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| 2. |
- Kalenga, T. M., et al.
(författare)
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Modified ent-Abietane Diterpenoids from the Leaves of Suregada zanzibariensis
- 2022
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Ingår i: Journal of Natural Products. - : American Chemical Society (ACS). - 0163-3864 .- 1520-6025. ; 85:9, s. 2135-2141
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Tidskriftsartikel (refereegranskat)abstract
- The leaf extract of Suregada zanzibariensis gave two new modified ent-abietane diterpenoids, zanzibariolides A (1) and B (2), and two known triterpenoids, simiarenol (3) and fi-amyrin (4). The structures of the isolated compounds were elucidated based on NMR and MS data analysis. Single-crystal X-ray diffraction was used to establish the absolute configurations of compounds 1 and 2. The crude leaf extract inhibited the infectivity of herpes simplex virus 2 (HSV-2, IC50 11.5 mu g/mL) and showed toxicity on African green monkey kidney (GMK AH1) cells at CC50 52 mu g/ mL. The isolated compounds 1-3 showed no anti-HSV-2 activity and exhibited insignificant toxicity against GMK AH1 cells at >= 100 mu M.
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| 3. |
- Umereweneza, Daniel, et al.
(författare)
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Antibacterial and cytotoxic prenylated dihydrochalcones from Eriosema montanum
- 2021
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Ingår i: Fitoterapia (Milano). - : Elsevier BV. - 0367-326X .- 1873-6971. ; 149
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Tidskriftsartikel (refereegranskat)abstract
- Two new prenylated dihydrochalcones (1,2) and eighteen known secondary metabolites (3−20) were isolated from the CH2Cl2-MeOH (1:1) extracts of the roots, the stem bark and the leaves of Eriosema montanum Baker f. (Leguminosae). The structures of the isolated compounds were characterized by NMR, IR, and UV spectroscopic and mass spectrometric analyses. The structures of compounds 5, 10, 11 and 13 were confirmed by single crystal X-ray diffraction. The antibacterial activity of the crude extracts and the isolated constituents were established against Gram-positive and Gram-negative bacteria. Among the tested compounds, 1–4 and 10 showed strong activity against the Gram-positive bacterium Bacillus subtilis with minimum inhibitory concentration (MIC) ranging from 3.1 to 8.9 μM, as did the leaf crude extract with an MIC of 3.0 μg/mL. None of the crude extracts nor the isolated compounds were active against Escherichia coli. Compounds 1, 3 and 4 showed higher cytotoxicity, evaluated against the human breast cancer cell line MCF-7, with EC50 of 7.0, 18.0 and 18.0 μM, respectively. These findings contribute to the phytochemical understanding of the genus Eriosema, and highlight the pharmaceutical potential of prenylated dihydrochalcones.
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| 4. |
- Umereweneza, Daniel, et al.
(författare)
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Antiviral iridoid glycosides from Clerodendrum myricoides
- 2021
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Ingår i: Fitoterapia. - : Elsevier BV. - 0367-326X .- 1873-6971. ; 155
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Tidskriftsartikel (refereegranskat)abstract
- The methanol root extract of Clerodendrum myricoides (Hochst.) Vatke afforded two new (1, 2) and two known (3, 4) iridoid glycosides. The structures of the isolated compounds were established based on NMR, IR, UV and MS data analyses. The crude extract and the isolated constituents were assayed for antiviral activity against the human respiratory syncytial virus (RSV) in human laryngeal epidermoid carcinoma (HEp-2) cells. The crude extract inhibited RSV infectivity at EC50 = 0.21 mu g/ml, while it showed cytotoxicity against HEp-2 cells with CC50 = 9 mu g/ml. Compound 2 showed 43.2% virus inhibition at 100 mu M, while compounds 1 as well as 3 and 4 had only weak antiviral and cytotoxic activities.
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| 5. |
- Umereweneza, Daniel, et al.
