CHEMISTRY OF MARKETED PLANTS OF EASTERN AND SOUTHERN AFRICA

Abstract

Different strategies have been developed by various research groups to determine a sound and practical basis for the selection of plants for scientific examination. Groups involved in drug discovery programs often use bioassay-guided fractionation to track, isolate and identify substances that have positive activity. Others employ ethnomedical information as leads. More recently combinatorial chemistry and high throughout robotic screening techniques have been employed mostly by the big multinational pharmaceutical companies. Each one of these approaches has it benefits and disadvantages and the selection depends upon the goals of the project and the resources available to the researchers. The selection of plant material for investigation by our research group has been guided the belief that plants that have acquired the status of marketed commodities have already been screened by traditional methods. This approach has led us to examine a number of plants and the results obtained in the course of training students has been stimulating and exciting. This paper will deal with examples of marketed plants from a number of countries in eastern, central and southern Africa. It will be selective rather than comprehensive. Reference will be made to the historically important Ethiopian anti-parasitic plant Hagenia abyssinica, and other marketed plants of current interest like Aloes, the devil's claw (Harpagophytum procumbens), Hypoxis spp. In addition results from our own laboratories will be presented Scilla nervosa (Burch) Jesssop sub-species rigidifiolia (Hyacinthaceae) is used in Zulu medicine to treat rheumatic fever and as purges for children. In Botswana the plant is alleged to enhance female fertility and to treat infections. The tubers yielded thirteen homoisoflavoniod (nine of which are new) and three-stilbene derivatives. Bulbine capitata V poellen (syn. B. Stenophylla Verdooorn) is used in Botswana as antibiotic. This plant us a rich source of furanonaphthoquinones, anthraquinones including knipholone type compounds which show interesting biological properties. We have investigated several species of Dorstenia (Moraceae): D. mannji, D. kameruniana, D. psiliris and D. poinsettifolia. They are rich sources of prenylated flavonoids, which undergo various cyclizations to yield furano-, pydrano-, and dihydropyrano derivatives. Rhamus prinoides L'Herit occurs widely in Africa and is commonly known as Gesho in Ethiopia and dogwood in southern Africa. We have reported several quinines, flavonoids and naphthalenic compounds from various parts of this plant and have established that geshoidine may be the flavoring principle of the plant responsible for the characteristic bitter tastes of the domestic beverages Tella and Tej. Further examinations of the more polar fractions of (Rhamnaceae) have yielded acylated glycosides of emodin and emodin anthrone. Rhus pyroides (Anacadiaceae) is a plant whose leaves are carefully avoided by the corn cricket. Examination of this plant has yielded novel bichalcones, which may have potential insecticidal properties. Marketed plants that are collected from the wild run a great risk of extinction. This lecture will urge the need to developed substainable use of these important plants.


Key Words: Marketed plants, Hagenia abyssinica, Rosaceae, Dorstenia species, Moraceae, chemical constituents.


Nig. J. Nat Prod. And Med. Vol.3 1999: 19-25