SYNTHESIS, STRUCTURAL CHARACTERISATION AND CYTOTOXICITY STUDY OF TIN(IV) COMPOUNDS CONTAINING ONS SCHIFF BASES

By

ENIS NADIA BINTI MD YUSOF

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, Malaysia and The University of Newcastle, Australia in Fulfilment of the

Requirements for the Degree of Doctor of Philosophy

December 2019

All material contained within the thesis, including without limitation text, logos, icons, photographs and all other artwork, is copyright material of Universiti Putra Malaysia unless otherwise stated. Use may be made of any material contained within the thesis for non-commercial purposes from the copyright holder. Commercial use of material may only be made with the express, prior, written permission of Universiti Putra Malaysia. Copyright © Universiti Putra Malaysia

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Abstract of thesis presented to the Senate of Universiti Putra Malaysia and The University of Newcastle in fulfilment of the requirement for the degree of Doctor of

Philosophy

SYNTHESIS, STRUCTURAL CHARACTERISATION AND CYTOTOXICITY STUDY OF TIN(IV) COMPOUNDS CONTAINING ONS SCHIFF BASES

By

ENIS NADIA BINTI MD YUSOF

December 2019

Chair : Associate Professor Thahira Begum, PhD (UPM) Associate Professor Alister J. Page, PhD (UON) Faculty : Science There is an urgent need for substantial investigation of non-platinum drugs with higher

activity and improved selectivity to address the problem associated with the use of

platinum-based compounds as therapeutic agents. In light of this, diphenyltin(IV),

dimethyltin(IV) and tin(IV) compounds were synthesised from the Schiff bases of three

series of dithiocarbazate (S-2-methylbenzyldithiocarbazate (S1), S-4-methylbenzyl

dithiocarbazate (S2), S-benzyldithiocarbazate (S3)) and two series of thiosemicarbazides

(4-methyl-3-thiosemicarbazide and 4-phenyl-3-thiosemicarbazide) with aldehydes, 2-

hydroxy-3-methoxybenzaldehyde (oVa) or 2,3-dihydroxybenzaldehyde (catechol). The

tin(IV) compounds formed were found to have a general formula of [R2Sn(ONS)] and

[Sn(ONS)2] (where R = Me and Ph). The compounds were fully characterised by physico-

chemical and spectroscopic methods. The spectroscopic results supported the coordination

geometry in which the Schiff bases behaved as tridentate ONS donor ligands coordinating

via azomethine nitrogen, thiolo sulphur and phenoxide oxygen atoms. A total of 11 crystal

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structures of the expected compounds were solved in this work. In order to verify the

experimental data, the compounds were optimised using the density functional theory

(DFT) method with the B3LYP hybrid exchange correlation functional with LanL2DZ

pseudopotential on tin and 6-311G(d,p) Pople basis set for all other atoms. Diphenyltin(IV)

compounds showed the most promising cytotoxicity with IC50 values ranging between

0.016 – 4.40 μM against a panel of twelve cancer cell lines (RT-112, EJ-28 (bladder), HT29

(colon), U87, SJ-G2, SMA (glioblastoma), MCF-7 (breast), A2780 (ovarian), H460 (lung),

A431 (skin), Du145 (prostate), BE2-C (neuroblastoma) and MIA (pancreatic)). The three

diphenyltin(IV) compounds of the oVa series were able to induce the production of

Reactive Oxygen Species (ROS) and acted as a cell apoptosis inducer. Good binding

interactions for all the diphenyltin(IV) compound series were observed and supported by

molecular docking analysis, where hydrogen, electrostatic and hydrophobic binding

interactions were observed. This highlights the important of two phenyl groups coordinated

directly to the tin ion to enhance the cytotoxicity by strong π-π stacking interactions to

biomacromolecules. Diphenyltin(IV) compounds could bring hope in the field of drug

development against various diseases including cancers.

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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia dan The University of Newcastle sebagai memenuhi keperluan untuk Ijazah Doktor Falsafah

SINTESIS, PENCIRIAN STRUKTUR DAN KAJIAN SITOTOSIK BAGI SEBATIAN TIN(IV) YANG MENGANDUNGI BES SCHIFF ONS

Oleh

ENIS NADIA BINTI MD YUSOF

Disember 2019

Pengerusi : Professor Madya Thahira Begum, PhD (UPM) Professor Madya Alister J. Page, PhD (UON) Fakulti : Sains Terdapat keperluan segera bagi penyiasatan penting ke atas ubat yang tidak mengandungi

platinum dengan aktitviti yang tinggi dan meningkatkan pemilihan untuk menyelesaikan

masalah berkaitan dengan penggunaan sebatian daripada platinum sebagai agen

terapeutik. Disebabkan keadaan ini, sebatian difenilstanum(IV), dimetilstanum(IV) dan

stanum(IV) telah disintesis daripada bes Schiff yang terdiri daripada tiga siri ditiokarbazat

(S-2-metilbenzilditiokarbazat (S1), S-4-metilbenzilditiokarbazat (S2), S-

benzilditiokarbazat (S3) dan dua siri tiosemikarbazid (4-metil-3-thiosemikarbazid dan 4-

fenil-3-tiosemikarbazid) dengan aldehid, 2-hidroksil-3-metoksibenzaldehid (oVa) atau

2,3-dihidroksibenzaldehid (katekol). Sebatian stanum(IV) yang dihasilkan telah ditemui

mempunyai formula umum [R2Sn(ONS)] dan [Sn(ONS)2] (di mana R = Me dan Ph).

