UvA-DARE (Digital Academic Repository) Novel antagonists for the human adenosine A2A and A3 receptor via purine nitration: synthesis and biological evaluation of C2-substituted 6- trifluoromethylpurines and 1-deazapurines Koch, M. Publication date 2011 Document Version Final published version Link to publication Citation for published version (APA): Koch, M. (2011). Novel antagonists for the human adenosine A2A and A3 receptor via purine nitration: synthesis and biological evaluation of C2-substituted 6-trifluoromethylpurines and 1- deazapurines. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). 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UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:05 Oct 2021 Novel antagonists for the human adenosine A Novel antagonists for the human adenosine Uitnodiging Novel antagonists for the voor het bijwonen van human adenosine de openbare verdediging van het proefschrift van A2A and A3 receptor via purine nitration Melle Koch op vrijdag 21 oktober 2011 om 14:00 uur in de Agnietenkapel van de Universiteit van Amsterdam Synthesis and biological evaluation Oudezijds Voorburgwal 231 of C2-substituted te Amsterdam 2A Na afloop van de promotie and A 6-trifluoromethylpurines zal hier tevens de receptie . and 1-deazapurines plaats vinden . 3 CF3 receptor via purine nitration . N NH N 2 CF3 N O2N N R N N Paranimfen: N Arnold van Loevezijn [email protected] O & Boris Rodenko N [email protected] N N N O2N N 06 - 480 10 663 CH3 Melle Koch R Melle Koch Oosterpark 28 II 1092 AJ Amsterdam [email protected] Melle Koch 06 - 28 33 99 10 Novel antagonists for the human adenosine A2A and A3 receptor via purine nitration Synthesis and biological evaluation of C2-substituted 6-trifluoromethylpurines and 1-deazapurines Melle Koch Novel antagonists for the human adenosine A2A and A3 receptor via purine nitration Synthesis and biological evaluation of C2-substituted 6-trifluoromethylpurines and 1-deazapurines ACADEMISCH PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit van Amsterdam op gezag van de Rector Magnificus prof. dr. D.C. van den Boom ten overstaan van een door het college voor promoties ingestelde commissie, in het openbaar te verdedigen in de Agnietenkapel op vrijdag 21 oktober 2011, te 14.00 uur door Melle Koch geboren te Amsterdam Promotiecommissie: Promotor: Prof. dr. G.J. Koomen Co-promotor: Dr. J.A.J. Den Hartog Overige Leden: Prof. dr. H. Hiemstra Prof. dr. A.P. IJzerman Prof. dr. R. Wever Dr. J.H. van Maarseveen Dr. G.M. Visser Faculteit der Natuurwetenschappen, Wiskunde en Informatica CONTENTS CHAPTER 1 INTRODUCTION 1.1 Adenosine and Adenosine Receptors 10 1.2 Adenosine (Ant-)agonists 1.2.1 A2A receptor (ant-)agonists 12 1.2.2 Ligand binding 12 1.2.3 Therapeutic potential 15 1.3 Parkinson’s disease and adenosine receptor antagonists 17 1.4 Development of A2A selective adenosine receptor antagonists 22 1.5 Strategy for new adenosine receptor antagonists 27 1.6 Outline of the thesis 29 1.7 References 31 CHAPTER 2 SYNTHESIS OF C6-TRIFLUOROMETHYL SUBSTITUTED PURINES VIA C-2 NITRATION 2.1 Introduction 34 2.2 Introduction of trifluoromethyl groups at C-6 37 2.3 Nitration of purine bases 39 2.4 Trifluoromethylation of nitrated purines 40 2.5 Boc protection of purines and purine nitration 41 2.6 Mechanism of purine nitration 2.6.1 Introduction 46 2.6.2 Trifluoroacetyl nitrate as nitrating species 46 2.6.3 Detecting a 7-nitramino purine intermediate 48 2.6.4 Nitramine rearrangement of purines 52 2.6.5 15N CIDNP NMR in purine nitration 54 2.6.6 Mechanism summary 58 2.7 Serendipitous finding of a new protective group: Bocom 58 2.8 Concluding remarks 59 2.9 Acknowledgements 60 2.10 Experimental 60 2.11 References 68 CHAPTER 3 SYNTHESIS OF 2-SUBSTITUTED-6-TRIFLUOROMETHYL PURINES 3.1 Introduction 72 3.2 Amination at the 2-position 72 3.3 2-Alkoxygroups at the 2-position 75 3.4 Conversion to 2-aminosubstituted 6-trifluoromethylpurine bases 76 3.5 Methylation at the purine N-9 position 77 3.6 Bocom protective groups and C-2 amination 79 3.7 6-Amino-2-phenethylamino-substituted purines, Boc chemistry 80 3.8 Concluding remarks 82 3.9 Acknowledgements 83 3.10 Experimental 83 3.11 References 89 CHAPTER 4 SYNTHESIS OF 8-SUBSTITUTED 9-METHYL-2- PHENETHYLAMINO-6-TRIFLUOROMETHYLPURINES 4.1 Introduction 92 4.2 8-Halopurine variants of 6-trifluoromethylpurines 94 4.3 8-Alkylaminopurines via nucleophilic substitution 96 4.4 8-Alkylaminopurines via palladium catalysis 4.4.1 Sonogashira reaction 98 4.4.2 Stille coupling 98 4.4.3 Suzuki Miyaura cross coupling 