isolation and selective reduction of mitragynine

ISOLATION AND SELECTIVE REDUCTION OF

MITRAGYNINE, SYNTHESIS AND

CHARACTERIZATION OF NEW INDOLE

DERIVATIVES AND THEIR SELECTED

BIOLOGICAL ACTIVITY STUDIES

GOH TEIK BENG

UNIVERSITI SAINS MALAYSIA

2015

ISOLATION AND SELECTIVE REDUCTION OF

MITRAGYNINE, SYNTHESIS AND

CHARACTERIZATION OF NEW INDOLE

DERIVATIVES AND THEIR SELECTED

BIOLOGICAL ACTIVITY STUDIES

BY

GOH TEIK BENG

Thesis submitted in fulfillment of the

requirements for the degree

of Doctor of Philosophy

September 2015

To my parents,

For their boundless love……

ACKNOWLEDGEMENT

I would like to express my gratitude and thanks to everyone involved. This

project could not accomplished without the guidance and help from all parties. First,

I would like to express my heartiness gratitude and appreciation to my project

supervisor, professor Sharif Mahsufi Mansor for his helpful advice, generous

encouragement, kind attention and guidance throughout this project. My special

thanks to my co-supervisor, associate professor doctor Mohammad Nizam Mordi for

her support throughout the whole experiments.

I acknowledge with gratitude the help and support of the lecturers from The

Drug Research Centre, Universiti Sains Malaysia. Not forgetting too, the help from

Encik Razak, Dr. Jayant, Mr. Gowda, Mrs. Juwita, Mr. Hilman, Mr. Zamri, Mr.

Rahim and Mr. Ashok

Last but not least, to my family, my friends and my beloved for their overwhelming

encouragement, support and care given to me throughout this project. I would also

like to acknowledge Universiti Sains Malaysia (RU grant : 1001 / CDADAH /

815020 and RUT Grant : 1001/CDADAH/855005) and Ministry of Science,

Technology and Innovation (304 / CDADAH / 650384/I119) for providing research

grant for the study carried out in this thesis.

Last but not least, thanks the support from all !

Goh Teik Beng (DD0001/04) February 2014

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TABLE OF CONTENTS

Page

ACKNOWLEDGEMENT ii

TABLE OF CONTENTS iii

LIST OF TABLES xi

LIST OF FIGURES xiii

LIST OF SCHEMES xix

LIST OF ABBREVIATIONS xx

LIST OF SYMBOLS xiv

LIST OF APPENDICES xxvii

LIST OF PUBLICATION xxxii

ABSTRAK xxxiii

ABSTRACT xxxv

CHAPTER 1 : INTRODUCTION

1.1 Chemistry of mitragynine (MTG) 1

1.2 Toxicological and Pharmacological effects of MTG 2

1.3 Other indole alkaloids of MTG 5

1.4 Structure and opioid agonist activity of mitragynine-related indole derivatives 7 1.5 β-carboline derivatives 10 1.6 Synthesis 18

1.6.1 Reduction of indole to indoline 18

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1.6.2 Total synthesis of tetrahydro-β-carbolines via Pictet-Spengler reaction 20

1.6.2.1 Mechanism of Pictet-Spengler reaction 22

1.6.2.2 Water as an effective medium of the Pictet-Spengler reaction 24 1.6.2.3 Dietary and endogeneous Pictet-Spengler reaction 25

1.7 Biological activity of the indole derivatives 26

1.7.1 Antinociceptive properties 26

1.7.1.1 Pain measurement model 28

1.7.2 Antioxidant properties 29

1.7.1.2 Antioxidant assay 33

1.7.3 In vitro cytotoxicity activities of β-Carbolines 34

1.7.3.1 Antiproliferative properties screening using MTT assay 47

1.7.3.1.1 Comparison of the MTT assay with other assays 49

1.7.3.2 Difference between apoptosis and necrosis 49 1.8 Research framework 52

1.9 Objective of the study 53

CHAPTER 2 : ISOLATION AND SELECTIVE REDUCTION OF MITRAGYNINE 2.1 Introduction 54

2.2 Materials and Methods 56

2.2.1 Materials, chemicals and solvents 56

2.2.2 Plant material identification 57

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2.2.3 Extraction and isolation of MTG 57

2.2.4 Purification of MTG by crystallization 58

2.2.5 Synthesis of silane reduced-mitragynine, (E)-methyl 2- ((2S,3S,12bS)-3-ethyl-8-methoxy-1,2,3,4,6,7,7a,12,12a,12b- decahydroindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate), (CDR80) 59

2.2.5.1 Purification of silane reduced-mitragynine (CDR80) 59 2.2.6 Instrumental analysis, qualitative characterization and structure elucidation of MTG and CDR80 60

2.2.6.1 UV 60

2.2.6.2 FT-IR 60

2.2.6.3 Preparative HPTLC 60

2.2.6.4 CHN elemental analysis 61

2.2.6.5 GC-MS 61

2.2.6.7 Melting Point 62

2.2.6.7 Differential Scanning calorimetry (DSC ) melting point analysis 62

2.2.6.8 Dissociation Constant, pKa 62

2.2.6.9 Long Term stability of stock solution 62

2.2.6.10 NMR 63

2.2.6.11 Statistical analysis 63

2.3 Results and Discussion 63

2.3.1 Purity of MTG extracts at various stage 63

2.3.2 GCMS method validation 65

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2.3.3 MTG yields and purity 66

2.3.4 Instrumental analysis and confirmation of purified MTG 67

2.3.5 Reduction of MTG using various silanes 70 2.3.6 Reduction of MTG using n-BS at different reaction conditions 70 2.3.7 Confirmation of the conversion of MTG to CDR80 75

2.3.8 Postulated indole group reduction 77

2.4 Conclusion 79

CHAPTER 3 : SYNTHESIS AND CHARACTERIZATION OF NEW 6- METHOXY β- CARBOLINE SCAFFOLD DERIVATIVES 3.1 Introduction 80

3.1.1 Background 80

3.1.2 Hypothesis and design approach 81

3.1.3 Objective 84

3.2 Materials and Methods 85

3.2.1 Materials 85

3.2.2 Synthesis of 6-methoxy-tetrahydro-ß-carboline derivatives 85

3.2.2.1 CDR81(6-methoxy-1-phenyl-2,3,4,9-tetrahydro-1H-pyrido[3,4- b]indole) 85 3.2.2.2 CDR82(6-methoxy-1-(4-methoxyphenyl)-2,3,4,9-tetrahydro-1H- pyrido[3,4-b]indole) 86 3.2.2.3 CDR83(6-methoxy-1-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4- b]indole. 87 3.2.2.4 CDR84(2-methoxy-4-(6-methoxy-2,3,4,9-tetrahydro-1H- pyrido[3,4b]indol-1-yl)phenol) 88

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3.2.3 Instrument Analysis 89

3.2.3.1 Accurate mass determination using high resolution –mass spectrometry (HR-MS) 89 3.2.3.2 Melting point, enthalpy and DSC measurement 90 3.2.3.3 Functional group and FTIR analysis 90 3.2.3.4 CHN elemental analysis 90 3.2.3.5 UV-Vis and electronic absorption 90 3.2.3.6 CD spectra and stereoisomerism profile 91 3.2.3.7 Structural assignment and NMR 91 3.2.3.8 Single X-ray Crystallography 91 3.2.3.8.1 Preparation of CDR83 crystal salt 91 3.2.2.8.2 Preparation of CDR83 crystal salt 92 3.2.2.8.3 Single Crystallography 92 3.3 Results and discussion 93

3.3.1 Synthesis of 6-methoxy ß-carboline scaffold derivatives 93 3.3.2 LC-ESI-MS and LC-ESI-TOF-MS/MS characterization 95

3.3.4 DSC Purity confirmation 106

3.3.5 FTIR 108

3.3.6 CHN elemental analysis 109

3.3.7 NMR assignments 110

3.3.8 Determination of the absolute configuration of the stereo-center on the C-1 position on the six membered ring C 125

3.3.9 Single crystallography analysis 138 3.3.10 CD profile and stereoisomerism 145 3.4 Conclusion 150

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CHAPTER 4 ANTIPROLIFERATIVE EFFECTS OF MITRAGYNINE AND ITS SILANE-REDUCED ANALOGUES ON COLON CARCINOMA AND LEUKAEMIA CELL LINES 4.1 Introduction 151

4.2 Materials and methods 153

4.2.1 Material 153

4.2.2 Method 153

4.2.2.1 MTT cell antiproliferation assay 153

4.2.2.2 Cell culture 153

4.2.2.3 Sample preparation for cell proliferation assay 153

4.2.2.4 MTT cell proliferation assay 154 4.2.2.5 Determination of Morphological Changes 155 4.2.2.6 Statistical analysis 155 4.3 Result and Discussion 156

4.3.1 Antiproliferation effects 156

4.3.2 Cells morphology and apoptosis 161

4.4 Conclusion 164

CHAPTER 5 ANTIPROLIFERATIVE ASSAYS OF 6-METHOXY TETRAHYDRO-β-CARBOLINE DERIVATIVES 5.1 Introduction 165 5.2 Materials and Methods 168 5.2.1 Sample preparation for the cell proliferation assay 168 5.2.2 Preparation of cell culture 169 5.2.3 MTT cell proliferation assay (cell viability assay) 170

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5.2.4 Determination of morphological changes 172 5.2.5 Statistical analysis 172 5.3 Results and discussion 173 5.3.1 Antiproliferation assay: Cytotoxicity screening of 6-methoxy β-carbolines scaffold (CDR81, CDR82, CDR83 and CDR84) on multiple human cancer cell lines with NIH / 3T3 as the reference. 173 5.3.2 Cell line morphology and apoptosis 183 5.3.3 Cytotoxicity at 100 µM for 6-methoxy-tetrahydro-β-carboline derivatives 188

5.4 Conclusion 190

CHAPTER 6 ANTIOXIDANT ACTIVITI OF 6-METHOXY- TETRAHYDRO- β-CARBOLINE 6.1 Introduction 197 6.2.2 Materials and Methods 206 6.2.2.1 Reagents 206 6.2.2.2 Determination of antioxidant activity 206 6.2.2.2.1 ABTS antioxidant assay 206 6.2.2.2.2 DPPH radical scavenging activity using the DPPH assay 208 6.2.2.2.3 Measurement of reducing power 209 6.2.2.3 Statistical analysis 209 6.2.3 Results and Discussion 210 6.2.3.1 Antioxidant activity 210

6.2.3.1.1 DPPH scavenging activity 210

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6.2.3.2.2 Trolox equivalent antioxidant capacity 215 6.2.3.2.3 Reducing power 221 6.4 Conclusion 223 CHAPTER 7 ANALGESIC ACTIVITY OF 6-METHOXY- TETRAHYDRO-β-CARBOLINE 7.1 Introduction 225 7.2 Materials and Methods 226

7.2.1 Animals 226

7.2.2 Preparation of the drug carrier and application of drugs 227

7.2.3 Hot plate test 228

7.2.4 Statistical analysis 229

7.3 Results and Discussion 230

7.3.1 Hot plate test 230

7.4 Conclusion 232 CHAPTER 8 GENERAL DISCUSSION 233

CHAPTER 9 CONCLUSION 247

FUTURE WORK 249

REFERENCES 250

APPENDICES 281

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LIST OF TABLES

TABLE TITLE PAGE

1.1 Summary of existing effective ß–carboline anticancer agents against respective types of cancer cell lines 39

1.2 Comparison between characteristics of apoptosis and necrosis 50

2.1 Comparison of GCMS purity of MTG extracts at various isolation stages between the developed and published methods 64 2.2 The yields (%) and GCMS purity (%) of MTG at various isolation stages 66 2.3 Comparison of purity and stability of MTG obtained by this method and MTG from IMR 67 2.4 Comparison of reduction effects on different types of silane and reagent in carbonyl and indole group of mitragynine 70 2.5 Comparison of the effects of temperature, time and reaction medium on the percentage of conversion using n-butylsilane 71 2.6 Key 1H and 13C NMR data for MTG and CDR80 (in CDCl3, δ in ppm, J in Hz) 76 3.1 Summary of Pictet-Spengler reaction condition and yields for CDR81- 84 94 3.2 Comparison of the protonated HR-LCMS found value, calculated protonated MS value and BPC/EIC retention time indexes of the pure synthetic 6-methoxy-tetrahydro-ß-carboline compounds (CDR81-84) 96 3.3 HR-MS/MS mass fragments summary of CDR81, CDR82, CDR83 and CDR84 98 3.4 DSC melting point, purity and enthalpy of 6-methoxy-tetrahydro-ß- carboline compound (CDR81-84) 107 3.5 CHN elemental analysis of CDR81, CDR82, CDR83 and CDR84 110

3.6 1H and 13C NMR data for CDR81, CDR82, CDR83 and CDR84 (in CDCl3 or CD3OD, δ in ppm, J in Hz) 116 3.7 Summary of multiplicities and coupling constants on protons at six member cyclic ring C of CDR81, CDR82, CDR83 and CDR84 136 3.8 Single crystal analysis puckering parameters for CDR82 and CDR83 140

