Thesis submitted in fulfillment of the requirements

`

The synthesis and evaluation of phthalimide analogues as inhibitors of monoamine oxidase B

Clarina I. Manley-King (MSc.)

Thesis submitted in fulfillment of the requirements

for the degree Philosophiae Doctor in Pharmaceutical Chemistry, at the North-West University, Potchefstroom Campus, South Africa

Promoter: Prof. J. P. Petzer Co-promoter: Prof. J.J. Bergh

November, 2011 Potchefstroom

The synthesis and evaluation of phthalimide analogues as inhibitors of monoamine oxidase B

Clarina I. Manley-King (MSc.)

Thesis submitted in fulfilment of the requirements

for the degree Philosophiae Doctor in Pharmaceutical Chemistry, at the North-West University, Potchefstroom Campus, South Africa

Promoter: Prof. J.P. Petzer Co-promoter: Prof. J.J. Bergh

November, 2011

Potchefstroom

DEDICATED TO THE ALMIGHTY GOD FOR THE STRENGTH AND COURAGE THROUGHOUT THE STUDY

“If you Behold, you will Become”

Thank you Lord for leading me. You Deserve All the Glory.

i

TABLE OF CONTENTS

TABLE OF CONTENTS.………...I PREFACE………...VII DECLARATION………..………...VIII FIGURES, SCHEMES AND TABLES…………...………...IX ACRONYMS AND ABBREVIATIONS……….………...XIII ABSTRACT………..…...………....XIV OPSOMMING………...…...XVI ACKNOWLEDGEMENTS………..……...XVIII LETTER OF PERMISSION………...XIX

