IN VITRO ANTICANCER ACTIVITY GUIDED INVESTIGATION
OF THE PHYTOCHEMICALS OF TYPHONIUM
FLAGELLIFORME (LODD.) BLUME (ARACEAE)
by
LAI CHOON SHEEN
Thesis submitted in fulfilment of the requirements
for the degree of
Doctor of Philosophy
June 2010
ACKNOWLEDGEMENTS
Praise be unto God the creator of heaven and earth, for His grace and mercy, that along with all other things, have faithfully and graciously provided me the capability to complete all the work required in fulfilment of this degree.
I would like to express my gratitude to my main supervisor, Professor
Emeritus Dr. V. Navaratnam, for giving me the opportunity to work in the area of my interest and also his constant support, help and encouragement throughout the course of my study. I thank my co-supervisor, Associate Professor Dr. Mas Rosemal Hakim
Mas Haris, for all the inspiring stories, motivation, guidance and support particularly in the area of structure elucidation. I would also like to thank Professor Dr. Sharif
Mahsufi Mansor for co-supervising this project and helping me to go through the many hiccups I faced throughout the course of my study. I am truly grateful to
Professor Nair for his invaluable advice and guidance on this work.
I thank all the support staff of Centre for Drug Research, for things would not have turned out smoothly if it were not for their help. Special thanks to Mr. Asokan
Muniandy and Mr. Arunacalam for maintaining a cheerful environment in the lab and rendering helping hands to make things right. Many thanks to Mr. Hilman for his assistance in acquiring the GC-MS data, Mr. Zamri, Mr. Nahari, Mr. Khoo, Mr.
Rahim and all the other lab staff and administrative staff for helping me in one way or another.
My sincere gratitude also goes to HISCO (M) Sdn Bhd and Varian, Germany for NMR spectral acquisition. Thanks are due to Research Instruments Sdn Bhd and
Waters Asia Ltd, Singapore too for obtaining the LC-MS data. I also thank Professor
ii Dr. Alex Matter from Novartis Institute for Tropical Disease (NITD) for his advice in this project and his staff, Dr. Sejal Patel and Ms. Jeasie Tan for their technical assistance in compound separation.
I thank my dear friends, Shubhadra, Peng Lin, Venkatesh and Vanessa for accompanying me through this part of the journey of my life, for sharing my ups and down and providing me encouragement in tough times. I would also like to thank all my church friends from Sungai Nibong Gospel Hall for their constant prayer and support.
Last but not least, I thank my dearest mom and dad, my brother Choon
Shyang, my sister Jun Shi and most importantly my beloved husband En Haur for all their encouragement, understanding and sacrifices made throughout these years so that I could complete my studies smoothly.
iii TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
TABLE OF CONTENTS iv
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF SYMBOLS AND ABBREVIATIONS xvii
ABSTRAK xxi
ABSTRACT xxiii
CHAPTER 1 INTRODUCTION 1
1.1 Medicines from Plants 1
1.2 Plants as a Source of Anti-cancer Agents 4
1.3 Typhonium flagelliforme (Lodd.) Blume 8
1.3.1 Taxonomy and Distribution 8
1.3.2 Ethnomedical Background 10
1.3.3 Pharmacological Studies 12
1.3.4 Phytochemicals 13
1.4 Methods of Plant Extraction 15
1.4.1 Maceration 16
1.4.2 Soxhlet Extraction 16
1.4.3 Ultrasonic-assisted Solvent Extraction 17
1.5 Techniques of Separation 17
1.5.1 Thin-layer Chromatography 17
1.5.2 Column Chromatography 18
iv 1.5.3 High Performance Liquid Chromatography 20
1.6 Compound Identification and Structure Elucidation 22
1.6.1 Ultraviolet-visible Spectroscopy 22
1.6.2 Infrared Spectroscopy 22
1.6.3 Nuclear Magnetic Resonance Spectroscopy 23
1.6.4 Mass Spectrometry 26
1.7 In Vitro Anticancer Assay 28
1.7.1 MTT Antiproliferative Assay 28
1.7.2 Apoptotic Cell Death 29
1.7.3 Photodynamic Therapy 30
1.8 Aims of the Study 31
CHAPTER 2 EXPERIMENTAL 33
2.1 Research Materials 33
2.1.1 List of Chemicals 33
2.1.2 List of Equipments and Instruments 35
2.2 Plant Material 35
2.2.1 Collection of Raw Material 35
2.2.2 Identification of Plant and Preparation of Voucher Specimen 36
2.3 Experimental Methods 36
2.3.1 Plant Extraction 36
2.3.1.1 Maceration 37
2.3.1.2 Ultrasonic-assisted Solvent Extraction 39
2.3.1.3 Soxhlet Extraction 39
2.3.1.4 Traditional Medicine Preparative Method 39
2.3.2 Comparison of Plant Extracts 40
v 2.3.2.1 Extraction Yields 40
2.3.2.2 Antiproliferative Assay 40
2.3.2.3 Chemical Composition 40
2.3.3 Scaled-up Production 41
2.3.4 Flash Column Chromatography 41
2.3.4.1 Column Packing 41
2.3.4.2 Fractionation of Crude Hexane Extract 42
2.3.4.3 Fractionation of Crude DCM Extract 43
2.3.5 Isolation and Characterisation of the Chemical Constituents of
Fraction D/F19 44
2.3.6 Identification of the Chemical Constituents of Fraction D/F21 46
2.3.7 Purification and Identification of the Chemical Constituents of
Fraction D/F15 48
2.3.8 Compound Characterisation and Identification 49
2.3.8.1 Physical Characterisation 49
2.3.8.2 Ultraviolet-visibile Spectroscopy 50
2.3.8.3 Infrared Spectroscopy 50
2.3.8.4 Nuclear Magnetic Resonance Spectroscopy 50
2.3.8.5 Gas Chromatography-Mass Spectrometry 51
2.3.8.6 Liquid Chromatography-Tandem Mass Spectrometry 51
2.3.9 Animal Cell Culture 52
2.3.9.1 Preparation of Culture Media 53
2.3.9.2 Preparation of Phospate Buffer Saline 53
2.3.9.3 Resuscitation of Cryopreserved Cells 53
2.3.9.4 Subculture 54
vi 2.3.9.5 Cryopreservation 54
2.3.9.6 Cell Counting 55
2.3.10 MTT Antiproliferation Assay 56
2.3.10.1 Determination of Optimum Seeding Concentration for
MTT Assay 56
2.3.10.2 Cell Plating 62
2.3.10.3 Test Sample Preparation 63
2.3.10.4 End Point Measurement 65
2.3.10.5 Screening Strategy and Criteria for Activity 66
2.3.11 Apoptosis 68
2.3.11.1 Cell Morphological Examination 68
2.3.11.2 DNA Nick-End Labelling 68
2.3.12 Photosensitizing Activity 69
CHAPTER 3 RESULTS 71
3.1 Evaluation of the Extraction Methodology 71
3.1.1 Extraction Yields 71
3.1.2 Antiproliferative Activity 73
3.1.3 Chemical Constituents 76
3.2 Fractionation of the Active Extracts 79
3.2.1 Hexane Extract 79
3.2.2 DCM Extract 84
3.2.3 Selectivity Studies on Several Active Fractions 88
3.3 Isolation and Identification of Active Constituents 89
3.3.1 Isolation of the Constituents of Fraction D/F19 89
3.3.2 Characterisation and Structure Elucidation 92
vii 3.3.2.1 D/F19/03 92
3.3.2.1.1 Physical Characteristic 92
3.3.2.1.2 Ultraviolet-visible Spectroscopy 96
3.3.2.1.3 Infrared Spectroscopy 97
3.3.2.1.4 Nuclear Magnetic Resonance Spectroscopy 100
3.3.2.1.5 Liquid Chromatography-Tandem Mass
Spectrometry 117
3.3.2.2 D/F19/05 122
3.3.2.2.1 Physical Characteristic 122
3.3.2.2.2 Ultraviolet-visible Spectroscopy 124
3.3.2.2.3 Infrared Spectroscopy 125
3.3.2.2.4 Nuclear Magnetic Resonance Spectroscopy 128
3.3.2.2.5 Liquid Chromatography-Tandem Mass
Spectrometry 143
3.3.3 Identification of the Chemical Constituents of D/F21 147
3.3.3.1 Gas Chromatogrgaphy-Mass Spectrometry Analysis 147
3.3.3.2 NMR Analysis 151
3.3.3.3 Further Purification and Analysis of Subfractions of
D/F21 153
3.3.4 Evaluation of Fraction D/F18 154
3.3.5 Identification of Pheophytine-a and Pheophytine-b 155
3.3.6 Purification and Identification of the Chemical Constituents in
Fraction D/F15/03 156
3.3.7 Purification and Identification of the Chemical Constituents
in D/F15/02 161
viii 3.3.7.1 Infrared Spectroscopy 161
3.3.7.2 Gas Chromatography-Mass Spectrometry 164
3.4 In Vitro Anticancer Activity of the Chemical Constituents of
Typhonium flagelliforme 168
3.4.1 Antiproliferative and Photosensitizing Activity of the Subfractions
of D/F19 168
3.4.2 Antiproliferative Activity of the Subfractions of D/F21 171
3.4.3 Antiproliferative Activity of the White Solid Obtained from
D/F15/03 172
3.4.4 Antiproliferative Activity of the Light Yellowish Oil Purified
from D/F15/02 174
3.4.5 Apoptotic Effect of D/F19/03, D/F19/05, D/F19 and D/F21 174
3.4.5.1 Microscopic Observation 174
3.4.5.2 DNA Nick-End Labelling 177
CHAPTER 4 DISCUSSION 180
CHAPTER 5 CONCLUSION 198
REFERENCES 201
APPENDICES 214
LIST OF PUBLICATIONS 234
ix LIST OF TABLES
Page Table 3.1 IC50 of the extracts obtained by various methods of 76 extraction
Table 3.2 Mass yield of fractions obtained from the hexane extract 81 and their chemical composition based on TLC.
