the course of this study were a contribution beyond measure. I am grateful to The University of British Columbia and to the National Research Council of Canada for the financial support which they provided. INTRODUCTION To a chemist, one of the roost fascinating aspects of nature is the abundance of highly complex molecules found in plant systems. Even more fascinating is the fact that these complex molecules are made by the plants from the minerals available in the soil, the gases available from the atmosphere, water and sunlight.
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