1. INTRODUCTION AND RESEARCH PROPOSAL...1

1.1. INTRODUCTION………...1

1.2. BACKGROUND...2

1.2.1. Isatins………...2

1.2.2. Cyclic imides………...4

1.2.3. Phthalonitriles...5

1.3. RATIONALE AND SELECTION OF COMPOUNDS...5

1.3.1. Isatins...5

1.3.2. Phthalimides………...7

1.3.3. Phthalonitriles and benzonitriles...8

1.3.4. Objectives of this study...10

1.4. SUMMARY………...11

Bibliography………...13

2. LITERATUREREVIEW………...17

ii

2.1. NEURODEGENERATIVEDISEASES...17

2.2. PARKINSON’SDISEASE...19

2.2.1. General background...19

2.2.1.1. Neurochemical and neuropathological features...19

2.2.1.2. Etiology...20

2.2.1.2.1. Age...21

2.2.1.2.2. Genetics...21

2.2.1.2.3. Environmental factors...22

2.2.1.3. Pathogenesis...23

2.2.1.3.1. Reactive oxygen species...23

2.2.1.3.2. MAO-B activity………...24

2.2.2. Symptomatic Treatment...24

2.2.2.1. Levodopa...24

2.2.2.2. Dopamine agonists...25

2.2.2.3. Carbidopa and benseraside...26

2.2.2.4. COMT inhibitors………...27

2.2.2.5. MAO-B inhibitors...27

2.2.2.6. (R)-Deprenyl, lazabemide and rasagiline...28

2.2.2.7. Anticholinergic drugs...30

2.2.2.8. Adenosine A2A receptor antagonists...31

2.2.2.9. NMDA ………...31

2.2.2.10. Zonisamide...32

2.2.2.11. α–Synuclein-directed therapies………...33

iii

2.2.2.12. Kinase inhibitors...33

2.2.3. DRUGS FOR NEUROPROTECTION...34

2.2.3.1. Dopaminergic drugs: Pramipexole and ropinirole...34

2.2.3.2. Antioxidant therapy...35

2.2.3.3. Mitochondrial energy enhancement drugs: Coenzyme Q10 and creatinine………….………...36

2.2.3.4. Anti-inflammatory drugs...37

2.3.3.5. Anti-apoptotic drugs: Minocycline, TCH346 and Cep-1347………...38

2.2.3.6. Trophic factors...39

2.2.3.7. Adenosine A2A antagonists………...39

2.2.3.8. Recent advances and future strategies in the treatment of PD………...41

2.2.4. MECHANISMFORNEUROPROTECTION………...41

2.2.4.1. Oxidative stress and mitochondrial dysfunction………...41

2.2.4.1.1. The role of iron in oxidative stress...…………...42

2.2.4.2. Protein aggregation and misfolding...43

2.2.4.3. Neuroinflammation………...43

2.2.4.4. Excitotoxicity………...44

2.2.4.5. Apoptosis………...45

2.2.4.6. Loss of trophic factors………...45

2.3. MONOAMINEOXIDASE………...46

2.3.1. General background and tissue distribution ………...46

2.3.2. Biological function of MAO-B………...48

2.3.3. Substrate and inhibitor specificities...48

2.3.4. Biological function of MAO-A………...49

iv

2.3.5. The cheese reaction………...50

2.3.6. MAO-A in depression……….…...50

2.3.7. The serotonin syndrome………...50

2.3.8. The role of MAO-B in Parkinson’s disease………...51

2.3.8.1. MAO-B and MPTP...51

2.3.8.2. MAO-B and the treatment of PD………...52

2.3.8.3. Metabolism of dopamine………...52

2.3.8.4. MAO levels in the brain and aging...53

2.3.8.5. The role of aldehyde dehydrogenase and glutathione peroxidase………...53

2.3.9. Irreversible inhibitors of MAO-B………...54

2.3.9.1. (R)-Deprenyl...54

2.3.9.2. Pargyline...54

2.3.9.3. Rasagiline... 55

2.3.9.4. Ladostigil...56

2.3.10. Reversible inhibitors of MAO-B………...56

2.3.10.1. Lazabemide...57

2.3.10.2. Isatin...57

2.3.10.3. 1,4-Diphenylbutene...58

2.3.10.4. (E)-8-(3-Chlorostyryl)caffeine...58

2.3.10.5. Trans,trans-farnesol...58

2.3.10.6. Safinamide...59

2.3.11. Inhibitors of MAO-A………...…60

2.3.11.1. Clorgyline………...60

v

2.3.11.2. Tranylcypromine and phenelzine………...61

2.3.11.3. Moclobemide and Brofaromine………...61

2.3.11.4. Iproniazid...62

2.3.12. Mechanism of action of MAO-B………...62

2.3.12.1. The SET mechanism………...63

2.3.12.2. Polar-nucleophilic pathway………...63

2.3.13. Three dimensional structure of MAO-B………...64

2.3.14. Three dimensional structure of MAO-A………...67

2.3.15. In vitro measurements of MAO activity ………...69

2.3.15.1. Direct measurements………...70

2.3.15.2. Indirect measurements...72

2.4. ENZYME KINETICS………...72

2.4.1. Michaelis-Menten kinetics………..73

2.4.2. The measurement of the kinetic parameters...74

2.4.2.1. Km and Vmax determinations………...74

2.4.2.2. Competitive inhibition………...75

2.4.2.3. IC50 and Ki determination………...76

2.5. ANIMALMODELSOFPARKINSON’SDISEASE………...77

2.5.1 MPTP...78

2.5.1.1. General background………...78

2.5.1.2. Mechanism of action………...78

2.5.2. Hydroxydopamine (6-OHDA)...79

2.5.3. Rotenone...80

vi

2.5.4. Paraquat...81

2.6. SUMMARY………...81 Bibliography………...82

3. ARTICLE 1:INHIBITIONOFMONOAMINEOXIDASEBYSELECTEDC5-ANDC6-

