Design, Synthesis, and Process Chemistry Studies of Agents Having
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A Dissertation entitled Design, Synthesis, and Process Chemistry Studies of Agents Having Anti-Cancer Properties by Amarjit Luniwal Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Medicinal Chemistry ___________________________________________ Paul W. Erhardt, Ph.D., Committee Chair ___________________________________________ Ronald E. Viola, Ph.D., Committee Member ___________________________________________ L. M. V. Tillekeratne, Ph.D., Committee Member ___________________________________________ Steven M. Peseckis, Ph.D., Committee Member ___________________________________________ Jeffrey G. Sarver, Ph.D., Committee Member ___________________________________________ Patricia R. Komuniecki, Ph.D., Dean, College of Graduate Studies The University of Toledo May 2011 Copyright 2011, Amarjit Luniwal This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author. An abstract of Design, Synthesis and Process Chemistry Studies of Agents Having Anti-Cancer Properties by Amarjit Luniwal Submitted to the Graduate Faculty in partial fulfillment of the requirements for the Doctor of Philosophy Degree in Medicinal Chemistry The University of Toledo May 2011 Breast cancer is the second leading cause of cancer deaths in American women. The use of estrogen receptor modulators is the most common treatment for early stage breast cancer and for prevention of its recurrence after surgery. However, among the available agents in this class, none display an ideal therapeutic profile. Therefore, it was aimed to design and synthesize selective estrogen receptor modulators (SERMs) which can overcome problems associated with the currently available agents. Toward that end, process chemistry studies were undertaken to enhance a synthetic route to natural glyecollin I (GLY I) which is a novel SERM that has promising anti-estrogenic and anti- cancer properties. Reaction yields across several steps were improved by optimizing reaction conditions and a few steps were improved by adopting alternative synthetic protocols. In doing so, not only were the total number of steps reduced from 15 to 13, but the overall yield was also tripled, i.e. from 3% to 9%. Molecular modeling and receptor docking studies were carried out during the design of GLY I related analogs obtained from intermediates produced during the scale-up syntheses. While performing such studies it was deduced that the active sites of the two subtypes of estrogen iii receptors(ERs), namely ERα and ERβ, are very similar except for two key aspects. First, the active site His residue in ERα lays slightly closer to the active site Arg and Glu as compared to the one found in ERβ. Second, the imidazole ring of the active site His residue in the two ERs is oriented quite differently in three-dimensional space. The new designed and synthesized GLY I related analogs possess pharmacophores that may be able to exploit these differences in the active sites. This, in turn, could lead to more selective estrogen receptor modulation. These analogs also possess varying degrees of flexibility while displaying their key pharmacophores important for receptor binding and selectivity. The pursuit of improved SERMs that can be derived directly from the GLY I chemistry turned next toward total synthesis of the second most prevalent member of the glyceollin family, namely GLY II. Unlike GLY I, for a specific synthesis of GLY II the 2,2-dimethylbenzopyran ring needs to be constructed first. Various chemical trials were made to accomplish this before linking two key synthons, namely 2,2- dimethylchromanone carboxylic methyl ester and an α-iodo ketone through an SN2 displacement reaction followed by an intramolecular Wittig olefination. The olefin has been instilled with the two dihydroxyl groups required for construction of a fused- benzopyran-benzofuran pterocarpan ring system. A robust, 12-step chemical route has been developed to the synthetic point of a key, late-stage intermediate which is just a few, additional steps away from the final target molecule. Model compounds were synthesized to develop and understand the chemistry associated with the key reactions utilized in the specific GLY II synthetic route. These compounds also led to the synthesis of three additional flavonoid natural products, iv namely 6a-hydroxymedicarpin, vestitol and bolusanthin III. Importantly, all of them possess key structural features required for binding to ERs. Therefore, they are additionally interesting for development of structure-activity relationships (SAR) that eventually can be translated into improved SERMs. Finally, analogs were similarly designed to explore SERM SAR after a