The aim of this thesis was to investigate the chemical and biochemical properties of the Malian medicinal plants Terminalia macroptera and Biophytum umbraculum, with main focus on its phenolic substances. This thesis is a part of a research project in which the ultimate goal is to provide efficient, non-toxic and inexpensive medicines for the Malian population.
Extraction and purification of fractions from T. macroptera resulted in the isolation of several polyphenolic compounds such as hydrolyzable tannins and flavonoids. Chebulic acid trimethyl ester is a novel compound isolated from T. macroptera. B. umbraculum was found to be a good source of flavone-C-glycosides, and cassiaoccidentalin A, a rare natural product, was the major one. The crude extracts and pure compounds obtained were tested in various in vitro bioassays to determine their bioactivity as antioxidants, α-glucosidase inhibitors, antimalarial agents as well as their toxicity.
Ethnopharmacological studies revealed that 86 % of the traditional practitioners used T. macroptera for a variety of medical indications such as wounds, pain, cough, tuberculosis, hepatitis, and diabetes. The semipolar extracts, the ethyl acetate (EtOAc) extract in particular, were found to be very strong α-glucosidase inhibitors, strong 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavengers and 15-lipoxygenase (LO) inhibitors, and moderate xanthine oxidase (XO) inhibitors. None of the extracts or the isolated compounds seemed to be very toxic towards brine shrimp larvae.
B. umbraculum was used for treating cerebral malaria (CM) by more than 50 % of the interviewed traditional practitioners, and was thus tested in two CM-related in vitro assays in addition to the antiplasmodial activity assay. The semipolar plant extracts showed high complement inhibition of the classical pathway and dose-dependent inhibition of nitric oxide (NO) release from activated macrophages. Additionally, the EtOAc extract displayed moderate antimalarial activity against the erythrocyte stages of Plasmodium falciparum. The antioxidant activity was also evaluated, and the semipolar extracts displayed strong radical scavenging and 15-LO inhibitory effects, but less activity towards XO.
List of papers. Papers I., III. and V. are removed due to publisher copyright policies.
Paper I Anh Thu Pham, Christina Dvergsnes, Adiaratou Togola, Helle Wangensteen, Berit Smestad Paulsen, Drissa Diallo and Karl Egil Malterud. Terminalia macroptera, its current medicinal use and future perspectives. Journal of Ethnopharmacology 2011, 137, 1486-1491. doi:10.1016/j.jep.2011.08.029.
Paper II Anh Thu Pham, Karl Egil Malterud, Berit Smestad Paulsen, Drissa Diallo and Helle Wangensteen. DPPH Radical scavenging and xanthine oxidase inhibitory activity of Terminalia macroptera leaves. Natural Product Communications 2011, 6, 1125-1128
Paper III Anh Thu Pham, Karl Egil Malterud, Berit Smestad Paulsen, Drissa Diallo and Helle Wangensteen. a-Glucosidase inhibition, 15-lipoxygenase inhibition and brine shrimp toxicity of extracts and isolated compounds from Terminalia macroptera leaves. Pharmaceutical Biology 2014, 52, 1166-1169. doi:10.3109/13880209.2014.880486.
Paper IV Anh Thu Pham, Celine Nguyen, Karl Egil Malterud, Drissa Diallo and Helle Wangensteen. Bioactive flavone-C-glycosides of the African medicinal plant Biophytum umbraculum. Molecules 2013, 18, 10312-10319, doi:10.3390/molecules180910312.
Paper V Ingvild Austarheim, Anh Thu Pham, Celine Nguyen, Yuan-Feng Zou, Sibylle Sax, Sergio Wittlin, Karl Egil Malterud, Drissa Diallo and Helle Wangensteen. The Malian medicinal plant Biophytum umbraculum as adjuvant treatment of cerebral malaria. Manuscript.