Sebatian tersebut telah dicirikan sepenuhnya dengan kaedah fiziko-kimia dan

spektroskopi. Hasil spektroskopi menyokong geometri pengkoordinatan di mana bes

Schiff bertindak sebagai ligan penderma tridentat ONS berkoordinat melalui atom-atom

nitrogen azometina, sulfur tiolo, dan oksigen fenoksid. Sebanyak 11 struktur hablur

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sebatian yang dijangkakan telah diselesaikan dalam kajian ini. Bagi mengesahkan data

eksperimen, sebatian-sebatian itu telah dioptimum menggunakan kaedah teori berfungsi

ketumpatan (DFT) dengan fungsian korelasi pertukaran hibrid B3LYP dengan keupayaan

pseudo LanL2DZ ke atas stanum dan set asas Pople 6-311G(d,p) bagi semua atom-atom

yang lain. Sebatian difenilstanum(IV) menunjukkan kesitotoksikan yang paling

memberangsangkan dengan nilai IC50 diantara 0.016 – 4.40 μM terhadap satu panel

daripada dua belas siri sel kanser (RT-112, EJ-28 (pundi kencing), HT29 (usus besar),

U87, SJ-G2, SMA (glioblastoma), MCF-7 (payudara), A2780 (ovari), H460 (paru-paru),

A431 (kulit), Du145 (prostat), BE2-C (neuroblastoma) dan MIA (pankreas)). Tiga

sebatian difenilstanum(IV) daripada siri oVa berkebolehan untuk mendorong penghasilan

Spesis Oksigen Reaktif (ROS) dan bertindak sebagai pendorong sel apoptosis. Ikatan

interaksi yang baik bagi kesemua siri sebatian difenilstanum(IV) telah diperhatikan dan

disokong oleh analisis molekul docking, di mana ikatan interaksi hidrogen, elektrostatik

dan hidrofobik telah diperhatikan. Ini menunjukkan bahawa pentingnya dua kumpulan

fenil yang berkoordinat secara terus kepada ion stannum untuk meningkatkan sifat

sitotosik melalui interaksi π-π yang kuat kepada biomakromolekul. Difenilstannum(IV)

memberi harapan dalam bidang pembangunan dadah terhadap pelbagai penyakit

termasuklah kanser.

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ACKNOWLEGEMENTS First of all, I would like thank to Allah for giving His blessing to complete my PhD

research project. I wish to express my deepest gratitude and appreciation to my principal

supervisors, Associate Professor Dr. Thahira Begum and Associate Professor Dr. Alister J.

Page as well as my co-supervisors, Professor Adam McCluskey, Dr. Mohamed Ibrahim

Mohamed Tahir, Professor Abhimanyu Veerakumarasivam and Dr. Muhammad Alif bin

Muhammad Latif, whose encouragement, guidance and support from the initial to the final

level. They spent countless hours clearing my doubts and problems with regards to my

research project. I would also like to extend my appreciation to Professor Karen Anne

Crouse for meaningful discussion, Dr. Michela Simone for her grateful NMR discussion,

Dr. Robert Burns for his kind suggestions about 119Sn NMR experiments, Dr. Jennette

Sakoff for anticancer screening and Professor Edward R. T. Tiekink for single crystal X-

ray structure analysis.

My special thanks to the wonderful computational chemistry group members, Ben,

Josh, Tilly, Kas, Krishna, Simone, Gareth, Izaac, Xinyu, Babu, Ryan, Thom, who had

guided me patiently and motivated me to get better in research. My special thanks also goes

to Inorganic Chemistry members, Nabihah, Nazhirah, Chee Keong, Lee Chin, Nabeel and

Ali for their kind assistance in helping me to complete my research. My sincere

appreciation goes to all lecturers and staff at Department of Chemistry, Faculty of Science,

Medical Genetic Laboratory, Faculty of Medicine and School of Chemistry, Faculty of

Environmental and Life Sciences and the Calvary Mater Hospital, Newcastle, Australia for

being helpful and cooperative throughout this research.

And finally, I would like to thank family members, especially my husband for his

endless love and encouragement, my parents, thank you for always loving, supporting and

wishing me the best for the whole of my life. To my siblings, thank you for always making

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me smile and releasing my tension during writing this thesis. Lastly, I offer my best wishes

to all of those who supported me in any aspect during the completion of this research.

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I certify that a Thesis Examination Committee has met on 2 December 2019 to conduct the final examination of Enis Nadia binti Md Yusof on her thesis entitled “Synthesis, Structural Characterisation and Cytotoxicity Study of Tin(IV) Compounds containing ONS Schiff Bases” in accordance with the Universities and University Colleges Act 1971 and the Constitution of the Universiti Putra Malaysia [P.U.(A) 106] 15 March 1998. The Committee recommends that the student be awarded the Doctoral of Philosophy.

