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Screening and Characterization of Some Anticancer Compounds from Salicaceae, Myrtaceae, Euphorbiaceae and Solanaceae Families

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SCREENING AND CHARACTERIZATION OF SOME ANTICANCER COMPOUNDS FROM SALICACEAE, MYRTACEAE, EUPHORBIACEAE AND SOLANACEAE FAMILIES CHIRCHIR DENIS KIPNGENO A Thesis Submitted to the Graduate School in Partial Fulfilment of the Requirement for the Doctor of Philosophy Degree in Chemistry of Egerton University EGERTON UNIVERSITY OCTOBER, 2019 DECLARATION AND RECOMMENDATION Declaration This research thesis is my original work and has not been submitted wholly or in part for any award in any institution Signature:…………………… Date:…………………… Chirchir Denis Kipngeno SD11/0342/12 Recommendation This thesis has been submitted with our approval as University supervisors. Signature:…………………… Date:…………………… Prof. Peter Kiplagat Cheplogoi, PhD (Posthumous) Department of Chemistry Egerton University Signature:…………………… Date:…………………… Prof. Josiah Ouma Omolo, PhD Department of Chemistry Egerton University ii COPYRIGHT © Copyright 2019 Chirchir Denis Kipngeno All rights reserved. No part of this work may be reproduced, stored in a retrieval system, or transmitted by any means, mechanical, photocopying, electronic process, recording, or otherwise copied for public or private use without the prior written permission from Egerton University. iii DEDICATION This work is dedicated to the late Prof Peter Kiplagat Cheplogoi. iv ACKNOWLEDGEMENT First I thank the Almighty God for the gift of life and strength to undertake this study. I appreciate Egerton University for allowing me to pursue PhD degree in Chemistry. I am thankful to my supervisors; the late Prof P.K Cheplogoi and Prof J. O. Omolo who have natured me to maturity in Natural Product Chemistry. My appreciation also goes to University of Kabianga for allowing me time to pursue PhD and partially funding the project. My deep appreciation goes to Dr. Langat Moses of Surrey University, Guild Ford UK for immense support in NMR spectra acquisition for the isolated compounds. I also acknowledge the support of my PhD colleagues; Dr. Alice Njue and Mrs Regina Kemunto Mayaka for their moral support, brilliant comments and constructive critics that shaped my work. Lastly my sincere appreciation goes to my lovely family, my parents and brothers for their encouragement, moral and material support. v ABSTRACT The chemistry of natural products is very important since it has been used in the search for bioactive compounds for management of various human diseases including cancer. The increase in the incidence of cancer coupled with the undesirable side effects observed with chemotherapic agents urges the discovery of new agents from natural sources. In this study the four ethnomedicinal plants; Dovyalis abyssinica (Salicaceae), Solanum mauense (Solanaceae), Syzigium guinense (Myrtaceae) and Croton dichogamous (Euphorbiaceae) were investigated for their unvalidated anticancer activities. Crude extracts for stem bark of S. guinense, fruits of S. mauense, and roots of both D. abbysinica and roots of C. dichogamous were prepared via cold extraction method. The crude extracts were purified by repeated column chromatography and Thin Layer Chromatography. This resulted in various pure compounds which were analysed by use of 1D NMR, 2D NMR spectroscopic techniques and MS spectrometry. The NMR spectral data obtained together with MS data were interpreted, the structures of the compounds elucidated and their chemical structures proposed. A total of twelve compounds were isolated, purified, their chemical structures proposed and four of these compounds were evaluated for their anticancer activity. Two previously reported compounds; β-sitosterol (47) and betulinic acid (21), were obtained from stem bark extracts of S. guinense as well as from the fruits extracts of S. mauense. Two previously reported compounds; Tremulacin (29) and Benzoic acid (48) were isolated from the roots extract of D. abyssinica. Eight compounds were isolated from roots extract of C. dichogamous; Acetyl aleuritolic acid (49), 3β,4β:15,16-diepoxy-13(16),14-ent-clerodadiene (50), 3β, 4β:15, 16-diepoxy-13(16), 14-ent-clerodadien-17,12S-olide (51), 15,16-epoxy-5, 13(16), 14-ent-halimatriene-3-ol (52), crotodichogamoin A (53), crotohaumanoxide (54), crotodichogamoin B (55) and Cadin-1(6),2,4,7,9-penta-ene (56). Selected compounds were evaluated for their anticancer activity by use of cancer cell lines. Betulinic acid (21) was screened against 57 cell lines and only 25 gave positive results. Acetyl aleuritolic acid (49), 15,16-epoxy-5,13(16),14-ent-halimatriene- 3-ol (52) and crotodichogamoin A (53) were also evaluated for their anticancer activity and and their one dose mean value percentage growth at 15 µg/ml were 97.86, 99.39 and 100.6, respectively. The mean values of growth inhibition of the three compounds tested against one dose NCI cell line panel did not meet the standards for further testing against the five-dose NCI cell line panel. The study recommends toxicological studies be done on the medicinal plants extracts to enhance their full exploitation. vi TABLE OF CONTENTS DECLARATION AND RECOMMENDATION ....................................................................... ii COPYRIGHT ............................................................................................................................... iii DEDICATION.............................................................................................................................. iv ACKNOWLEDGEMENT............................................................................................................ v ABSTRACT .................................................................................................................................. vi TABLE OF CONTENTS ........................................................................................................... vii LIST OF TABLES ........................................................................................................................ x LIST OF FIGURES ..................................................................................................................... xi LIST OF ABBREVIATIONS AND ACRONYMS .................................................................. xii CHAPTER ONE ........................................................................................................................... 1 INTRODUCTION......................................................................................................................... 1 1.1 Background Information ....................................................................................................... 1 1.2 Statement of the Problem ...................................................................................................... 4 1.3 Objectives .............................................................................................................................. 5 1.3.1 General Objective ........................................................................................................... 5 1.3.2 Specific Objectives ......................................................................................................... 5 1.4 Justification ........................................................................................................................... 5 CHAPTER TWO .......................................................................................................................... 6 LITERATURE REVIEW ............................................................................................................ 6 2.1 The Traditional Medicine in Drug Discovery ....................................................................... 6 2.2 Plants With Anticancer Activity ......................................................................................... 11 2.3 Plant Derived Anticancer Agents in Clinical Use ............................................................... 13 2.4 Plant-Derived Anticancer Agents for Future Development ................................................ 15 2.5 The Chemistry of Euphorbiaceae Family............................................................................ 17 2.6 Chemical Constituents of the Croton Genus....................................................................... 18 2.7 Compounds Isolated from Myrtaceae Family ..................................................................... 19 2.8 Compounds from Salicaceae Family................................................................................... 20 2.9 Compounds from Solanaceae Family ................................................................................. 22 2.10 Biosythetic Pathways ........................................................................................................ 23 2.10.1 Biosynthesis of Diterpenoids ...................................................................................... 23 2.10.2 Biosynthesis of Triterpenoids ..................................................................................... 25 2.10.3 Lupane Triterpenoids .................................................................................................. 30 vii 2.10.4 Synthesis of Betulinic Acid ........................................................................................ 31 2.10.5 Biosynthesis of Sitosterol ........................................................................................... 31 2.10.6 Furan Ring Formation via Side-Chain Oxidation....................................................... 32 2.11 Thin Layer Chromatography (TLC).................................................................................
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