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3.9 Summary of UV absorptivity at λmax and CD spectrum results 145 4.1 Cytotoxicity activity presented as median inhibitory concentration (IC50) in µm and selectivity index (SI = IC50 normal cell lines / IC50 cancerous cell lines ) of MTG and CDR80 on cancer cell lines and normal cell after 48 h.of treatment, results are shown as average ± SD (n=3) 157 5.1 Cytotoxicity screening of 6-methoxy-tetrahydro-β-carboline derivatives (CDR81, CDR82, CDR83 and CDR84) on multiple cancer cell lines and normal cell lines 174

5.2 Selectivity index (SI) of CDR81, CDR82, CDR83 and CDR84 after 48 h of

Treatment 175 5.3 Cytotoxic activity (IC50) of CDR81, CDR82, CDR83 and CDR84 against cancer (HCT116 and K562) and normal (CCD-18Co and B98-5) cell lines 177

5.4 Selectivity index (SI = IC50 normal cell lines / IC50 cancerous cell lines) of CDR81, CDR82, CDR83 and CDR84 after 72 h of treatment 178 5.5 Cytotoxicity (%) of CDR83, CDR82, CDR81 and CDR84 at 100 µM against cancer (K 562 and HCT 116) and normal (B98-5 and CCD-18Co ) cell lines 193 5.6 Cytotoxicity (%) at 100 µM of CDR83, CDR82, CDR81 and CDR84 against cancer and normal cell lines 195 6.1 IC50 (μg/mL and µM) of standard antioxidant (BHT, Quercetin) and pure 6-methoxy-tetrahydro-β-carboline derivatives. Each value is expressed as mean ± SD (n = 3) 213 7.1 The antinociceptive effects of 6-methoxy-tetrahydro-β-carboline derivatives in the hot plate test using three single doses 231

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LIST OF FIGURES

FIGURE TITLE PAGE

1.1 Structure of mitragynine (MTG). 2

1.2 Mitragynine [(E)-methyl 2-(3-ethyl-8-methoxy-1,2,3,4,6,7,12,12b- octahydroindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate] related indole alkaloids. 6

1.3a Structures and common name of some β-carbolines. 12

1.3b Structures and IUPAC Scientific name of some β-carbolines 13

1.4 Pictet-Spengler reaction 21

1.5 Mechanism of Pictet-Spengler reaction 23

1.6 Some examples of naturally occurring antioxidants 30 1.7 The structure features of ß-carboline derivatives affecting its antitumour activities against cancer cells 36 1.8 A microtiter plate after an MTT assay. Increased purple colouring indicates increasing amounts of viable cells. 48 1.8 Reduction of MTT salt to formazan 48 2.1 Improved isolation and purification procedure of MTG 59 2.2 Pure mitragynine calibration curve 65

2.3 Structure of MTG with numbering system 69

2.4 HPTLC 2D densitogram profile of the crude reaction product with CDR80 (RF=0.52) 72 2.5 DSC melting point of CDR80 73 2.6 GCMS chromatogram (A) of CDR80 and its mass spectrum (B) 74 2.7 Structure and carbon numbering of MTG and CDR80 75 2.8 Postulated mechanism of indole double bond reduction on mitragynine 78 3.1 IUPAC scientific name and carbon numbering for 6-methoxy-tetrahydro- ß-carboline derivatives (CDR81-84) 83

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3.2 Proposed mass fragmentation pathway for CDR81 (Symbols : π refers to ionization on π bond, i refers to inductive cleavage, rHx refers to hydrogen rearrangement or hydrogen transfer in atom and rH1,2 refers to hydrogen 1,2-rearrangement or Whitmore 1,2-shift) 99

3.3 Proposed mass fragmentation pathway for CDR82 (Symbols : π refers to ionization on π bond, i refers to inductive cleavage, rHx refers to hydrogen rearrangement or hydrogen transfer in atom and rH1,2 refers to hydrogen 1,2-rearrangement or Whitmore 1,2-shift) 101 3.4 Proposed mass fragmentation pathway for CDR83 (Symbols : π refers to ionization on π bond, i refers to inductive cleavage, rHx refers to hydrogen rearrangement or hydrogen transfer in atom and rH1,2 refers to hydrogen 1,2-rearrangement or Whitmore 1,2-shift) 103 3.5 Proposed mass fragmentation pathway for CDR84 (Symbols : π refers to ionization on π bond, i refers to inductive cleavage, rHx refers to hydrogen rearrangement or hydrogen transfer in atom and rH1,2 refers to hydrogen 1,2-rearrangement or Whitmore 1,2-shift) 105 3.6 Overtone vibration of mono-substituted p-disubstituted benzene ring of CDR81 and CDR 82 109 3.7 Proton 1H and Carbon 13C NMR for CDR81 (Operating frequencies, 500.13 MHz for 1H and 125.77 MHz for 13C) 112 3.8 Proton 1H and Carbon 13C NMR for CDR82 (Operating frequencies, 500.13 MHz for 1H and 125.77 MHz for 13C) 113

3.9 Proton 1H and Carbon 13C NMR for CDR83 (Operating frequencies, 500.13 MHz for 1H and 125.77 MHz for 13C) 114

3.10 Proton 1H and Carbon 13C NMR for CDR84 (Operating frequencies, 500.13 MHz for 1H and 125.77 MHz for 13C) 115

3.11 Selected HMBC and DQF COSY correlations representation of CDR81, CDR82, CDR83 and CDR84 (Data obtained from HMBC and DQF COSY from Appendix). Key: HMBC (bold red arrows) and DQF COSY (dashed blue arrows) correlations 121 3.12 1 D NOE Diff spectrum for CDR81 128 3.13 1 D NOE Diff spectrum for CDR82 129 3.14 1 D NOE Diff spectrum for CDR83 130 3.15 1 D NOE Diff spectrum for CDR84 131

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3.16 1D NOE Diff interaction for CDR81, CDR82, CDR83 and CDR84. Key Axial-axial trans 3JH-H interaction(bold solid red arrows), germinal 2JH-H interaction (dashed blu arrows) and other weaker NOE (solid orange arrows) correlations. Ha = Hα and Hb = Hβ. 132 3.17 NOESY proton coupling or interaction at ring C of CDR81, CDR82, CDR83 and CDR84 (Data obtained from Appendices C52-C55). 134 3.18 Patterns of coupling tree (splitting patterns) for H-3α, H-3β, H-4α and H-4β of CDR81, CDR82, CDR83 and CDR84 137 3.19a Molecular structure of crystal salt of CDR82 138 3.19b Molecular structure of crystal salt of CDR83 139 3.20 Overlay for molecular structure of CDR82 and CDR83 139

3.21 Single crystal of CDR82 and CDR83 141

3.22 The crystal packing of CDR82. Dashed lines indicate hydrogen bonds. 143 3.23 The crystal packing of CDR83. Dashed lines indicate hydrogen bonds. 144 3.24 CD spectrum profile of CDR81, CDR82, CDR83 and CDR84 147

3.25 Structure of CDR82 and CDR 83, A CDR82, [(S)-6-methoxy-1-(4-methoxyphenyl)-2,3,4,9-tetrahydro- 1H-pyrido [3,4-b]indole] and B CDR 83, [(S)-6-methoxy-1-methyl- 2,3,4,9-tetrahydro-1H- pyrido[3,4-b]indole] 148

3.26 Assignment of S configuration of CDR81, CDR82, CDR83 and CDR 84 using the Cahn-Ingold priority principle 149 4.1 Effect of MGT, CDR80 on A) K 562, B) HCT 116 human tumor cell lines inhibition (%) and C) NIH/3T3, D) CCD 18 Co normal cell line inhibition (%) at concentrations of 6.5, 12.5,12.5, 25, 50, 100 and 200 µM. Betulinic acid (selective to leukemia) and 5-Fluorouracil (selective to colon cancer) was used as the reference compound. The MGT and CDR80 show inhibition against cells proliferation in dose dependent manner. Values are means of three experiments (n=3), error bars equal ± SEM 159

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4.2a Human erythromyeloblastoid leukemia K562 (1) and NIH/3T3 (2) cell images were taken under an inverted phase-contrast microscope at × 200 magnification with a digital camera at 48 h. after treatment with the samples, respectively. Photomicrograph A depicts the control group formed a compact confluent layer. Photomicrograph B depicts the cytotoxic effect of the MTG with clearly seen moderately reduced cell population. Photo image C depicts that treatment with CDR80 demonstrated significant cytotoxic effect on cell proliferation. Treatment with BA showed marked inhibition in cell proliferation in image D. 162

4.2b Colon cancer carcinoma HCT 116 (3) and human normal colonic fibroblast cell line CCD-18Co (4) cell images were taken under an inverted phase-contrast microscope at × 200 magnification with a digital camera at 48 h. after treatment it the samples, respectively. Photomicrograph (A) depicts the control group formed a compact confluent layer. Photomicrograph B depicts the cytotoxic effect of the MTG, with clearly seen moderately reduced cell population. Photo image C depicts that treatment with CDR80 demonstrated significant cytotoxic effect on cell proliferation. The image D shows the drastically reduced cell population upon treatment with 5-FU. drastically with 5-FU (3-4D). 163 5.1 Structures of 6-methoxy-tetrahydro-β-carbolines derivatives (CDR81, CDR82, CDR83 and CDR84) 167 5.2 Image of human erythromyeloblastoid leukaemia cell line K562 were taken with a digital camera and an inverted phase-contrast microscope at 200× magnification after 48 h of treatment. The photomicrographs (A) show the control group formed a compact confluent layer. Strong cytotoxic effects of CDR82 was seen in image B with drastic cell population reduction treatment. Treatment with CDR83 showed considerable inhibition of cell proliferation clearly seen in image C. Treatment with CDR81 had a potent cytotoxic effect on cell proliferation as shown in im age D. Cell treatment with CDR84 in image E was found to be ineffective on cell proliferation, the viability of the treated cells was unaffected similar to untreated cells. Image F reveals drastic reduction in cell population treatment with BA indicating marked cell proliferation inhibition. 184

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5.3 Images of human colon carcinoma cancer line HCT116 were taken with a digital camera and an inverted phase-contrast microscope at 200× after 48 h of treatment. The control group in image A showed fully confluent growth of compactly proliferating cells. Image B showed treatment with CDR83 led to a significant inhibition in cell proliferation and appearance of the characteristics autophagy and an abnormally large number of vacuoles in cytoplasm. Image C show the strong cytotoxic effect of CDR82 on most cells in the group as the cells lost their normal pseudopodial extensions morphology and showed reduced viability. CDR81 exhibited marked cytotoxicity as the population of cells was drastically reduced in image D.Image E showed the CDR84 had no significant effect on cell growth compared to untreated cells. Cells treated with 5-FU in image F showed decreased viability with the characteristic features of apoptosis, such as cell membrane blebbing and nuclear condensation. 185 5.4 Images of human normal colonic fibroblast cell line CCD-18Co were taken with a digital camera and an inverted phase-contrast microscope at 200× magnification after 48 h of treatment. Image A of the control group showed normal features. Treatment with CDR82 in image B led to a significant inhibition in cell proliferation with the morphology of the treated cells was distorted. CCD-18Co cells treated with CDR81 in image C exhibited potent cytotoxicity as the doubling of the cell population was significantly reduced. CDR84 showed poor cytotoxicity against CCD-18Co cells in image E. Cells treated with the 5-FU as shown in image F induced toxicity in normal colonic fibroblasts. 186 5.5 Human B98-5lymphocytes cells images were taken with a digital camera and an inverted phase-contrast microscope at 200× magnification after 48 h of treatment. Image A showed the control group formed a compact confluent layer . Image B depicts some cytotoxic effect of CDR83 with slightly reduced cell population. Image C showed considerable inhibition of cell proliferation with the treatment of CDR82. Image D showed CDR81 demonstrated the cytotoxic effect on cell proliferation. Treatment of CDR84 in image E was found to be less effective in terms of cell proliferation inhibition, the viability of the cells was unaffected and treated cells were similar to untreated cells. Treatment with BA in image F showed moderate inhibition of cell proliferation with moderate cell population reduction and well-separated apoptotic bodies indicating a late stage of apoptosis. 187

5.6 Comparison of the % inhibition of CDR83, CDR82, CDR81 and BA (betulinic acid) on K562 cells at concentrations of 3.125, 6.25, 12.5, 25, 50 and 100 µM. Values are means of three experiments (n=3), error bars equal ± SEM. 189 5.7 Comparison of the % inhibition of CDR83, CDR82, CDR84 and CDR81 on B98-5 cells at concentrations of 6.25, 12.5, 25, 50 and 100 µM.Values are means of three experiments (n=3), error bars equal ± SEM. 190