Members of the Thesis Examination Committee were as follows: Lim Hong Ngee, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Chairman) Tan Kar Ban, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Internal Examiner) Christopher Scarlett, PhD Professor School of Environmental and Life Sciences The University of Newcastle Australia (Internal Examiner) Jagadese J. Vittal, PhD Professor Department of Chemistry National University of Singapore Singapore (External Examiner)

__________________________________ ZURIATI AHMAD ZUKARNAIN, PhD Professor and Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date: 2 January 2020

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This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirement for the degree of Doctor of Philosophy. The members of the Supervisory Committee were as follows:

Thahira Begum, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Chairman) Alister J. Page, PhD Associate Professor School of Environmental and Life Sciences The University of Newcastle, Australia (Member) Mohamed Ibrahim Mohamed Tahir, PhD Senior Lecturer Faculty of Science Universiti Putra Malaysia, Malaysia (Member) Abhimanyu Veerakumarasivam, PhD Professor Department of Biological Sciences School of Science and Technology Sunway University, Malaysia (Member) Muhammad Alif bin Muhammad Latif, PhD Senior Lecturer Centre of Foundation Studies for Agricultural Sciences Universiti Putra Malaysia, Malaysia (Member) Adam McCluskey, PhD Professor School of Environmental and Life Sciences The University of Newcastle, Australia (Member)

______________________________ ZALILAH MOHD SHARIFF, PhD Professor and Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date:

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Declaration by graduate student

I hereby confirm that: this thesis is my original work; the thesis contains no material which has been accepted, or is being examined, for

the award of any other degree or diploma in any university or other tertiaryinstitution;

quotations, illustrations and citations have been duly acknowledged and appropriatecopyright permissions have been obtained for the content to be made availableelectronically;

ownership of intellectual property from the thesis is as stipulated in the Memorandumof Agreement (MoA), or as according to the Universiti Putra Malaysia (Research)Rules 2012, in the event where the MoA is absent;

permission from supervisor and the office of Deputy Vice-Chancellor (Research andInnovation) are required prior to publishing it (in the form of written, printed or inelectronic form) including books, journals, modules, proceedings, popular writings,seminar papers, manuscripts, posters, reports, lecture notes, learning modules or anyother materials as stated in the Universiti Putra Malaysia (Research) Rules 2012;

there is no plagiarism or data falsification/fabrication in the thesis, and scholarlyintegrity is upheld as according to the Universiti Putra Malaysia (Graduate Studies)Rules 2003 (Revision 2012-2013) and the Universiti Putra Malaysia (Research)Rules 2012 and the University of Newcastle Rules Governing Higher Degrees byResearch. The thesis has undergone plagiarism detection software;

i give consent to the final version of my thesis being made available worldwide whendeposited in the University’s Digital Repository, subject to the provisions of theCopyright Act 1968 and any approved embargo;

the thesis has been submitted to Universiti Putra Malaysia and the University ofNewcastle as part of a Jointly Awarded Doctoral Degree.

Signature: ___________________________ Date: 9/7/2019__________________

Name and Matric No.: Enis Nadia binti Md Yusof (GS44510 (UPM) and 3285394 (UON))

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Declaration by Members of Supervisory Committee

This is to confirm that: the research conducted and the writing of this thesis was under our supervision; supervision responsibilities as stated in the Universiti Putra Malaysia (Graduate

Studies) Rules 2003 (Revision 2012-2013) and the University of Newcastle RulesGoverning Higher Degrees by Research and University of Newcastle Code ofPractice are adhered to.

Signature: Name of Chairman of Supervisory Committee: Thahira Begum

Signature: Name of Member of Supervisory Committee: Alister J. Page

Signature: Name of Member of Supervisory Committee: Mohamed Ibrahim Mohamed Tahir

Signature: Name of Member of Supervisory Committee: Abhi Veerakumarasivam

Signature: Name of Member of Supervisory Committee: Muhammad Alif bin Muhammad Latif

Signature: Name of Member of Supervisory Committee: Adam McCluskey

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TABLE OF CONTENTS Page ABSTRACT i ABSTRAK iii ACKNOWLEDGEMENTS v APPROVAL vii DECLARATION ix LIST OF TABLES xvi LIST OF FIGURES xviii LIST OF SCHEMES xxiii LIST OF ABBREVIATIONS xxiv CHAPTER

1 COORDINATION CHEMISTRY AND CYTOTOXICITY OF TIN(IV) COMPOUNDS

1

1.1 Introduction 1 1.2 Long-Standing Chemotherapeutic Agents 4 1.3 Non-Platinum-Based Preclinical Investigations for

Anticancer Drug Applications 7

1.3.1 Titanium Compound 8 1.3.2 Ruthenium Compounds 9 1.3.3 Gallium Compounds 10 1.3.4 Iron Compounds 12 1.3.5 Cobalt Compounds 13 1.3.6 Gold Compounds 14 1.4 Tin(IV) compounds as potential anticancer agents 15 1.4.1 Tin(IV) Compounds of Oxygen and/or Nitrogen

Donor Ligands 17

1.4.2 Tin(IV) Compounds of Sulphur Donor Ligands 23 1.5 Chemistry and Bioactivities of Schiff Bases and Their

Tin(IV) Compounds 27

1.5.1 Anticancer Activity of Dithiocarbazate Schiff Bases and Their Tin(IV) Compounds

28

1.5.2 Anticancer Activity of Thiosemicarbazone Schiff Bases and Their Tin(IV) Compounds

31

1.6 Mechanism of Action 36 1.6.1 DNA Binding 36 1.6.2 Apoptosis 38 1.7 Knowledge Gap 40 1.8 Project Aims 41 1.9 Thesis Outline 42 2 SYNTHESIS, STRUCTURAL EVALUATION AND

