Browsing by Author "Makangara, John Joseph"

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    Chemical investigations of the cytotoxic plants: Lettowianthus stellatus and secamone parvifolia
    (University of Dar es Salaam, 1995) Makangara, John Joseph
    This Thesis reports on phytochemical investigations of the root barks of two cytotoxic plants. Lettowianthus stellatus of the family Annonaceae and Secamone parvifolia of the family Asclepiadaceae. Chemical investigations on L. stellatus yielded two new compounds, a sesquiterpenoid 10-hydroxyhimachalen-1-one (53), and a dioxoaporphine alkaloid (55). These compounds were isolated from the chloroform and chanol extracts, respectively. Compound 53 was found to be mildly active when tested against shrimp larvae in the brine shrimp test whereas compound 55 was not tested due to the small amount of this compound as obtained during these investigations. The plant also yielded two known methyl esters of farnesoic acid derivatives, namely methyl 10, 11-epoxy-3,7,11-trimethyl- 10,11 –dihydroxy -3, 7, 11 –trimethyl- 2, 6 –dodecadienoate (28). The compounds were isolated from the chloroform and ethanol extracts, respectively. Compound 27 exhibited a mild toxicity against shrimp larvae in the brine shrimp test. Furthermore, two known compounds, liriodenine (7) and 3,4,5-trimethoxyphonol (52), together with a C18 acetylenic fatty acid 29 were isolated from the ethanol extract. Compound 29 was also isolated from the pet ether extract and it was found to have a mild toxicity against shrimp larvae and a mild antimalarial activity, having IC50 value of 29 and 28 µg/ml respectively against the multidrug resistance strain K1 and chloroquine sensitive strain NF54 of Plasmodium falciparum malaria parasites. The rest of the compounds were not tested for their lethality in the brine shrimp test. They were also not evaluated for their antimalarial activities. Plant materials of L. stellatus were collected from both the Udzungwa mountains (Morogoro region) and from Easter Usambara mountains (Tanga region). Plant materials collected from both localities were found to be containing the same constituents as revealed by TLC analysis and the compounds isolatedduring these investigations. Although Verdcourt had suggested that the plant materials growing from the two localities belong to two Lettowianthus species, the phytochemical results obtainedduring investigations reported in this thesis strongly suggest that the plant materials belong to one and the same plant species, viz. L. stellatus. Phytochemical studies on S.parvifolia afforded one tetracyelic triterpenoid. Namely cupha-7, 24,-dien-3β-o1 (butyrospermol) (56). The compound was isolated from the pet ether. Dichloromethane and water extracts. The compound was inactive in the brine shrimp test. It was also inactive against P. falciparum malaria parasite strains.
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    Novel natural products from four annonaceae species
    (University of Dar es Salaam, 2001) Makangara, John Joseph
    This Thesis reports on phytochemical investigations of four plants of the family Annonaceae, namely Monodora angolensis Welw., Isolona cauliflora Verdc., Uvaria puguensis D.M. Johnson and Lettowianthus stellatus Diels, whereby two known cytotoxic and antimalarial monoprenylated indoles 6-(3-methyl-2-butenyl)-1H-indole and 6-(3-methylbuta-l,3-dienyl)-1H-indole, 4-(indoyl-6-yl)-3-buten-2-one, 3-geranylindole and the hitherto unreported 5-formylindole, 2-indolelactam and annonidine G were isolated from M. angolensis. From I. cauliflora, the monoprenylated indoles 5-(3-methyl-2-butenyl)-1H-indole and 5-(3-methylbuta-l,3dienyl)-1H-indole, the diprenylated indoles caulidine A and caulidine B, and Diels Alder type adducts of monoprenylated indoles were obtained, together with the pentitol ribitol that occurred only in the flower stalks. The stem bark of the newly described Uvaria puguensis D.M. Johnson yielded the hitherto unreported phenanthrenoid 6-hydroxy-3-methoxy-4-oxapyren-5-one, the C-benzyldihydrochalcone 5'-methyluvaretin and known antimalarial C-benzyldihydrochalcones. The root bark of Lettowianthus stellatus Diels from Tanzanian coastal forests yielded two hitherto unreported telisatin type aporphine alkaloids, liriodenine, 3,4,5-trimethoxyphenol, 7-octadecen-9-ynoic acid, the insect juvenile hormone III [methyl (2E,6E,lOR)-10,11-epoxy-3,7,11-trimethyl-2,6dodecadienoate] together with its diol derivative and the new guaiane sesquiterpene 11-hydroxyguaia-4,6-dime. These results indicated that the genus Lettowianthus has only one species, viz. L. stellatus, whose fruits also yielded six hitherto unreported non-cytotoxic and non-antimalarial geranylated quinone derivatives, insect juvenile hormone III, an unidentified C t g acetylenic fatty acid and an aporphine alkaloid. Structures of all the compounds were determined by extensive spectroscopic and chemical methods.