Browsing by Author "Jonker, Stephan A."

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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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    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.