CYTOTOXICITY STUDIES OF O-VANILLIN DERIVED DITHIOCARBAZATE SCHIFF BASES

43

2.1 Introduction 43 2.2 Experimental and Computational Methods 44 2.2.1 Materials 44

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2.2.2 Synthesis 45 2.2.2.1 S-N-R-Benzyldithiocarbazates (N = 2,

3, R = Methyl) 45

2.2.2.2 S-2-Methybenzyl-β-N-(2-hydroxy-3-methoxybenzyl methylene) dithiocarbazate (1)

46

2.2.2.3 S-4-Methybenzyl-β-N-(2-hydroxy-3-methoxybenzyl methylene) dithiocarbazate (2)

47

2.2.2.4 S-Benzyl-β-N-(2-hydroxy-3-methoxybenzylmethylene) dithiocarbazate (3)

47

2.2.3 Physical Measurements 48 2.2.4 Single Crystal X-ray Structure Determination 48 2.2.5 Density Functional Theory (DFT) Calculations 49 2.2.6 MTT Assays 50 2.3 Results and Discussion 52 2.3.1 Synthesis 52 2.3.2 IR Spectral Analysis 53 2.3.3 NMR Spectroscopic Analysis 54 2.3.4 Mass Spectral Analysis 55 2.3.5 UV-vis Absorption Spectroscopy 55 2.3.6 X-ray Crystallography 56 2.3.7 In vitro Cytotoxicity 58 2.4 Conclusions 61 3 ORGANOTIN(IV) COMPOUNDS OF O-VANILLIN

SCHIFF BASES: SYNTHESIS, STRUCTURAL CHARACTERISATION, IN-SILICO STUDIES AND CYTOTOXICITY

62

3.1 Introduction 62 3.2 Experimental 64 3.2.1 Materials 64 3.2.2 Synthesis 65 3.2.2.1 Diphenyltin(IV) Compounds 65 3.2.2.2 Dimethyltin(IV) Compounds 66 3.2.3 Physical Measurements 68 3.2.4 Single Crystal X-ray Structure Determination 68 3.2.5 Computational Methods 69 3.2.5.1 DFT Calculations 69 3.2.5.2 Molecular Docking Studies 70 3.2.6 Biological Assays 71 3.2.6.1 MTT Assays 71 3.2.6.2 Quantification of Apoptosis by

Annexin V 71

3.2.6.3 Measurement of Reactive Oxygen Species (ROS)

72

3.2.6.4 DNA Binding Studies 73 3.3 Results and Discussion 73 3.3.1 Synthesis 73

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3.3.2 IR Spectral Analysis 74 3.3.3 NMR Spectroscopic Analysis 75 3.3.4 X-ray Crystallography 76 3.3.5 UV-vis Absorption Spectroscopy 85 3.3.6 Biological Assays 86 3.3.6.1 Cytotoxicity 86 3.3.6.2 Annexin V Assays of 4, 5 and 6-

Treated RT-112 Cells 88

3.3.6.3 Measurement of Reactive Oxygen Species (ROS) in RT-112 Cells Treated with 4 and 5

89

3.3.6.4 DNA Interaction Studies 92 3.3.7 Molecular Docking Studies 93 3.4 Conclusion 98 4 SELECTIVE CYTOTOXICITY OF ORGANOTIN(IV)

COMPOUNDS CONTAINING CATECHOL DITHIOCARBAZATE SCHIFF BASES

101

4.1 Introduction 101 4.2 Experimental 102 4.2.1 Materials and Physical Measurements 102 4.2.2 Synthesis 102 4.2.2.1 S-N-R-benzyldithiocarbazate

(N = 2, 3; R = methyl) 102

4.2.2.2 Schiff bases 102 4.2.2.3 Diphenyltin(IV) Compounds 104 4.2.2.4 Dimethyltin(IV) Compounds 106 4.2.3 X-ray Crystallographic Analysis 107 4.2.4 DFT Calculations and Molecular Docking

Studies 108

4.2.5 MTT Assay 108 4.3 Results and Discussion 108 4.3.1 Synthesis 108 4.3.2 IR Spectral Analysis 111 4.3.3 NMR Spectroscopic Analysis 112 4.3.4 Mass Spectral Analysis 114 4.3.5 UV-vis Absorption Spectroscopy 114 4.3.6 Structure Descriptions for 12, 14, 15, 17 and 18 115 4.3.7 In vitro Cytotoxicity 125 4.3.8 DNA Binding Analysis 126 4.3.9 Molecular Docking Analysis 127 4.4 Conclusions 134 5 HOMOLEPTIC TIN(IV) COMPOUNDS OF

DINEGATIVE ONS DITHIOCARBAZATE SCHIFF BASES: SYNTHESIS, X-RAY CRYSTALLOGRAPHY, DFT AND CYTOTOXICITY STUDIES

136

5.1 Introduction 136 5.2 Experimental 137 5.2.1 Materials and Physical Measurements 137

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5.2.2 Synthesis 138 5.2.2.1 Synthesis of Schiff Bases 138 5.2.2.2 Synthesis of Tin(IV) Compounds (19-

