Synthesis and Structure Activity Relationships of a Series
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SYNTHESIS AND STRUCTURE ACTIVITY RELATIONSHIPS OF A SERIES OF SIGMA RECEPTOR LIGANDS A Dissertation Presented to the: Chemistry Faculty of the Graduate School University of Missouri – Columbia In Partial Fulfillment of The Requirements for the Degree Doctor in Philosophy by ROGER I. NAHAS Dr. Susan Z. Lever, Dissertation Supervisor DECEMBER 2007 The undersigned, appointed by the dean of the Graduate School, have examined the dissertation entitled SYNTHESIS AND STRUCTURE-ACTIVITY RELATIONSHIPS OF A SERIES OF SIGMA RECEPTOR LIGANDS presented by Roger Nahas, a candidate for the degree of doctor of philosophy, and hereby certify that, in their opinion, it is worthy of acceptance. Professor Susan Lever Professor John Lever Professor Timothy Glass Professor Silvia Jurisson Professor Kent Gates Professor Paulette Saab ACKNOWLEDGMENTS I would like to offer my deepest gratitude to the University of Missouri-Columbia and especially to the Graduate School and the Department of Chemistry for accepting me in the PhD program, and offering me the opportunity of acquiring an excellent education along with a financial assistantship throughout the full period of those four years. My foremost appreciation in this journey goes to my advisor Dr. Susan Lever. She has offered me full guidance, advice and support and I deeply appreciate the fruitful conversations we had. I would also like to extend my appreciation to my co-advisor Dr. John Lever for being a great mentor. I would like to sincerely thank my committee members: Dr. Paulette Saab, Dr. Silvia Jurisson, Dr. Kent Gates, and Dr. Tim Glass for the valuable input in this work. I also thank the Harry S. Truman’s Veterans Affairs hospital where I conducted some of my training and experiments (and the NSF CHE-95-31247 for parts of the financial support). I would like to thank all the former and current members of both Drs. Lever’s groups for creating an excellent work environment, and for their friendship. I sincerely acknowledge the amiability and efficiency of Mr. Jerry Brightwell (Chemistry Department) and the International Center for helping and advising regarding my affairs. Finally, I would like to express my gratitude to my parents and siblings to whom I owe a lot because of their continuous love, support, and for always being proud of me. ii ABSTRACT Sigma receptors are involved in several biological processes, and sigma ligands might be promising as cancer treatment agents, cocaine abuse medicines, and valuable psychiatric drugs. In an attempt to elucidate effectual structure-activity relationships, a series of N- phenylpropyl-N’-benzylpiperazine and N-phenylpropyl-4-benzylpiperidine analogs systematically substituted on both phenyl rings was synthesized. These ligands were specifically designed to have certain substituents and substitution pattern representing three physico-chemical parameters denoting size, hydrophobicity, and electronic characteristics, in order to study the effect of those properties on the biological activity. X R R' N X=CH,N Structure-activity relationships (SAR) were evaluated qualitatively to describe the effect of the systematic benzyl substitution in comparison to the phenylpropyl substitution. High quality mathematical equations were derived to quantitatively express the statistical correlation between the biological activity and the physico-chemical parameters associated with the benzyl ring substitution. Finally, the effect of the piperidine moiety was compared to the piperazine in a systematic and coherent fashion. This SAR study will result in a better comprehension of the interaction between the sigma protein receptors and the ligands, a better understanding of the pharmacophore profile, and a more effective design for future potent sigma receptor ligands. iii TABLE OF CONTENTS ACKNOWLEDGMENTS……………………….………………………………………..ii ABSTRACT……………………………………………………………………………...iii LIST OF ABBREVIATIONS………………………………………………………….....ix LIST OF TABLES………………………………………………………………………..xi LIST OF FIGURES………………………………………………………………..……xiii LIST OF GRAPHS……………………………………………………….……………...xv CHAPTER I: LITERATURE REVIEW I.1 Introduction…….………………………………………………..…………………...1 I.1.1-Protein receptors………………………………………….…………….………1 I.1.2-Protein receptors pharmacology………………………….………………….…2 I.1.3-Rational drug design and SAR…………………………………………………3 I.2 Sigma receptors……….………..…………………………………………………….5 I.2.1-History………………………………………………………………………….5 I.2.2-Sigma receptors: biology and pharmacology…….…………………………….6 I.2.3-Pharmacological potentials and clinical uses of sigma receptor ligands………7 iv I.2.4-Sigma ligand selectivity………………………………………………………10 CHAPTER II: SPECIFIC AIMS AND HYPOTHESES II.1 Objectives…………………………………………………………………………..16 II.2 Hypotheses………………………………………………………………………….17 II.3 Experimental steps…………………..