Table 3.3 Mass yield of subfractions of H/F1 and H/F13 and their 82 chemical composition based on TLC.
Table 3.4 Mass yield of fractions obtained from the DCM extract and 85 their chemical composition based on TLC.
Table 3.5 Single bond correlation between 13C and 1H in 106 pheophorbide-a (1) determined using the HSQC data.
1 13 Table 3.6 H, C and 2D NMR data of pheophorbide-a (1) in CDCl3 116 acquired at 600 MHz.
Table 3.7 Single bond correlation between 13C and 1H in 132 pyropheophorbide-a (2) determined using the HSQC data.
Table 3.8 1H, 13C and 2D NMR data of pyropheophorbide-a (2) in 142 CDCl3 acquired at 600 MHz.
Table 3.9 Four major chemical constituents of D/F21 determined 149 using GC-MS.
Table 3.10 Chemical constituents of D/F21 subfractions as suggested 154 by GC-MS.
Table 3.11 GC-MS data of the chemical constituents of the white solid 159 from D/F15/03.
Table 3.12 Four major chemical constituents of the oil sample 166 obtained from fraction D/F15/02 determined using GC- MS.
Table 3.13 Inhibitory effect of D/F19/03, D/F19/05 and their 171 respective standards on NCI-H23 and HS578T cells in the case where it was irradiated and not irradiated.
Table 3.14 Antiproliferative activity of D/F21 and its subfractions 171
x LIST OF FIGURES
Page Figure 1.1 Drugs approved by FDA from Jan 1981 to June 2006 by 3 source (total number of drugs, N = 1184).
Figure 1.2 Anticancer agents derived from plants. 7
Figure 1.3 Picture of Typhonium flagelliforme. 9
Figure 1.4 Geographical distribution of Typhonium flagelliforme. 10
Figure 1.5 Chemical structures of the compounds isolated from 14 Typhonium flagelliforme.
Figure 1.6 Cleavage of MTT structure by the dehydrogenase 28 enzyme to form MTT formazan.
Figure 2.1 Flow chart of sample preparation procedure for 38 extraction to be carried out using various extraction methodologies.
Figure 2.2 Prep-HPLC chromatogram of D/F19 detected at 365 nm. 46
Figure 2.3 Optical density corresponding to the various cell seeding 58 concentrations of NCI-H23 cells at 0, 48 and 72 h.
Figure 2.4 NCI-H23 cell growth profile at various seeding 59 concentrations.
Figure 2.5 Optical density corresponding to the various cell seeding 60 concentrations of BALB/c 3T3 cells at 0, 48 and 72 h.
Figure 2.6 BALB/c 3T3 cell growth profile at various seeding 60 concentrations.
Figure 2.7 Optical density corresponding to the various cell seeding 61 concentrations of HS578T cells at 0, 48 and 72 h.
Figure 2.8 HS578T cell growth profile at various seeding 61 concentrations.
Figure 2.9 Schematic diagram of the layout of a 96-well plate 63 arranged for a six-concentration assay.
Figure 2.10 Percentage inhibition versus concentration profile of 65 vincristine sulphate (N = 3 × 3)
xi
Figure 3.1 Extraction yields of fresh plant and dried plant obtained 71 using various extraction methods (Mean ± S.D., N = 3).
Figure 3.2 Total extraction yield of all the extracts obtained using 73 various extraction methods (N = 3).
Figure 3.3 Percentage inhibition versus concentration profile of (A) 74 hexane extracts, (B) DCM extracts, (C) MeOH extracts, obtained using various extraction methods and (D) juice extract (N = 3 × 3).
Figure 3.4 Thin-layer chromatogram of hexane extracts obtained by 77 various extraction methods.
Figure 3.5 Thin-layer chromatogram of DCM extracts obtained by 78 various extraction methods.
Figure 3.6 Thin-layer chromatogram of MeOH extracts obtained by 79 various extraction methods.
Figure 3.7 Growth inhibitory effect shown by the fractions and 83 subfractions of hexane extract at 100 µg/ml on NCI-H23. Dark coloured bars indicate >85 % inhibition (Mean ± S.E.M., N = 3 × 3).
Figure 3.8 IC50 of the active fractions and subfractions of hexane 84 extract. Dark coloured bars indicate samples that inhibited NCI-H23 cells at IC50 <15 µg/ml (Mean ± S.E.M., N = 3 × 3).
Figure 3.9 Growth inhibitory effect shown by the fractions of DCM 87 extract at 100 µg/ml on NCI-H23. Dark coloured bars indicate >85 % inhibition (Mean ± S.E.M., N = 3 × 3).
Figure 3.10 IC50 of the active fractions of DCM extract. Dark 88 coloured bars indicate samples that inhibited NCI-H23 cells at IC50 <15 µg/ml (Mean ± S.E.M., N = 3 × 3).
Figure 3.11 Inhibitory effect of the active fractions on BALB/c 3T3 89 and NCI-H23 (Mean ± S.E.M., N = 3 × 3).
Figure 3.12 HPLC chromatogram of (A) D/F19/00, (B) D/F19/01, 91 (C) D/F19/02, (D) D/F19/03, (E) D/F19/04 and (F) D/F19/05 obtained on an Atlantis dC18, 4.6 × 150 mm, 5 µm column.
xii Figure 3.13 UPLC chromatograms of D/F19/03 obtained by UV 92 detection (top) and MS (bottom).
Figure 3.14 Expanded mass spectrum and elemental composition of 94 the first constituent of D/F19/03.
Figure 3.15 Expanded mass spectrum and elemental composition of 95 the second constituent of D/F19/03.
Figure 3.16 Chemical structure of pheophorbide-a (1). 96
Figure 3.17 UV-Vis spectrum of D/F19/03. 97
Figure 3.18 Infrared spectrum of D/F19/03 prepared in KBr pellet. 99
13 Figure 3.19 C NMR spectrum of D/F19/03 in CDCl3 obtained at 101 150 MHz.
1 Figure 3.20 H NMR spectrum of D/F19/03 in CDCl3 obtained at 104 600 MHz.
Figure 3.21 Part I (top) and part II (bottom) of the expanded COSY 105 spectra of D/F19/03.
Figure 3.22 Part I (top), part II (bottom) and part III (next page) of 108-109 the expanded HMBC spectrum of D/F19/03.
