Studies in Natural Products: Sesquiterpenoids of Brachylaena hutchinsii

The chemical constituents of Brachylaena hutchinsii, a hardwood indigenous to East Africa, have been examined, and sesquiterpenoids of the heartwood extract and of the steam-volatile oil (Essential Oil Muhuhu) have been investigated. The first part of the thesis is concerned with the chemical composition of the heartwood and, in particular, with the structures of the Brachylaenalones, principal sesquiterpenoid constituents of an extract of the heartwood. In the present work, structures (A), proposed earlier, for these compounds, are re-examined and revised to structures (B) in the light of further evidence. In addition, the products of hydride reduction of the Brachylaenalones, previously reported to be three diastereomeric diols, are re-investigated and, in consequence of a refinement in analytical procedure, the occurrence of the fourth, expected diol is established. This work has necessitated the use of a wide range of analytical techniques, and physico-chemical data of the Brachylaenalones, the diols and the corresponding ketols have been recorded and analysed. Chemical correlation of the Brachylaenalones with the expected parent hydrocarbons, copaene and ylangene, has been attempted by several routes, but the desired transformations have been accompanied by side reactions, leading to complex mixtures of products in each case. Reduction of the dithioketal derivative of one ketoaldehyde over Raney nickel catalyst yielded a mixture of products comprising neither copaene nor ylangene: reduction of each ketoaldehyde according to the Wolff-Kishner method, however, afforded the parent hydrocarbons as minor products. In the second part of the thesis, a survey of the chemical constituents of the steam-volatile oil from the heartwood is described, and comparisons are drawn with the composition of the heartwood extract. Separations of the oil into fractions by gas-liquid chromatography (analytical and preparative), together with combined gas chromato-graphic-mass spectrometric analyses of individual fractions, supplemented in some instances by infra-red spectrometry, has allowed the documentation of molecular weights and functional types present in the oil, and the tentative identifications of copaene (C), ylangene (D) and ylangenol (E). The Brachylaenalones were not present in the oil, which comprised mainly compounds of molecular weights in the range 200-222