SUBSTITUTEDISATINANALOGUES………...107

4. ARTICLE 2: INHIBITIONOFMONOAMINEOXIDASEBYC5-SUBSTITUTED

PHTHALIMIDEANALOGUES………...159

5. ARTICLE 3:MONOAMINEOXIDASEINHIBITIONBYC4-SUBSTITUTED

PHTHALONITRILES...193

6.CONCLUSION………...239

ANNEXURE A:SUPPLEMENTARY INFORMATION-ARTICLE 1

ANNEXURE A:SUPPLEMENTARY INFORMATION-ARTICLE 2

ANNEXURE C: SUPPLEMENTARY INFORMATION- ARTICLE 3

vii

PREFACE

The experimental work described in this thesis was carried out in the School of Pharmacy of the North-West University, Potchefstroom Campus, South Africa. André Joubert and Johan Jordaan of the SASOL Centre for Chemistry, North-West University, Potchefstroom Campus, South Africa recorded the NMR spectra, while the MS spectra were recorded by Marelize Ferreira of the Mass Spectrometry Service, School of Chemistry, University of the Witwatersrand. Support with the HPLC analysis was provided by Jan du Preez from the Analytical Technology Laboratory, North-West University.

The thesis is presented in an article format and each paper is an individual entity. The research conducted represents original work undertaken by the author, and has not been previously submitted for degree purposes to any other University. To the best of my knowledge and belief, this thesis contains no material previously published or written by another person, except where due reference is made in the text of this thesis. Permission of the co-authors of the papers used in the study as well as guide to authors for each journal have also been included.

Copyright transfer to the editors of the published papers (Elsevier) gives the author the right to

publish papers as part of a thesis. No additional permission is therefore needed from the

editors.

viii DECLARATION

This thesis is submitted in fulfillment of the requirements for the degree of the Philosophiae Doctor in Pharmaceutical Chemistry, at the School of Pharmacy, North-West University.

I, Clarina Ilara Manley-King, hereby declare that the dissertation with the title:

The synthesis and evaluation of phthalimde analogues as inhibitors of monoamine oxidase B

is my own work and has not been submitted at any other University either in whole or in part.

Signed at Potchefstroom on the 14

day of November, 2011.

---

Clarina Ilara Manley-king

November, 2011

ix

FIGURES

Figure 1: Structure of isatin...2

Figure 2: General structures of the C5 and C6 substituted isatins (a) and C3 and C4 substituted anilines (b) that will be investigated in this study ………....6

Figure 3: Structure of C5 substituted phthalimides...7

Figure 4: Structure of C4 substituted phthalonitriles...9

Figure 5: Structures of C3 substituted (a) and C4 substituted benzonitriles (b)………..9

Figure 6: Neuropathology of Parkinson’s disease………...20

Figure 7: Structure of levodopa………...25

Figure 8: Structure of carbidopa………....26

Figure 9: Structure of benserazide ………...26

Figure 10: Structures of anticholinergic drugs used in the treatment of Parkinson's disease...31

Figure 11: Structure of amantadine….………...32

Figure 12: Chemical structure of zonisamide...33

Figure 13: Structure of pramipexole………..34

Figure 14: Structure of ropinirole………...35

Figure 15: Structure of coenzyme Q10……….36

Figure 16: Structures of caffeine and KW-6002………..40

Figure 17: Examples of human MAO substrates………....49

Figure 18: Structure of R-deprenyl……….54

Figure 19: Structure of pargyline ………...55

Figure 20: Structure of rasagiline ………...55

Figure 21: Structure of ladostigil ...56

x

Figure 22: Structure of lazabemide ………...57

Figure 23: The structures of isatin, 1,4-diphenyl-2-butene, (E)-8-(3-chlorostyryl)caffeine and trans,trans-farnesol………57

Figure 24: Structure of safinamide………...59

Figure 25: Illustration of safinamide bound to the MAO-B active site……….……..60

Figure 26: Structure of clorgyline ………...61

Figure 27: Structures of some MAO-A inhibitors...61

Figure 28: Structure of moclobemide...61

Figure 29: Structure of brofaromine...62

Figure 30: Structure of iproniazid...62

Figure 31: A model of the active site of human recombinant MAO-B...65

Figure 32: The crystal structure of human recombinant MAO-B...65

Figure 33: The active site of human recombinant MAO-B with isatin bound to the substrate cavity ………...66

Figure 34: The active site of human recombinant MAO-B with 1,4-diphenyl-2-butene bound…………...67