Figure 3.23 NOESY spectrum of D/F19/03. 110
Figure 3.24 Structures of (132R)-pheophorbide-a (top) and (132S)- 115 pheophorbide-a (bottom) with arrows indicating NOESY correlation.
Figure 3.25 UPLC chromatogram of D/F19/03 (top) and 117 pheophorbide-a standard (bottom) at approximately 3 µg/ml.
Figure 3.26 MS/MS spectra of (A) second constituent of D/F19/03, 119 (B) first constituent of D/F19/03, (C) second constituent of pheophorbide-a standard and (D) first constituent of pheophorbide-a standard.
Figure 3.27 Expanded MS/MS spectrum of the first constituent of 120 D/F19/03.
Figure 3.28 Fragment ions of pheophorbide-a (1). 121
Figure 3.29 UPLC chromatograms of D/F19/05 obtained by UV 122 detection (top) and MS (bottom).
xiii Figure 3.30 Expanded mass spectrum and elemental composition of 123 D/F19/05.
Figure 3.31 Chemical structure of pyropheophorbide-a (2). 124
Figure 3.32 UV-Vis spectrum of D/F19/05. 125
Figure 3.33 Infrared spectrum of D/F19/05 prepared in KBr pellet. 127
13 Figure 3.34 C NMR spectrum of D/F19/05 in CDCl3 obtained at 129 150 MHz.
1 Figure 3.35 H NMR spectrum of D/F19/05 in CDCl3 obtained at 133 600 MHz.
Figure 3.36 COSY spectrum of D/F19/05. 134
Figure 3.37 Part I (top), part II (bottom) and part III (next page) of 136-137 the expanded HMBC spectrum of D/F19/05.
Figure 3.38 NOESY spectrum of D/F19/05. 138
Figure 3.39 Structure of pyropheophorbide-a (2) with arrows 141 indicating NOESY correlation.
Figure 3.40 UPLC chromatogram of D/F19/05 (top) and 143 pyropheophorbide-a standard (bottom) at approximately 8 µg/ml.
Figure 3.41 Expanded MS/MS spectrum of D/F19/05. 145
Figure 3.42 Fragments ions of D/F19/05. 146
Figure 3.43 Total ion chromatogram (TIC) of fraction D/F21 148 obtained on a HP-5MS column (30 m × 0.25 mm).
Figure 3.44 Chemical structures of methyl hexadecanoate (3), 1- 150 hexadecene (4) and phytol (5).
1 Figure 3.45 H NMR spectrum of fraction D/F21 in CDCl3 acquired 152 at 400 MHz.
Figure 3.46 TLC of the subfractions of D/F21 observed at (A) 254 153 nm and (B) 365 nm using a mobile phase of CHCl3- EtOAc, 19:1 (v/v).
Figure 3.47 HPLC chromatogram of (A) fraction D/F19 and (B) 155 fraction D/F18 obtained on Nucleosil C18, 4.6 × 250 mm, 5 µm, using ACN-0.1% acetic acid, 95:5 (v/v).
xiv Figure 3.48 Chemical structures of pheophytine-a and pheophytine-b 156
Figure 3.49 Overlay of the chromatograms of the white solid purified 158 from D/F15/03 and the stigmasterol standard.
Figure 3.50 Chemical structures of campesterol (6), stigmasterol (7) 160 and β-sitosterol (8).
Figure 3.51 Infrared spectrum of the oil sample obtained from D/F15. 162
Figure 3.52 Infrared spectral data match for the oil sample from 163 D/F15/02 (top) and linoleic acid (bottom) obtained from the Thermo Nicolet Sampler library.
Figure 3.53 Total ion chromatogram (TIC) of the oil sample obtained 165 from D/F15/02.
Figure 3.54 Chemical structures of palmitic acid (9), oleic acid (10), 167 linoleic acid (11) and linolenic acid (12).
Figure 3.55 Inhibitory effect of D/F19 and its subfractions on NCI- 169 H23 in the case where it was irradiated and not irradiated (Mean ± S.E.M., N = 3 × 2).
Figure 3.56 Inhibitory effect of D/F19, D/F19/03 and D/F19/05 on 170 HS578T in the case where it was irradiated and not irradiated (Mean ± S.E.M., N = 3 × 2).
Figure 3.57 Growth inhibition profile of the sterol mixture and the 173 stigmasterol standard on NCI-H23 (Mean ± S.E.M., N = 3 × 2).
Figure 3.58 Growth inhibition profile of the sterol mixture and 173 stigmasterol standard on HS578T (Mean ± S.E.M., N = 3 × 2).
Figure 3.59 Morphology of NCI-H23 after 24 h of incubation with 175 (A) control cells, 12.50 µg/ml of (B) D/F19/03 (pheophorbide-a), C) D/F19/05 (pyropheophorbide-a) and D) D/F19 (arrows show cell shrinkage and membrane blebbing).
Figure 3.60 Morphology of NCI-H23 after 24 h of incubation with 176 (A) control cells and (B) 50 µg/ml of fraction D/F21 (original magnification: 32 ×).
xv
Figure 3.61 Morphology of HS578T after incubation for 24 h with 177 (A) control cells, (B) 50.00 µg/ml of D/F19/03, (C) 25.00 µg/ml of D/F19/05 and (D) 25.00 µg/ml of D/F19 (arrows indicate accumulation of sample in cell).
Figure 3.62 Images of NCI-H23 treated with (A) control cells, (B) 178 3.13 µg/ml of D/F19, (C) 12.50 µg/ml of D/F19/03 and (D) 6.25 µg/ml of D/F19/05 (arrows show stained cell nuclei which mark DNA fragmentation).
Figure 3.63 Images of NCI-H23 (A) control cells and (B) cells 179 treated with 12.50 µg/ml of D/F21 (arrows show stained cell nuclei which mark DNA fragmentation).
Figure 3.64 Images of HS578T (A) control cells and (B) cells treated 179 with 12.50 µg/ml of D/F19 (arrows show stained cell nuclei which mark DNA fragmentation).
xvi LIST OF SYMBOLS AND ABBREVIATIONS
δ Chemical shift
J Coupling constant
I Spin quantum number
1D One dimensional
2D Two dimensional
ACN Acetonitrile
AR Analytical grade reagent
ATCC American Type Culture Collection
BPI Base peak intensity
BuOH Butanol
CDCl3 Deuterated chloroform
CHCl3 Chloroform
COSY Homonuclear Shift Correlation Spectroscopy
DAB Diaminobenzidine
DCM Dichloromethane dd Doublet of doublet
DEPT Distortionless Enhancement by Population Transfer
DMEM Dulbeco’s Modified Eagle’s Medium
DMSO Dimethyl sulphoxide
DNA Deoxyribonucleic acid dq Doublet of quadruplet
DQF Double quantum filtered dUTP Biotin-16-deoxyuridine triphosphate
xvii EDTA Ethylenediaminetetracetic acid
EI Electron impact ionisation
EtOAc Ethyl acetate
EtOH Ethanol
FBS Fetal bovine serum
FDA Food and Drug Administration, United States
FT Fourier Transform
GC Gas chromatography
GR General purpose reagent, for analysis
HEPES N-2 hydroxyethylpiperazine-N'-2-ethanesulphonic acid
HMBC Heteronuclear Multiple Bond Coherence
HPLC High performance liquid chromatography
HSQC Heteronuclear Single Quantum Correlation
IC50 Concentration of a test substance that is required for 50 %
inhibition in vitro
ICCVAM Interagency Coordinating Committee on the Validation of
Alternative Methods i.d. Internal diameter
IR Infrared
IUPAC International Union of Pure and Applied Chemistry m Multiplet
MEM Eagle’s Minimal Essential Medium
MeOH Methanol
MS Mass spectrometry
MS/MS Tandem mass spectrometry
xviii MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide
NCI National Cancer Institute, United States
NIST National Institute of Standards and Technology
NMR Nuclear magnetic resonance
NOE Nuclear Overhauser effect
NOESY NOE difference spectroscopy
OD Optical density
PBS Phosphate buffer saline
PDA Photodiode array
PDT Photodynamic therapy ppm Parts per million prep-TLC Preparative thin-layer chromatography prep-HPLC Preparative high performance liquid chromatography q Quadruplet
Q-TOF Quadrupole-Time of flight
Rf Retention factor rpm Revolution per minute
RPMI Rosewell Park Memorial Institute rTdT Recombinant terminal deoxynucleotidyl transferase s Singlet
S.E.M. Standard error mean
Streptavidin-HRP Horseradish-peroxidase-labeled streptavidin t Triplet
TIC Total ion chromatogram
TLC Thin layer chromatography
xix TMS Tetramethylsilane
TUNEL rTdT mediated dUTP Nick-End Labelling
UV Ultraviolet v/v Volume by volume
Vis Visible
WHO World Health Organisation
xx KAJIAN FITOKIMIA TYPHONIUM FLAGELLIFORME (LODD.) BLUME
(ARACEAE) BERPANDUKAN AKTIVITI ANTIKANSER IN VITRO
ABSTRAK
Typhonium flagelliforme (Lodd.) Blume merupakan sejenis tumbuhan tempatan yang digunakan sebagai ubat herba tradisional terhadap berbagai jenis penyakit kanser. Untuk mengetahui tindakan farmakologi, keselamatan dan keberkesanan tumbuhan herba ini dengan lebih terperinci, kandungan kimia dan kesan biologinya perlu dikenalpasti dan dicirikan terlebih dahulu.
