Terpenoids and other constituents of three bioactive Tanzanian plants: Greenwayodendron Suaveolens, Anisophyllea Obtusifolia and Ekebergia Benguelensis.

This thesis reports on phytochemical investigations of three biologically active plants viz. Anisophyllea obtusifolia Ridl. (Anisophylleaceae), Greenwayodendron suaveolens ssp. usambaricum Verd. (Annonaceae) and Ekebergia benguelensis C.DC and C.DC (Meliaceae). The root bark of A. obtusifolia yielded bryonolic acid and a mixture of stigmasterol and b-sitosterol, the latter mixture being a usual constituent of many plants. Bryonolic acid, whose structure was established on the basis of its spectral data and on comparison of these data with those reported in the literature, was not active in the brine shrimp test. However, the compound is reported in the literature to have antiallergic activity in mammals. From the root bark of G. suaveolens ssp. usambaricum a tetracyclic triterpenoid polycarpol was obtained which has anti-cancer activity, and it is of chemotaxonomic importance for it is restricted to the family Annonaceae. Due to the small quantity of the isolated sample no bioassays were conducted on this compound. An indolosesquiterpenoid, a-polyalthenol, was isolated from the chloroform and pet ether extracts of Greenwayodendron suaveolens ssp. usambaricum. a-Polyalthenol is a hitherto unreported diastereomer of polyalthenol, which was first isolated from Greenwayodendron suaveolens ssp. suaveolens. a-Polyalthenol differs from polyalthenol at the C-3 configuration. Thus, whereas polyalthenol has a C-3 b-hydroxyl group a-polyalthenol has this group in the a-position, as revealed by extensive NMR studies on the latter compound. a-Polyalthenol was inactive in the brine shrimp test. The ethanol extract of E. benguelensis yielded two squalene derivatives 2,6,10,15,19,23-hexamethyl-2,3,22,23-tetrol-6,10,14,18-tetracosatetraene and 2,6,10,15,19,23-hexamethy l1,2,3,22,23-pentol-6,10,14,18-tetracosatetraene, together with the hitherto unknown coumarin 4-methoxy-5-hydroxmethylcoumarin, besides a mixture of triterpenoids, 3a-hydroxy-l2-oleanen-28-oic acid and 3-oxo-l2-oleanen-28oic acid. The squalene derivatives obtained in these investigations can be considered as being artifacts, formed from the corresponding squalene dioxides which were probably less stable under the isolation conditions. Squalene dioxides are known to be intermediates in the biosynthesis of triterpenoids and sterols. To that effect these compounds and their derivatives are considered to have potential properties as cholesterol biosynthetic inhibitors. The compounds isolated in these investigations can, therefore, also be considered to have this potential usefulness.