new and highly practical synthetic route to a benzofuran scaffold was discovered during the specific synthesis of GLY II. The benzofuran type system represents an interesting and novel scaffold to pursue ER modulation because it is able to display polar hydroxyl groups at almost equivalent distances to those found in estradiol. These analogs were synthesized to experimentally test the two thereotical concepts pertaining to differential spacing and altered orientation of the His-imidazole ring within the ERs active site. As a second, major part of this dissertation work, the research has contributed toward the Center for Drug Design and Development‟s (CD3‟s) pursuit of chemotherapeutic treatments for advanced, hormone-independent cancer of the prostate (CaP). Similar to breast cancer in women, CaP is the second leading cause of cancer deaths in American men. Presently, there are no agents available that effectively address late-stage, advanced CaP. In this same regard, however, the CD3 previously has identified a very promising small, peptidomimetic molecule that may be able to provide some benefit in this setting. This lead compound has been designated as „CD3-246.‟ Moving forward with this technology, these thesis-related efforts involved scale-up synthetic studies and a new epimerization-free convergent route to CD3-246. In addition, an exploration of the reaction mechanism for pentamethylbenzene-mediated O-debenzylation of phenolic ethers was investigated because of its key role in the CD3-246 process chemistry. v Experimental evidence was gathered to support that this reaction predominantly follows an SN1 pathway. vi Acknowledgments Today, when I thankfully reflect upon my experiences over the last five years; I feel privileged for getting help, guidance and well wishes from so many people. I am truly gratified and owe thanks to all of them. First and foremost, it gives me immense joy and pleasure to thank my mentor, advisor and local guardian Dr. Paul Erhardt. Without his guidance, encouragement and constant support, I could never have accomplished this. His impressive enthusiasm and dedication to his work, has made a profound impact upon me. Without a doubt he is a great scientist with great accomplishments, but what makes him so special and wonderful is his caring and loving attitude toward his students. He has been and will always remain a source of my inspiration and motivation. Vocabulary fails to describe how privileged and indebted I feel to have him as my mentor and guide. I would also like to thank all my research committee members, Drs. Tillekeratne, Viola, Sarver, and Peseckis. I am truly honored to have them on my committee and I greatly appreciate their time, help and valuable suggestions. I feel joyous in thanking all former and current CD3 group and synthetic lab members, Jill, Nicole, Mike Reese, Pam, Dr. Nagy, Crystal, Lei, Jidong, Mohammed, Rahul, Dhana, Renuka, Rachael, Neha and Mike for all their support and companionship. vii I sincerely thank Dr. Y. W. Kim, Mr. Steven Moder, Tony and all other chemistry stockroom staff members for all their help during this entire time. I owe special thanks to all MBC and College of Pharmacy colleagues, staff and faculty for their support and friendship. I am very thankful to all former and current members of organic chemistry journal club for providing a very useful platform for organic chemistry discussions and learning. I am grateful to all my friends, especially Shan and Ritesh, for their support, encouragement and companionship during entire course of my PhD studies. I owe special thanks to my „buddy‟ Shan. He has been very helpful, encouraging and cooperative thoughout this entire duration. I am so pleased to thank my parents, brothers, sisters, sisters-in-law, brothers-in-law, nieces and nephews for their blessing, wishes and love. I owe special thanks to my elder brother, Naresh, for his unwavering support, affection, and encouragement. Finally, my heartfelt thanks and appreciations go to my beloved wife, Rekha, for all her love, care, and for the compromises and adjustments she has made so that I can realize my dreams. I greatly appreciate her support and encouragement during this entire time, especially when the „going gets tough.‟ Last but not least, I thank the almighty for providing strength to endure and for all His blessings. viii Contents Abstract iii Acknowledgments vii Contents ix List of Tables xiii List of Figures xiv List of Schemes xvi List of Abbreviations xix List of Spectra and Chromatograms xxii 1 Introduction 1.1 Overview 1 1.2 Estrogens and Estrogen Receptors 2 1.3 Selective Estrogen Receptor Modulators (SERMs) 5 1.4 Isoflavonoids 6 1.4.1 Phytoalexins and Glyceollins 7 1.5 Initial Biological Testing of SERM