Suatu kaedah pengekstrakan yang sesuai telah dipilih dengan teliti pada peringkat awal kajian ini. Tiga jenis kaedah pengekstrakan yang mempunyai cara tindakan yang berlainan, iaitu soxhlet, pengekstrakan yang dibantui ultrasonik dan rendaman telahpun dikaji. Kaedah rendaman merupakan kaedah pengekstrakan yang paling sesuai kerana ekstrak yang diperolehi adalah lebih aktif dan mempunyai kepelbagaian kandungan kimia yang tinggi, walaupun ia mempunyai peratusan hasil yang lebih rendah berbanding dengan kaedah-kaedah lain. Kajian juga menunjukkan bahawa pelarut-pelarut tidak polar seperti heksana dan diklorometana paling sesuai digunakan untuk mengekstrak sebatian-sebatian aktif dalam tumbuhan ini.
Tiga fraksi daripada ekstrak diklorometana, iaitu D/F19, D/F21 dan D/F15 telah dikaji. D/F19 merupakan fraksi yang paling aktif terhadap turunan sel NCI-H23
(kanser paru-paru manusia) tetapi ia juga didapati aktif terhadap turunan sel bukan kanser BALB/c 3T3. D/F21 merupakan fraksi yang kedua paling aktif dan mempunyai spesifikasi yang bagus terhadap NCI-H23 berbanding dengan BALB/c
3T3. D/F15 merupakan fraksi utama Typhonium flagelliforme yang mempunyai
xxi kesan antiproliferat yang sederhana. Feoforbid-a dan pirofeoforbid-a merupakan dua sebatian utama yang dipencilkan daripada fraksi D/F19. Metil heksadekanoat, 1- heksadekena, fitol dan suatu terbitan fitol merupakan kandungan kimia yang mungkin terdapat dalam D/F21. Kampesterol, stigmasterol, β-sitosterol, asid palmitik, asid oleik, asid linoleik dan asid linolenik merupakan kandungan kimia
D/F15.
Kesan antiproliferat D/F19 didapati bukan dihasilkan oleh komponen tunggal tetapi adalah hasil tindakan sinergistik daripada campuran komponen-komponen.
D/F19 megaruhkan kematian sel mengikuti laluan apoptosis. Di samping itu, D/F19 juga didapati mempunyai kesan pengfotopekaan terhadap NCI-H23 dan suatu turunan sel payu dara manusia, HS578T, yang dihasilkan daripada aktiviti feoforbid- a, pirofeoforbid-a dan suatu lagi subfraksinya, iaitu D/F19/04. Feoforbid-a dan pirofeoforbid-a merupakan agen pengfotopekaan cahaya yang telah dibuktikan berkesan secara in vitro dan in vivo untuk digunakan dalam terapi fotodinamik.
Fraksi D/F21 didapati mempunyai aktiviti antiproliferat dan dapat mengaruhkan apoptosis. Kesan ini mungkin adalah disebabkan oleh aktiviti fitol. Walaupun kandungan kimia D/F15 merupakan sebatian-sebatian yang biasa ditemui dalam tumbuh-tumbuhan, sebatian-sebatian ini dipercayai dapat menyumbang kepada kesan rawatan Typhonium flagelliforme terhadap kanser berdasarkan kepada hasil-hasil penyelidikan lain yang telah dilaporkan.
Secara keseluruhan, kandungan kimia Typhonium flagelliforme yang mempunyai aktiviti antikanser secara in vitro telah berjaya dikenalpasti melalui pendekatan bioaktiviti berpandu. Kajian ini menyokong penggunaan Typhonium flagelliforme secara etnoperubatan terhadap kanser.
xxii IN VITRO ANTICANCER ACTIVITY GUIDED INVESTIGATION OF THE
PHYTOCHEMICALS OF TYPHONIUM FLAGELLIFORME (LODD.)
BLUME (ARACEAE)
ABSTRACT
Typhonium flagelliforme (Lodd.) Blume is an indigenous plant of Malaysia used as a traditional herbal medicine to treat various types of cancer. In order to effectively understand its pharmacological action, safety and efficacy, it is essential to firstly identify and characterise its chemical constituents and their biological relevance to the healing effect of the plant.
A suitable extraction methodology was carefully selected at the preliminary stage of this study. Three types of extraction methods with different modes of action, namely soxhlet, ultrasonic-assisted extraction and maceration methods were evaluated. The maceration method proved to be the most suitable extraction methodology for the purpose of this study with regard to the better activity and greater diversity of the chemical constituents obtained in the extract although the extraction yields were lower. The study also found that extraction carried out using non-polar solvents like hexane and dichloromethane is most suitable in obtaining the active chemical constituents.
Three fractions of the dichloromethane extracts, namely D/F19, D/F21 and
D/F15 were evaluated. D/F19 was the most active fraction on NCI-H23 (human lung cancer) cell line but the fraction was also active on BALB/c 3T3 non-tumourous cell line. D/F21 was the second most active fraction with good specificity for NCI-H23 as compared to BALB/c 3T3. D/F15 was the major fraction of Typhonium
xxiii flagelliforme with moderate antiproliferative effect on NCI-H23. Pheophorbide-a and pyropheophorbide-a were the two major constituents isolated from D/F19. Methyl hexadecanoate, 1-hexadecene, phytol and a derivative of phytol were tentatively suggested to be the constituents in D/F21. Campesterol, stigmasterol, β-sitosterol, palmitic acid, oleic acid, linoleic acid and linolenic acid were the chemical constituents of D/F15.
The antiproliferative effect of D/F19 did not originate from a single component but was due to synergistic action from a mixture of components. Cell death was induced by D/F19 via the apoptotic pathway. In addition, D/F19 was also found to possess photosensitizing effect on NCI-H23 and a breast cancer cell line,
HS578T, mainly due to the activity of pheophorbide-a, pyropheophorbide-a and another of its subfraction, D/F19/04. Pheophorbide-a and pyropheophorbide-a are photosensitizers proven in vitro and in vivo to be effective for use in photodynamic therapy. Fraction D/F21 was found to be antiproliferative and apoptosis inducing.
This effect may be due to the result of the activity of phytol. Although the chemical constituents of D/F15 were commonly found in plants, these compounds are believed to also contribute to the healing effect of Typhonium flagelliforme against cancer as supported by many reported studies.
