Browsing by Author "Sung'hwa, F."

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    Kawain derivatives and other natural products from Ophrypetalum Odoratum and Lettowianthus Stellatus.
    (University of Dar es Salaam, 1996) Sung'hwa, F.
    The investigations reported in this Thesis were aimed at the isolation of bioactive and other natural products from the leaves of Ophrypetalum odoratum and the stem bark and seeds of Lettowianthus stellatus, both plants belonging to the family Annonaceae. The leaves of Ophrypetalum odoratum which were collected from Pugu forest near Dar es Salaam and Kiloka pass near Morogoro were extracted consecutively with pet ether, chloroform and ethanol at room temperature. The leaf extracts yielded the kawain derivatives (+)-6-styryl-7,8-dihydroxy-4-methoxy-pyr-2 -one and (±)-5-methoxy-7phenyl-[4-methoxy-2-pyronyl]-1-(E)-styryl-2-oxabicyclo-[4.2.0]-octa-4-en-3-one, the latter compound being an unsymmetrical dimer of 6-traps-styryl-4methoxy-pyr-2-one, another kawain derivative which was not isolated during the investigations reported in this Thesis. The two flavonoids 5-hydroxy-7-methoxyflavone and 5, 7-dihydroxyflavone were also isolated in these investigations, besides the carotenoid lutein and a mixture of ketonic steroids. This is the first time that (+)-6-styryl-7,8-dihydroxy-4-methoxy-pyr-2one has been isolated from natural sources. Previously, the racemic mixture of this compound was made synthetically as an analogue of the naturally occurring herbicidal compound, pestalotin. The dimeric compound (±)-5-methoxy-7-phenyl-[4-methoxy-2pyronyl]-1-(E)-styryl-2-oxabicyclo-[4.2.0]-octa-4-en-3-one obtained in these investigations and which was previously isolated from Aniba gardeners , can be regarded as an artifact, formed through photo-induced dimerisation of the highly reactive styrylpyrone, 6-traps -styryl-4-methoxy-pyr-2-one during workup. In the investigations reported in this Thesis two annonaceous acetogenins were also isolated from the leaves of Ophrypetalum odoratum collected from Kiloka pass, one of the acetogenins being desacetyluvaricin, which is also known to occur in several other plants of the family Annonaceae. The second acetogenin was shown by spectroscopic analysis to be trihydroxylated, being isomeric to squamocin and having the relative con threo l cis l threo l cis l eryhtro starting from C-15 to C-24. The compound ; been described in the literature and it was given a trivial name isosquamo compound showed toxicity on brine shrimp larvae in the brine shrimp test, with an IC value of 0.4 mg/ml. It also exhibited the same activity against Trypanosoma brucei rhodesiense in vitro. The leaves from Kiloka pass also yielded a l:l mixture of two unknown lactonyl acetogenins whose spectral features indicated the presence of two oxirane rings in each of the two compounds, these being separated by a dimethylene group and having a double bond along the aliphatic chain. The position of the oxirane rings was tentatively established on the basis of biosynthetic considerations and the available spectral data, and that of the double bond could not be confirmed by spectral information which was available. Since annonaceous acetogenins were only isolated from the leaves obtained from Kiloka pass which were younger than those collected from Pugu forest, one can speculate that in Ophrypetalum odoratum and probably in other plants of the family Annonaceae there is a better chance of finding annonaceous acetogenins from young leaves than from mature ones. Chemical investigations on the stem bark of Lettowianthus stellatus afforded two methyl esters of farnesoic acid, juvenile hormone III and its diol, methyl 10,11dihydroxy-3,7,11-trimethyl-2,6-dodecadienoate, the latter compound being obtained as a hydrolysis product of the former. Furthermore, the stem bark yielded the C 18 acetylenic fatty acid, 9-(Z)-octadecen-11-ynoic acid and its triglyceride derivative. In previous investigations the berries of L. stellatus yielded four bis-geranyl substituted polyketides, which were not obtained from or even detected in the seeds during investigations being reported in this Thesis. Instead the seeds yielded two unkown sugars and a mixture of C 24 and C22 acyl tryptamines. This indicated that the polyketides previously isolated from the berries are probably constituents of the fruit pulp, and not the seeds.