Browsing by Author "Nkunya, Mayunga H. H."

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    Antifungal Enantiomeric Styrylpyrones from Sanrafaelia ruffonammari and Ophrypetalum odoratum
    (Springer Link, 2014) Malebo, Hamisi M.; Kihampa, Charles; Mgina, Clarence A.; Sung’hwa, Fortunatus; Waibel, Reiner; Jonker, Stephan A.; Nkunya, Mayunga H. H.
    Phytochemical investigation of Sanrafaelia ruffonammari Verd and Ophrypetalum odoratum Diels that belongs to the rare genera confined to East African coastal forests led to the isolation of enantiomeric styrylpyrone dimer, (±)-5-methoxy-7-phenyl-[4-methoxy-2-pyronyl]-1-(E)-styryl-2-oxabicyclo-[4.2.0]-octa-4-en-3-one (1) alongside (+)-6-styryl-7,8-epoxy-4-methoxypyran-2-one (2) and the enantiomeric (+)- (3) and (-)-6-styryl-7,8-dihydroxy-4-methoxypyran-2-ones (4). Their structures were established by means of spectroscopic methods. In this paper we reveal for the first time the occurrence of styrylpyrones in East African biodiversity. (+)-6-Styryl-7,8-epoxy-4-methoxypyran-2-one (2) and the dihydroxystyrylpyrone enantiomer (3) showed in vitro antifungal activity against Candida albicans at a concentration of 24.4 and 26.2 µM with zones of inhibition of 17 and 9 mm, respectively. Compound 2 exhibited strong activity in the brine shrimp test with LC50 = 1.7 µg/mL. Their high cytotoxic and antifungal activities render them candidates for further scientific attention for drug development programs against cancer and microbial infections.
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    Cleistenolide and cleistodienol: Novel bioactive constituents of Cleistochlamys kirkii
    (2007-01) Nyandoro, Stephen S.; Mdachi, Stephen; Nkunya, Mayunga H. H.; Irungu, Beatrice N.; Moshi, Mainen; Moulton, Brian; Luisi, Brian S.
    (-)-5-Acetoxy-6-(1-benzoyloxy-2-acetoxyethyl)-pyr-3-en-2-one (cleistenolide) and (-)-2, 6-diacetoxy-5-hydroxy-cyclohex-3-enylidenemethyl benzoate (cleistodienol) were isolated as novel antimicrobial and cytotoxic constituents of Cleistochlamys kirkii (Annonaceae), together with (Z)-(+)-5-(2, 3-dihydroxy-propylidene)-5H-furan-2-one and its acetyl and benzoyl derivatives, (-)-1, 6-desoxy-β-senepoxide, pinocembrin and polycarpol. Structural determination was achieved based on spectroscopic and other physical data. The structure of cleistenolide was confirmed by single crystal X-ray crystallographic analysis.
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    New Antimicrobial, Mosquito Larvicidal and Other Metabolites from Two Artabotrys Species
    (Taylor & Francis, 2013) Nyandoro, Stephen S.; Joseph, Cosam C.; Nkunya, Mayunga H. H.; Hosea, Ken M.
    Azabicycloheptenoylditerpene 1-((2E,6E,10E)-3,7,11,15-tetramethylhexadeca-2,6,10,14-tetraenyl)-2-azabicyclo[2.2.1]hept-5-en-3-one (artamodamide, 1), diphenylpentanoid (E)-1,5-bis(4-hydroxyphenyl)-pent-1-en-3-one (artamenone, 2) and N-methoxy-5-oxoaporphinoid (artamonteirine, 3) were isolated as new metabolites from Artabotrys modestus Diels ssp macranthus Verdc. and Artabotrys monteiroae Oliv. (Annonaceae), together with several known compounds. Structures of the isolated compounds were established based on analysis of their spectroscopic data. Some of the compounds exhibited antimicrobial activity (minimum inhibitory concentration values between 2.5 and 20 µg mL−1) and varying levels of mosquito larvicidal potency. These results further indicate the versatility of the family Annonaceae in accumulating bioactive natural products with diverse chemical structures and wide spectra of biological activities, and hence suggesting the need to conserve Annonaceae species that are potentially vulnerable to extinction.
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    New antimicrobial, mosquito larvicidal and other metabolites from two Artabotrys species
    (Taylor & Francis, 2012-09) Nyandoro, Stephen S.; Joseph, Cosam C.; Nkunya, Mayunga H. H.; Hosea, Ken M.
    Azabicycloheptenoylditerpene 1-((2E,6E,10E)-3,7,11,15-tetramethylhexadeca-2,6,10,14-tetraenyl)-2-azabicyclo[2.2.1]hept-5-en-3-one (artamodamide, 1), diphenylpentanoid (E)-1,5-bis(4-hydroxyphenyl)-pent-1-en-3-one (artamenone, 2) and N-methoxy-5-oxoaporphinoid (artamonteirine, 3) were isolated as new metabolites from Artabotrys modestus Diels ssp macranthus Verdc. and Artabotrys monteiroae Oliv. (Annonaceae), together with several known compounds. Structures of the isolated compounds were established based on analysis of their spectroscopic data. Some of the compounds exhibited antimicrobial activity (minimum inhibitory concentration values between 2.5 and 20 µg mL−1) and varying levels of mosquito larvicidal potency. These results further indicate the versatility of the family Annonaceae in accumulating bioactive natural products with diverse chemical structures and wide spectra of biological activities, and hence suggesting the need to conserve Annonaceae species that are potentially vulnerable to extinction.
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    Ophrypetalin and Other Annonaceous Acetogenins From Ophrypetalum Odoratum
    (Taylor and Francis, 1999-05) Sung'hwa, Fortunatus; Mgina, Clarence A.; Jonker, Stephan A.; Nkunya, Mayunga H. H.; Waibel, Reiner; Achenbach, Hans
    Ophrypetalin, a new bis-tetrahydrofuran acetogenin, was isolated from Ophrypetalum odoratum (Annonaceae) together with the known acetogenins desacetyluvaricin, rolliniastatin-1, dieporeticenin and a mixture of dieporeticanin-1, dieporeticanin-2, and diepoxyrollin. the structures were elucidated by spectroscopic methods. the absolute configurations were established by Mosher's method and by CD measurements.