In short, the chemical constituents of Typhonium flagelliforme which possess in vitro anticancer activity have been identified based on a bioactivity guided approach. The study supports the ethnomedical use of Typhonium flagelliforme as a herbal remedy towards cancer.
xxiv CHAPTER 1
INTRODUCTION
1.1 Medicines from Plants
Plants have formed the basis for treatment of diseases in traditional medicine for thousands of years. It is the oldest and most natural form of medicine even at the present time. The World Health Organisation (WHO) estimated that about 80% of the world’s inhabitants today still rely on plants as their primary source of medicine and health care agents (Farnsworth et al., 1985). Early drugs or so called ‘folk medicine’ took the form of crude drugs prepared as tinctures, teas, poultices, powders, infusions and inhalants (Geddes & Grosset, 2000). The drug discovery trend then evolved into the isolation of their active constituents such as codeine, aspirin, quinine and morphine of which some are still in use today (Ng, 2004). Out of
119 chemical substances that were isolated as drugs, above 74 % were discovered as a direct result of chemical studies which focused on the isolation of active substances from plants used in traditional medicine (Farnsworth et al., 1985). However, despite the many successes of plants as a source of medicine, the process of drug discovery from natural products has been a historically slow process, and the traditional natural product extract libraries were not compatible with high-throughput screening (Koehn
& Carter, 2005).
In the beginning of 1990s, with the advent of combinatorial chemistry, many big pharmaceutical companies switched their drug discovery strategies to include a large proportion of combinatorial chemistry (Balkenhohl et al., 1996). The ability of combinatorial chemistry to generate huge amount of compound libraries which would then undergo high-throughput screening to identify the lead compounds has been thought to be an efficient approach and thus carries great promise (Lee &
1 Breitenbucher, 2003). In addition, most of the synthetic compound libraries have no issues with intellectual property right and biodiversity conservation as those experienced with natural products (Baker et al., 1995; Fischli et al., 2002). However, by the mid to end of 1990s, results from the early combinatorial libraries had been a great disappointment with almost no lead compounds ever generated despite a few hits (Lahana, 1999). The inability of the synthetic libraries to generate lead compounds of biological relevance is mainly due to the different chemical space occupied by the synthetic compounds compared to natural products (Butler, 2004).
Synthetic compounds have lower molecular weights, higher number of nitrogen, halogen and sulphur atoms but lower content of oxygen than natural products
(Henkel et al., 1999). In addition, these compounds have less chiral centres, less complex structures and are greater in flexibility compared to natural products.
Structural flexibility results in entropic losses that weaken the binding with protein molecules where the therapeutic effect is exerted (Feher & Schmidt, 2003).
In the present decade, there has been a renewed interest in natural product research due to the failure of other alternative drug discovery methods to produce lead compounds in key therapeutic areas particularly immunosuppresion, antiinfectives, anticancer and metabolic diseases (Butler, 2004). Although natural products isolated as the active compounds were sometimes not suitable for direct development into an effective drug, it can provide a suitable lead for conversion into clinically useful agents (Young, 1999; Hall et al., 2001). Some of the examples of new drugs derived from natural sources are apomorphine, which is a morphine derivative isolated from Papaver comniferum used to treat Parkinson’s disease; arteether, an antimalarial drug developed from artemisinin isolated from Artemisia annua; vinflunine, an improved anticancer agent derived from vinblastine isolated
2 from Catharanthus roseus; tiotropium, a derivative of atropine isolated from Atropa belladonna for the treatment of bronchospasm associated with chronic obstructive pulmonary disease and many others (Balunas & Kinghorn, 2005; Chin et al., 2006).
Statistics have shown that among the drugs approved by FDA from 1981 to 2006, those of natural products origin contributed a substantial amount of 52 % (Cragg et al., 1997; Newman et al., 2003; Newman & Cragg, 2007) as shown in Figure 1.1.
Thus this indicates that natural products still play an important and irreplaceable role as a source of modern pharmaceuticals.
S*/NM V S* B 10% 4% 4% 14% S/NM N 10% 5%
ND S 23% 30%
Legends: V = vaccine B = biological such as peptide or protein N = natural product ND = derived from a natural product (semisynthetic) S = totally synthetic S* = synthetic but pharmacophore was from a natural product NM = natural product mimic
Figure 1.1: Drugs approved by FDA from Jan 1981 to June 2006 by source (total number of drugs, N = 1184). (Source: Newman & Cragg, 2007, p.472).
3 1.2 Plants as a Source of Anti-cancer Agents
According to the National Cancer Institute (NCI) of the United States, cancer is defined as ‘a disease in which abnormal cells divide without control and are able to invade other tissues’ (National Cancer Institute, 2009). This disease occurs mainly due to the mutation of certain genes that resulted in the disruption of cell growth regulation, repair of cell damage and growth inhibition (King & Robins, 2006).
Human cancers can generally be classified into several categories. Carcinomas are malignant tumours that originated from epithelial tissues. Sarcoma refers to cancer that is mesenchymal in origin, such as the bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Neoplasms of the hematopoietic system are termed leukemia if it originates from the blood forming tissue, or lymphoma if it begins from the cells in the immune system (Ruddon, 1995).
Cancer is one of the major diseases affecting mankind with approximately
10.9 million people around the world diagnosed with cancer every year of which
45% are from Asia (Ferlay et al., 2004). Mortality as a result of cancer is estimated to be 6.7 million per year, which is 12% of total deaths that occur annually (Ferlay et al.,
2004; Ma & Yu, 2006). In Malaysia, cancer is the fourth leading cause of death among the medically certified deaths with an annual incidence of 30,000 people (Lim,
2002). It is estimated that out of four Malaysians, one is expected to get cancer in his/her lifetime. The most common cancers found among men are lung, nasopharynx, colon, leukaemia, rectum and prostate while in women the common types of cancer are breast, cervix, colon, ovary, leukaemia and lung (Lim et al., 2003).
The approaches to the treatment of cancer are surgery, radiotherapy, immunotherapy and chemotherapy. Surgery is usually the first choice of treatment with the goal to remove totally or at least reduce the mass of tumour. However, in
4 many cases, secondary tumours have established by the time the primary tumour is detected, thus chemotherapy and radiotherapy usually follow after surgery (King &
Robins, 2006). Chemotherapy involves the use of cytotoxic or cytostatic drugs to kill or prevent malignant cells from proliferating (Cragg et al., 1996). The efficacy of the drug depends on the concentration of the drug that reaches the tumour, the duration of exposure and the proportion of the population that is proliferating. In many cases however, the action of chemotherapeutic drugs are not specific towards malignant cells alone but affects proliferating cells throughout the body and can be toxic to vital organs such as the heart and kidney, resulting in numerous untoward side effects. To minimise these unwanted effect, many chemotherapists use combinations of drugs which have additive effects against tumours but have less toxicities to normal cells
(Boyer & Tannock, 1998).
Alkylating agents are drugs that act through covalent bonding of the alkyl groups to intracellular macromolecules. The formation of a positively charged intermediate compound combines with the electron-rich nucleophilic groups such as amino, phosphate, sulfhydryl or hydroxyl moiety that are present in the DNA, resulting in lethal toxicity to the cell. Examples of anticancer drugs in this category are such as the nitrogen mustards and nitrosoureas (Neidle & Thurston, 2005).
Antimetabolites are drugs that inhibit nucleic acid synthesis and prevent normal cell division from occurring. Examples of drugs in this category are methotrexate, 5-fluorouracil and cytosine arabinoside. These drugs are cell cycle- specific and exert toxicity on other proliferating cells such as the bone marrow cells and gastrointestinal mucosa (Highley et al., 2009).
The third category of anticancer drugs is the natural products. It covers a substantial percentage of the total amount of anticancer drugs introduced in the time
5 frame of 1981–2006, whereby 77.8% were either natural products per se or derived from natural products (Newman & Cragg, 2007). There are four major classes of natural products based anticancer drugs which are derived from plants and these have quite diverse mechanism of actions. The first anticancer drugs of this category are the vinca alkaloids, vincristine and vinblastine, isolated from the Madagascar periwinkle, Caranthus roseus. These compounds block mitosis with metaphase arrest by binding specifically to tubulin resulting in its depolymerization (Okouneva et al.,
2003) and are useful for the treatment of leukaemia, lymphoma, breast and lung cancers (Cragg & Newman, 2005). Another class of compounds which also affect the microtubules by causing tubular bundling are the taxanes, paclitaxel and docetaxel, extracted from pacific yew tree Taxus brevifolia (Hirose & Takiguchi,
1995). Paclitaxel is used primarily for the treatment of breast, ovarian and non-small cell lung cancer (Wall & Wani, 1996). The epipodophyllotoxins, etoposide and teniposide, derived from the mandrake plant Podophyllum peltatum are DNA topoisomerase II inhibitors. These drugs are used against lymphoma, bronchial and testicular cancers (Gordaliza et al., 2004). Camptothecin is a selective inhibitor of topoisomerase I which was isolated from the stem bark of the Chinese tree
Camptotheca acuminate. It is used against breast, lung and colorectal cancers (Wall
& Wani, 1996). Many other drugs which are derived from these four major classes of compounds are currently under clinical trials (Balunas & Kinghorn, 2005). The chemical structures of some of the anticancer agents derived from plants are given in
Figure 1.2.