99 4.5 Concluding remarks 104 4.6 Acknowledgements 105 4.7 Experimental 105 4.8 References 112 CHAPTER 5 SYNTHESIS OF C-2 SUBSTITUTED 1-DEAZAPURINES VIA NITRO- AND NITROSO CHEMISTRY 5.1 Introduction 116 5.2 Synthesis of the 1-deazapurine system 119 5.3 Direct alkylation of 1-deazapurines 122 5.4 Nitration of alkylated 1-deazapurines 124 5.5 Boc-protection of 1-deazapurines 124 5.6 TBAN/TFAA nitration of Boc protected 1-deazapurines 125 5.7 Boc deprotection of nitrated 1-deazapurines 127 5.8 Azide introduction at nitrated 1-deazapurines 127 5.9 N-9 methylation of 6-azido-2-nitro-1-deazapurines 128 5.10 Attempted direct nucleophilic substitution with amines 130 5.11 Reduction and oxidation of the 6-azido-2-nitro 1-deazapurine system 130 5.12 Functionalization of the 2-nitroso system 132 5.13 Diels Alder reactions with dienes 133 5.14 Hydrogenation of Diels Alder products 134 5.15 Attempted Mills coupling with amines 134 5.16 Amine condensations with 2-nitroso-1-deazapurines 135 5.17 Mechanistic aspects of 1-deazapurine and pyridine nitration 137 5.18 Concluding remarks 143 5.19 Acknowledgements 143 5.20 Experimental 144 5.21 References 152 CHAPTER 6 BIOLOGICAL EVALUATION OF SUBSTITUTED 6-TRIFLUORO- METHYLPURINES AND 1-DEAZAPURINES ON ADENOSINE RECEPTORS 6.1 Introduction 154 6.2 Adenosine receptor screening 155 6.2.1 Biological evaluation of substituted 6-trifluoromethyl- purine derivatives 157 6.2.2 Lipophilicity 163 6.2.3 Modeling studies in A2A adenosine receptor 164 6.2.4 Pharmacological function of the A3 receptor antagonists 171 6.3 Biological evaluation of substituted 1-deazapurines 173 6.4 Concluding remarks 175 6.5 Acknowledgements 175 6.6 Experimental 176 6.7 References 178 LIST OF ABBREVIATIONS 181 SUMMARY 183 SAMENVATTING 189 NAWOORD 197 1 Introduction Chapter 1 1.1 ADENOSINE AND ADENOSINE RECEPTORS 1.1.1 ADENOSINE Adenosine belongs to the group of nucleosides, consisting of an adenine molecule connected with a ribose. Adenosine and its analogues play a vital role in a variety of biochemical processes, like energy transfer in the body via adenosine triphosphate (ATP), signal transduction via cyclic adenosine mono phosphate (cAMP) or as a neurotransmitter. Adenine is a building block in DNA, as it readily forms complexes via hydrogen bonding with thymine. Since DNA of living organisms can be compared with a blue print code for cell expression and protein formation, adenines and its analogues are highly important in biochemical processes. Year over year adenosine and its derivatives have been associated with biological reactions. Since Drury and Szent-György reported the action of adenosine compounds on mammalian heart in the early 1920’s, it is well known that adenosine influences circulation, respiration and gastrointestinal motility.1 Later, important roles of adenosine were reported in brain tissue. Exposure to adenosine was found to increase accumulation of adenosine 3',5'-cyclic monophosphate (cAMP) in brain slices.2 This effect was also observed after electrical stimulation. Both processes were blocked by methylxanthines. The presence of methylxanthine-sensitive adenosine receptors on nerve and glial cells from several species was widely established. Later it was found that adenosine was able to block the release of neurotransmitters like dopamine, acetylcholine, serotonin and noradrenalin, indicative for an important regulatory role for adenosine. 10 Introduction Under normal conditions there is continuous generation of adenosine both intracellularly and extracellularly. The intracellular production is mediated either by a 5'-nucleotidase, that dephosphorylates AMP, or by hydrolysis of S-adenosyl-homocysteine. Intracellular generated adenosine can be transported into the extracellular space via specific bidirectional transporters that efficiently control the intra- and extracellular levels of adenosine. In striatum, stimulation of dopamine D1 receptors is found to enhance the NMDA (N-methyl d-aspartate) receptor- dependent increase of extracellular adenosine levels via ion channels. Adenosine can be converted into AMP through phosphorylation by adenosine kinase or degraded to inosine by adenosine deaminase. The normal levels of adenosine in rodent and cat brain have been determined by different techniques and have been estimated to be ca 30-300 nM. 1.1.2 ADENOSINE RECEPTORS In 1980 it was found that different adenosine derivatives were able to either increase or decrease the concentration of intracellular cAMP, which indicated a mechanism via different receptors.