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5.8 Comparison of the % inhibition of CDR83, CDR82, CDR81, CDR84 and 5-fluorouracil on HCT116 cells at concentrations of 3.125, 6.25, 12.5, 25, 50 and 100 µM.Values are means of three experiments (n=3), error bars equal ± SEM. 191 5.9 Comparison of the % inhibition of CDR83, CDR82, CDR84 and CDR81 on CCD 18-Co cells at concentrations of 6.25, 12.5, 25, 50 and 100 µM. Values are means of three experiments (n=3), error bars equal ± SEM. 192 6.1 a (2íS)-N-(1-hydroxy-2-methylpropan-2-yl)-9H-β-carboline-3- carboxamide, b (3S)-N-(4-hydroxy-2-methylbutan-2-yl)-2,3,4,9-tetrahydro -1H-β-carboline-3-carboxamide, c (R,S)-3-methyl-1-(pyridin-3-yl)- 2,3,4,9-tetrahydro-1H-β-carboline, d Harmaline, e Harmine and f 5-methoxytryptamine (Francik et al., 2011,; Herraiz et al., 2004). 205 6.2 DPPH scavenging activity (%) versus concentration of 6-methoxy- tetrahydro-β-carbolines, BHT and quercetin. Values are means of three experiments (n=3), error bars equal ± SEM. 212 6.3 IC50 of standard antioxidant (BHT,Quercetin) against pure 6-methoxy -tetrahydro-β-carbolines. Each value is expressed as mean ± SEM (n = 3). 214 6.4 TEAC value (mM) of 6-methoxy-tetrahydro-β-carbolines compared to a standard antioxidant. Values are means of three experiments (n=3), error bars equal ± SEM. 216 6.5 Tetrahydro-β-carboline generates an indolyl cation and a neutral radical upon a single electron transfer to the free radical ABTS•+ . 220 6.6 Reducing power of the 6-methoxy-tetrahydro-β-carbolines compared to BHT and quercetin. Values are means of three experiments (n=3), error bars equal ± SEM. 222

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LIST OF SCHEMES

SCHEME TITLE PAGE

1.1 Reduction of indole to indoline using platinum on activated charcoal as catalyst 19

2.1 Reduction of MTG to CDR80 using n-BS and Tris(pentafluorophenyl)borane as catalyst in dichloromethane 70

3.1 Reaction of 5-methoxytryptamine with benzaldehyde in aqueous to produce CDR81 85 3.2 Reaction of 5-methoxytryptamine with anisaldehyde in aqueous to produce CDR82 86 3.3 Reaction of 5-methoxytryptamine with anisaldehyde in aqueous to produce CDR83 87 3.4 Reaction of 5-methoxytryptamine with benzaldehyde in aqueous to produce CDR84 88 3.5 Reaction of L-tryptophan with various aldehyde in aqueous to produce the β-Carboline (Herraiz et al., 2003) 94

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LIST OF ABBREVIATIONS

ABTS

BA

BHT

BZRs

CD

CDR80

CDR81

2,2'-azino-bis(3-ethylCDR81zothiazoline-6-sulphonic acid) Betulinic acid Butylhydroxytoluene Benzodiazepine receptors

Circular dichroism

Silane reduced mitragynine ((E)-methyl 2-((2S,3S,12bS)-3-ethyl-8-methoxy-1,2,3,4,6,7,7a,12,12a,12b-decahydroindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate).

6- methoxy-1-phenyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole.

CDR82

CDR83

6-methoxy-1-(4-methoxyphenyl)-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole. 6-methoxy-1-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole.

CDR84 2-methoxy-4-(6-methoxy-2,3,4,9-tetrahydro-1H-pyrido[3,4- b]indol-1-l)phenol.

CHN

CV

Carbon, hydrogen and nitrogen

Coefficient of variation

DEPT Distortionless enhancement by polarization transfer

DES Diethylsilane

DMSO Dimethyl sulphoxide

DMEM Dulbecco’s modified eagle medium

DNA Deoxyribonucleic Acid

1D –NMR

2D-NMR

One dimensional nuclear magnetic resonance spectroscopy Two dimensional nuclear magnetic resonance spectroscopy

1D NOE Diff

DPPH

One dimensional nuclear overhauser effect difference 2,2-diphenyl-1-picrylhydrazyl xx

DQF-COSY Double quantum filter 1H-1H correlation spectroscopy

DSC Differential scanning calorimetry

ESI-LCMS

ESI-TOF-HR-LC-MS/MS

Electrospray ionization liquid chromatography mass spectroscopy

Electrospray ionization tandem liquid chromatography mass spectrometry

FRAP Ferric reducing antioxidant power

FTIR Fourier transform infrared spectroscopy

5-Fu 5-Fluorouracil

GABA Gamma-aminobutyric acid receptor

GCMS Gas chromatography mass spectrometer

HMBC

HPTLC

Heteronuclear multiple-bond coherence

High performance thin layer chromatography

HR-MS

HSQC

5-HT

IMR

JRES

High resolution mass spectroscopy

Heteronuclear single quantum coherence

5-hydroxytryptamine receptor

Institute Medical Research

J-resolved couplings

HSQC Heteronuclear single quantum coherence

IUPAC International union of pure and applied chemistry

LLOQ Lower limit of quantification

LOD Limit of detection

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MeOH Methanol

MTG

5-M-TRP

Mitragynine [(E)-methyl 2-(3-ethyl-8-methoxy-1,2,3,4,6,7,12,12b-

octahydroindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate)]

5-methoxytryptamine

MTT 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay

n-BS n-Butylsilane

NMR Nuclear magnetic resonance

NOESY Nuclear overhauser effect spectroscopy

OH Hydroxyl group

p-TsOH Para toluene sulfonic acid

PBS

PFTBA

Phosphate buffered saline

Perfluorotributylamine

PMHS

hRf

Polydimethylhydroxysilane

Homologous retention factor

ROS

SAR

Reactive oxygen species

Structure-activity relationship

SD Standard deviation

SEM Standard error mean

SI Selectivity index

SIM Selected ion monitoring

TEAC Trolox equivalent antioxidant capacity

TES Triethylsilane

xxii

http://en.wikipedia.org/wiki/Di-

http://en.wikipedia.org/wiki/Di-

http://en.wikipedia.org/wiki/Thiazole

http://en.wikipedia.org/wiki/Phenyl

TFA

TOCSY

Trifluoroacetic acid

Total Correlation spectroscopy

UV Ultra-violet spectroscopy

xxiii

LIST OF SYMBOLS

Å Angstrom

α Alfa

ß

γ

κ

ca.

Beta

Gamma

Kappa

Approximately

d Doublet

dd Doublet doublet

m Multiplet

q Quartet

ddd Doublet doublet doublet

m/z Mass per charge

t Triplets

s Singlet

ºC Degree Celsius

e.g. For example

et al. Co Workers

∆H Enthalpy

h Hours

Hz Hertz

xxiv

IC50

J

Median inhibitory concentration

Coupling constant in hertz

Jg-1 Joule per gram

Kjmol-1 Kilojoule per molar

µL Microlitre

µM Micromolar

Mg Miligram

mM Milimolar

Min Minutes

mL Mililitre

eV Electron volt

n Number of replicates

pKa Ionisation constant

ppm Part per million

r Correlation coefficient

s Second

S Sinister isomer

R Rectus isomer

Tm Melting temperature

v/v Volume by volume

w/w Weight by weight

< Less Than

xxv

> More than

=

±

Equal

Plus/minus

% Percent

δ NMR chemical shift in ppm

xxvi

Appendix List of Appendices PAGE

Appendix A1 pKa curve for MTG 281

Appendix A2 UV spectra for MTG 281 Appendix A3 FTIR spectra for MTG 282 Appendix A4 HPTLC fingerprint of isolated MTG and the IMR standard MTG 283 Appendix A5 a. HPTLC profile under UV 365 nm for fractions 4-8 (Path 9a-11b) containing MTG after flash chromatography. 9a is IMR standard. b. Same HPTLC profile under UV 254 nm254 283 Appendix A6 GCMS spectrum of MTG 284 Appendix A7a 1H of MTG (Aromatic Expansion region) 285 Appendix A7b 1H of MTG (Methoxy Expansion region) 285 Appendix A7c 1H of MTG (Aliphatic Expansion region) 286 Appendix A8 13C of MTG 286 Appendix A9 Stability of MTG stock solution upon storage at -20 ºC 287 Appendix A10 Existing Isolationa and purification procedures 287 Appendix B1 Medium pressure chromatography setting of CDR80 288 Appendix B2 Purification fractions and fractions containing CDR80 288 Appendix B3 UV spectrum of CDR80 289 Appendix B4 FTIR spectrum of CDR80 290 Appendix B5 CD Spectrum of CDR80 291 Appendix B6 1H NMR spectrum of CDR80 291 Appendix B6a 1H NMR – Expanded Aromatic Region of CDR80 292 Appendix B7 13C NMR spectrum of CDR80 292 Appendix B8 Dept- 90 of CDR80 293 Appendix B9 DQF-COSY- Aliphatic expansion region of CDR80 293

xxvii

Appendix B10 HSQC-Aromatic Expanded Region of CDR80 294 Appendix B11 HSQC- Aliphatic expansion region of CDR80 294 Appendix B12 HSQC- Aliphatic expansion region of CDR80 295 Appendix B13 APT 13C of CDR80 295 Appendix B14 DEPT 135 of CDR80 296 Appendix B15 DEPT- 45 of CDR80 296 Appendix B16 TOCSY full spectrum of CDR80 297 Appendix B16a TOCSY aromatic expansion region of CDR80 297 Appendix B16b TOCSY aliphatic expansion region of CDR80 298 Appendix B17 DQF-COSY full spectrum of CDR80 298 Appendix B17a DQF-COSY aromatic expansion region of CDR80 299 Appendix B17b-f DQF-COSY aliphatic expansion region of CDR80 299-301 Appendix B18 HSQC of CDR80 302 Appendix B18a-b HSQC aromatic expanded region of CDR80 302-303

Appendix B18c HSQC methoxy group of CDR80 303

Appendix B18e-i HSQC aliphatic expansion region of CDR80 304-306

Appendix B19 HMBC of CDR80 307

Appendix B20 NOESY full Spectrum of CDR80 307

Appendix B20a NOESY aliphatic expansion region of CDR80 308

Appendix B21 Result summary of MTG and CDR80 308-309

Appendix B22 HPTLC fingerprint of the CDR80 and the impurity/side product 310 Appendix C1 Medium pressure chromatography setting for CDR81 311

Appendix C2 Purification fractions and fractions containing pure CDR81 311

Appendix C3 Medium pressure chromatography setting for CDR82 312

xxviii






Appendix C9 Total Ion Chromatogram (TIC) from LC-MS analysis of (a) 50 ppm CDR81 315 Appendix C10 Total Ion Chromatogram (TIC) from LC-MS analysis of (a) 50 ppm CDR82 316 Appendix C11 Total Ion Chromatogram (TIC) from LC-MS analysis of (a) 50 ppm CDR83 317 Appendix C12 Total Ion Chromatogram (TIC) from LC-MS analysis of (a) 50 ppm CDR84 318 Appendix C13 Total Ion Chromatogram (TIC) from LC-MS analysis of (a) 50 ppm CDR81 Insets: (a) Mass spectrum and chemical structure of CDR81 319 Appendix C14 Total Ion Chromatogram (TIC) from LC-MS analysis of (a) 50 ppm CDR82 Insets: (a) Mass spectrum and chemical structure of CDR82 320 Appendix C15 Total Ion Chromatogram (TIC) from LC-MS analysis of (a) 50 ppm CDR83 Insets: (a) Mass spectrum and chemical structure of CDR83 321 Appendix C16 Total Ion Chromatogram (TIC) from LC-MS analysis of (a) 50 ppm CDR84 Insets: (a) Mass spectrum and chemical structure of CDR84 322 Appendix C17 APT 13C and 13C NMR spectrum of CDR81 323 Appendix C18 DEPT 90, DEPT 45 and DEPT 135 NMR Spectrum of CDR81 324 Appendix C19 HSQC NMR spectrum of CDR81 325

Appendix C20 HMBC for CDR81 325 Appendix C21 DQF COSY spectrum for CDR81 326 Appendix C22 APT 13C and 13C NMR spectrum of CDR82 326

xxix

Appendix C23 DEPT 135, DEPT 45 and DEPT 90 NMR spectrum of CDR82 327

Appendix C24 HSQC of CDR82 327

Appendix C25 HMBC of CDR82 328

Appendix C26 DQF COSY of CDR82 329

Appendix C27 APT 13C and 13C NMR spectrum of CDR83 Appendix C28 DEPT 135, DEPT 45 and DEPT 90 NMR spectrum of CDR83 329 Appendix C29 HSQC of CDR83 330

Appendix C30 HMBC of CDR83 330

Appendix C31 DQF COSY of CDR83 331

Appendix C32 APT 13C and 13C NMR spectrum of CDR84 331 Appendix C33 DEPT 135, DEPT 45 and DEPT 90 NMR spectrum of CDR84 332 Appendix C34 HSQC of CDR84 332

Appendix C35a-b HMBC of CDR84 (Aromatic and aliphatic expanded Region) 333-334 Appendix C36 DQF COSY of CDR83 335 Appendix C37 DSC melting point for CDR81 335

Appendix C38 DSC melting point for CDR82 336



Appendix C41 FTIR for CDR81 338




Appendix C45 FTIR characterisation of pure 6-methoxy-tetrahydro-β-carboline compounds 342-346 Appendix C46 UV spectra of CDR81 347

xxx

Appendix C47 UV spectra of CDR82 347



Appendix C50 JRES coupling for CDR83 (H-1) 349

Appendix C51 JRES coupling for CDR83 (CH3-H-1’) 350

Appendix C52 NOESY for CDR81 351




Appendix C56 Multiplicities and coupling constants of diastereostropic proton of H-3 and H-4 on CDR81, CDR82, CDR83 and CDR84 353