6 N OH
O N N H O N N O O O H O N O OH O R H OH O O
Vinblastine: R = CH3 Campthothecin Vincristine: R = CHO
O O O O O O OH OH O
H O NH O H O NH O
O O O O O O OH O O OH OH OH O O O O
Docetaxel Paclitaxel
H S O O O O O O O HO O HO OH OH O O O O O O O O
O O O O
OH OH
Etoposide Teniposide
Figure 1.2: Anticancer agents derived from plants.
There are approximately 250,000 plant species distributed throughout the world and more than half of these are found in the tropical rainforests (Wilson, 1988).
7 So far, only 1% of tropical species have been explored for their pharmaceutical potentials and there remain a substantial opportunity for finding more new compounds of pharmaceutical interests (Zuhud, 1991; Fakim, 2006). The vast variety of flora and fauna hosted by the tropical rainforests provide natural product chemists with numerous compounds as starting point for the development of new anticancer drugs.
Malaysia is home to about 40,000 species of higher plants of which about
36,000 are flowering plants, 3,600 are ferns and 87 are conifers (Soepadmo, 1998).
In addition to the magnificent array of plant species, Malaysia has a unique confluence of traditional medicine system due to the diverse ethnic communities in the country. The rich ethnobotanical and ethnopharmacological knowledge in the use of plants has provided a good starting point for Malaysian scientists for locating useful tropical plants for phytochemical investigation. To make use of these advantages, the present study selected Typhonium flagelliforme as the subject of study since it has been used locally as an alternative treatment for cancer but has not been investigated in depth scientifically.
1.3 Typhonium flagelliforme (Lodd.) Blume
1.3.1 Taxonomy and Distribution
Typhonium flagelliforme (Lodd.) Blume is a herbal plant indigenous to
Malaysia which belongs to the family of Araceae under the subfamily of Aroid. The tuber of the plant is nearly round and measures about 1 cm in diameter. The leaves are green and smooth, typically narrowly hastate with spreading basal lobes but may be elliptic sometimes. The size of the blade is about 6 × 4 cm. The petiole is yellowish and thin, it measures about 6–20 cm long, partially enclosed in the spathe.
8 The colour of the spathe is green with brownish margin, the limb is linear acute, dilated and round at the base. The flowers are unisexual (Hsuan et al., 1998;
Nicolson & Sivadasan, 1981). A picture of Typhonium flagelliforme is given in
Figure 1.3.
Figure 1.3: Picture of Typhonium flagelliforme.
Typhonium flagelliforme, which was previously mistakenly regarded as
Typhonium divaricatum, is distributed across IndoChina, Peninsular Malaysia,
Northern Queensland, South India, Sri Lanka and Luzon as shown in Figure 1.4
(Nicolson & Sivadasan, 1981). It grows wild in waste grounds and is native to several parts of Peninsular Malaysia such as the ditches in Melaka town and the
Sepoy lines in Penang (Ridley, 1967). However, due to developments and
9 deforestations, these plants are no longer found in the mentioned areas but are mostly cultivated in pots and garden yards for personal consumption.
Figure 1.4: Geographical distribution of Typhonium flagelliforme (Source: Nicolson
& Sivadasan, 1981, p.491).
1.3.2 Ethnomedical Background
Typhonium flagelliforme, known by its vernacular name of Keladi Tikus
(Malay) or Rodent Tuber (English), is described as toxic, warming and phlegm- resolving in the Malaysian Traditional Chinese Medicine. The leaves or whole plant is often applied over swellings and used against various kinds of malignancy. The roots are used to eliminate expectoration (Lee & Wong, 2004). There have been many accounts on the uses of Typhonium flagelliforme for treating cancer, including colon, breast, prostrate, liver, lung and bone cancer. Many cancer patients who have tried such alternative therapy have claimed successes while others who took this
10 during the course of chemotherapy have experienced significant improvement in appetite, reduction in hair loss with no cases of nausea and vomiting (Teo & Ch’ng,
1999).
The use of three other species of Typhonium has also been documented in the
Traditional Chinese Medicine and Ayurvedic system for the treatment of cancer. In
China, the tuber of Typhonium giganteum, the major component of Herbal Medicine
Rhizoma Typhonii is applied externally in the form of paste to the lesion for the treatment of reticulocytic sarcoma and lymphoma (Chang, 1992). In India, the poultice of Typhonium trilobatum is used to treate Scirrhous tumours and cancerous tumours, while Typhonium orixense is used by the Indians and Pakistanis to treat
Scirrhous tumours (Hartwell, 1982).
Each preparation of Typhonium flagelliforme requires the use of approximately 50 g of the fresh whole plant. The plant is pounded briefly using a mortar and pestle to break the cell walls and the juice is then forced out through a thin cloth. The juice extract is then mixed with honey in order to prevent irritation to the throat and is recommended to be consumed immediately. Initially, the juice is to be drunk 3 times daily and can be reduced to a maintenance dose of twice a week if improvement is observed. This can either be used as a single therapy or taken while undergoing the course of chemotherapy or radiotherapy (Neoh, 1992; Teo & Ch’ng,
1999). There are also other less commonly used preparative methods of Typhonium flagelliforme, such as wrapping 2–6 pieces of the plant leaves in Longan flesh for direct consumption (Lee & Wong, 2004) and pulverising the dried plant material to prepare as a drink which is not documented. Of late, encapsulated dried plant powder of the plant is also available commercially (Global Bioscience, 2007).
11 1.3.3 Pharmacological Studies
In vitro studies carried out on the various extracts of Typhonium flagelliforme
(then wrongly referred as Typhonium divaricatum (Nicolson & Sivadasan, 1981) revealed that the hexane, chloroform (CHCl3) and ethyl acetate (EtOAc) extracts exhibited significant cytotoxic effect on a murine lymphoid cell line with the rate of inhibition above 90%. However, the concentration of the extract tested and the cell line designation was not specified (Neoh, 1992). Choo et al. (2001a) had also observed cytotoxic activity for the hexane and CHCl3 extracts on P388 leukemia cells and the IC50s were found to be 15 µg/ml and 6 µg/ml respectively for the root extracts, 65 µg/ml and 8 µg/ml respectively for the stems/leaves extracts. Chan et al.
(2005) also found the hexane, CHCl3 and n-butanol (n-BuOH) extracts to be active towards NCI-H23 human lung cancer cell line at IC50 1.8, 5.2 and 1.2 µg/ml, respectively, and T-47D human breast cancer cell lines at IC50 12.2, 23.0 and 54.6
µg/ml, respectively.
A study on the effect of T. flagelliforme on the immune system of cat fish found that the plant, given as intraperitoneal injections, was able to increase phagocytic activity and other non-specific immune response. Resistance of the cat fish against live Vibrio parahaemolyticus was also found to have increased (Lam,
1998). Another in vivo study conducted in rats showed that T. flagelliforme juice extract had a similar effect as glycyrrhizin in preventing hepatocarcinogenesis
(Karuppiah et al., 1999). Other pharmacological studies also showed that the water, alcohol and ester extracts of Typhonium flagelliforme is antiasthmatic, antiinflamatory, analgesic, sedative, antiexpectoration and cough relieving (Zhong et al., 2001).
12 1.3.4 Phytochemicals
Chen et al. (1997) reported the isolation of benzenetridecanoic acid (synonym:
13-phenyltridecanoic acid) and methyl benzenetridecanoate (synonym: methyl 13- phenyltridecanoate) from the ethyl acetate extract of Typhonium flagelliforme. Four other esters, namely methyl hexadecanoate, methyl octadecanoate, methyl 9- octadecenoate and methyl 9, 12-octadecadienoate were also identified by Choo et al.