Figure 35: The membrane-binding regions of MAO-A ………..67

Figure 36: 3-Dimensional structure of recombinant human monoamine oxidase A (hMAO-A) as its clorgyline-inhibited adduct……….…68

Figure 37: Illustration of the binding site of MAO-A complexed with the inhibitor, harmine……….69

Figure 38: A graph of rate, V versus substrate concentration, [S] illustrating the Michaelis-Menten behaviour of enzymes……….73

Figure 39: The Lineweaver-Burke double-reciprocal plot………..75

xi

Figure 40: An example of a double reciprocal plot or Lineweaver-Burke plot

in the presence of various concentrations of a competitive inhibitor………...…..76

Figure 41: Plot of the rate of enzyme oxidation versus the logarithm of inhibitor concentration, Log [I]……….…………...76

Figure 42: Secondary plot of the slopes from the double reciprocal plot versus inhibitor concentration………...77

Figure 43: The structures of MPPP, meperidine and MPTP………..78

Figure 44: The chemical structure of rotenone………....80

Figure 45: Comparison of the structure of MPP⁺ and paraquat………....81

SCHEMES

Scheme 2: The MAO catalyzed oxidation of dopamine ……….48

Scheme 3: The MAO-catalyzed oxidation of MPTP...51

Scheme 4: Scheme for the overall oxidative reaction catalyzed by MAOs……….52

Scheme 5: The proposed SET oxidation pathway for MAO catalysis as illustrated with MPTP as substrate...63

Scheme 6: The proposed polar nucleophilic mechanism for the MAO catalyzed oxidation of benzylamine………...64

Scheme 7: Oxidation of amines by MAO...69

Scheme 8: The MAO-B catalyzed oxidation of benzylamine to benzaldehyde………..71

Scheme 9: The MAO catalyzed oxidation of MMTP to the dihydropyridinium species, MMDP⁺……...71

Scheme 10: The oxidation of kynuramine by MAO-B ………....72

xii

Scheme 11: Enzyme-catalyzed reaction...73

Scheme 12: Formation of enzyme complexes ...75

Scheme 13: The redox cycling of 6-OHDA produces H2O2 as a neurotoxin………...80

Scheme 14: The redox cycling reaction of paraquat………...81

TABLES

Table 2: The substituents considered for the design of the phthalimide derivatives in this study……….…8

Table 3: The substituents considered for the design of the phthalonitrile derivatives in this study ………..9

Table 4: The substituents considered for the design of the benzonitrile derivatives in this study ………..10

Table 5: Summary of mechanisms of PD pathogenesis and targets for therapy………...46

xiii

ACRONYMS AND ABBREVIATIONS

AD Alzheimers’ disease

ALS Amylotrophic lateral sclerosis CNS Central nervous system COMT Catechol-O-methyltransferase CSC (E)-8-(3-Chlorostyryl)caffeine

E Enzyme

ES Enzyme-substrate complex FAD Flavin adenine dinucleotide GABA Gamma-aminobutyric acid GSH Glutathione

HRP Horseradish peroxidise

HPLC High Performance Liquid Chromatography K

The turnover number

K

Enzyme-inhibitor dissociation constant K

The Michaelis constant

L-AAAD L-Aromatic amino acid decarboxylase

LBs Lewy bodies

L-DOPA Levodopa

MAO Monoamine oxidase MAO-A Monoamine oxidase A MAO-B Monoamine oxidase B MPP

1-Methyl-4-phenylpyridinium

MPTP 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine NMDA N-Methyl-D-aspartate

ODT Orally disintegrating tablet PCP Phencyclidine

PD Parkinson’s disease PEA Phenylethylamine ROS Reactive oxygen species S Substrate

SET Single electron transfer SOD Superoxide dismutase UPS Ubiquitin proteasome system V Reaction rate

V

Maximum velocity

xiv

ABSTRACT

Parkinson’s disease (PD) is a multifactorial neurodegenerative disease believed to be caused by a number of factors. This has made the successful treatment of the disease very difficult, as the underlying cause of degeneration is still unknown. Monoamine oxidase (MAO-B) inhibitors have been used in the treatment of PD. MAO-B is known to be involved in the catalytic oxidation of biogenic amines, a reaction which produces aldehydes and hydrogen peroxide as by- products. Both these by-products can be toxic if not rapidly cleared. Inhibitors of MAO-B conserve the depleted supply of dopamine and also stoichiometrically decreases the amount of toxic by-products formed. Thus, MAO-B inhibitors may offer both symptomatic and neuroprotective effects that can aid in the treatment of PD.