Appendix C57 Part of 3D crystal structure of CDR83 354

Appendix C58 Part of 3D crystal structure of CDR82 355

Appendix C59 Centro symmetry of CDR82 (Monoclinic, space group P21/C) 356

Appendix C60 Centro symmetry of CDR83 (Monoclinic, space group P21/C) 357

Appendix C61 Human Lymphocyte preparation procedures by Caputo et al. (1991) 358-360 Appendix D1 Animal Ethics Committee approval letter with reference number USM/PPSF/50 (050) Jld 361

xxxi

LIST OF PUBLICATIONS

1. Goh, T.B., Siddiqui, J., Razak, H., Mordi, M.N. & Mansor, S.M. (2011). A simple and cost effective isolation and purification protocol of MTG from M. Speciosa Korth leaves. The Malaysian J. of Anal. Sci., 15 (1): 54 – 60. (Scopus index). 2. Goh, T.B., Mordi, M.N., Mansor, S.M. & Fun, H.K. (2012a). Bis(6-methoxy-1- methyl- 2,3,4,9-tetrahydro-1H-β-carbolin-2-ium)tetrachloridozincate(II) dihydrate. ActaCrystallographica. E, 68: 464–465, [doi:10.1107/S1600536812011130]. (IF=0.35) 3. Goh, T.B., Mordi, M.N., Mansor, S.M. & Fun, H.K. (2012b).6-Methoxy-1-(4- methoxyphenyl)-1,2,3,4-tetrahydro-9H-β-carbolin-2-ium acetate.ActaCrystallographica.E, 68: o1483, [doi:10.1107/S1600536812016753].(IF = 0.35) 4. Goh T.B., Ramu,M., Mordi, M.N. & Mansor, S.M.(2013). Unexpected reduction of the indole double bond in MTG using n-butylsilane and catalytic tris(pentafluorophenyl)boranes. Synth. Comm. 44(9): 1291-1295.(IF = 1.02) [doi: 10.1080/00397911.2013.853798]. 5. Goh, T.B., Mordi, M.N. & Mansor, S.M. (2013). Demethylation of MTG picrate with BBr3 and C12H25-SH/NaOMe: A new entry for ester derivatives g preparation based on position carbon 9. Asian J. Research Chem.,6(9): 863-867.(Scopus index) 6. Goh, T.B., Mordi, M.N. & Mansor, S.M. (2015). NMR structural assignment of four new 6-methoxy- tetrahydro-β-carboline derivatives. Magnetic Resonance in Chem. In press. (IF = 1.55) 7. Goh, T.B., Mordi, M.N. & Mansor, S.M. (2014). Conformational stereoisomerism and absolute configuration of 6-methoxy-tetrahydro-β-carboline derivatives. Magnetic Resonance in Chem. In Press. (IF = 1.52). 8. Goh, T.B., Mordi, M.N. & Mansor, S.M. (2014). Mass Spectrometry (LCMS/MS) as a tool in the reaction optimisation and characterisation of new 6-methoxy- tetrahydro-β-carboline Derivatives. Sains Malaysiana. 44(1), 127-137. (IF = 0.40) 9. Goh, T.B., Mordi, M.N. & Mansor, S.M. (2014). Antioxidant value and antiproliferation efficacy of MTG and its silane reduced analogues. Asian pacific journal of cancer prevention. 15(14), 5659-5665. (IF = 1.60). 10. Goh, T.B., Mordi, M.N., Kho, R.Y., Yam, M.F., Azhar, M.E. & Mansor, S.M. (2015). 5-Methoxytryptamine reacts with natural food flavour to produce 6- methoxy scaffold ß-carbolines: In vitro investigation of their antioxidant and cytotoxicity properties. Food Chemistry. 183, 208-216. (IF = 3.30). 11 Goh, T.B., Mordi, M.N., Kho, R.Y., Yam, M.F., Azhar, M.E. & Mansor, S.M. (2014). 6-methoxy-tetrahydro-ß-carbolines induce cytotoxicity and apoptosis on colon and leukaemia cell lines Food Chemical Toxicology. In review. (IF = 3.20).

xxxii

PEMENCILAN DAN PENURUNAN SELEKTIF MITRAGININA, SINTESIS DAN PENCIRIAN TERBITAN INDOL BARU DAN KAJIAN KEAKTIFAN BIOLOGI

TERPILIH MEREKA

ABSTRAK

Mitraginina (MGT) memiliki sifat analgesik yang poten tetapi ketoksikan MGT telah

juga dilaporkan. Objektif utama tesis ini adalah untuk memencilkan MGT bagi

pengubahsuaian lanjutan struktur dan juga untuk mensintesis terbitan indolnya bagi menilai

aktiviti antiproliferatif, antioksida dan antinosiseptif masing-masing. MGT telah dipencilkan

daripada daun M. speciosa dengan menggunakan prosedur penulenan yang ringkas dan

berkesan. Pelbagai silana telah digunakan untuk menurunkan kumpulan karbonil dan ikatan

dubel indol bagi MGT tetapi hanya ikatan berkembar indol telah berjaya diturunkan kepada

indolina [CDR80 ((E)-metil 2-((2S,3S,12bS)-3-etil-8-metoksi-1,2,3,4,6,7,7a,12,12a,12b-

dekahidroindolo[2,3-a]quinolizin-2-il)-3-metoksiakrilat)]. Tindak balas Pictet-Spengler telah

diubahsuai dengan menggunakan 5-metoksitriptamina dan asid trifluoroasetik dalam medium

akueus untuk mensintesis terbitan indol yang baru yang telah dicirikan dan dikenalpastikan

sebagai CDR81 (6- metoksi-1-fenil-2,3,4,9-tetrahidro-1H-pyrido[3,4-b]indol) , CDR83 (6-

metoksi-1-metil-2,3,4,9-tetrahidro-1H-pirido[3,4-b]indol), CDR82 (6-metoksi-1-(4-

metoksifenil)-2,3,4,9-tetrahidro-1H-pirido[3,4-b]indol) dan CDR84 (2-metoksi-4-(6-metoksi-

2,3,4,9-tetrahidro-1H-pirido[3,4-b]indol-1-l) fenol). Konfigurasi mutlak C-1 telah

dikenalpastikan sebagai S dengan menggunakan analisis NMR, analisis CD (circular

dichroism) spektra dan analisis data kristal tunggal dengan merujuk kepada peraturan

keutamaan Cahn-Ingold. Empat terbitan indol baru iaitu CDR81, CDR82, CDR83 dan

CDR84 telah dinilai menggunakan pelbagai panel sel kanser manusia: HT 29, K 562,HCT

116, MCF -7, CEM SS, HEPG2, SH - 5YSY, MDA -MB- 231 dan Hela. Sebagai tambahan,

CDR80 dan MTG juga telah diuji terhadap barisan sel kanser K 562 dan HCT 116. CDR82

telah didapati paling aktif terhadap barisan sel kanser K 562 , HCT 116 dan HT29 dengan

xxxiii

selektiviti yang baik berbanding dengan barisan sel kawalan iaitu NIH/3T3 , CCD18 -Co dan

B98 -5. Di samping itu, CDR82 menunjukkan aktiviti dan selekviti yang lebih baik daripada

ubat-ubatan antikanser piawai iaitu cisplatin , asid betulinik dan 5 -fluorourasil bagi barisan

sel kanser HT29 (SI = 3.89 ), K 526 (SI = 8.71 ) dan HCT116 (SI = 5.68 ) masing-masing.

CDR81 merupakan terbitan yang kedua paling aktif, CDR83 menunjukkan aktiviti yang

lemah dan CDR84 tiada mempunyai aktiviti antiproliferatif. Terbitan indol ini telah didapati

mempamerkan ciri antioksida yang sederhana berdasarkan gabungan cerakin DPPH, ABTS

dan kuasa penurunan. CDR84 mempamerkan aktiviti antioksida yang paling aktif

disebabkan kehadiran kedua-dua kumpulan indol dan fenolik pada strukturnya sedangkan

terbitan β-karbolina yang lain tidak mempunyai kumpulan fenolik tersebut. Akan tetapi tiada

satu pun daripada keempat-empat terbitan ini menunjukkan aktiviti analgesik pusat seperti

yang dipamerkan oleh mitraginina.

xxxiv

ISOLATION AND SELECTIVE REDUCTION OF MITRAGYNINE, SYNTHESIS

AND CHARACTERIZATION OF NEW INDOLE DERIVATIVES AND THEIR

SELECTED BIOLOGICAL ACTIVITY STUDIES

ABSTRACT

Mitragynine (MTG) possesses potent analgesic properties but the toxic effects of MTG

have also been reported. The main objective of this thesis is to isolate MTG for further

structural modification and also to synthesize its indole derivatives and evaluate their

antiproliferative, antioxidant and antinociceptive activities. MTG was isolated from M.

speciosa leaves using a simple and effective purification procedure. Various silanes were

used to reduce the carbonyl and indole double bonds of MTG but only the indole double bond

was successfully reduced to indoline [CDR80 ((E)-methyl 2-((2S,3S,12bS)-3-ethyl-8-

methoxy-1,2,3,4,6,7,7a,12,12a,12b-decahydroindolo[2,3-a]quinolizin-2-yl)-3-methoxy acryl

ate)]. The Pictet-Spengler reaction was modified using 5-methoxytryptamine and

trifluoroacetic acid in an aqueous medium to synthesize new indole derivatives which were

identified and characterized as CDR81 (6- methoxy-1-phenyl-2,3,4,9-tetrahydro-1H-

pyrido[3,4-b]indole), CDR82 (6-methoxy-1-(4-methoxyphenyl)-2,3,4,9-tetrahydro-1H-

pyrido[3,4-b]indole), CDR83 (6-methoxy-1-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-

b]indole) and CDR84 (2-methoxy-4-(6-methoxy-2,3,4,9-tetrahydro-1H-pyrido[3,4- b]indol-

1-l)phenol). The absolute configuration of C-1 was determined as S using NMR analysis, CD

(circular dichroism) spectra analysis and single crystal data analysis with reference to Cahn-

Ingold priority rule. Four new indole derivatives, namely CDR81, CDR82, CDR83 and

CDR84 were evaluated on a panel of human cancer cell line namely HT 29, K 562, HCT 116,

MCF-7, CEM SS, HEPG2, SH-5YSY, MDA-MB-231 and HELA. In addition, CDR80 and

MTG were tested against K 562 and HCT 116 cell lines. CDR82 was found to be the most

active derivative, with good selectivity on the K 562, HCT 116 and HT29 cancer cell lines as

xxxv

compared to the non-tumorous cell lines of NIH/3T3, CCD18-Co and B98-5. In addition,

CDR82 showed better activity and selectivity than the standard anticancer drugs cisplatin,

betulinic acid and 5-fluorouracil on the HT29 (SI=3.89), K 526 (SI=8.71) and HCT116

(SI=5.68) cancer cell lines respectively. CDR81 was the second most active, CDR83 showed

only mild activity while CDR84 has no activity. The indole derivatives were found to exhibit

moderate anti-oxidative properties, based on a combination of DPPH, ABTS and reducing

power assays. CDR84 showed the highest antioxidant activity due to both indole and

phenolic groups in its structure whilst other β-carboline derivatives do not have the phenolic

group. However, none of these derivatives showed the central analgesic activity exhibited by

mitragynine.

xxxvi

1

Thesis Title

Comment Page Correction Page Title of the thesis needs to be improved to highlight the chemistry part, which forms a significant part of the work (Title of the thesis does not reflect the chemistry part since this thesis carries quite a lot of chemistry work).

- Thesis title has been changed to : “Isolation and selective reduction of mitragynine, synthesis and characterization of new indole derivatives and their selected biological activity studies.”

-

Table of content

Comment Page Correction Page Spelling error on overhauser.

Page xxi

Corrected xx

Wrong name on DPPH-Name should stops at “…hydrazyl”.

Page xxi

Corrected xx

Electrospray is one word. Page xxi

Corrected xxi

Include abbreviation for ESI.

Page xxii Corrected xxii

Correct term for OH is hydroxyl group.

Page xxii Corrected xxii

The correct term should be Phosphate Buffered Saline.

Page xxiii Corrected xxii

Include abbreviation for hRf (pg61).


Formatted: Indent: First line: 0.5"

2

Include abbreviation for SAR (pg 34).


SI should be Selectivity not selective.


Abtstract (Both in English and Bahasa Malaysia)

Comment Page Correction Page The English and Malay versions of the abstract need to be corrected for some wordings.

Abstrak Page xxxii-xxxiii

Abstract

Page xxxiv-xxxv

Amended Abstrak Page xxxii-xxxiii

Abstract

Page xxxivii-xxxiv

A small improvement might be suitable by mentioning how the absolute configuration of C-1 was determined.

Abstrak Page xxxii-xxxiii

Abstract

Page xxxiv-xxxv

Amended. The absolute configuration of C-1 was determined using NMR analysis, single crystal data analysis with reference to Cahn-Ingold priority rule.