24) 138

5.2.3 Single Crystal X-ray Structure Determination 141 5.2.4 DFT Calculations and Molecular Docking

Studies 141

5.2.5 MTT Assays 142 5.3 Results and Discussion 142 5.3.1 Synthesis 142 5.3.2 IR Spectral Analysis 143 5.3.3 NMR Spectroscopic Analysis 144 5.3.4 UV-vis Absorption Spectral Analysis 145 5.3.5 X-ray Crystallography 145 5.3.6 In vitro Cytotoxic Activity 151 5.3.7 Molecular Docking Analysis 151 5.4 Conclusions 156 6 TIN(IV) COMPOUNDS OF THIOSEMICARBAZONE

SCHIFF BASES: SYNTHESIS, STRUCTURAL CHARACTERISATION AND IN VITRO CYTOTOXICITY

158

6.1 Introduction 158 6.2 Experimental 159 6.2.1 Materials and Physical Measurements 159 6.2.2 Synthesis 160 6.2.2.1 Schiff Bases 160 6.2.2.2 Tin(IV) Compounds derived from 25

and 27 162

6.2.2.3 Tin(IV) Compounds derived from 26 165 6.2.2.4 Tin(IV) Compounds derived from 28 166 6.2.3 DFT Calculations and Molecular Docking

Simulations 168

6.2.4 MTT Assay 168 6.3 Results and Discussion 169 6.3.1 Synthesis 169 6.3.2 IR Spectral Analysis 170 6.3.3 NMR Spectroscopic Analysis 171 6.3.4 Mass Spectral Analysis 173 6.3.5 UV-vis Absorption Spectral Analysis 173 6.3.6 In vitro Cytotoxic Activity 174 6.3.7 DNA Binding Studies 176 6.3.8 Molecular Docking Analysis 177 6.4 Conclusions 182 7 CONCLUSIONS AND FUTURE RECOMMENDATIONS 184 7.1 Conclusions 184 7.2 Future Recommendations 187

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REFERENCES 189 APPENDICES 215 BIODATA OF STUDENT 344 LIST OF PUBLICATIONS 345

xvi

LIST OF TABLES Table

Page

1.1 Cytotoxic activity of tin(IV) compounds against a panel cancer cells and survival of MRC-5 cells, compared to cisplatin.

20

2.1 Physical data of synthesised S-substituted dithiocarbazate derivatives.

46

2.2 Crystal data and refinement details for Schiff base 3

50

2.3 Hydrogen-bond geometry (Å, °) of 3 obtained from single crystal X-ray diffraction analysis. The structure is shown in Figure 2.2.

57

2.4 Summary of the in vitro cytotoxicity of compounds 1-3 in several cell lines, determined by MTT assay and expressed as GI50 values with standard errors. (GI50 is the concentration at which cell growth is inhibited by 50% over 72 h).

60

3.1 Crystal data and refinement details for compounds 7, 8 and 9.

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3.2 Selected geometric parameters (Å, °) for 7, 8 and 9.

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3.3 Summary of the in vitro cytotoxicity of the Schiff bases and their organotin(IV) compounds.

90

3.4 Binding constants (Kb), hypochromism (%), bathochromic shifts (nm) and Gibbs free energy (kJ mol−1) values for the interaction of organotin(IV) compounds with calf thymus DNA (CT-DNA).

94

3.5 Molecular docking data for the organotin(IV) compounds with B-DNA (PDB ID: 1BNA) dodecamer d(CGCGAATTCGCG)2.

96

4.1 Crystallographic data and refinement details for 12, 14, 15, 17 and 18.

110

4.2 Selected geometric data (Å, °) characterising 12, 14, 15, 17 and 18.

120

4.3 Summary of the in vitro cytotoxicity of the Schiff bases (10-12) and their organotin(IV) compounds (13-18) in several cell lines, determined by MTT assay, expressed as GI50 values with standard errors. GI50 is the concentration at which cell growth was inhibited by 50% over 72 h.

129

4.4 Binding constants (Kb), hypochromism (%), bathochromic shifts (nm) and Gibbs free energy (kJ mol-1) values for the interaction of organotin(IV) compounds with CT-DNA.

131

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4.5 Molecular docking data for the organotin(IV) compounds with B-DNA (PDB ID: 1BNA) dodecamer d(CGCGAATTCGCG)2.

133

5.1 Crystal data and refinement details for complexes 20 and 21.

142

5.2 Selected geometric parameters (Å, °) for 20 and 21.

147

5.3 Summary of the in vitro cytotoxicity of tin(IV) compounds in several cell lines, determined by the MTT assay and expressed as a GI50 value with standard error. GI50 is the concentration of tin(IV) compounds at which cell growth is inhibited at 50% over 72 hours.

153

5.4 Molecular docking data for the tin(IV) compounds with B-DNA (PDB ID: 1BNA) dodecamer d(CGCGAATTCGCG)2.

154

6.1 In vitro cytotoxicity of tin(IV) compounds (29-30, 32-40) derived thiosemicarbazone Schiff bases (25-28) in several cell lines, determined by the MTT assay and expressed as a GI50 value with standard error. GI50 is the concentration at which cell growth is inhibited by 50% over 72 hours.

