Design and Synthesis of Novel Cannabinergic Analogs with Controlled Detoxification

Design and Synthesis of Novel Cannabinergic Analogs with Controlled Detoxification ------------------------------------------------------------------------------ Thesis Presented by Rishi Sharma to The Bouve’ Graduate School of Health Sciences in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Pharmaceutical Sciences with specialization in Medicinal Chemistry and Drug Development NORTHEASTERN UNIVERSITY BOSTON, MASSACHUSETTS April, 2011 Signature page 1 Northeastern University Bouve’ Graduate School of Health Sciences Thesis title: Design and synthesis of novel cannabinergic analogs with controlled detoxification Author: Rishi Sharma Program: Pharmaceutical Sciences with specialization in Medicinal Chemistry and Drug Development Approval for thesis requirement of the Doctor of Philosophy in Pharmaceutical Sciences Thesis Committee (Chairman) ________________________ Date ___________ ________________________ Date ___________ ________________________ Date ___________ ________________________ Date ___________ ________________________ Date ___________ Director of the Graduate School ________________________ Date ___________ Dean ________________________ Date___________ Copy Deposited in Library ________________________ Date___________ Signature page 2 Northeastern University Bouve’ Graduate School of Health Sciences Thesis title: Design and synthesis of novel cannabinergic analogs with controlled detoxification Author: Rishi Sharma Program: Pharmaceutical Sciences with specialization in Medicinal Chemistry and Drug Development Approval for thesis requirements of the Doctor of Philosophy in Pharmaceutical Sciences Thesis Committee (Chairman) ________________________ Date ___________ ________________________ Date ___________ ________________________ Date ___________ ________________________ Date ___________ ________________________ Date ___________ Director of the Graduate School ________________________ Date ___________ Table of Contents Page Abstract iv Acknowledgements vi List of Tables ix List of Figures xi List of Schemes xiv List of Abbreviations xvi Chapter 1 Introduction 1 1.1 Chemical Constituents of Cannabis 2 1.2 Cannabinoid Receptors 5 1.3 Endocannabinoid System (ECS) 7 1.4 Effects of Cannabis 9 1.5 Cannabinoid-based Drugs on the Market 11 1.6 Clinical Viability and PK/PD of Cannabinoids 13 1.7 Need for Novel THC-based Therapies 18 Chapter 2 Objectives and Specific Aims 24 2.1 Long-term Objective 24 2.2 Rational Drug Design 24 2.3 Specific Aims 26 i Chapter 3 Synthesis of Novel Cannabinergic Analogs with Controlled Detoxification 34 3.1 Analogs with Ester group at C2′ 34 3.2 Reverse Ester Analog, C1′-Methyl Substituted Ester Analog and Analogs Lacking Gemial Dimethyl at C1′ position 37 3.3 11-Hydroxyhexahydro, 11-Hydroxy and 9-Hydroxy Ester Analogs 45 3.4 β-Lactone at C1′ Position, Lactone in the C-Ring of DMH-Δ8-THC 57 3.5 DMH-Δ8-THC Analogs with Amide and Thioester at C2′ Position 63 3.6 Biaryl Analogs with Ester group at C2′ position 64 3.7 Cyclobutyl at C1′ Position in place of DMH-Δ8-THC 68 3.8 Analogs with Reduced cLogP and Increased tPSA 70 Chapter 4 Experimental Section 72 Chapter 5 Pharmacological Evaluation of Novel Cannabinergic Analogs with Controlled Detoxification 127 5.1 Ester Functionality at C2′ Position 132 5.2 Analogs Designed to Facilitate Enzymatic Hydrolysis 136 5.3 Cannabinergic Analogs with Increased Polarity 142 5.4 Analogs with β-lactone at C1′ position and Lactone in the C-ring 149 5.5 Analogs with Amide and Thioester group at C2′ position 151 5.6 Biaryl Analogs with Short Ester chain 152 ii 5.7 Analogs with Cyclobutyl at C1′ Position 153 5.8 Analogs with Reduced cLogP and Increased tPSA 155 Chapter 6 Discussion and Conclusion 158 Chapter 7 Future directions 174 References 176 iii Abstract Cannabis has been used medicinally and recreationally for several centuries, commonly in the form of the plant‟s dried leaf/flower (“marijuana”). Δ9- Tetrahydrocannabinol (Δ9-THC) is the primary psychoactive component of cannabis and is prescribed as a pharmaceutical (Dronabinol®) to stimulate appetite in AIDS patients, and to treat nausea and vomiting for patients undergoing chemotherapy. Δ9-THC is also under clinical investigation as an agonist- based therapy to combat cannabis dependence and addiction. Nabilone® is a synthetic Δ9-THC analog sold as a prescription medication for treating emesis and as an analgesic for neuropathic pain. However, Dronabinol® and Nabilone® therapies suffer from several drawbacks, including unpredictable duration of action, poor bioavailability, and variable efficacy and detoxification, primarily due to high lipophilicity and the production of pharmacologically active metabolites after metabolic biotransformation. In order to