The use of indigenous plants by native healers has been in healthcare system for a long time. It is prevalent in many developing countries because of its wide benefits and rising popularity. But less is known about the chemistry behind the medicinal properties of those indigenous plants. Unraveling the knowledge helps develop drugs based on the indigenous plants and understand their mechanisms of the action. Malaria happens to be a vector borne protozoan parasitic disease which has been reported to affect 229 million people in 2019. Use of indigenous plant for treating malaria is widely practiced and this had led to the development of two anti-malarial drugs, artemisinin, and quinine. Clerodendrum polycephalum, also known as ‘egungun eja’ or ‘ewe agbosa’ or ‘aporo’ by different tribes of Nigeria, is used by native healers as an anti-malarial treatment. However, the anti-malarial effect is not well studied and the chemical compounds responsible for its activity is unknown. The understanding of the chemical composition and their antimalarial activities will provide scientific evidence for its traditional application in malaria treatment. This project was a collaborative research between A/Prof Yunjiang Feng at Griffith Institute for Drug Discovery and Prof. Francis B. Adewoyin at Drug Research and Production Unit, Obafemi Awolowo University, and Prof. Alexander B. Odaibo at Department of Zoology, University of Ibadan; mediated by BIO Ventures for Global Health (BVGH). The Nigerian group analysed the crude extract of Clerodendrum polycephalum based on its traditional use; but lack of expertise in natural product chemistry led to this collaboration. The overall objective was to use bioassay as a guide to isolate antimalarial natural products against Plasmodium falciparum 3D7 drug resistant cell lines. Any novel/new compounds will also be targeted by using 1H NMR guided isolation strategy. Knowing the wide distribution of Clerodendrum around the world, several Australian Clerodendrum sp. were investigated by LC-MS to understand the chemical compositions of samples from different geographic locations. The thesis was started with an introduction chapter which included different concepts such as traditional medicine, malaria, Clerodendrum, bioassay guided fractionation, NMR guided isolation and a brief outline of the project. Traditional medicine (TM) was introduced with a detailed description on African traditional medicine (ATM). It then proceeded with a brief discussion on malaria, its causes, and the current treatment. The chapter then provided a detailed description of genus Clerodendrum, its geographical distribution, traditional use and the biological activity of the plant extract and secondary metabolites. The chapter continued with a brief of bioassay guided fractionation. Finally, the chapter ended with a description of NMR guided isolation of compounds with biological activity. Chapter 2 described detailed experimental procedures involved in this project, including isolation and purification of natural products from the plant species. The chapter also detailed the biological assays as well as the spectroscopic data of the pure compounds. Chapter 3 started with an introduction of Clerodendrum polycephalum, then moved on to the bioassay guided isolation which resulted in four pure compounds, including the new clerodane diterpene lactone A. Considering the difficulties in the isolation process due to the presence of large amount of methyl pheophorbide a, the next batch of crude extract was purified using a revised strategy where the fractionation procedure was modified and 1H NMR was utilized to guide the isolation. This resulted in ten compounds, including four new clerodane diterpene lactone (A-D), one new 12,16-Epoxy-11,14,17-trihydroxy-17(15→16)-abeo- 5,8,11,13,15-abietapentaen-7-one, as well as 5 known compounds, namely, acacetin, methyl pheophorbide a, loliolide, bis (2-ethylhexyl) phthalate and 12,16-Epoxy-6,11,14,17- tetrahydroxy-17(15→16)-abeo-5,8,11,13,15-abietapentaen-7-one. The chemical structures were elucidated by comprehensive analysis of 1D-, 2D-NMR and MS spectroscopic data assisted by density functional theory (DFT) calculated NMR and circular dichroism (CD). The in-vitro activity evaluation against P. falciparum 3D7 revealed that methyl pheophorbide a was active with IC50 values of 4.49 M. The compound showed no cytotoxicity against neonatal foreskin fibroblast (NFF) mammalian cells. Our results provided scientific evidence for the traditional use of Clerodendrum polycephalum in malarial treatment. Chapter 4 aims to investigate whether Clerodendrum sp. collected from different geographic location contain similar chemistry. The chapter started with an introduction of Australian Clerodendrum sp., Griffith University’s NatureBank and the use of LC-MS for screening compounds in plant extracts. Fifteen Australian Clerodendrum were extracted and analyzed by LC-MS. Our results suggested that every compound isolated from Clerodendrum polycephalum was detected in the Australian species. Large scale isolation of Nature Bank sample NB020858 yielded verbascoside, diosmetin-5-o-glucuronide, 4-hydroxywogonin-5-oglucuronide and acacetin-5-o-8-hydroxyglucuronide; among these four compounds verbascoside and an analogue of acacetin-5-o-8-hydroxyglucuronide were also detected in the Nigerian plant extract. Based on the results, we conclude that Clerodendrum plant species from Nigeria and Australia contained same classes of compounds, and chemistry can be used as a tool for plant taxonomic identification.