178

6.2 Molecular docking data for 27, 32, 33 and 34 with B-DNA (PDB ID: 1BNA) dodecamer d(CGCGAATTCGCG)2.

181

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LIST OF FIGURES

Figure

Page

1.1 Estimated number of new cancer cases and mortality in 2018, worldwide, all cancers, both sexes and all ages.

2

1.2 Structure of different platinum-based anticancer drugs.

5

1.3 Schematic diagram showing the cytotoxic pathway for cisplatin. After entering the tumour cells, cisplatin is equated, then binds to cellular DNA.

6

1.4 The new cancer drug allows for low-dose cancer chemotherapy and promises fewer side effects.

7

1.5 The titanium-based compounds, budotitane (left) and titanocene dichloride (right).

9

1.6 The ruthenium-based compounds, NAMI-A (left) and KP1019 (right).

10

1.7 Structure of gallium-based compound, KP46 which was designed and used in clinical trials.

11

1.8 Schematic representation of the mechanism of action of gallium-based compounds. Tf = transferrin; NDP = nucleoside diphosphate; dNDP = desoxynucleoside diphosphate; BAX = a proapoptotic protein.

12

1.9 The iron-based compounds, ferrocenium picrate (left) and ferrocenium trichloroacetate (right).

13

1.10 The cobalt-based compounds, hexacarbonyldicobalt complex of the propargylic ester of acetylsalicylic acid (Co-ASS).

14

1.11 The gold-based compounds, auranofin (left) and [Au(dppe)2]Cl (right).

15

1.12 The structure of tin(IV) compounds containing oxygen and/or nitrogen donor ligands.

21

1.13 The structures of tin(IV) compounds containing sulphur donor ligands.

25

1.14 Tautomerism in (a) DTC and (b) TSC Schiff bases.

28

1.15 Different substituents at position R in dithiocarbazate derivatives.

30

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1.16 The structure of tin(IV) compounds derived from dithiocarbazate Schiff bases.

31

1.17 Chemical structure of (a) Methisazone and (b) Triapine.

32

1.18 The structure of tin(IV) compounds derived from thiosemicarbazone Schiff bases.

35

1.19 Molecular docked model of diphenyltin(IV) complex with DNA dodecamer duplex of sequence d(CGCGAATTCGCG)2 (PDB ID: 1BNA). The image provides the side view of the docked model of complexes.

37

1.20 a) Molecular docking simulation of diethyltin(IV) complex-DNA complex (binding site of topoisomerase II) b) detailed molecular interactions of diethyltin(IV) complex with amino acid residues.

38

1.21 Mechanism of extrinsic and intrinsic apoptotic pathway.

40

2.1 The structures of (a) vanillin and (b) o-vanillin.

43

2.2 The (a) thione and (b) thiol tautomeric forms of the Schiff bases 1-3.

54

2.3 HOMO-LUMO of (a) 1, (b) 2 and (c) 3.

56

2.4 The molecular structure of 3, showing the atom- labelling scheme and displacement ellipsoids at the 50% probability level.

57

2.5 Molecular packing in 3: (a) a perspective view of the supramolecular layer sustained by thioamide-N-H…S(thione) and phenyl-C-H…O(hydroxy) interactions and, (b) a view of the unit-cell contents shown in projection down the b axis, highlighting one layer in space-filling mode. The N-H…S and C-H…O interactions are shown as blue and orange dashed lines, respectively. For (a), non-interacting H atoms have been omitted.

58

3.1 The structures of Schiff bases (1-3) and organotin(IV) compounds (4-9).

64

3.2 Molecular structures of the first independent molecules of (a) 7, (b) 8 and (c) 9 showing atom labelling schemes. (d) Overlay diagram.

79

3.3 Crystallographic diagrams for 7: (a) Molecular structure of the second independent molecule, molecule b, (b) overlay diagram of molecules a (red image) and inverted-b (green) drawn so the SnC2 atoms of the Me2Sn moiety are overlapped and (c) a view of the supramolecular layer in the ab-plane (left image) and a view of the unit cell contents in projection down the a-axis with one layer

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highlighted in space-filling mode (right image). The C‒H…O and C‒H…π interactions are shown as orange and purple dashed lines, respectively.

3.4 Crystallographic diagrams for 8: (a) Molecular structure of the second independent molecule, molecule b, (b) overlay diagram of molecules a (blue image) and inverted-b (pink) drawn so the SnC2 atoms of the Me2Sn moiety are overlapped and (c) a view of the supramolecular dimer sustained by C‒H…π (chelate) interactions (left image; non-participating hydrogen atoms have been omitted) and a view of the unit cell contents in projection down the a-axis. The C‒H…O and C‒H…π interactions are shown as orange and purple dashed lines, respectively.

80

3.5 Crystallographic diagrams for 9: (a) Molecular structure of the second independent molecule, molecule b, (b) overlay diagram of molecules a (yellow image) and b (aqua) drawn so the five-membered rings are overlapped and (c) supramolecular dimer sustained by edge-to-edge chelate ring…benzene interactions (upper image) between Sn1-containing molecules, supramolecular layer sustained by edge-to-edge π (chelate ring)…π (ethoxybenzene) and phenyl-C‒H…π (methoxybenzene) interactions occurring between Sn2-containing molecules and a view of the unit cell contents in projection down the b-axis. The edge-to-edge π (chelate ring)…π (ethoxybenzene) and C‒H…π interactions are shown as blue and purple dashed lines, respectively.