Abstrak Page xxxii

Abstract

Page xxxivii Para 2 of the abstract, 2nd line Rewrite sentence to omit (:) sign.

Page xxxiv Amended Page xxxivii

3

Objective of the study

Comment Page Correction Page (i) Objective 1-Not convinced with the word

“effective”, not really development. The isolation method is quite standard. Should be on the “Isolation of mitragynine for further evaluation…..

Objectives 1 and 2 suggested to combine. (ii) Objective 2- Needs to be more specific to

synthesize all the compounds (4+1). (iii) Objective 3-To identify and characterize

(4+1). (iv) Objective 4- Add … Indole

derivatives synthesized.

53 Amended.

The study objective has been modified accordingly as suggested.

545

In the 1.9 scope of study, only reduction of indole double bonds was mentioned (p. 53). The main objective of chapter 3 is to discover a simple and mild approach to reduce the carbonyl group or the double indole bond of MTG. However, the indole double bond was reduced instead (SRMSRM). What do you want to suggest, reducing both the carbonyl group and indole double bond or merely indole double bond?

53 Amended. In the revised thesis, with reference to section, 1.9 - Objective of the study, the “reduction of the indole double bond” has been modified to “To develop a simple semisynthetic approach to reduce the isolated mitragynineTo synthesize and characterize silane reduced-mitragynine (CDR80)” to generalize the reduction process to tie in with the main objective of chapter 2 -Either to reduce the double bond or carbonyl group.

53,545&568

Formatted: Left

4

Problem Statement

Comment Page Correction Page The title “Problem statement” should change to highlight the research framework.

51 Amended 523

Chapter 1 (Introduction)

Comment Page Correction Page

Need to write the full name of a species if it is at the beginning of a sentence.

1 Amended 1

Should subtitle be changed to ‘Toxicological…’ instead of ‘Pharmacological…’ or add both?

2 Amended 2

Para 2, last line Cited ref. should be shifted to earlier sentence.

3 Amended 43

Fig. 1.2 Font size of figure is too small Should also include mitragynine with nomenclature label of carbon numbers because in the next few pages you are discussing on the different positional substituents of the indoles & their activity. And also need scientific names in their captions (eg. 6-methoxy-tetrahydro-β-

6 Amended. Font size has been adjusted, mitragynine included with nomenclature labels of carbon numbers. The compounds in figure 1.2 are mitragynine related indole alklaoids and the scientific name of mitragynine

6

5

carboline derivatives). has been included. Para 1, last line The alkaloids may not be the most potent compounds in that species or when compared to other species?

7 Amended 7

Para 2, 1st and 2nd line Please correct the IUPAC names, no space in substituents name or position number and also no hyphen before “indoles”.

11 Amended 11

Delete the hyphen before ‘Key…’. 13 Amended 13

Para 1, Last line-Rewrite sentence, Unclear.

16 Amended 16

Para 2, Line 2, Rewrite to omit colon sign :

17 Amended 17

Suggestion for clarity (1.6.1)- Please add a general reduction scheme for the reduction reaction of indole to indoline structure.

18 Amended. A general reduction scheme has been added as shown in Scheme 1.1

19

Add movement of electron i.e. the push arrows. i.e. apply to this Pictet Spengler mechanism scheme catalyzed by H+.

22 Amended. Movement of electron with push arrow has been added as shown in Figure 1.5

23

Para 2, sentence 1 - rewrite sentence construction to remove brackets.

26 Amended 27

Para 1, Last line Insert ‘ …. Hotplate method’.

27 Amended 28

Para 1, last line Replace ‘.. In this thesis’ with ‘ … of this study’.

29 Amended 30

6

Para 1, last line-correct term, need to add species and replace ‘number’ with ‘concentration’.

30 Amended 312

Give the name of the β-carboline.

38-44 Amended. Their scientific name has been given as shown in Table 1.1.

3940-46

Chapter 2 & Chapter 3

Comment Page Correction Page Include structure and reaction schemes in chapters 2 and 3.

- Reaction scheme of mitragynine to silane reduced-mitragynine has been included as shown in scheme 2.1 Structures are as shown in figures 2.3, 2.7 and 2.8.

6972,704, 758, 7881

It is suggested that chapters 2 and 3 be combined.

- Chapters 2 and 3 have been combined and the title has been changed to ‘Isolation and selective reduction of mitragynine’.

-

It is suggested that MTG extraction process need to be simplified in the form of a flow chart for clearer explanation.

- Done The MTG extraction process has been explained in text and simplified in the flow chart as shown in Appendix A 10 and Figure 2.1..

5860, 2889

7

The candidate needs to pay attention to his tendency of repeating things. Conciseness is an important element in good piece of scientific work. The same results/discussion or arguments are repeated several times, need to rectify them. Clarity needed with an improved & rectified figure presentation of the full chemical structure of all synthesized derivatives. There are lots of repetition in the methodology section (Extraction of Mitragynine). For example, the explanation in p. 59 has already been mentioned in p. 55; again the crystallization procedure mentioned on p 56 is repeated on p.60. All the procedures should be mentioned in the methodology chapter while the discussion of the results should be elaborated in a different chapter.

55-56,

59-60

Amended. Chapters 2 and 3 are combined together, revised and the repeated parts have been deleted.

-59-61

Need to define what is ‘first column’ and ‘second column’ of the flash chromatography and the mobile phase which is the eluting solvent.

60 The ‘first column’ and the ‘second column’ together with the mobile phase eluting solvent have been defined in the foot note of tTable 2.1 (Appendix A10, pp.288).

647

How did you determine the retention factor hRf? hRf is a ratio and thus should not have unit(cm) value. The number should be less than 100.

61, 63 Homologous retention factor, hRf = [(Distance between starting line and middle of substance spot)/(Distance between starting line and solvent front)]x100 as shown

61, 6769-70

8

in equation 2.1. The unit cm has been deleted in the revised thesis.

Line 2 How did you get 100 % value as in the table, it is 99 %? Check 99 % versus 100 % of purity for mitragynine.

62 Amended. The purity is 99 %

6770

Table 2.3. What are these columns 2 and 3. Different runs? Different methods?

63 Same method and run, the difference is only in the unit. (Column 2 in g and column 3 in percentage).

66-

In the characterization work using IR (pg. 64, there are two absorptions (1640 and 1704 cm-1) for the carbonyl group off the carboxyl methyl group. Do these two represent the C=O stretching of the carbonyl groups? What is the different between 2870 and 2952.9 cm-1. What do you mean by allo? Rephrase on the spectrum write up about trans double bond geometry

64 There only one absorption peak that represents the C=O stretching group at 1704.5 cm-

1. The absorption peak at 1640cm-1 represents the C=C stretching. The FTIR spectra shows the symmetry sp3 hybridised CH stretching band at 2800.0 and 2870.0 cm-1 in addition to the strong asymmetry sp3 hybridised CH stretching absorption band at 2952.9 cm-1. FTIR alone would not be able to confirm the allo structure and trans double bond geometry. Therefore the sentence of allo has been deleted

767-680-71

Line 10 needs full name of n-BS and put abbreviation terms in brackets.

67 Amended as suggested. 557

9

Para 2 1st sentence Clarify- ‘…. Without involving hydrogen’?

68 Amended as suggested 568

Need full name of SRM on title


Line 1 wrong term- Dichloromethane solution?


Line 4, Need to add details – ‘Flash’


Line 7, 12 –‘.. Mixture of..’


3.2.2.3 Need a much clearer subtitle. 69 Subtitle has been deleted in revised thesis.Amended as suggested

-63

Instrument name of HPTLC? Need to delete please refer.

70 Full instrument name of HPTLC have been added. Amended

640

3.2.2.6 What is the full terms of DSC? 70 Full term of DSC is differential scanning calorimetry. Amended.

625

3.3.1 Need to add ‘ respectively.’ after mentioning the different reducing agents


Improve the subtitle of the study : Reduction of MTG using n-BS

72 Adding in “at different reaction conditions”. Amended

703

Para 1, last sentence Explanation unclear-Rewrite in proper chemical mechanism terms

77 Amended 7780

10

Add movement of electrons i.e. the push arrows. Apply to all mechanism schemes. Either remove that or to maintain it must correct with arrow in the mechanism.

78 Amended 7881

When writing the NMR data, if a compound shows multiplet, the value should be written in range.

6577 Amended. It is triplet, not multipley.corrected

6871

Figures and numbers used for comparison in order to draw the conclusion about the efficiency of isolation of mitragynine are premature.

60-63 Figures and numbers have been amended as suggested. The developed effective method has been changed to a developed simple improved approach.

674, 669-6770

Picric acid is dangerous but it only improves purity by 1 % only?

- Other organic acid such as acetic acid, acetic anhydride yields no crystals.

-

Why do you not use HPLC instead of GCMS to analyse the compounds qualitatively

- In HPLC, compounds with the same retention time may not be the same compounds and pure standard is required for comparison. For qualitative identification, in this case GCMS, we can obtain the exact parent mass number and this serves its purpose and therefore is used instead of HPLC

-

Font size of Figure 3.1 not eligible 74 Font size has been corrected accordingly as shown in Figure 2.4

725

11

Chapter 4

Comment Page Correction Page Figures Add chiral center to all molecules synthesized

- Chiral centerre have been added to CDR81, CDR82, CDR83 and CDR84.

1325, 1347, 14851, 14952

Rationale of synthesis Add rationale on why you synthesize the 4 indole derivatives. i.e. how structure difference affects activity. This is lacking in the discussion. This can explain why some derivatives are having good activity and some are not. i.e. do explain the result in connection to the structure (Connect activity with structure-SAR).can be more comprehensive by accommodating sources in area of quantitative-structure activity

- Amended The rationale of the synthesis is based on designing the molecules with good anti-proliferative activity. Antioxidant and analgesic activity is just value added properties. The discussion on their relationship between structure and activity has been added in the text.

1831-1825

Add a statement about carbonyl activity. Do they have analgesic activity?

85 A statement about the carbonyl activity has been added.

825

Add one page to have all the molecule structure with numbers and with their IUPAC name. Don’t use ANI, VAN and etc. Use proper name for the reduced mitragynine product and adopt a numbering system for chemical compounds throughout the thesis

85 Amended SRM, BEN, ANI, ACE and VAN have been changed to CDR80, CRR81, CDR82, CDR83 and CDR84 respectively throughout the thesis. The proper name and numbering of the compounds are shown in Figure 2.7 and 3.1

758, 836

12

4.2.2 Line 5, Need to add in the actual method name, flash chromatography.

87-90 Amended 859-8892

Line 3 insert ‘Mobile phase solvent. 88 Amended 859-8892

Add equation/scheme accordingly for each product synthesized. Where are all your chemical structures for the respective desired products/ Scheme of reaction equations.

87-89

Chemical reactions scheme (Scehme 3.1-3.4) for CDR81, CDR82, CDR83 and CDR 84 have been added to the methodology part of Chapter 3 in revised thesis.

859-8892

Add a reaction scheme for the similar reaction from literature.

94 Chemical reaction scheme for Pictet-Spengler reaction between tryptophan and aldehyde has been added as shown in scheme 3.5

947

Did you check the right chemical structure database ‘.. Cam Spider.?’

96 Amended 958

Fig. 4.16 Wrong structure for ANI and ``VAN (Both looked like BEN).

134 Amended 1325

Para 2 Line 3-Perhaps useful to refer to chemical structure of Fig 3.4, pg. 78

154 Amended 1527

Para 2 lines 6 & 10. Need to set up equations with designated eq. numbers and define terms.

156 Amended 1547-1558

5.2.2.1.5 line 2 Insert ‘.. and SRM respectively..’

157 Amended 1558

Line 1-3 discrepancy with values of Table 5.1-All wrong values inserted in statement.

159 The wrong values in the discussion statement have been corrected accordingly as what

157-15860

Formatted Table

13

is listed in table 4.1.

Para Line 4 ‘..of MTG-related analogues (Fig 5.1).’ Actually was it ‘… MTG and its SRM analogues…’??

160 Amended 15861

Chapter 5

Comment Page Correction Page Para 2 Either add chemical structure or mention the figures we need to refer to

153-154 The structure-activity relationship of β-carboline derivatives for anti-tumor has been has been revised to refer to Figure 1.7 on page 356 and Figure 2.87 on page 7581.

1514-1525

Explain briefly about apoptosis & necrosis.i.e. add advantage.

163 Apoptosis advantage has been added and amended.

1614

Don’t over claim –“Potent lead compounds for the development of future cancer therapeutics”.

163 The sentence has been modified accordingly

1614

14

Chapter 6

Comment Page Correction Page Revise some of the captions. Captions must be concise, specific and stand alone

164-165,

184-187

Captions have been simplified and revised accordingly.

1625-1636, 1847-18790

Fig 6.1. Draw full proper structures, relevant for pg. 181-182 discussions. Correct the structure of Fig. 6.1. The double bond missing

169 Full proper structures of CDR81, CDR82, CDR83 and CDR 84 have been drawn and shown in Figure 5.1 for the relevant discussion on structure and activity on page 1815-182.6

16770

Line 2(6.2.1) and Line 1 (6.2.3)-Insert ‘… and VAN respectively.’

