Through a continuing search for anticancer compounds as part of an International Cooperative Biodiversity Grant program, the extracts of two plants were selected for study on the basis of their cytotoxic activity. These extracts were further fractionated to yield four compounds. The structures of these compounds were elucidated with mass spectrometry and 1-D and 2-D NMR spectroscopy. The ethyl acetate extract of the twigs of Garcinia macrophylla from Suriname was weakly cytotoxic in the A2780 human ovarian cancer cell bioassay. The known benzophenone guttiferone A and a new guttiferone analog, named guttiferone G, were isolated from the extract and found to be responsible for the bioactivity. A known triterpene, friedelin, was also isolated from the extract and found to be inactive. The structure of guttiferone A was determined by comparison of its NMR data to those found in the literature. The structure of guttiferone G was determined by comparison to guttiferone A and through careful examination of both 1D and 2D NMR data. An extract of Bridelia tulasneana from Madagascar yielded one compound. It was identified as the known lignan deoxypodophyllotoxin and was responsible for the bioactivity. It was identified by a comparison of its spectral data to those found in the literature and those of an authentic sample. / Master of Science

MSc (Chemistry) / Department of Chemistry / Bridelia micrantha (Hochst) Baill (B. micrantha) is a South African medicinal plant used by traditional healers in the treatment of different human ailments including diabetes, gastrointestinal ailments, joint aches, cough, conjunctivitis, skin problems and malaria. Previous studies have demonstrated the antidiabetic activities of B. micrantha crude extracts in in vivo studies. However, there are no studies on the compounds responsible for the antidiabetic activity of the plant. The purpose of this study was to isolate and characterize the antidiabetic constituents from B. micrantha. Materials and methods Crude methanolic extracts of root, stem and leaf were investigated using in vitro antidiabetic enzyme assays. Antioxidant activities were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing power assays. The isolation of the antidiabetic constituents was carried out using column chromatography on silica gel. Purification of the active fraction was carried out using preparative thin layer chromatography (pTLC). Structure elucidation of the compound was carried out using Nuclear Magnetic Resonance (NMR) spectroscopy and by comparison with literature. Results The results obtained in this study indicated that root, stem and leaf extracts exhibited high inhibition activity against α-glucosidase (98.52, 98.62 and 81.62% respectively). A moderate inhibition against α-amylase enzyme was observed for root (65.62%) and stem (61.86%) extracts. Leaf fraction LFR5 exhibited a high inhibition activity of 96.19% against α-glucosidase. Moreover, the isolated compound showed 96.74% inhibition against α-glucosidase. DPPH results revealed that antioxidant activity of crude extracts was not significantly different and they were concentration-dependent. Reducing power results revealed that stem (119.31 μg/mL) extract had higher activities compared to root (125.17 μg/mL) and leaf (291.88 μg/mL) extracts. Conclusion Quercetin-3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnoside was successfully isolated from B. micrantha leaves. Furthermore, quercetin-3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnoside demonstrated the ability to inhibit significantly the carbohydrate hydrolysing enzyme α-glucosidase and therefore validate the ethnomedicinal use of B. micrantha in the management of diabetes / Bridelia micrantha (Hochst) Baill (B. micrantha) is a South African medicinal plant used by traditional healers in the treatment of different human ailments including diabetes, gastrointestinal ailments, joint aches, cough, conjunctivitis, skin problems and malaria. Previous studies have demonstrated the antidiabetic activities of B. micrantha crude extracts in in vivo studies. However, there are no studies on the compounds responsible for the antidiabetic activity of the plant. The purpose of this study was to isolate and characterize the antidiabetic constituents from B. micrantha. Materials and methods Crude methanolic extracts of root, stem and leaf were investigated using in vitro antidiabetic enzyme assays. Antioxidant activities were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing power assays. The isolation of the antidiabetic constituents was carried out using column chromatography on silica gel. Purification of the active fraction was carried out using preparative thin layer chromatography (pTLC). Structure elucidation of the compound was carried out using Nuclear Magnetic Resonance (NMR) spectroscopy and by comparison with literature. Results The results obtained in this study indicated that root, stem and leaf extracts exhibited high inhibition activity against α-glucosidase (98.52, 98.62 and 81.62% respectively). A moderate inhibition against α-amylase enzyme was observed for root (65.62%) and stem (61.86%) extracts. Leaf fraction LFR5 exhibited a high inhibition activity of 96.19% against α-glucosidase. Moreover, the isolated compound showed 96.74% inhibition against α-glucosidase. DPPH results revealed that antioxidant activity of crude extracts was not significantly different and they were concentration-dependent. Reducing power results revealed that stem (119.31 μg/mL) extract had higher activities compared to root (125.17 μg/mL) and leaf (291.88 μg/mL) extracts. Conclusion Quercetin-3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnoside was successfully isolated from B. micrantha leaves. Furthermore, quercetin-3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnoside demonstrated the ability to inhibit significantly the carbohydrate hydrolysing enzyme α-glucosidase and therefore validate the ethnomedicinal use of B. micrantha in the management of diabetes.