(författare)
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Chemical Composition and Antifungal Activity of Essential Oils Extracted from Leaves of Eucalyptus Melliodora and Eucalyptus Anceps Grown in Rwanda
- 2019
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Ingår i: Journal of Essential Oil-Bearing Plants (JEOBP). - : TAYLOR & FRANCIS LTD. - 0972-060X .- 0976-5026. ; 22:1, s. 151-158
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Tidskriftsartikel (refereegranskat)abstract
- Essential oils were extracted from leaves of Eucalyptus melliodora and Eucalyptus anceps by steam distillation and chemically analysed using GC/MS.The main components obtained in both Eucalyptus species oils were, monoterpenes: 1,8-cineole (47.7 %, 33.49 %) and -pinene (7.8 %, 13.69 %) as dominant components, and sesquiterpenes: aromandrene (1 %, 18.01 %) and allo-aromandrene (1.5 %, 2.37 %), respectively. Caryophyllene (5.1 %) and bicyclogermacrene (4.6 %) were found only in E. melliodora. The antifungal efficacy of these essential oils was assessed against R. nigricans, A. flavus, A. niger, A. parasiticus, F. oxysporum and P. digitatum.The obtained results indicated that essential oil from E. melliodora was the most effective against all tested fungi with minimal inhibitory concentration (MIC) at 3.3 mg/mL for A. flavus. The anti-aflatoxin production test was conducted with essential oil from E. melliodora and A. flavus and A. parasiticus, as aflatoxins producers. The findings clearly showed that concentrations of 6 L/mL and 7 L/mL of the essential oil completely inhibited production of aflatoxins by A. parasiticus and A. flavus, respectively. However, further studies on this essential oil should be conducted to assure its standard use as antiaflatoxin agent.
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| 6. |
- Umereweneza, Daniel
(författare)
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Discovery of Secondary Metabolites from Rwandese Medicinal Plants : Isolation, Characterization and Biological Activity
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plants have served as the principal source of medicines in different parts of the world through the ages. Herb-derived medicines have been used as decoctions, infusions, tinctures or single substance drugs. Due to their impressive possibility of diversification, plants have also provided an immense universe of creativity for synthetic chemists, who constantly make useful new molecules inspired by the natural molecular architecture.The goal of this thesis work was to investigate secondary metabolites isolated from selected Rwandese medicinal plants. It focused specifically on the isolation, the characterization and the determination of the biological activity of natural products. The investigated plants belong to the families of Myrtaceae (Eucalyptus melliodora and Eucalyptus anceps), Fabaceae (Eriosema montanum), Lamiaceae (Clerodendrum myricoides) and Asteraceae (Senecio mannii). These were selected from the Rwandese flora based on information collected from traditional healers, and from the literature. The study made use of chromatographic, spectroscopic and spectrometric methods for separation, purification and structure elucidation of the plant constituents.In paper I, the chemical composition and antifungal activity of essential oils of E. melliodora and E. anceps were discussed. The essential oils were composed of mono- and diterpenes, and their alcohol derivatives. The essential oil mixtures exhibited antifungal activity against food spoilage fungi.In paper II, E. montanum was investigated and a total of 20 compounds were isolated including two new prenylated dihydrochalcones and eighteen known secondary metabolites. Their antibacterial activities and cytotoxicity were determined. In paper III, the isolation of three new and two known iridoid glycosides from C. myricoides was reported along with the antiviral activities of the crude extract and of the isolates. In paper IV, the phytochemical investigation of S. mannii was reported. It afforded one new silphiperfolanol angelate ester, two new macrocyclic pyrrolizidine alkaloids, and five known secondary metabolites. Two new synthetic derivatives were obtained by structural modification of 2-angeloyloxy-5,8-dihydroxypresilphiperfolane. The relative stereochemistry of senaetnine was investigated by NAMFIS and confirmed to be 7R, 12R, and 13R.The new compounds isolated in this study have shown biological activities, and may provide lead compounds for drug discovery and technological applications.
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| 7. |
- Umereweneza, Daniel, et al.
(författare)
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Macrocyclic Pyrrolizidine Alkaloids and Silphiperfolanol Angelate Esters from Solanecio mannii
- 2023
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; 26:8
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Tidskriftsartikel (refereegranskat)abstract
- Three new compounds, the silphiperfolanol angelate ester umutagarananol (1), the macrocyclic pyrrolizidine alkaloids umutagarinine A and B (2-3), and five known secondary metabolites (4-8) were isolated from the CH2Cl2-MeOH (1 : 1) extract of the roots and the stem bark of Solanecio mannii (Hook. f.) (Asteraceae). The isolated compounds were characterized by NMR and IR spectroscopic, and mass spectrometric analyses, whereas the relative stereochemistry of 4 was established by NAMFIS-based combined computational and solution NMR analysis. Synthetic modification of 5 provided two new compounds, 2-angeloyloxy-4,8-epoxypresilphiperfolane (9) and 2-angeloyloxy-4,8-epoxypresilphi-perfolane (10). The crude extracts and the isolated constituents showed weak antibacterial activities (EC50 0.7-13.3 mM) against the Gram-negative Escherichia coli and the Gram-positive Bacillus subtilis. Compounds 2, 3 and 4 exhibited strong cytotoxicity against MCF-7 human breast cancer cells, with EC50 values of 35.6, 21.7 and 12.5 mu M, respectively.
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