170-171 Amended 16871, 1703

Table 6.1 use smaller font size to accommodate column

175 Corrected as shown in Table 5.1

1747

Table 6.4 Column 1-compound names?

179 Corrected as shown in Figure 5.1

17881

Para 2 Wrong chemical substituent designation? Last sentence-‘…. The hydroxyl methoxy group at VAN…’??? -did you mean methoxyphenol of VAN?

182 Amended 1814

Para 3 last sentence-Explanation is unclear. Need to rewrite.

182 Amended 1814

Line 5-‘.. Both compounds…’ So which compounds are these?

188 Amended 18891

15

Efficiency based on what? Is it SI or IC50. 194 Amended. The efficiency is based on IC50

1947

Chapter 7

Comment Page Correction Page Line 4. So, what is the role of those mineral acids?

198 The mineral Acids serve as catalyst.

197200

Last sentence, rewrite. Wrong term used?-‘.. the derivatives may inherit…’

198 Amended 198 (Line 14-17)201

IC50 value exhibited by of the compounds in the antioxidant assays especially the DPPH assay indicates that they are not active. Check calculation for concentration for IC50 in the antioxidant assay.

212 & 213 The concentration for IC50 is in μM, not mM and has been modified accordingly.

2134-2146

Check the unit of the compound concentration.

207 & 210 Amended. It is in μM. 208, 21210 & 2133

Scale of DPPH activity (Figure 7.2). 211 Scale of DPPH activity has beend modified accordingly as shown in Figure 6.2

2124

Change the labeling of Figure 7.4. 215 Labeling has been changed accordingly as shown in Figure 6.4

2168

16

Chapter 8

Comment Page Correction Page Last sentence-how has the dosage range been chosen? Add the rationale of the dose selected, meaning how the dose was calculated.

226 The rationale of the dosage range selection is based on LD50 of the mitragynine which is 1098 mg/Kg (Sabetghadam et al., 2013b), and according to the OECD guidelines about 10 times lower is used as ceiling limit of the testing dosage, as revised in thesis.

22830

Based on Table 8.1, pg. 229- only 3, not 5 different dose were studied as mentioned in line 13 (Pg. 227).

227 & 229 Amended 22832 & 2313

17

Chapter 9

Comment Page Correction Page For e.g Correlate and postulate whether R is important or not for respective activity. If R is not important for activity, which part of the molecule causes activity.

245-246 Postulation of R (Substituents at C-1) for respective activity has been revised.

a) Anti-Proliferation activity-1830-1825, 2479

b) Analgesic activity-2446-2457, 24850

c) Antioxidant activity-21920-2213, 24850

Line 1-Is this synthesis method has been done beforea novel step?

234 The word ‘modified’ has been added to the text. The product Synthesized (CDR81, CDR82, CDR83 and CDR 84) is new as published in Goh et al., 2015a and Goh et al., 2015b. These new products were synthesized using modified Pictet-Spengler reactions. [Please refer list of publications No. 6 and No. 10]

234-

General Discussion and Conclusion

Comment Page Correction Page General Discussion and Conclusion too long and

- Conclusion separated from general discussion. Done.

-

18

repetitious, Separate the conclusion.

References

Comment Page Correction Page Some book sources need range of page number in their bibliographies. Year of journal not to be repeated.

250, 253, 261, 267, 271, 273, 277 and 278

Amended. The page numbers of the reference book have been added.

2524, 2557, 2635, 26971, 2745, 275, 279, 2807 and

2812

Some formatting & typing errors in bibliography and citation (ie pg. 196).

196 The errors have been corrected.

196201

Appendices

Comment Page Correction Page Correct Appendix A3. Add the molecular structure of mitragynine

280 Corrected 2834

Appendix A5 caption a

Path 9b instead of 9a for fraction 4?

281 Amended 2845

Formatted: Underline

19

Check structure of mitragynine placed on spectra in appendices.

280,283,284 Done. 2834,2867,2878

Indicate & Clarify i.e add solvents.

284 Amended 28790

Update the list of publications 357 The list of publications has been updated accordingly.

3633

1

CHAPTER 1

INTRODUCTION

1.1 Chemistry of mitragynine (MTG)

Mitragyna speciosa Korth (ketum) is widely recognised in Southeast Asia as a

unique medicinal plant because of its opioid-like effects. As the principal indole alkaloid

from M. speciosa, mitragynine (Figure 1.1) is effective in the treatment of diarrhoea,

intestinal infections, muscle pain and to reduce coughing (Suwanlert, 1975; Jansen and

Prast, 1988a; Watanabe et al., 1997; Vicknasingam et al., 2010) although it is an illegal

and controlled substance (Adkins et al., 2011). It has also been used as a tonic to

improve work performance and as an alternative to opium (Burkill and Haniff, 1930;

Burkill, 1935; Suwanlert, 1975; Apryani et al., 2010). Mitragynine (MTG) is the main

alkaloid derived from M. speciosa. It has a molecular formula of C23H30N2O4 and a

molecular weight of 398.50. Mitragynine has a melting point range of 102-106 ºC and

boiling point of 230-240 ºC (Jansen and Prast, 1998). It is soluble in chloroform, alcohol

and acetic acid. It has UV absorbance with lambda maximum of 254nm due to

conjugated indole rings (Jansen and Prast, 1988) and is stable in plasma upon storage for

at least 2 days at room temperature and up to 1 month when stored at −20 °C

(Parthasarathy et al., 2010).

2

N

CH3

O CH3

O

O

CH3

OCH3

NH H

H

A CB

D

9

H

Figure 1.1 Structure of mitragynine (MTG).

1.2 Toxicological and pharmacological effects of MTG

Macko et al. (1972) found no evidence of toxicity when the evaluation measured

as tremors or convulsions in dogs at doses as high as 920 mg/kg. Sabetghadam et al.

(2013a) demonstrated that MTG is relatively safe at lower sub-chronic doses (1–

10mg/kg) but exhibited toxicity at the highest dose of 100mg/kg (sub-chronic: 28 days)

in rats. The lethal effects of 200 mg/kg total alkaloid extract of M. speciosa and oral

dose of 200 mg MTG were reported recently in rats (Janchawee et al., 2007; Azizi et al.,

2010). The acute oral LD50 toxicity levels in mice for methanolic and alkaloid extracts

of M. speciosa were reported as 4.90 g/kg and 173.20 mg/kg respectively (Reanmongkol

et al., 2007). In addition, Sabetghadam et al. (2013b) found that the oral lethal dosage,

LD50, of pure MTG was 1098 mg/kg. MTG has been reported to cause less respiratory

depression in animal models as compared to other narcotics (Jansen and Prast, 1988).

3

Sabetghadam et al. (2013a) discovered significant reduction of relative body weight and

food intake in female rats when treated with 100mg/kg dose of MTG. Alterations in

biochemical and hematological parameters, together with histopathological changes

were observed especially in the high dose (100 mg/kg) treatment group.

Acute oral administration of standardized methanolic extract of M. speciosa did

not affect spontaneous motor activity, or food and water consumption in rats. The

methanolic extract, however, led to a significant increase in alanine transaminase (ALT)

and argininosuccinate lyase (ASL) (Harizal et al., 2010; Kapp et al., 2011).

Nephrotoxicity was seen only at a 1000 mg/kg dose as evidenced by elevated creatinine

levels. A histological examination showed the congestion of sinusoids, hepatocyte

haemorrhage, fatty change, centrilobular necrosis and increased number of Kuppfer cells

in the liver. However, an acute treatment with the methanolic extract (100, 500 and

1000 mg/kg doses) did not induce damage in the axons and dendrites of hippocampal

neurons (Harizal et al., 2010).

Chronic M. speciosa users suffered anorexia, weight loss, hyperpigmentation,

psychosis, constipation, insomnia, fatigue, poor concentration and hypothyroidism

probably due to its suppression effect on thyroid-stimulating hormones (Suwanlert, 1975;

Vicknasingam et al., 2010). Besides, M. speciosa users have been reported to experience

nausea, vomiting, and diarrhoea with occasional reports of nystagmus and tremor

(Grewal, 1932). Roche et al. (2008) reported the case of a 32-year-old male who was

found having seizure-like movements and mouth-foaming. These movements persisted

despite the person being given benzodiazepine treatment and intubation.

4

Seizures and coma have been reported in humans when ketum extract was

consumed and used whether it being for pain management, in combating opioid

withdrawal symptons or as a recreational drug (Chan et al., 2007; Nelson et al., 2010;

Vicknasingam et al., 2010). MTG is extensively metabolized in rat and human liver via

phase I (hydrolysis and dealkylation) and II (conjugation to glucuronides and sulphates)

reactions (Philipp et al., 2009). The MTG elimination half-life in rats was found to be

approximately 4–9 h after a single dose (Janchawee et al., 2007). Parthasarathy et al.

(2010) found that MTG has a mean half-life of 2.9±2.1 h after intravenous

administration. Furthermore, Parthasarathy et al. (2010) has shown MTG has poor

calculated absolute oral bioavailability of merely 3.03 % probably due to its poor

aqueous solubility. Seizures were observed at very low doses (10 mg/kg) whilst

convulsions were evident at a very high dosage (920 mg/kg) (Reanmongkol et al., 2007).

MTG demonstrated cytotoxic effects in vitro in human neuronal cells but toxicity

could be lessened by using naloxone, an opioid antagonist. However, no genotoxicity

was found in the mouse lymphoma gene mutation assay (Saidin et al., 2008; Saidin,

2008). There was also no mutagenic activity using the Ames test in the presence and

absence of metabolic activator S9 systems (Ghazali et al., 2011). The aqueous M.

speciosa extract shows strong antimutagenic properties.

In summary, the various case studies on animals and humans suggest potentially

toxic and lethal effects of M. speciosa preparations. The reasons are either due to long

term consumption and accumulating effects or an acute overdose (Hassan et al., 2013).

Therefore, the need for new analogues which possess good pharmacological activity and

less toxicity has arisen and this is one of the rationales of the study in this thesis.

5

1.3 Other indole alkaloids of mitragynine (MTG)

The total alkaloid content in the M. speciosa leaves was in the range of 0.5% -

1.5% (Shellard, 1974). Mitragynaline, corynantheidaline, mitragynalinic acid and

corynantheidalinic acid were discovered as new types of alkaloidsfrom Malaysian M.

speciosa (Houghton et al., 1991). Other minor constituents found in mature leaves

included mitragynaline, pinoresinol, mitralactonal, mitrasulgynine, 9-

methoxymitralactonine and mitralactonine and 3, 4, 5, 6-tetradehydromitragynine

(Takayama et al., 1998). Nine corynanthe-type indole alkaloids namely MTG,

speciogynine, speciociliatine, paynantheine, 7-hydroxymitragynine, mitragynaline,

corynantheidaline, corynantheidine and isocorynoxeine were isolated from the leaves

(Takayama et al., 2004) (Figure 1.2). 7-Hydroxyspeciociliatine was another indole

alkaloid found in M. speciosa fruits (Kitajima et al., 2007). Two major metabolites:

mitragynine pseudoindoxyl and 7-hydroxymitragynine, were obtained from microbial

transformation (Zarembo et al., 1974) (Figure 1.2).

6

N

CH3

O CH3O

OCH3

OCH3

NH

Mitragynine Pseudoindoxyl

O

H

N

CH3

O CH3O

OCH3

OCH3

N

7-Hydroxymitragynine

OH

H

N

CH3

O CH3O

OCH3

OH

NH

9-Hydroxycorynantheidine

H

9 9

9

N

CH3

O CH3O

OCH3

NH

Corynantheidine

H

9

H

H

N

CH3

O CH3O

OCH3

OCH3

N

Speciociliatine

H

9

N

CH3

O CH3O

OCH3

OCH3

N

Speciogynine

H

9

N

CH3

O CH3O

OCH3

OCH3

N

7-Hydroxyspeciociliatine

H

9 OH

N

CH2

O CH3O

OCH3

OCH3

N

Paynantheine

H

9

N

CH3

OCH3

N

Mitragynaline

9

O

CH

O

CO O CH3

NN

(-)- Mitralactonine

9

CH3

O

OO

O O CH3

Isocorynoxeine

9 HN

O

N

CH2

O

OCH3

N

CH3

O CH3O

OCH3

OCH3

NH

4-Quinolone derivative of mitragynine

H

9

O

N

CH3

O CH3O

OCH3

OCH3

NH H

H

A CB

D

9

H

8

13

10

1211

76

5

43

1819

21

201514

22

1617

2

1

Mitragynine (MTG)

CH3

Figure 1.2 Mitragynine [(E)-methyl 2-(3-ethyl-8-methoxy-1,2,3,4,6,7,12,12b- octahydroindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate] related indole alkaloid.

7

Major indole alkaloids of young leaves of Thai M. speciosa are MTG (66%),

paynantheine (9%), speciogynine (7%), 7-hydroxmitragynine (2%), and speciociliatine

(1%) in which the relative composition varies greatly according to the geographical

region and the season (Takayama et al., 2004) (Figure 1.2). Of the above mentioned

alkaloids, MTG, paynantheidine, speciogynine, corynantheidine and 7-

hydroxmitragynine are known to be pharmacologically active (Takayama et al., 1998;

Takayama et al., 2002; Matsumoto et al., 2004; Takayama et al., 2004). MTG possesses

analgesic, antitussive, antidiarrheal, adrenergic and antimalarial activities whilst

paynatheidine and speciogynine act as smooth muscle relaxants. With 66 % of the total

alkaloid mixture, MTG is the main active alkaloid present in M. speciosa leaves that

triggers opioid agonistic activity though it may not be the most potent psychoactive

component when compared to other species (Grewal , 1932; Suwanlert, 1975; Shellard,

1989; Takayama et al., 2002; Takayama et al., 2004).