(2001b) from the hexane extract of Typhonium flagelliforme in addition to methyl
13-phenyltridecanoate. However, despite the earlier report by Choo et al. (2001a) which showed that the CHCl3 extracts were more active than the hexane extracts, no study was carried out on the CHCl3 extracts. Huang et al. (2004a,b) had isolated several glycosides, namely coniferin, methylconiferin, 12-hydroxy-N-(3-hydroxy-1-
O-β-glucopyranosyloctadeca-4E,8E-dienyl)octadecanamide and two sterols, β- sitosterol and β-daucosterol from the n-BuOH fraction of Typhonium flagelliforme.
The chemical structures of the constituents are illustrated in Figure 1.5. Except for methyl 13-phenyltridecanoate that was found to be inactive in vitro, none of the chemical constituents had been tested for anticancer activity in the studies mentioned and none was used to support its ethnopharmacological application against cancer.
13 O
OCH3
O Methyl 13-phenyltridecanoate
OH
13-Phenyltridecanoic acid O
H3CO
Methyl octadecanoate O
H3CO Methyl hexadecanoate O
H3CO
O Methyl 9,12-octadecadienoate
H3CO
Methyl 9-octadecenoate
OH
O HO O OCH3 OH HO OH H CO O 3 HO O OH HO OH Methyl coniferin H3CO
Coniferin OH O OH NH O HO O HO OH OH 2-Hydroxy-N-(3-hydroxy-1-O-β-glucopyranosyloctadeca-4E, 8E-dienyl)octadecanamide
OH HO OH
HO O O OH β-Sitosterol β-Daucosterol
Figure 1.5: Chemical structures of the compounds isolated from Typhonium flagelliforme.
14 1.4 Methods of Plant Extraction
Extraction can be carried out on either fresh or dried plants. Ideally, fresh plant tissues should be used for phytochemical investigation right after collection
(Harborne, 1998). However, if extraction is to be carried out a few days after collection, it should be stored dry in a plastic bag (Harborne, 1998). Alternatively, dried plants can also be used and has several advantages. Unlike in the case of fresh plant, solubility of the chemical constituents in the dried plants is not affected by the presence of water. It is also easier to handle when large scale extraction is carried out due to the lower mass to plant ratio (Eloff, 1998). However, when dried plant is intended for use, the material needs to be dried rapidly to prevent degradation of the components by air or microorganisms. If a vacuum system is used for drying, care should be taken in order to avoid excessive loss of the volatile constituents which may possess interesting biological activity (Fakim, 2006).
Nowadays, many extraction methods are available. The more commonly used methods are such as cold extraction, hot percolation, soxhlet, supercritical fluid extraction, ultrasonic-assisted solvent extraction and pressurized liquid extraction
(Péres et al., 2006; Barnes et al., 2009). However, careful selection of the right extraction methodology is needed so that it is adaptable to the intended study (Fakim,
2006). The improper extraction methods may result in degradation and loss of bioactive natural products which seriously hampers the outcome of the study (Davey et al., 2009). Three common and inexpensive extraction methodologies that were evaluated in this study are briefly introduced in the following sections.
15 1.4.1 Maceration
The maceration method is the simplest but yet still widely used procedure.
Pulverised plant material is allowed to soak in solvents of differing polarity in a closed container at room temperature (Fakim, 2006). The metabolites are allowed to diffuse into the solvent and the period of extraction may differ from few hours to several weeks. Occasional or constant stirring is used sometimes to speed up the extraction. The disadvantage of this method is that it consumes large volumes of solvents and some of the poorly soluble metabolites may not be extracted efficiently since extraction is carried out at room temperature (Seidel, 2006).
1.4.2 Soxhlet Extraction
Soxhlet extraction is a classical and most widely used extraction method.
Pulverised plant material is placed in a cellulose thimble in an extraction chamber which is located above a collecting flask but beneath a reflux condenser. A suitable solvent is then added into the soxhlet apparatus and the solvent is heated to a boil.
The solvent vapour rises and condenses into the thimble. When the thimble is filled with the solvent, it is siphoned back into the distillation flask and the whole cycle is then repeated (Pavia et al., 1995). The main advantage of Soxhlet extraction is that the solvent, when saturated with solubilized metabolites, is emptied into the distillation flask and fresh solvent is recondensed into the extraction thimble continuously, thus making the extraction procedure more efficient and solvent saving.
However, the major disadvantage of this method is that the extraction carried out at high temperature may degrade thermolabile compounds and initiate the formation of artefacts (Seidel, 2006).
16 1.4.3 Ultrasonic-assisted Solvent Extraction
The ultrasonic-assisted solvent extraction is a technique modified from the maceration method. This solvent extraction method is facilitated by the use of ultrasound (frequency pulses approximately 20 kHz) and is one of the well established and commonly used methods today for extracting plant materials for bioactive principles (Sališová et al., 1997; Trusheva et al., 2007). The pulverised plant material is soaked in a suitable solvent in a container and ultrasound is used to induce mechanical stress on the plant which results in the formation of cavitations in the sample. The cellular breakdown allows easier access of the solvent into the cells thereby increases the solubility of the metabolites in the solvent. In addition the ultrasound also facilitates mass transfer and thus is a more efficient method of extraction (Vinatoru et al., 1997). However, the huge amount of energy generated increases extraction temperature and thus a cooling system is required in order to control the temperature.
1.5 Techniques of Separation
1.5.1 Thin-layer Chromatography
Thin-layer chromatography (TLC) is a simple, cheap and quick method for analysis and screening of natural products. Thin layers of adsorbents, usually silica gel or alumina, is coated on glass, plastic and aluminium sheets. The TLC sheets can be cut into strips of various sizes according to the desire of the user. A mixture of natural products is then spotted near the bottom of the thin strip and developed in a jar that contains saturated atmosphere of the eluting solvent. The eluting strength of the solvent is varied by mixing two or more solvents with different polarity. As the mobile phase moves up the plate through capillary action, the components of the
17 mixture are carried along at different rates and hence separate from one another. The development of the plate is complete when the solvent front has advanced nearly to the top of the plate. The separated compounds on the TLC plate can be detected by ultraviolet (UV) illumination or spray with suitable detection reagent. TLC is frequently used to determine the optimal combinations of solvent for preparative column chromatography separations and to monitor the progress of separation by column chromatography (Gilbert & Martin, 1998).
Preparative thin-layer chromatography (prep-TLC) is a scaled up procedure of TLC and is used to separate compound mixtures at a larger scale. Prep-TLC is normally used as a final purification step in compound isolation, most frequently after column chromatography. The chromatographic conditions for prep-TLC can be predetermined using a TLC plate by trial and error experimentation and then scale up in proportion using a similar or slightly less polar solvent combination. The separated compounds are either detected by the non-destructive UV method or by using a spray reagent. When using a reagent, only a small section at the edge of the plate is sprayed, and the unreacted section of a particular separation band is scraped from the plate and desorbed from the silica sorbent using an appropriate solvent that is able to dissolve the compound (Gibbons, 2006).
1.5.2 Column Chromatography
Column chromatography plays a very important role in the separation of compounds from a complex mixture of natural products. The principle of separation takes place through selective distribution of the components between the mobile phase, which is the eluting solvent, and the stationary phase, which is usually the silica gel. Different compounds have different adsorption affinities for the surface of
18 the stationary phase and the extent of adsorption is governed by the types of interaction between the compound molecule and the stationary phase such as hydrogen bonding, Van der Waals forces, dipole-dipole interactions, acid-base properties and others (Gilbert & Martin, 1998). The column can be developed using various eluting techniques such as gravity, application of nitrogen pressure at the inlet, vacuum suction or controlled by a pump. A solvent gradient is applied for separation of complex mixtures of compounds where the composition of the solvents is varied in steps so as to gradually increase the eluting strength of the mobile phase.
The different rate of movement of the chemical constituents along the column then results in the separation of the compound mixture (Reid & Sarker, 2006). However, for a complex mixture of natural products such as crude extracts, compounds with similar polarity often co-elute in the same fraction and thus, chromatography may be carried out several times using different chromatographic conditions in order to obtain reasonably pure compounds.