……………………………………………..18 CHAPTER III: CHEMOMETRIC DESIGN III.1 Leads and assumptions………………...…………………………………………20 III.1.1-Designation of leads and choice of structural skeleton……………………..20 III.1.2-Phenyl ring substitution as structural modification for the SAR……………23 III.2 Design of substituents, substitution pattern, and number of compounds……..25 III.2.1-Quantitative Structure-Activity Relationships (QSAR)………………….…25 III.2.2-Factorial Design method…………………………………………………….27 III.2.3-Statistical validation of preliminary data…………………………………....32 III.3 Synthesis schemes…………………………………………………………………38 III.3.1-Series-1 and series-2 (benzyl substituted N-phenylpropyl- N’-benzylpiperazine and N-phenylpropyl-4-benzylpiperidine)...……….......38 v III.3.2-Series-3 and series-4 (phenylpropyl substituted N-phenylpropyl- N’-benzylpiperazine and N-phenylpropyl-4-benzylpiperidine)..............................40 CHAPTER IV: EXPERIMENTAL PROCEDURES IV.1 Synthesis………………………………………………………………………...…42 I.V.1.1-Series-1 (benzyl substituted N-phenylpropyl-N’-benzylpiperazine)....……..43 I.V.1.2-Series-2 (benzyl substituted N-phenylpropyl-4-benzylpiperidine)……....…49 I.V.1.3- Series-3 and series-4 (phenylpropyl substituted N-phenylpropyl- N’-benzylpiperazine and N-phenylpropyl-4-benzylpiperidine).....................70 IV.2 Binding assays…………………………………………..…….…………………...70 I.V.2.1-In vitro Inhibition of [3H](+)-Pentazocine (sigma-1)………………....……71 I.V.2.2-In vitro Inhibition of [3H]DTG (sigma-2)………………………………….72 IV.2.3-Phenytoin modulation of ligand binding to sigma-1 receptors……………..73 IV.2.4-In vitro Inhibition of [3H]NTI (δ), [3H]DAMGO (µ), and [3H]U69,593 (κ) opioid receptors…………………………………..……….73 IV.3 QSAR………………………………………………………………………………75 IV.3.1-Descriptors used…………………………………………………………….75 I.V.3.2-Regression type…………………………………………………………….77 vi CHAPTER V: RESULTS AND DISCUSSION V.1 Series-1 (benzyl substituted N-phenylpropyl-N’-benzylpiperazine)....……..…..79 V.1.1-Results……………………………………………………………………….79 V.1.2-Discussion…………………………………………………………...……….85 V.2 Series-3 (phenylpropyl substituted N-phenylpropyl-4-benzylpiperidine)….......98 V.2.1-Results……………………………………………………………..…………98 V.2.2-Discussion……………………………………………………………………99 V.3 Series-2 and 4 (respectively benzyl substituted N-phenylpropyl- N’-benzylpiperazine and phenylpropyl substituted N-phenylpropyl-4- benzylpiperidine) selected compounds and piperazine versus piperidine SAR…………………………………………………………………….104 V.3.1-Results of selected compounds from series-2and series-4…………...…….104 V.3.2-Qualitative SAR and discussion……………………………………...…….109 CHAPTER VI: EVALUATION OF RESULTS, CONCLUSIONS AND FUTURE GOALS VI.1 Prediction power of the QSAR equations, limitations, and future goals for series-1 compounds…………………………………………..……….114 VI.2 Conclusions on the SAR of series-3, and future plans for series-2 and series-4………………………………………………………………..……..120 VI.3 Qualitative SAR (piperidine versus piperazine)…………………………...…..126 vii VI.4 Significance of results and contribution towards sigma receptor research….130 APPENDIX…………………………………………………………………………….133 REFERENCES………………………………………………………………...………241 CURRICULUM VITAE...………………..……………………………………….…..248 viii CHAPTER I: LITERATURE REVIEW I.1 Introduction I.1.1-Protein receptors: Receptors are proteins that exist on the cell membrane, inside the cytoplasm or in the nucleus. Once they bind to a specific molecule, they can become activated resulting in several physiological functions which constitute the biological activity of the ligand. The biological significance of drug-receptor interaction caused by molecular recognition was clearly acknowledged when Donald Cram, Jean-Marie Lehn and Charles Pederson won the Nobel Prize in Chemistry in 1987.1 Multicellular eukaryotic organisms rely on small chemical molecules to coordinate the activities and communication between cells.2 Unlike enzymes, proteins do not modify the structures of the ligands; they simply read the encoded information via an amazing process which is not fully elucidated yet.3 Complementarity in shape and properties between the protein receptor and the ligand results in a protein-receptor complex. Structurally dissimilar ligands belonging to different chemical classes can bind to the same protein receptor site, which suggests that the binding is associated with the physical and chemical properties of the ligand, and not necessarily the chemical structure itself.4 The main intermolecular forces between the 1 receptor and the drug (ligand) are: hydrogen bonding, electrostatic interactions, hydrophobic interactions, and others.4,5 I.1.2-Protein receptors pharmacology: A bioassay is an experiment that is conducted to measure and quantify the effect or the potency of a substance (drug) in terms of biological response. The interaction