1.4 Structure and opioid agonist activity of mitragynine-related indole derivatives Opioid agonistic activity is defined as the inhibition of the twitch contraction,

which is reversed by the opioid antagonist naloxone. The opioid agonistic activities of

the natural analogues of MTG and semisynthetic MTG derivatives were evaluated in

guinea pig ileum contraction induced by electrical stimulation. MTG inhibited the twitch

contraction, induced by electrical stimulation in a concentration-dependent manner,

which was reversed by the addition of naloxone. However, the potency was one-fourth

that of morphine.

8

Takayama et al. (2002) found that corynantheidine (Figure 1.2) without a

methoxy group at C-9 position (9-demethoxy analogues of MTG) lost agonistic activity

in guinea pig ileum preparation when investigating the relationship between opioid

agonist activity and the structure of indole alkaloids. This finding has indicated that the

methoxy group on C-9 in the MTG indole ring is essential for eliciting analgesic activity

(Takayama et al., 2002). Corynantheidine did not show any opioid agonistic activity but

had reversed the morphine-inhibited twitch contraction in guinea pig ileum. Takayama

et al. (2002) later discovered that corynantheidine has a selective opioid antagonistic

property on µ-opioid receptors based on receptor binding assays. Its antagonistic effect

was in a concentration-dependent manner. These results suggest that corynantheidine

inhibits the effect of morphine through functional antagonism of opioid receptors.

Another analogue of MTG, 9-hydroxycorynantheidine (Figure 1.2), demonstrated

inhibition on electrically induced twitch contraction in guinea pig ileum, but its

percentage of maximum inhibition was less than that of MTG indicating lesser potency

(Takayama et al., 2002). Thus, it is suggested that 9-hydroxycorynantheidne is a partial

agonist of opioid µ-receptors based on receptor binding assay. Put together, it is an

interesting finding showing a shift in activity from full agonist via partial agonist to that

of an antagonist on opioid receptors when there is a fine transformation of the functional

group on C-9 from OCH3 (methoxy) to OH (hydroxy) or to H. Hence, it is found that the

functional group on C-9 of mitragynine-related compounds determines the relative

opioid agonistic activity (Takayama et al., 2002). On the other hand, the replacement of

the methoxy functional group by the ethoxy and propoxy groups at C-9 on the indole

ring resulted in the reduction in both intrinsic opioid agonistic activity and the potency

9

as compared with those of MTG (Takayama et al., 2002). These results suggest that the

methoxy group at the C-9 position determines its intrinsic compound activities on the

opioid receptors and is the most suitable functional group for pharmacophore binding to

opioid receptors (Takayama et al., 2002). In summary, although MTG derivatives

possess basic skeleton which are completely different from that of morphine, they

exhibit potent agonistic properties on opioid receptors in guinea pig ileum. The

structural functions of methoxy group at position C-9 of the indole ring of the

Corynanthe type indole alkaloid skeleton essentially contribute to the opioid agonistic

activity (Takayama et al., 2002). By altering the functional group at the C-9 position,

e.g., OCH3 > OH > H, of MTG, the activities of the compounds dramatically shifted

from that of full agonists through partial agonists to that of antagonists on opioid

receptors (Takayama et al., 2002).

Speciociliatine (Figure 1.2), which is a minor constituent of M. speciosa, is the

C-3 stereoisomer of MTG which takes a folded cis-quinolizidine conformation in the

C/D-ring junction. The potency of this compound towards opioid receptors was 14-fold

weaker than that of MTG in the guinea pig ileum test, indicating that the flat trans-

quinolizidine form of MTG was a more efficient conformation for exhibiting opioid

agonist activity than the folded cis form of speciociliatine. Besides, the 4-quinolone

derivative (Figure 1.2) retained almost the same opioid agonistic activity as that of MTG

(Takayama et al., 2002) in the guinea pig ileum test.

The oxidized derivatives of MTG (mitragynine pseudoindoxyl and 7-

hydroxymitrgynine) (Figure 1.2), exhibited a higher opioid agonist potency than MTG

in the guinea pig ileum contraction test. The 7-hydroxymitragynine which showed full

10

agonistic intrinsic activity on opioid receptors was found to exhibit approximately 13

and 46 times higher potency than those of morphine and MTG respectively. The

introduction of a hydroxyl group at the C-7 position led to higher potency as compared

with that of MTG. 7-hydroxymitragynine tended to show higher selectivity and affinity

for µ receptors than that of MTG. However, the introduction of a methoxy or an ethoxy

group at the C-7 position led to a dramatic reduction in both intrinsic activity and

potency for opioid receptors. It is concluded that the presence of the hydroxyl

functional group at the C-7 position in MTG is essential for its improved potency

towards opioid receptors.

1.5 ß-carbolines derivatives

The de novo synthesis of MTG suffered the setback of having too many reaction

steps (more than 22) and low yields (3-13 %) (Takayama et al., 1995; Ma et al., 2007;

Ma et al., 2009; Isabel, 2012). In addition, it requires a laborious purification process in

order to obtain pure MTG. Therefore, total synthesis of mitragynine for further structure

modification to obtain new analogues is not the objective of this thesis. 6-Methoxy-

tetrahydro-β-carboline derivatives (Figure 1.3a) were chosen as targeted synthesized

compounds since they resemble intermediate products in the total synthesis of MTG,

trans-tetrahydro-β-carboline, as shown in Figure 1.3b (Takayama et al., 1995; Ma et al.,

2007; Ma et al., 2009, Isabel, 2012). Furthermore, it is interesting to explore whether

tetrahydro-β-carboline compounds possess similar analgesic or other useful biological

activities as for mitragynine-related compounds. The Pictet-Spengler reaction mediated

cyclization which served as an important key step in the total synthesis of MTG, is used

11

with modification, for the synthesis of 6-methoxy-tetrahydro-β-carboline in this study.

The synthesis in this thesis for 6-methoxy-tetrahydro-β-carboline derivatives envisions

much simpler reaction schemes with just a one pot reaction step. Therefore, the product

yields are expected to be higher compared to that of the reaction involving many steps

(Takayama et al., 1995; Ma et al., 2007; Ma et al., 2009, Isabel, 2012).

Tetrahydro-ß-carbolines (tetrahydro-pyrido(3,4-b)indole) and ß-carbolines

(pyrido(3,4-b)indole) are naturally-occurring indole alkaloids with a β-carboline nucleus

(Figure 1.3a and Figure 1.3b). They exhibit a broad range of potent pharmacological and

biological activities (Patel et al., 2012). The reported pharmacological effects of this

class of compounds comprise of antitumor, antiparasitic, antineoplastic (tubulin binding),

anticonvulsive, hypnotic and anxiolytic, antiviral, antimicrobial as well

as topoisomerase-II inhibition, cGMP-dependent processes inhibition and

antiplasmodial activity (Hamsa et al., 2011,; Frost et al., 2011; Patel et. al., 2011). They

may have other endocrinological functions especially 6-methoxytetrahydro-β-carboline

derivatives (e.g. pinoline, an example of endogeneous β-carboline), which will be

synthesized and studied in this thesis.

12

NH

Pinoline (Endogeneous β-carboline)

H3CO

NH

Melatonine (Endogeneous β-carboline)

H3CO

NH

NH

N

CH3

Harman

NH

N

CH3

O

Harmine

NH

N

O

Harmaline

NH

N

Norhaman

NH

N

Harmalan

HN

O

Figure 1.3a Structures and common name of some β-carbolines.

13

NH

N

CO2Bn

OMe

H

I

CO2CH3

trans-tetrahydro-b-carboline (a,b-unsaturated ester), Key intermediate in mitragynine total synthesis

NH

N

O

OH

CH3

1-methyl-1,2,3,4-tetrahydro-b-carboline-3-carboxylic acid

NH

NH

O

OH

CH2H3C

1-methyl-2,3,4-tetrahydro-b-carboline-1-vinyl-3-carboxylic acid

NH

NH

O

OH

OHH3C

O1-methyl-2,3,4-tetrahydro-b-carboline-1,3-dicarboxylic acid

1

1

1

1

3

3

3

3

2

2

2

2

45

4

4

4

5

5

5

Figure 1.3b Structures and IUPAC Scientific name of some β-carbolines.

14

On the other hand, tetrahydro-ß-carbolines (tetrahydro-pyrido (3, 4-b)-indole)

such as harmine and harmaline are central nervous system stimulants and act as

selective but reversible inhibitors of MAO-A (RIMAs) (Santos et al., 2011; Santos et al.,

2012) that are similar to tyramine-containing foods, as compared to synthetic MAOIs

such as phenelzine (Pardo et al., 2012). RIMAs help to replenish the body's supply of

monoamines by slowing the breakdown of neurotransmitter and are used

as antidepressants. Some examples are moclobemide, tranylcypromine, selegiline and

phenelzine. The monoamines include neurotransmitters (serotonin, dopamine) and

hormones (melatonin) (Santos et al., 2011; Santos et al., 2012). Harmine and harmaline

can be safely consumed together with foods containing tyramine such as wine and aged

cheese since they are RIMAs and they do not bind permanently to MAO (Pardo et al.,

2012). Therefore, tyramine would be competing with harmaline for binding site on the

MAO-A enzyme. Harmala alkaloids (alkaloids from Perganum harmala including

harmine and harmaline) have been used to treat Parkinson's disease and essential tremor

since they are benzodiazepine inverse agonist (Sourkes, 1999).

The BZRs (benzodiazepine receptors) in mammalian CNS (central nervous

system) are known to mediate anxiolytic, anticonvulsant and sedative action. ß-carboline

alkaloids are non-benzodiazepine antagonists that have been discovered to bind with

high affinity to the BZRs and shown to antagonize the principle pharmacological actions

of benzodiazepine. For example, 3-(ethoxycarbonyl)-ß-carboline and 3-

(methoxycarbonyl)-ß-carboline are benzodiazephine antagonists that block the BZRs

and exhibit opposite effects as to those of benzodiazepines in various animal behaviour

models (Cao et al., 2007). Although pinoline (an endogeneous β-carboline) does not

http://en.wikipedia.org/wiki/Antidepressants

15

have any affinity for the BZRs, significant anxiogenic, anticonvulsive and

antidepressant properties of pinoline have also been found in some animal models at

pharmacological dosage. These findings have suggested that the neuropharmacological

effects of pinoline involve non-BZRs interaction mechanisms (Mcisaac, 1961; Mcissaac

et al., 1961; Squires et al., 2004).

ß-carbolines molecules cause various side effects on the CNS including

hallucinations, tremors, anxiety, anxiolytic, convulsions, anticonvulsant and sedation

(Riba et al., 2001). Oral or intravenous harmine doses ranging from 30–300 mg have

been reported to cause agitation, tachycardia, blurred vision and hallucinations. These

pharmacological effects are partially due to the interaction of the ß-carboline molecules

with various receptor systems in the mammalian CNS, such as 5-HT receptors and

BZRs (Giorgio et al.,2004; Cao et al., 2007). Both harmine and harmaline have been

proven to act as acetyl cholinesterase inhibitors that stimulate striatal dopamine

secretion in rats at high dose, thereby causing hallucinogenic effects in humans (Patel et

al., 2012, Geyer and Franz, 2012). However, a lower dose (25-50 mg) indicates CNS

stimulation, increases mental activity and produces a pleasant dreamy state for several

hours. Whereas a higher doses (200-750 mg) cause the hallucinogenic effects. Harmine

also causes some hallucinogenic effects at a dose of 150-200 mg via intravenous

administration in humans (Riba et al., 2001; Cao et al., 2007; Santos et al., 2011; Santos

et al., 2012 ). However, harmaline has been found to be hallucinogenic at doses greater

than 1mg/kg after intravenous administration. In fact, harmaline is also orally active at a

dose of 4mg/kg. Tetrahydroharmine has been reported to induce hallucinogenic effects

at 300mg (Cao et al., 2007).

16

In addition to this, 6-methoxyharmalan produces hallucinogenic effects and

induces modest psychoactive action at oral doses of 1.5mg/kg (Cao et al., 2007; Geyer

and Franz, 2012). The harmala alkaloids are psychoactive in humans at oral doses of

25-750 mg. Noticeable classic hallucinogens are thought to produce psychoactive

effects via interaction with 5-HT2 serotonin receptors in the brain (Cao et al., 2007).

However, so far, it has been inconclusive as to whether the ß-carboline alkaloids elicite

hallucinogenic actions in a similar way to classical hallucinogen. It seems that the 6-

methoxyl moiety contributes to hallucinogenic effects of the compounds and higher

conjugation in the tricyclic rings produces higher hallucinogenic effects (Geyer and

Franz, 2012).