Nowadays, the use of flash column chromatography has largely replaced classic column chromatography techniques. Flash column chromatography is an air pressure driven column chromatography which has been optimized for rapid separations. The smaller particle size of the silica gel and rapid flow rate was able to overcome poor separation recovery which is a problem faced in classic column chromatography due to band tailing (Landgrebe, 1993). In addition, the technique is inexpensive, easy to operate and allows separation of samples weighing between
0.01–10.0 g in a short period of time (Still et al., 1978). This method is currently a preferred technique for routine large scale purification of natural products.
19 1.5.3 High Performance Liquid Chromatography
High performance liquid chromatography (HPLC) is a modern day analytical technique derived from the same working principle as for column chromatography.
Compared to classical column chromatography, HPLC offers major advantages in convenience, speed, accuracy, selectivity and the ability to carry out difficult separations owing to the improvements in equipment sophistication, material, technique and the application of theory (Rouessac & Rouessac, 2007). The general setup of a HPLC system consists of a high-pressure pump, an injection port, a column which is the stationary phase, and a detector. The sample is introduced into the injection port and is carried by the stream of mobile phase delivered by the pump which then passes through the column where the separation takes place. Separation is then monitored with a detector.
Two modes of adsorption chromatography are available in HPLC, i.e. normal-phase and reversed-phase chromatography. Reversed-phase HPLC is generally preferred by many researchers as it is applicable to a wide range of chemical compounds. This mode of separation utilises the combination of a non- polar stationary phase and a polar mobile phase which is usually a combination of acetonitrile and/or methanol with an aqueous solution. Acids, bases or buffers are frequently used as the aqueous solution with the purpose of suppressing compound ionisation and to control the degree of ionisation of free unreacted silanol groups in the column that can result in peak tailing which in turn affect the separation (Snyder
& Kirkland, 1979).
For a long time the size of the HPLC column have been standardised around the internal diameter of 3–4.6 mm, which requires a mobile phase flow rate of 0.5–2 ml/min. However, a wide choice of column now exists such as narrow-bore (2–4 mm
20 i.d.), microbore (1–2 mm i.d.) and even packed capillaries (<1 mm), for which the flow rate descends to a few µl/min and thus requires special pumps and detectors.
Such developments were necessary as there has been increased demand for the determination of analyte at trace level concentrations over the recent years (Rouessac
& Rouessac, 2007). Ultra high-performance liquid chromatography with the trade name of UPLC (Waters) or UHPLC (Agilent) is an improved version of HPLC. With the UPLC or UHPLC pump capable of operating at extremely high pressure limit, the system is designed to be used with sub-2 µm particle columns leading to exceptionally better resolution, sensitivity and separation speed due to the much improved column efficiency. Furthermore, when the system is integrated with a mass spectrometer, often termed as ‘hyphenation’, it allows provisional identification of an unknown natural product sample, thus further expand the potential and versatility of the analytical instrument (Niessen, 1999).
While an analytical HPLC is used for qualitative and quantitative determination of a compound, a preparative HPLC (prep-HPLC) is meant for isolation and purification of a compound. Purification of natural products using prep-
HPLC has been widely adopted by many synthetic and natural product chemists to date as the demand for higher throughput could be better met in an automated prep-
HPLC system. Moreover, the reproducibility, efficiency and consistency in compound separation are better in prep-HPLC compared to conventional column chromatography. Depending on the amount of sample intended to be purified, a wide range of prep-HPLC columns are available to cater for sample from µg scale up to kg level (Huber & Majors, 2004).
21 1.6 Compound Identification and Structure Elucidation
1.6.1 Ultraviolet-visible Spectroscopy
Natural products absorb light in the ultraviolet or visible (UV-Vis) region of the electromagnetic spectrum. Absorption of the UV-Vis light occurs when the energy of the incident radiation is the same as the electronic excitation of the molecule (Lambert et al., 1976). An unknown natural product can be identified according to the complexity of its spectrum and the general position of the wavelength maxima. Different classes of compounds have their characteristic light absorption spectra and the identification of the class of compounds can be enhanced by performing measurements on the sample solution at different pH or in the presence of a particular inorganic salt and then observing the shift of the absorption band (Harborne, 1998).
1.6.2 Infrared Spectroscopy
Infrared (IR) radiation is the part of electromagnetic spectrum in between the visible and microwave regions. The portion which is of greatest practical use for a natural product chemist is the mid-IR region, which ranges from 4000 – 400 cm-1. A molecule that possesses an oscillating dipole absorbs energy from the oscillating electric field of a beam of infrared radiation when the IR frequency of the applied electric field is similar to the frequency of the oscillating dipole. Except for homonuclear diatomics, practically all molecules have some vibrations that produce a change of dipole moment (Lambert et al., 1976). The wavelength of absorption depends on the relative masses of the atoms, the force constants of the bonds between the atoms and the geometry of the atoms (Silverstein, et al., 2005).
22 A mid-IR spectrum can generally be evaluated in two parts. The region between 4000 – 1300 cm-1 is called the functional group region where characteristic stretching frequencies for important functional groups, such as O-H, N-H, C-H, C=O and C=C, are observed. The region between 1300–900 cm-1 is referred to as the
“fingerprint” region where the complex absorption bands originated from interacting vibrational modes. Absorption at this region is unique for every type of molecule and can be used to cross examine the types of vibration in reference to the other regions.
Due to its simplicity and reliability in identifying the functional groups, IR spectroscopy is an extremely useful method of assigning a compound to its class
(Silverstein et al., 2005; Harborne, 1998).
1.6.3 Nuclear Magnetic Resonance Spectroscopy
Nuclear Magnetic Resonance (NMR) Spectroscopy is practically an indispensable tool used for the identification and structure elucidation of natural products. Akin to IR and UV spectroscopy, it is another form of absorption spectroscopy that takes place in the radio frequency region. All nuclei are charged particles and some in addition have spin angular momentum. The nuclei of interest are those that have appropriate spin properties (spin quantum number, I ≠ 0) and generate a magnetic field. 1H and 13C nuclei (both having I = ½) have the widest application for identification of organic molecules.
In the presence of an external magnetic field, a spinning nucleus absorbs radiofrequency radiation, which has a magnitude that is identical to the Larmor frequency, resulting in nuclear transition to a higher energy spin state (Silverstein et al., 2005). However, a nucleus within a molecule experiences a lesser magnetic field than the applied external field. This phenomenon is due to the presence of electron
23 cloud around the nucleus which generates an induced magnetic field opposed to the external field termed as the “shielding effect”. The density of the shielding varies with the chemical environment of the nucleus and the variation gives rise to differences in chemical shift positions and the ability to distinguish among individual absorptions, hence the usefulness of NMR spectroscopy (Macomber, 1998).
Chemical shift is measured relative to a reference compound, which is usually tetramethylsilane (TMS).
Based on a 1H NMR spectrum, the relative positions of the various types of protons in a molecule can be determined by evaluation of its chemical shifts, spin- spin couplings and peak integral. Similarly, a 13C NMR spectrum provides information on the relative positions of various types of carbons in a molecule. Due to the low abundance of 13C nucleus and high abundance of 1H nucleus in nature as well as the large C-H coupling constants, a proton-coupled carbon spectrum usually shows complex overlapping multiplets which are difficult to interpret. Thus, for routine analysis of sample, a broadband proton-decoupled 13C spectrum is frequently used, where each type of carbon nucleus is represented by a single peak, making the interpretation much simpler (Silverstein et al., 2005). Distortionless enhancement by
13 population transfer (DEPT) C NMR displays separate subspectra for CH, CH2 and
CH3 carbon signals. Three types of DEPT experiments using three different pulse angles, θ, at 45°, 90° and 135° are available. A combination of DEPT experiments helps distinguish the types of protonated carbons. Any remaining carbon signal in the normal 13C spectrum which is not present in the DEPT subspectra would belong to the quaternary carbons (Macomber, 1998).
Two-dimensional (2D) NMR spectroscopy is also referred to as correlation spectroscopy where the correlation between two or more types of the same or
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