Browsing by Author "Wachira, Sabina Wangui"

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    Novel antimicrobial terpenoids and other natural products from four annonaceae species.
    (University of Dar es Salaam, 2002) Wachira, Sabina Wangui
    This thesis reports on phytochemical investigations of four plant species of the family Annonaceae, namely Artabotrys brachypetalus, Monanthotaxis fornicata, Polyalthia tanganyikensis and Uvaria scheffleri. The pet ether extract of the root bark of U. scheffleri yielded the novel compounds 3,5-dimethoxycarvacrol, a mixture of two dimers of a quinone methide of 3,5-dimethoxycarvacrol and the trimer schefflone. All the compounds showed antifungal activity in vitro against a Fusarium species, Botryodiplodia theobromae and Aspergillus niger, and antibacterial activity in vitro against Pseudomonas phaseolicola and Staphyloccocus aureus. The dimers and schefflone have been envisioned as products of a conceivable Diels Alder cycloaddition reaction involving the quinone methide as the dime and dienophile respectively. Schefflone was racemic, as established by X-ray diffraction analysis. The dichloromethane extract of the stem bark of A. brachypetalus yielded a tetrahydroxylated, monotetrahydrofuran annonaceous acetogenin whose stereochemistry is still not fully established due to inadequate spectral and other information. The relative positions of the tetrahydrofuran and the hydroxyl groups were deduced based on NMR and MS data. This is the first time that an annonaceous acetogenin has been isolated from the genus Artabotrys. This compound showed antifungal and antibacterial activities in vitro against the above stated organisms. P. tanganyikensis yielded a mixture of benzopyranyl terpenoids that are related to tocopherols which constitute vitamin E. From the pet ether extract of the stem bark of M. fornicata a unique partial ring A aromatized flavone dasytrichone, which was previously reported from Dasymaschalon trichophorum (Annonaceae), was isolated. These results have again demonstrated the occurrence of a diversity of natural product classes in the family Annonaceae.