Interestingly, ß-carboline alkaloids have been demonstrated to play a crucial

role in the processes of substance abuse and dependence (Cao et al., 2007). Cappendijk

et al. (1993b) has reported that norharman produces prominent inhibitory effects on the

naloxone-precipitated withdrawal syndrome in morphine dependent rats. Besides, high

plasma levels of harman and norharman have been found in chronic alcoholics and

heroin dependent humans. Chronic infusion of harman increases voluntary ethanol

intake in rats and rapid discontinuation of these MAO inhibitors can cause a serious

withdrawal syndrome. Aricioglu-Kartal et al. (2003) has reported that harman and

harmine have some beneficial effects on naloxone-precipitated withdrawal syndrome in

rats, and harmine is more effective than harman in reducing the signs of morphine

withdrawal syndrome. The use of β-carbolines has an advantage over the conventional

treatment approach based on the alleviation of drug withdrawal symptoms (Howard et

al., 1997). This group of compounds provides an alternative and effective approach to

17

interrupting and attenuating the consumption and craving for drugs such as heroin,

fentanyl, methadone, codeine, opium, nicotine, amphetamine, caffeine and their

combinations which upon ingestion or administration, leads to addiction. These have

been shown to be intractable to treatment by other reagents (Howard et al., 1997).

Currently, researches have confirmed the effects of numerous ß-carboline and

tetrahydro-ß-carbolines alkaloids of norharman, harman, harmine, harmaline, harmalan

on the CNS and their affinity with BZRs and 5-HT receptors (Cappendijk et al., 1993a;

Cappendijk et al., 1993b; Yin et al., 2010). They are able to bind to GABA and I2

(Imidazoline) receptors. These compounds might function as mild neuromodulators via

inhibition effects on MAO, monoamine uptake and benzodiazepine receptor binding.

Simultaneously, they have been increasingly studied in relation to alcoholism, where

they might play a role in alcohol addiction either in etiological or in pathological states

(Cappendijk et al., 1993a; Yin et al., 2010). Harmaline causes no known physical or

psychological dependence. Howard et al. (1997) describes a method for treating various

chemical dependencies via the administration of harmaline and other ß-carbolines.

Surprisingly, it has been discovered that the β-carboline alkaloids are effective in the

treatment of chemical dependency disorders, abuse syndromes or their combination in

mammals (Howard et al., 1997).

Collins and his co-workers (1985 and 2009) have reported that N-methylated

tetrahydro-ß-carbolines and ß-carbolines can be bioactivated to give endogenous

neurotoxins. 1-Methyl-1,2,3,4-tetrahydro-ß-carboline-3-carboxylic acid is a precursor of

mutagenic N-nitroso compounds and shows cytogenetic effects, and can cause neuronal

cell death. Some ß-carbolines might act as co-mutagenic substances, precursors of N-

18

nitroso compounds, and toxic compounds (Jing et al., 2014). Harmaline has both

protective and toxic effects on neurons (Lee et al., 2000). A single injection of

harmaline at 40 mg/kg in rats has very visible neurotoxic effects. The prototypic β-

carboline, 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid detected in some

food items, is the possible causative substance of the eosinophilia-myalgic syndrome

(Pari et al., 2000). Some of the β-carbolines have been shown to be phototoxic to

bacteria and insects and this might correlate with their ability to produce reactive

oxygen species upon irradiation (Richard et al., 2008). ß-carbolines are DNA

intercalating agents and DNA enzymes inhibitors which exhibit toxic and mutagenic

effects either in prokaryotic or eukaryotic cells (Pari et al., 2000).

1.6 Synthesis

1.6.1 Reduction of indole to indoline

Lloyd and Gordon (2009) developed an efficient method of chemically reducing

indole to indoline by using zinc dust and 85% phosphoric acid without polymerization.

It has been reported that an efficient, palladium-catalyzed reduction of N-(tert-

butoxycarbonyl) indoles gives N-(tert-butoxycarbonyl) indolines in good yields, in the

presence of polymethylhydrosiloxane (PMHS) as a reducing agent at room temperature

(Chandrasekhar et al., 2006). A Brønsted acid catalyzed the process of transfer

hydrogenation of indole derivatives with Hantzsch dihydropyridine as the hydrogen

source enables an efficient synthesis of various optically active indolines with high

enantioselectivities (Rueping and Antonchik, 2010). Sodium borohydride (NaBH4) in

neat carboxylic acids sequentially reduces the indole double bond and alkylates nitrogen

19

atoms to produce N-alkylindolines (Gribble, 1998). An environmentally benign

procedure for the hydrogenation of unprotected indoles is described by Aditya et al.

(2011). The hydrogenation reaction is catalyzed by platinum on activated carbon and

accelerated by p-toluenesulfonic acid in water as a solvent. The efficacy of the method is

illustrated by the hydrogenation of a variety of substituted indoles to their corresponding

indolines which were obtained in excellent yields (Scheme 1.1).

NH

RR'

NH

RR'Pt/C, H2, HA, H2O

rt, 10-50 bar, 3h

Scheme 1.1 Reduction of indole to indoline using platinum on activated charcoal as catalyst.

Borane-tetrahydrofuran (THF) in trifluoroacetic acid produces acid-stable

H[OC(O)CF3]2.THF and constitutes a convenient, rapid, high yield method for the

selective reduction of indoles to indoline in the presence of other functional groups

(Bruce and David, 1978). Sodium cyanoborohydride in acetic acid or sodium

borohydride in trifluoroacetic acid only reduces the double bond of indole to give

indoline (Yatendra and Lennart, 1983). Tetrakis (dimethylamino) ethylene (TDAE), has

been exploited for the first time as a mild reagent for the reduction of arenediazonium

salts to aryl radical intermediates through a single electron transfer (SET) pathway.

Cyclization of the aryl radicals produced in this way has led, in appropriate substrates, to

the synthesis of indolines and indoles. There is also a report regarding cascade radical

cyclizations of aryl radicals that are derived from arenediazonium salts. The relative

ease of removal of the oxidized by-products of TDAE from the reaction mixture makes

20

the methodology synthetically attractive (Mohan et al., 2009). A method of reducing

indole compounds to the corresponding indoline compounds substantially to be free of

undesirable side reactions involves contacting an indole compound with a borane

complex reagent, dioxyborane, in the presence of trifluoroacetic acid. This method is

instantaneously and readily carried out and provides an excellent method for preparing

certain indoline compounds from the corresponding indole compounds.

1.6.2 Total synthesis of tetrahydro-β-carbolines via Pictet-Spengler reaction

Modification of the Pictet-Spengler reaction since its invention in 1911 has

provided better enantiomeric purity, diastereo-selectivity, simplicity, shorter reaction

time and higher yields. The modification process also includes the use of different types

of catalysts, reactants, reaction mediums and conditions (Pedro et al., 1990; Mark and

Eric, 2004; Tschantz, 2012; Paresh et al., 2013). Bing and Anthony (2002) have

designed a modified microwave method using solid wang resin with 1 % TFA in

toluene as a catalyst to shorten the reaction time at room temperature significantly from

days to minutes with a high yield (> 80 %). Furthermore, tetrahydro-ß-carboline exhibits

a broad spectrum of potent biological activities (4). Therefore, a simple and mild Pictet-

Spengler procedure has been designed to produce the 6-methoxy-tetrahydro-ß-carboline

which contains no carbonyl group.

The Pictet–Spengler reaction, as depicted in Figure 1.4, is a special case of

Mannich reaction in which a β-aryl ethylamine, such as tryptamine, undergoes

condensation and ring closure with either an aldehyde or ketone (Rodolfo et al., 2013;

Agarwal et al., 2013) using acidic catalyst at room or higher temperature (Pirc et al.,

http://en.wikipedia.org/wiki/Chemical_reaction

http://en.wikipedia.org/wiki/Tryptamine

http://en.wikipedia.org/wiki/Aldehyde

http://en.wikipedia.org/wiki/Ketone

21

2011; Devesh et al., 2013). Amé Pictet and Theodor Spengler had, in 1911, reported the

discovery of this reaction when they isolated 1-methyl-1, 2, 3, 4-tetrahydroisoquinoline

from the cyclo condensation of β-phenethylamine with formaldehyde dimethyl acetal in

the presence of hydrochloric acid. The reaction was later modified to accept other β-

phenethylamines such as N-alkyl, N-acyl and N-sulfonyl derivatives, proceeding via

iminium, N-alkyliminium, N-acyliminium or N-sulfonyliminium ion formation,

respectively (Larghi et al., 2005; Benjamin et al., 2006).

NH

NH

RNH

NH2 RCHO

H+

H3COH3CO

Figure 1.4 Pictet-Spengler Reaction.

Nucleophilic indole or pyrrole rings give products with good yields under mild

conditions, whereas less nucleophilic phenylic aromatic rings give poor yields despite

the use of higher temperature and stronger acid presence. The original Pictet–Spengler

reaction refers to the reaction of β-phenethylamine with

dimethyl acetal of formaldehyde using hydrochloric acid as the catalyst to produce

tetrahydro isoquinoline (Larghi et al., 2005; Benjamin et al., 2006). Pictet-Spengler

reaction tends to show similar trends in reaction rate as the Mannich reaction where the

aldehydes give better yields than the ketones. Currently, this reaction has been

http://en.wikipedia.org/wiki/Am%C3%A9_Pictet

http://en.wikipedia.org/wiki/Nucleophilic

http://en.wikipedia.org/wiki/Indole

http://en.wikipedia.org/wiki/Pyrrole

http://en.wikipedia.org/wiki/Phenyl

http://en.wikipedia.org/wiki/Phenethylamine

http://en.wikipedia.org/wiki/Acetal

http://en.wikipedia.org/wiki/Formaldehyde

http://en.wikipedia.org/wiki/Hydrochloric_acid

http://en.wikipedia.org/wiki/Tetrahydroisoquinoline

22

successfully applied in solid-phase combinatorial chemistry (Nielsen et al., 2003;

Nielsen et al., 2005).

1.6.2.1 Mechanism of Pictet-Spengler reaction

The Pictet-Spengler condensation reaction mechanism to form tetrahydro-β-

carboline is characterised by its initial formation of an iminium intermediate ion (4)

after the acid catalyses the reaction of a tryptamine derivative and an aldehyde (Figure

1.5) (Larghi et al., 2005). This is followed by 6-endo intramolecular cyclization of the

imine and electrophilic substitution at the indole double bond (4). After de-protonation

(5), the desired product (6) is formed (Larghi et al., 2005). It is the electrophilic imine

double bond that drive through the cyclization. The reaction mechanism shown in

Figure 1.5 is an example of a 6-endo-trig reaction, which is favoured by Baldwin's ring

closure rules.

http://en.wikipedia.org/wiki/Solid-phase_synthesis

http://en.wikipedia.org/wiki/Combinatorial_chemistry

http://en.wikipedia.org/wiki/Electrophilic_substitution

http://en.wikipedia.org/wiki/Baldwin%27s_rules

http://en.wikipedia.org/wiki/Baldwin%27s_rules

23

H3CO

NH

NH2

O

HR

H3CO

NH

NH2

O

HR+

H3CO

NH

N HH

C OHR

H

H3CO

NH

N HH

C OR

H

H+

H3CO

NH

N H

C OH2R

H

H3CO

NH

N H

CHR

OH2

H3CO

NH

N

CHR

O H

H

H

H3CO

NH

N H

CHR

H

H3CO

NH

H3CO

NH

NH

R

N H

HHR

Ring ClosureH2O

12

3

4

56

Figure 1.5 Mechanism of Pictet-Spengler reaction.

24

1.6.2.2 Water as an effective medium of Pictet-Spengler reactions

The Pictet–Spengler reaction strategy in water medium for C–C bond

forming would contribute greatly to the development of an environmentally friendly

process since it is cheap, readily available, and nontoxic compared to organic solvents.

A recent review on C–C bond formation showed a significant improvement of the

reaction rate in aqueous conditions which has been attributed to solvent polarity,

hydration and hydrogen bonding. Condensation reaction of an amine and an aldehyde to

give tetrahydro-β-carbolines in water with an acid catalyst is a mild, convenient and

simple procedure and indicates the new variants of modified Pictet-Spengler reactions.

Saha et al. (2007) discovered that in 10% TFA–water, aryl aldehydes have either

electron-withdrawing or donating groups that undergo the Pictet–Spengler reaction with

L-tryptophan or tryptamine to furnish endo cyclized products in good yields in

comparison to 10% TFA–dichloromethane or p-TsOH–toluene.

Unlike the traditional Pictet–Spengler protocol which involves aprotic solvents

wherein aldehydes bearing electron-donating substituents have failed to undergo

cyclization and furnished imines as the only product. This has been attributed to the

decrease in the reactivity of the iminium ion intermediate in the aprotic solvent which in

turn prevented the formation of tetrahydro-β-carbolines. Thus, water, probably due to

its unique abilities such as hydrogen bonding and high dielectric constant, appears to be

a more efficient medium than toluene or dichloromethane in promoting the Pictet-

Spengler reaction (Saha et al., 2007). The driving force for endo cyclization, contributed

by the electrophilicity of the aldiminium ions derived from aryl aldehydes, appears to be

enhanced in water. Furthermore, the Pictet–Spengler reaction in water exhibited better

isolation and selective reduction of mitragynine

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