The major part of the thesis is concerned with the isolation and structural elucidation of four new crystalline sesquiterpenoids, constituents of the heartwood of Warburgia ugandensis (Sprague) Canellaceae, a tree native to East Africa. The principal method used in the assignment of structure and absolute configuration has been chemical degradation to products for comparison with known compounds. Extensive use has been made of chromatographic and spectroscopic techniques. Two of the components isolated have been shown to be members of the eremophilane group of sesquiterpenoids. A brief description of the proof of constitution of these compounds has been made in two preliminary communications. The known sesquiterpene alcohol drimenol was also proved to he a heartwood constituent of Warburgia ugandensis. Further work with a second consignment of the heartwood has resulted in the isolation and identification of two sesquiterpenoids of the bicyclofarnesane group, a butenolide hydroxyacetate named ugandensolide and a dialdehyde (ugandonsidial). Ugandensidial has been proved to be identical with cinnamedial, a constituent of Cinnamosma fragrans (Baillon) Canellaceae. The final section of the thesis describes biosynthetic studies with the eremophilane sesquiterpenoids of the plant Petasites hybridus (L.) Compositae. These are compounds of the petasin type. Preliminary results in this long-term project, which involves the feeding of 14C-labelled precursors to the plant, are briefly reported and proposals for further research are discussed
