Recent results from natural product research at the University of
Botswana*
Runner R. T. Majinda1**, Berhanu M. Abegaz1, Merhatibeb Bezabih1, Bonaventure
T. Ngadjui2, Cornelius C. W. Wanjala1, Ladislaus K. Mdee1, Gomotsang
Bojase1, Alfonse Silayo1, Ishmael Masesane, and Samuel O. Yeboah1
1Department of Chemistry, University of Botswana, Private
Bag 0022, Gaborone, Botswana; 2Department of Organic Chemistry, University
of Yaounde, BP 812, Yaounde, Cameroon
Abstract: Marketed plants are very important items of trade
in many parts of the world. The community uses these for a variety of
purposes such as foods, cosmetics, flavors, spices, and medicines. It
seems that plants that are used for medicinal purposes form the most
common category. Four plants used for treatment of microbial infections,
viz., Bolusanthus speciosus, Erythrina latissima, Crotalaria podocarpa,
and Elephantorrhiza goetzei, were investigated, and these yielded several
known and novel structures, some with appreciable antibiotic activity
against the test organisms. The activity of some of the isolated plants
and the parts of the plant from which these were obtained lend support
to their traditional use. Bulbine abyssinica and B. capitata yielded
phenylanthraquinones, some of which were shown to possess strong antiplasmodial
activity. In addition, these yielded isofuranonaphthoquinones, which
were also found to be weakly antiplasmodial and antioxidant. Scilla
nervosa yielded several known and novel homoisoflavoinds of the 3-benzylchroman-4-ones
and 3-benzylidinechroman-4-one type, as well as some stilbenoids. The
homoisoflavonoids showed strong antitumor activity against various cancer
cell lines. Rhus pyroides gave a novel bichalcone, which showed weak
antifeedant activity, consistent with the observation by farmers that
the plant was avoided by corn cricket. Results from investigated Dorstenia
species originating from Cameroon, Ethiopia, and Tanzania yielded styrenes,
coumarins, chalcones, and flavonoids. The chalcones and flavonoids showed
various levels of prenylation or geranylation, and an observation made
so far is that prenylated flavonoids are only found in Dorstenia species
of African origin. The only example of a bis-geranylated chalcone is
found in Dorstenia.
*Lecture presented at the 8th International
Chemistry Conference in Africa (8th ICCA), 30 July-4 August 2001, Dakar,
Sénégal. Other presentations are published
in this issue, pp. 1147-1223.
**Corresponding Author
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