This study is part of the ongoing investigation into the development of new selective reversible inhibitors of MAO-B. Literature reports that isatin, a small, reversible, endogenous MAO inhibitor, found in the brain, can inhibit both MAO-A and MAO-B enzymes. Previous studies have shown that (E)-5-styrylisatin and (E)-6-styrylisatin are reversible inhibitors of human MAO- A and -B. Both homologues are reported to exhibit selective binding to the MAO-B isoform with

relationships (SAR), in the present study, additional C5- and C6-substituted isatin analogues were synthesized and evaluated as inhibitors of recombinant human MAO-A and MAO-B. A series of structurally related corresponding anilines, which are synthetic precursors in the synthesis of isatin derivatives, were also evaluated as MAO inhibitors. This study is part of an attempt to identify new inhibitors with enhanced potencies and specificities for both MAO-A or MAO-B.

In general, C5- and C6-substitution of isatin leads to enhanced binding affinity to both MAO

isozymes, compared to isatin, and in most instances result in selective binding to the MAO-B

isoform. The most potent MAO-B inhibitor 5-(4-phenylbutyl)isatin, exhibited an IC

value of 0.66

nM and the most potent MAO-A inhibitor was found to be 5-phenylisatin with an IC

value of

562 nM. Crystallographic and modelling studies suggest that the isatin ring binds to the

substrate cavities of MAO-A and -B and is stabilized by hydrogen bond interactions between the

NH and the C2 carbonyl oxygen of the dioxoindolyl moiety and water molecules present in the

substrate cavities of MAO-A and -B.

xv

Based on these observations and the close structural resemblance between isatin and its phthalimide isomer, a series of phthalimide analogues were synthesized and evaluated as MAO inhibitors. The results showed that the C5 substituted phthalimides were very potent competitive inhibitors with IC

values ranging 0.007 to 2.5 µM for MAO-B and IC

values ranging 0.22 to 9.0 µM for MAO-A. The 5-(4-benzyloxy)phthalimide was the most potent MAO-B inhibitor in the phthalimide series, with an IC

value of 0.007 µM. The results of modelling studies showed that hydrogen-bond interactions between the phthalimide carbonyl oxygen and the enzyme amino acid residues and the integral water molecules are important for the binding of phthalimide to the active site of MAO-B.

The potent competitive inhibition and activities of the C5 substituted phthalimide analogues towards MAO-B has led us to investigate a structurally similar series of C4-substituted phthalonitriles. A series of C4- substituted phthalonitriles were prepared and evaluated as inhibitors of MAO-B. In general, the phthalonitriles were very potent competitive inhibitors of MAO-B with IC

values ranging from 0.005–6.02 µM. 5-(4-benzyloxy)phthalonitrile was found to be the most potent inhibitor for human MAO-B with an IC

value of 0.005 µM.

To further investigate the effect of the nitrile group in this class of compounds, C3 and C4

substituted benzonitriles were prepared and evaluated for MAO inhibition. The results showed

that similar to the phthalonitriles, the benzonitriles were also potent inhibitors of human MAO-B,

with IC

values ranging from 0.785-1.39 µM. The benzonitriles, however, were not as potent as

the corresponding phthalonitriles. These findings suggest that, although two nitrile groups are

more optimal for inhibition, the presence of a second nitrile group is not a necessity for potent

MAO-B inhibition. Placement of the nitrile group at C3 resulted in more potent MAO-B inhibition

compared to placement of the nitrile at C4.