address the current unmet medical need for clinically viable, cannabis-based medications, novel cannabinergic analogs were designed, synthesized and pharmacologically evaluated using a „controlled inactivation approach‟. This approach integrates „soft drug design‟ and „modulation of polarity‟ within the key pharmacophoric sites of a compound to facilitate enzymatic inactivation in a predictable manner after producing a desired pharmacological response. In addition, the metabolites formed after enzymatic inactivation had no (or minimal) activity at cannabinoid receptors. An ester group hydrolyzable by ubiquitous plasma esterases was incorporated within the key pharmacophoric sites of dimethylheptyl (DMH)-Δ8-THC, in such a manner that the resulting iv novel compound demonstrated desired pharmacological responses at cannabinoid receptors and underwent enzymatic inactivation by plasma esterases in a predictable manner. Various polar functional groups were also incorporated at strategic positions of DMH-Δ8-THC ester analogs to modulate the compound polarity and lipophilicity, duration of action, and CNS penetration. In conjunction with pharmacological characterization, the synthetic endeavor resulted in two lead cannabinoid agonists [compounds 57 (AM 7418) and 54 (AM 7499)] with predictable duration of action, improved efficacy and controlled detoxification. Preliminary pharmacological evaluation (in vivo hypothermia) suggested that two cannabinoid agonists [compounds 17 (AM 7428) and 18 (AM 7488)] may be peripherally restricted, for they did not elicit hypothermia in spite of their high in vitro cannabinoid receptor affinity and functional activity at cannabinoid receptors. Additional pharmacological evaluation of these peripherally restricted agonists in select in vivo models is underway. v Acknowledgements It gives me immense pleasure to acknowledge all those who contributed towards the completion of my Ph.D. dissertation. I would like to express my deepest gratitude to my thesis committee chair, Professor Alexandros Makriyannis, for his gracious support, guidance and encouragement throughout this process. I would like to extend my gratitude to Dr. David Janero for proofreading and fine tuning my research project and for continuous guidance throughout Ph.D. dissertation. I am also grateful to Dr. Carol Paronis for serving on my thesis committee and providing me with all the in vivo data essential for my thesis. I also wish to thank Dr. Robert Hanson and Dr. Anthony Rossomando for serving on my thesis committee and offering valuable input throughout my dissertation work. I am indebted to my seniors and colleagues for providing a stimulating and enjoyable lab environment which enabled me to learn and evolve as a chemist. Special thanks to Dr. Ganesh Thakur for teaching me basic synthetic skills and initial fine tuning my thesis project. I am also grateful to Dr. Kumara Vadivel and Dr. Rick Duclos for helping me learn the attitude and approach towards chemistry problem solving and being always available in difficult times. I would like to thank Dr. Spyros P Nikas for valuable discussion during patent application and proof reading the experimental section of my thesis draft. I thank Dr. Aneetha Halikhedkar for helping me understand and analyze the functional data essential for dissertation progress. Likewise, I will never forget the late hours and weekends, I shared with Dr. Vidyanand Shukla, Dr. Paresh Sargoankar and Dr. Ioannis Papanastasiou toiling in the lab. Their friendship and support guided me through the best and worst of times, and I am forever grateful to them. vi I would like to acknowledge the CDD biochemistry group for performing in vitro studies and give a special thanks to Dr. JodiAnne Wood for performing the plasma stability studies. I also wish to express my gratitude to Dr. Roger Kautz who taught me and helped me in many occasions during 500 MHz NMR operations. I would like to extend my special thanks to the CDD office staff, especially Shawntelle Dillon, Sarah Strassburger and Brett Greene for their support and help throughout this process. Words alone cannot express the thanks I owe to Shafali Khajuria, my wife, for her support, encouragement and love ever since she entered my life. I would like to thank my parents Smt. Padma Devi and my father Mr. C. R. Sharma, who taught me to stay strong when faced with any situation life might present me. I am also thankful to my sisters and their families for continuous encouragement ever since I started my Ph.D. dissertation. Lastly, I would like to thank my late elder brother Mr. Vinod Sharma (4th Feb 1975 - 5th Apr 2010), who cared for our family in India so that I could finish my Ph.D. here in the U.S. I miss him greatly and know he would be proud of me. vii

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