Recent results from natural product research at the University of Botswana

Marketed plants are very important items of trade in many parts of the worl d. The community uses these for a variety of purposes such as foods, cosmet ics, flavors, spices, and medicines. It seems that plants that are used for medicinal purposes form the most common category. Four plants used for tre atment of microbial infections, viz., Bolusanthus speciosus, Erythrina lati ssima, Crotalaria podocarpa, and Elephantorrhiza goetzei, were investigated , and these yielded several known and novel structures, some with appreciab le antibiotic activity against the test organisms. The activity of some of the isolated plants and the parts of the plant from which these were obtain ed lend support to their traditional use. Bulbine abyssinica and B. capitat a yielded phenylanthraquinones, some of which were shown to possess strong antiplasmodial activity. In addition, these yielded isofuranonaphthoquinone s, which were also found to be weakly antiplasmodial and antioxidant. Scill a nervosa yielded several known and novel homoisoflavoinds of the 3-benzylc hroman-4-ones and 3-benzylidinechroman-4-one type, as well as some stilbeno ids. The homoisoflavonoids showed strong antitumor activity against various cancer cell lines. Rhus pyroides gave a novel bichalcone, which showed wea k antifeedant activity, consistent with the observation by farmers that the plant was avoided by corn cricket. Results from investigated Dorstenia spe cies originating from Cameroon, Ethiopia, and Tanzania yielded styrenes, co umarins, chalcones, and flavonoids. The chalcones and flavonoids showed var ious levels of prenylation or geranylation, and an observation made so far is that prenylated flavonoids are only found in Dorstenia species of Africa n origin. The only example of a bis-geranylated chalcone is found in Dorste nia.