xvi

OPSOMMING

Parkinson se siekte (PD) is ʼn multifaktoriële, neurodegeneratiewe siekte. Dit word aanvaar dat PD deur ʼn aantal faktore veroorsaak word. Suksesvolle behandeling van die siekte is egter problematies omdat die onderliggende oorsake daarvan nog onbekend is. Monoamienoksidase- B (MAO-B) -remmers is reeds gebruik vir die behandeling van PD. MAO-B is betrokke by die katalitiese oksidasie van biogeniese amiene, waartydens aldehiede en waterstofperoksied as neweprodukte gevorm word. Beide hierdie neweprodukte mag toksies wees indien dit nie vinnig opgeruim word nie. MAO-B-remmers veroorsaak dat die verminderde voorraad dopamien bewaar word en verlaag die hoeveelheid toksiese neweprodukte wat stoïgiometries vorm. MAO- B-remmers mag dus simptomatiese verligting sowel as neurobeskerming bied, wat bruikbaar kan wees vir die behandeling van PD.

Hierdie studie vorm deel van ʼn deurlopende ondersoek na die ontwikkeling van nuwe, selektiewe, omkeerbare MAO-B-remmers. Volgens die literatuur is isatien ʼn klein, omkeerbare, endogene MAO-remmer wat in die brein aangetref word en wat daartoe in staat is om beide MAO-A- en MAO-B-ensieme te inhibeer. Vorige ondersoeke het getoon dat (E)-5-stirielisatien en (E)-6-stirielisatien menslike MAO-A en -B omkeerbaar inhibeer. Beide homoloë bind selektief aan die MAO-B isoform, met (E)-5-stirielisatien wat die mees potente remming vertoon. Ten einde hierdie struktuuraktiwiteitsverwantskappe (SAV), verder te ondersoek in die huidige studie, is addisionele C5- en C6-gesubstitueerde isatienanaloë gesintetiseer en geëvalueer as remmers van rekombinante, menslike MAO-A en -B. ʼn Reeks struktureelverwante, ooreenstemmende aniliene, wat sintetiese voorlopers in die sintese van isatienderivate is, is ook as MAO-remmers geëvalueer. Hierdie studie vorm deel van ʼn poging om nuwe remmers met verbeterde potensie en spesifisiteit vir beide MAO-A en MAO-B bekend te stel.

In die algemeen lei C5- en C6-substitusie van isatien tot verhoogde bindingsaffiniteit vir beide

MAO-isosieme, vergeleke met isatien, en in die meeste gevalle ook tot selektiewe binding aan

die MAO-B-isoform. Die mees potente MAO-B-remmer, 5-(4-fenielbutiel)isatien, se IC

-waarde

was 0.66 nM en die mees potente MAO-B-remmer, 5-fenielisatien, het ʼn IC

-waarde van 562

nM getoon. Kristallografiese en modelleringstudies dui daarop dat die isatienring in die

substraatholtes van MAO-A en -B bind en gestabiliseer word deur waterstofbindingsinteraksies

tussen die NH en die C2-karbonielsuurstof van die dioksoïndoliel-eenheid en watermolekules

wat in die substraatholtes van MAO-A en -B teenwoordig is.

xvii

Na aanleiding van hierdie waarnemings en die noue strukturele verwantskap tussen isatien en sy ftaalimiedisomeer, is ʼn reeks ftaalimiedanaloë gesintetiseer en as MAO-remmers geëvalueer. Die resultate toon dat die C5-gesubstitueerde ftaalimiede besonder sterk kompetitiewe remmers is met IC

-waardes van 0.007 tot 2.5 µM vir MAO-B en IC

-waardes van 0.22 tot 9.0 µM vir MAO-A. 5-(4-Bensieloksie)ftaalimied was die sterkste MAO-B-remmer in die ftaalimiedreeks met ʼn IC

-waarde van 0.007 µM. Modelleringstudies het getoon dat die waterstofbindingsinteraksies tussen die karbonielsuurstof van die ftaalimied en die aminosuurresidue van die ensiem en die integrale watermolekules belangrik is vir die binding van ftaalimied aan die aktiewe setel van MAO-B.

