New prenyl indoles from isolona cauliflora and constituents of three other annonaceous plants.

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Date
1998
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University of Dar es Salaam
Abstract
This thesis reports on phytochemical investigations of two plant species belonging to the family Annonaceae, namely Isolona cauliflora Verdc. and Uvaria dependens Engl. and Diels from East Usambara Mountains, Muheza District, Tanzania. The Thesis also reports on the studies on the chemical composition of essential oils from three annonaceous plants, namely Mkilua fragrans, Uvaria lucida ssp. lucida and Xylopia mwasumbii. Phytochemical investigations of the methanol extract of the stem bark of Isolona cauliflora yielded three simple prenylated indoles and five dimeric prenylindoles. The simple indoles have one indole unit and the dimeric indoles have two. The simple indoles isolated were the monoprenylated indoles, 5-(3-methyl-but-2-enyl)-1H-indole and (E)-5(3-methyl-2-buta-l,3-dienyl)-1H-indole and the diprenylated indole named caulindine A. The new dimeric indoles were named caulindole A, caulindole B, caulindole D, caulindole E and caulindole F. Structural determination of all the isolated compounds was achieved from extensive NMR experiments including 1H and 13C NMR, HETCOR, H-H COSY, NOE, HMBC and HMQC. Unfortunately, at the time of writing this Thesis MS data for all the compounds from Isolona cauliflora were not available. Although prenylated indoles have previously been isolated from plants, those which are conceivable Diels Alder cycloaddition products like the caulindoles, are not common. In these investigations both the endo and exo compounds as expected from Diels Alder cycloaddition reactions, were obtained. The formation of these compounds raises a question as to whether enzymatic or non-enzymatic reactions may be involved in the biosynthesis of the caulindoles. Apparently, one of the compounds isolated in these investigations, caulindole A, showed optical activity. This may suggest that the compound is biosynthesised enzymatically. However sufficient evidence in this regard requires the determination of optical activities of all the isolated compounds. Moreover, the presence of optical activity may as well be a result of kinetic resolution of nonenzymatically formed Diels Alder products, whereby the resolution takes place in the presence of enzymes. This makes the question of the biosynthesis of the caulindoles to remain unresolved in the present investigations. However, the fact that all the caulindoles could be detected in fresh plant materials, and that the conceivable monomeric prenylated indoles did not react when exposed to the isolation conditions, indicates that the caulindoles are true natural products, and not artefacts. Phytochemical investigations of the ethanol extract of the stem bark of Uvaria dependens yielded 2-hydroxy-3,4,6-trimethoxychalcone and two flavonoids, 5,7,8-trimethoxyflav-3-ene and 5-hydroxy-7,8-dimethoxyflava. The latter compound is reported to be isolated from this plant for the first time while the other two were isolated in previous investigations. The structure of the flavanone was established on the basis of 1H and 13CNMR spectral data. Steam distillation of stem barks of Mkilua fragrans and Uvaria lucida ssp. lucida and the root barks of Xylopia mwasumbii gave essential oils with varying oil contents whereby Uvaria lucida ssp. lucida had the highest oil content. The structures of several of the essential oil constituents were deduced on the basis of comparison of the corresponding MS of these compounds with those reported in data bases, or from the literature. The oils from M. fragrans and U. lucida ssp. lucida consisted mainly of sesquiterpenes. In addition, the oil from U. lucida ssp. lucida also contained benzopyranyl sesquiterpenes similar to those previously isolated from U. angolensis, U. tanzaniae and U. lucida ssp. lucida. However, structures of these compounds could not be elucidated since only MS was available and this was not enough for structural determination. The constituents of the essential oil from X. mwasumbii belong to various classes of compounds, most of whose MS could not be correlated with MS data reported in data bases or in the literature. All the essential oils showed mild activity in the brine shrimp test, with the oil from U. lucida ssp. lucida and X. mwasumbii showing the highest activity.
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Keywords
Annonaceae, Indole
Citation
Juma, S. R. (1998). New prenyl indoles from isolona cauliflora and constituents of three other annonaceous plants. Master dissertation, University of Dar es Salaam. Available at (http://41.86.178.3/internetserver3.1.2/search.aspx?formtype=advanced)