Synthesis and Bioactivity Investigation of Bridged Bicyclic Compounds and a Mechanistic Investigation of a Propargyl Hydrazine Cycloaddition Catalyzed by an Ammonium Salt by Elijah St.Germain A Dissertation Submitted to the Faculty of the Charles E. Schmidt College of Science In Partial Fulfilment of the Requirements for the Degree of Doctor of Philosophy Florida Atlantic University Boca Raton, FL August 2018 Copyright 2018 by Elijah St.Germain ii Acknowledgements I would like to express sincere gratitude to my committee members for their invaluable critiques and advice, and especially to my advisor Dr. Salvatore Lepore during the preparation of this manuscript. I would like to thank the National Institute of Health for financial support, the Dawson-Scully research group for their collaboration, and my lab mates in the Lepore group for their support and camaraderie. iv Abstract Author: Elijah J. St.Germain Title: Synthesis and Bioactivity Investigation of Bridged Bicyclic Compounds and a Mechanistic Investigation of a Propargyl Hydrazine Cycloaddition Catalyzed by an Ammonium Salt Institution: Florida Atlantic University Thesis Advisor: Dr. Salvatore D. Lepore Degree: Doctor of Philosophy Year: 2018 We report the development of a general route to the synthesis of [4.3.1], [3.3.1], an especially [3.2.1] bicyclic compounds structurally related to vitisinol D, a natural product. This allows for diastereoselective synthesis of bicyclic compounds with five adjacent chiral centers. This route was employed in a preliminary SAR investigation into the neuroprotectant effect of small molecules in an in vivo experiment measuring the degree of restorative effect of synaptic transmission in the neuromuscular junction of Drosophila melanogaster larvae under acute oxidative stress. One of the compounds exhibited intriguing potential as a neuroprotectant and outperformed resveratrol in restoring synaptic function under oxidative stress. The hypothesis that bridged bicyclic compounds may hold promise as drug scaffolds due to their conformational rigidity and ability to orient functional appendages in unique orientations is developed. v The second focus is a mechanistic investigation into a tetrabutylammonium-catalyzed cycloaddition as evidence of a novel ammonium-alkyne interaction. A carbamate nitrogen adds to a non-conjugated carbon–carbon triple bond under the action of an ammonium catalyst leading to a cyclic product. Studies in homogeneous systems suggest that the ammonium agent facilitates cyclitive nitrogen–carbon bond formation through a cation–π interaction with the alkyne unit. Using Raman spectroscopy, this cation–π interaction is directly observed for the first time. DFT modeling elucidated the mechanistic factors in this cycloaddition. A teaching experiment was developed based on this mechanistic investigation. Control experiments were employed to demonstrate the testing of two alternative mechanistic hypotheses. Cyclization reactions were performed with a soluble base (sodium phenoxide) with and without tetrabutylammonium bromide under homogeneous conditions. Students observed that ammonium salt accelerates the reaction. They were encouraged to develop a testable hypothesis for the role of the ammonium salt in the cyclization mechanism: typical phase transfer or other. IR spectroscopy was used to directly observe a dose dependent shift of the alkyne stretching mode due to a cation−π interaction. Undergraduates were able to employ the scientific method on a contemporary system and see how data are generated and interpreted to adjudicate between rival hypotheses in a way that emulates authentic and current research in a lab setting. vi Dedication This work is dedicated to my wife Tatiana and my daughter Phaedra. Synthesis and Bioactivity Investigation of Bridged Bicyclic Compounds and a Mechanistic Investigation of a Propargyl Hydrazine Cycloaddition Catalyzed by an Ammonium Salt List of Tables .................................................................................................................... xii List of Figures .................................................................................................................. xiii List of Schemes ................................................................................................................ xvi Chapter 1 ............................................................................................................................. 1 Annulation of allenoates to form [4.3.1], [3.3.1], and [3.2.1] bridged bicycles and medium-sized carbocycles ............................................................................................ 1 1.1 Introduction .......................................................................................................... 1 1.1.1 Biological significance of bridged bicyclic compounds................................... 1 1.1.2 Synthesis of [4.3.1] systems ............................................................................. 3 1.1.3 Synthesis of [3.3.1] systems ............................................................................. 4 1.1.4 Synthesis of [3.2.1] bicyclic systems.............................................................. 10 1.1.5 Synthesis of medium sized ring compounds .................................................. 13 1.2 Method Development ......................................................................................... 14 1.2.1 Synthetic strategy ........................................................................................... 14 1.2.2 Synthesis of bicyclo[4.3.1]decane-2,10-diones .............................................. 15 1.2.3 Generality study and synthesis of medium-sized rings .................................. 17 1.3 Medicinal investigation of compounds .............................................................. 20 1.4 Conclusion .......................................................................................................... 22 viii 1.5 Experimental section .......................................................................................... 23 Chapter 2 ........................................................................................................................... 36 Bioactivity Investigation of [3.2.1] bicyclic compounds as modified functional isomorphs of resveratrol and vitisinol D in a neuroprotective model ......................... 36 2.1 Introduction ........................................................................................................ 36 2.1.1 Biological relevance ....................................................................................... 36 2.1.2 Phenotypic models of anoxic shock and oxidative stress ............................... 36 2.1.3 Small molecule neuroprotectants .................................................................... 38 2.1.4 Possible mechanisms of neuroprotection ....................................................... 40 2.1.5 Vitisinol D hypothesis .................................................................................... 43 2.1.6 Resveromorph conception for potential sirtuin activation ............................. 47 2.1.7 Other design considerations............................................................................ 49 2.2 Synthesis of vitisinol D analogues ..................................................................... 53 2.2.1 Synthesis of cyclic β-ketoester ....................................................................... 53 2.2.2 Synthesis of allenoates.................................................................................... 53 2.2.3 Convergent synthesis of bicyclo[3.2.1]oct-2-ene-4,8-diols............................ 56 2.2.4 Diastereoselectivity and mechanistic hypothesis ........................................... 57 2.2.5 End stage synthesis ......................................................................................... 61 2.3 Biological testing................................................................................................ 63 2.4 Conclusion .......................................................................................................... 66 2.5 Experimental Section ......................................................................................... 67 Chapter 3 ........................................................................................................................... 76 Ammonium catalyzed cycloadditions and evidence for a cation-π .................................. 76 ix interaction with alkynes .................................................................................................... 76 3.1 Introduction ........................................................................................................ 76 3.1.1 Cation-π Interaction ........................................................................................ 76 3.1.2 Cyclization reactions ...................................................................................... 78 3.1.3 Synthesis of propargyl hydrazines .................................................................. 80 3.2 Mechanistic Investigation .................................................................................. 81 3.2.1 Initial Transition State Hypotheses ................................................................. 81 3.2.2 Rate experiments ............................................................................................ 83 3.2.3 Raman evidence .............................................................................................