Die kragtige kompetitiewe inhibisie en aktiwiteit van die C5-gesubstitueerde ftaalimiedanaloë vir MAO-B het gelei tot die ondersoek van ʼn struktureel soortgelyke reeks van C4-gesubstitueerde ftalonitriele. ʼn Reeks C4-gesubstitueerde ftalonitriele is gesintetiseer en as MAO-B-remmers geëvalueer. Oor die algemeen was die ftalonitriele hoogs potente MAO-B-remmers met IC

-waardes wat van 0.005 tot 6.02 µM gestrek het. Dit is bevind dat 5-(4- bensieloksie)ftalonitriel die kragtigste remmer vir menslike MAO-B was met ʼn IC

-waarde van 0.005 µM.

Ten einde die invloed van die nitrielgroep op hierdie klas verbindings verder te ondersoek, is die C3- en C4-gesubstitueerde bensonitriele berei en geëvalueer as MAO-remmers. Die resultate het getoon dat die bensonitriele, soos die ftalonitriele, ook kragtige remmers van MAO-B is, met IC

-waardes van 0.785-1.39 µM. Die bensonitriele was egter minder potent as die ftalonitriele.

Hierdie bevindings dui daarop dat, alhoewel twee nitrielgroepe optimaal vir remming is, die teenwoordigheid van ʼn tweede nitrielgroep nie noodsaaklik is vir potente MOA-B-remming nie.

Verbindings met die nitrielgroep in die C3-posisie was kragtiger MAO-B-remmers as dié met die

nitrielgroep in die C4-posisie.

xviii

ACKNOWLEDGEMENTS

I am deeply indebted to my supervisors Prof. Jacques Petzer and Prof. Kobus Bergh, for their constant support and guidance throughout my PhD study especially the immense contributions to this thesis. I would also like to thank Dr (Mrs). Gisella Terre’Blanche for her invaluable assistance and encouragement over the years. You have always being available and deservemy sincere thanks.

I am very much thankful to all the members of the Faculty of Health Sciences, especially the Pharmaceutical Chemistry department and the School of Pharmacy for the support and helpful discussions in creating a warm atmosphere making this University a great place to study. I am particularly thankful to Mrs. Maré Nel, for being so supportive throughout my entire studies.

I highly acknowledge the financial assistance for this study from the Organization for Women in Science for the Developing World (OWSDW) [Formerly the Third World Organization for Women in Science (TWOWS)], National Research Foundation and Medical Research Council and I’m very grateful for the financial assistance towards presenting my results at international conferences.

I am very grateful to Mrs Annelishe van der Spoel and the staff at the International Office, NWU, Potchefstroom Campus and the international students for their warm hospitality, friendship and support that they gave throughout the period of my study especially in making Potchefstroom a home away from home.

I would like to express my most sincere thanks and appreciation to the pastoral team and members of His People Christian Church, Potchefstroom, especially Pastors Willem & Celeste Nel. I deeply appreciate the prayer support, encouragement, and most of all, the remarkable fellowship with all the brethren.

My deep appreciation especially goes to my family and all my friends, for their prayers, encouragement, love and enormous support throughout the period of this study. Their role in my academic success is immeasurable as they always believed in me. Therefore, I owe them a lot.

My sincere and greatest thanks to my husband, friend and brother, Dr David N’Da for giving me

all the encouragement, love and understanding I needed throughout my studies.

xix

LETTER OF PERMISSION

TO WHOM IT MAY CONCERN

Department of Pharmaceutical Chemistry, Tel +27 18 299 2263

Fax +27 18 2994243

email: jacques.petzer@nwu.ac.za 14

November, 2011

Dear Sir / Madam,

CO-AUTHORSHIP ON RESEARCH PAPERS

The undersigned, as co-authors of the research articles listed below, hereby give permission to Miss Clarina Ilara Manley-King to submit the papers as part of the degree PhD in Pharmaceutical Chemistry at the North-West University, Potchefstroom Campus:

I.

II.

III.

Yours sincerely,

--- ---

J. P. Petzer J. J. Bergh