Phytochemical and Bioactivity Investigations on Aptosimum Elongatum Engl
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Phytochemical and bioactivity investigations on Aptosimum elongatum Engl. extracts Tsebo Sentle Molahloe Phytochemical and bioactivity investigations on Aptosimum elongatum Engl. extracts By Tsebo Sentle Molahloe A dissertation submitted in fulfilment of the requirements for the degree of Master of Science In the Faculty of Natural and Agricultural Sciences Department of Chemistry At the University of the Free State Supervisors: Dr. Susan L. Bonnet Co-Supervisor: Dr. Anke. Wilhelm January 2019 DECLARATION I declare that the dissertation hereby submitted by me for the M.Sc. degree at the University of the Free State is my own independent work and has not previously been submitted by me at another University/Faculty. I further more cede copyright of the dissertation in favour of the University of the Free State. Tsebo Sentle Molahloe Date This dissertation is dedicated to my son, Akhumzi Tsentle Molahloe Acknowledgements The present work was performed at the Chemistry Department of the University of the Free State. At the end of this road, I would like to express my sincere gratitude and appreciation to the following people for their contributions towards this study: A special thanks to My Heavenly Father, GOD, for granting me the opportunity for postgraduate studies, and giving me the strength to finish this degree. His grace is sufficient, and he truly is an awesome GOD. My supervisor, Dr Susan Bonnet; thank you for your patience, guidance, advice, and encouragement throughout the period of my studies. My co-supervisor, Dr Anke Wilhelm; thank you for your guidance and valuable advice. Also a special thanks to Dr Pieter Zietsman (National Museum, Bloemfontein, South Africa) for the collection and identification of plant material. In addition I want to thank Mr E. van Schalkwyk (The Central Analytical Facilities, Stellenbosch University) for performing high resolution mass spectrometry, Dr M. Cawood (Department of Plant science, University of the Free State) for high-pressure liquid chromatography and Dr Marco Stadler (Department of Pharmacology and Toxicology, University of Vienna, Austria) for GABAA receptor activity screening. I am grateful to my colleagues in the Chemistry Department for their help and kindness. A special thank you to the colleagues from my research group for the assistance and especially for the friendly environment and good times we shared. Without your support this dissertation would not have been possible. My parents, Mrs Puseletso Molahloe and Mr Advisor Molahloe; thank you for a lifetime of love, support and encouragement and for giving me the opportunity to further my education. Thank you for believing in me when I sometimes ceased to believe in myself. Finally, I would like to thank the University of the Free State and the National Research Foundation (NRF) for their financial support. Tsebo Sentle Molahloe Table of contents Abstract ................................................................................................................................ List of figures....................................................................................................................... i List of tables ...................................................................................................................... iv List of schemes ................................................................................................................... v Abbreviations .................................................................................................................... vi Chapter 1: Introduction and Aims ................................. 1 Chapter 2: Literature Review ......................................... 4 2. History of phytomedicines and drug discovery .......................................... 4 2.1. Medicinal plants....................................................................................... 4 2.2 Significance of medicinal plants in drug discovery ................................... 7 2.2.1 Analgesic and anticoagulants ............................................................................... 13 2.2.2 Anti-malarial ........................................................................................................ 13 2.3 Approaches to Natural Products Drug Discovery ............................... 15 2.3.1 Traditional methods ............................................................................................. 15 2.3.2 Modern methods .................................................................................................. 16 2.3.2.1 High-throughput screening (HTS) ................................................................ 16 2.3.2.2 Innovative extraction methods ...................................................................... 17 2.3.2.3 Systems biology approach ............................................................................. 18 2.3.3 Advantages and disadvantages of drug discovery from natural products ............ 19 2.4 Selection and collection of plants ............................................................ 20 2.4.1 Criteria for selection of plants of interest............................................................. 20 2.4.2 Collection and identification of a plant specimen ................................................ 20 2.4.3 Preparation of a plant specimen as a herbarium voucher .................................... 20 2.5 General review of the Aptosimum elongatum .......................................... 21 2.5.1 The Scrophulariaceae family ............................................................................... 21 2.5.1.1 The scientific classification of Scrophulariacease family ............................. 21 2.5.1.2 Distribution of the Scrophulariaceae family ................................................. 21 2.5.1.3 Morphology of the Scrophulariaceae family ................................................. 22 2.5.2 The genus Aptosimum ......................................................................................... 22 2.5.2.1 The scientific classification of the Aptosimum genus82 ............................................... 22 2.5.2.2 Distribution of Aptosimum genus ................................................................. 22 2.5.2.3 Morphology of Aptosimum genus ................................................................ 24 2.5.2.4 Phytochemistry of Aptosimum ...................................................................... 26 2.6 A review of analytical methods used in natural product research ........... 27 2.6.1 Phytochemistry screening .................................................................................... 28 2.6.2 Preparation and extraction of plant material ........................................................ 29 2.6.3 Removal of tannins .............................................................................................. 30 2.6.4 Techniques ........................................................................................................... 30 2.6.4.1 Thin layer chromatography ........................................................................... 30 2.6.4.2 Column chromatography ............................................................................... 30 2.6.4.3 High-performance liquid chromatography .................................................... 32 2.6.4.4 Mass spectrometry......................................................................................... 32 2.6.4.5 NMR spectroscopy ........................................................................................ 33 2.6.4.6 Infrared (IR) spectroscopy ............................................................................ 34 2.7 Biological Assays ..................................................................................... 34 2.7.1 Antioxidant activity (Radical scavenging) ........................................................... 34 2.7.1.1 Qualitative testing via thin layer chromatography (TLC) plates ................... 36 2.7.1.2 Quantitative antioxidant testing113 ............................................................................................... 36 2.7.2 Acetylcholinesterase (AChE) inhibition .............................................................. 37 2.7.2.1 TLC bioautographic assay test ...................................................................... 37 2.7.3 Gamma-aminobutyric acid (GABA) .................................................................... 38 2.7.3.1 GABAA receptors .......................................................................................... 38 2.7.3.2 Modulation of GABAA receptors by pharmacological agents ....................... 40 2.8 Conclusion ................................................................................................ 42 Chapter 3: Results and discussion ................................ 43 3.1 Introduction ............................................................................................. 43 3.2 General review of Aptosimum elongatum .............................................. 43 3.2.1 Scientific classification of A. elongatum ............................................................. 43 3.2.2 Distribution of the Scrophulariaceae family ................................................ 44 3.2.3 Morphology of A. elongatum ................................................................... 44 3.3 Phytochemical investigation of A. elongatum ........................................ 45 3.3.1 Plant Collection ...................................................................................................