84

3.6 HOMO-LUMO of (a) 4, (b) 5, (c) 6, (d) 7, (e) 8 and (f) 9.

86

3.7 Apoptosis detection through fluorescence microscopy. Cells were treated for 24 h with 4 (0.31 µM), 5 (1.66 µM) and 6 (0.58 µM), and the negative control (DMSO) in complete media. After staining with Annexin V and PI, necrotic and apoptotic cells were detected by fluorescence microscopy (20×).

91

3.8 Percent reactive oxygen species (ROS) production in RT-112 cells treated with (a) 4 (0.31 μM) (b) 5 (1.66 μM) for 24 h and stained with 1 mM DCFH-DA for 60 minutes at 37 °C. DMSO and H2O2 acted as negative and positive controls, respectively.

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3.9 (a) Electronic absorption spectra of (i) 4, (ii) 5 and (iii) 6; (b) Plot of [DNA]/εa − εf vs [DNA] for absorption titration of DNA with (i) 4, (ii) 5 and (iii) 6. The arrow indicates the change in absorbance in tandem with increasing DNA concentration.

95

3.10 (a) Schematic representation of organotin(IV) compounds that fit well in the grooves of the DNA strand obtained by docking simulations.

97

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4.1 The structures of catechol dithiocarbazate Schiff bases (10-12) and

their organotin(IV) compounds (13-18).

102

4.2 (a) Thione and (b) thiol tautomerism of Schiff bases 10-12.

109

4.3 Frontier molecular orbitals LUMO and HOMO of the optimised (a) 10, (b) 11, (c) 12, (d) 13, (e) 14, (f) 15, (g) 16, (h) 17 and (i) 18 using B3LYP functional.

116

4.4 Molecular structure of 12 and atom labelling scheme.

117

4.5 ORTEP structures showing atom labelling scheme and overlay diagrams for (a) the two independent molecules of 14, (b) the two independent molecules of 15, (c) 17, (d) 18 and (e) overlay diagram for 17 and 18. For the overlay diagrams, molecules have been overlapped so that the CS2 residues are coincident.

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4.6 A view of the linear supramolecular chain along [1̄ 0 4] in the crystal of 12. The hydroxyl-O‒H…O(hydroxyl) and thioamide-N‒H…S(thione) hydrogen bonds are shown as orange and green dashed lines, respectively.

123

4.7 A view of the zig-zag chain along [0 0 1] in the crystal of 14. The hydroxyl-O‒H…O(hydroxyl) and thioamide-N‒H…S(thione) hydrogen bonds are shown as orange and green dashed lines, respectively. For reasons of clarity, the hydrogen atoms have been removed and only the ipso-carbon atoms of the tin-bound phenyl rings shown.

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4.8 (a) Electronic absorption spectra of (i) 16, (ii) 17 and (iii) 18; (b) Plot of [DNA]/εa - εf vs [DNA] for absorption titration of DNA with (i) 16, (ii) 17 and (iii) 18. (The arrow indicates the change in absorbance in tandem with increasing DNA concentration).

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4.9 (a) Schematic representation of organotin(IV) compounds that fit well in the grooves of the DNA strand obtained by docking simulations. The two double-stranded DNA comprised of the phosphate deoxyribose backbone with guanine (DG, red), cytosine (DC, blue), adenine (DA, pink) and thymine (DT, orange). (b) Molecular interactions of organotin(IV) compounds within the grooves of double stranded DNA residues.

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5.1 The structures of homoleptic tin(IV) compounds (19-24).

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5.2 Frontier MOs of (a) 19, (b) 20, (c) 21, (d) 22, (e) 23 and (f) 24.

146

5.3 Molecular structures of the molecules in (a) 20 (first independent molecule; the structure for the second independent molecule is

148

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shown in Appendix Figure A5.1) and (b) 21, showing atom labelling schemes and 50% displacement ellipsoids. (c) Overlay diagram of the molecules in 20 (red image for the first independent molecule), 20a (green, inverted second molecule) and 21 (blue). Molecules have been overlapped so the Sn,S1,N2 chelate rings are coincident.

5.4 Homoleptic tin(IV) compounds that have been studied.

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5.5 (a) Schematic representation of 19 (cyan), 21 (yellow), 22 (blue), 23 (grey) and 24 (green) that fit well in the grooves of the DNA strand obtained by docking simulations. The two double-stranded DNA comprised of the phosphate deoxyribose backbone (grey) with guanine (green), cytosine (purple), adenine (DA, red) and thymine (cyan). (b) Molecular interactions of 19, 21, 22, 23 and 24 within the grooves of double stranded DNA residues. Hydrogen bond, electrostatic and hydrophobic interactions are depicted by green, orange and pink dot lines, respectively.

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5.6 The small modification (blue) of backbone of (a) dithiocarbazate Schiff bases to produce (b) thiosemicarbazone Schiff bases.

157

6.1 The structures of (a) dithiocarbazate and (b) thiosemicarbazone Schiff bases.

159

6.2 Frontier MOs (a) 25, (b) 26, (c) 27, (d) 28, (e) 29, (f) 30, (g) 31, (h) 32, (i) 33, (j) 34, (k) 35, (l) 36, (m) 37, (n) 38, (o) 39 and (p) 40.

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6.3 Electronic absorption spectra of (i) 27, (ii) 32, (iii) 33 and (iv) 34. The arrow indicates the change in absorbance in tandem with increasing DNA concentration.

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6.4 Molecular interactions of (a) 27, (b) 32, (c) 33 and (d) 34 within the grooves of double stranded DNA residues. Hydrogen bond, electrostatic and hydrophobic interactions are depicted by green, orange and pink dot lines, respectively.

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LIST OF SCHEMES

Scheme

Page

2.1 Synthetic pathway for the formation of 1-3.

53

3.1 Synthesis of organotin(IV) compounds (4-9).

74

4.1 Synthetic pathway for the formation of Schiff bases 10, 11 and 12.

109

4.2 Synthetic pathway for the synthesis of organotin compounds 13-18.

111

5.1 Synthetic pathway for the synthesis of 19-24.

143

6.1 Synthetic pathway of thiosemicarbazone Schiff bases 25-28.

169

6.2 Synthetic pathway of tin(IV) compounds (29-40) of thiosemicarbazone Schiff bases.

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LIST OF ABBREVIATIONS

3677 Human melanoma cell line A2780 Human ovarian carcinoma cancer cell line A431 Human skin cancer cell line A549 Human lung carcinoma line B16F10 Murine melanoma cell line B3LYP Berke's three-parameter exchange potential and the

Lee–Yang–Parr correlation functional Bcap37 Mammary tumour cell line BE2-C Neuroblastoma cancer cell line Bel-7402 Hepatocellular carcinoma line BGC-823 Gastric carcinoma cell line BSA Bovine serum albumins CDCl3 Deuterated chloroform CH3OH Methanol CHO Chinese hamster ovary cell line CIF Crystallographic Information File CML-T1 Chronic myeloid leukemic cell line CoLo205 Colon carcinoma cell line CT-DNA Calf thymus deoxyribonucleic acid DCF 2′,7′-Dichlorodihydrofluorescein DCF-DA Dichloro-dihydro-fluorescein diacetate DCM Dichloromethane DFT Density Functional Theory DMEM Dulbecco’s modified Eagle’s medium DMSO-d6 Deuterated dimethylfulfoxide DNA Deoxyribonucleic acid DTC Dithiocarbazate Du145 Human prostate carcinoma cancer cell line EJ-28 Muscle invasive bladder cancer cell line Et3N Triethylamine FT-IR Fourier transform infrared spectroscopy GI50 Concentration of the anti-cancer drug that inhibits the growth of

cancer cells by 50% relative to untreated control H2981 Human lung adenocarcinoma cell line H460 Human non-small lung carcinoma cell line HCT116 Human colorectal carcinoma cell line HCT-8 Colon carcinoma cell line HeLa Human cervical epithelioid carcinoma cell line HepG2 Human liver carcinoma cell line HL-60 Human acute myeloid leukemia cell line HT29 Human colon adenocarcinoma cell line IC50 Concentration of compound that inhibits a biological activity by

50% K562 Human myelogenous leukemia cell line KB Nasopharyngeal carcinoma cell line KP1019 Indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] KP46 Tris(8-quinolinolato)gallium(III)

xxv

LanL2DZ Los Alamos National Laboratory 2-double-z LMCT Ligand-metal charge transfer LMS Leiomysarcoma cell line LOX Lipoxygenase m/z Mass-to-charge ratio MCF-10A Normal breast cell line MCF-7 Human breast carcinoma with positive oestrogen receptor cell line MDA-MB-231 Human breast carcinoma with negative oestrogen receptor cell line Me2SnCl2 Dimethyltin(IV) dichloride MeOH Methanol MIA Pancreatic cancer cell line MKT4 Titanocene dichloride MRC-5 Normal foetal lung fibroblast cell line MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide NAMI-A Imidazolium trans-[tetrachloro(dimethylsulfoxide)(1H-

imidazole)ruthenate(III)] NCI National Cancer Institute NMR Nuclear magnetic resonance ONS Oxygen-nitrogen-sulphur oVa o-Vanillin; 2-hydroxy-3-methoxybenzaldehyde P388 Lymphocytic leukaemia cell line PDB Protein Data Bank Ph Phenyl Ph2SnCl2 Diphenyltin(IV) dichloride PI Propidium Iodide r.m.s Root-mean-square ROS Reactive Oxygen Species RR Ribonucleotide reductase RT-112 Minimum muscle invasive bladder cancer cell line S1 S-2-Methylbenzyldithiocarbazate S2 S-4-Methylbenzyldithiocarbazate S3 S-Benzyldithiocarbazate SJ-G2 Pediatric glioblastoma cell line SMMC-7721 Human hepatocellular carcinoma cell line TiO2 Titanium oxide Tris-HCl Tris(hydroxymethyl)aminomethane hydrochloride U2-OS Human osteosarcoma cell line U87 Human glioblastoma cell line UV-vis Ultraviolet-visible WiDr Human colon carcinoma cell line WRL-68 Normal liver cell ORTEP Oak Ridge thermal ellipsoid plot PBS Phosphate buffer saline PEG Polyethylene glycol