FACULTY OF SCIENCE

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1966 - 19683

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Start date: 1966End date: 1969

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    EXTRACTIVES FROM KHAYA SPECIES
    (1968-03) ADESOGAN, E. K.
    The chemistry of ß-furan-containing extractives obtained from trees of the family Meliaceae (and one tree from the family Rutaceae) is briefly reviewed and their biogenesis is discussed. In continuation of our study of the extractives from the family Meliaceae in this department, five species of the genus Khaya have been examined. The seed, timber, bark, root, and root-bark of three species, K. senegalensis, K. ivorensis, and K. grandifoliola, and the seeds of the two others, K. anthotheca, and K. nyasica were examined. The extracts are mainly the tetranortriterpenes with a ß-substituted furan, and about thirty of these were isolated and structures were assigned to nearly all of them. The known ones include khivorin, 7-deacetoxy-7-oxo-khivorin, 7-cleacetoxy-7-oxogedunin, methyl angolensate, mexicanolide, and deacetylgedunin. Those characterised and reported for the first time include khayasin, 6-deoxy-3ß-tigloyloxyswietenolide, 6-deoxy-3ß-benzoyloxyswietenolide, khayanthone, 3-deacetylkhivorin, 3-deacetyl-7-deacetoxy-7-oxokhivorin, methyl 6-hydroxyangolensate, grandifoliolin, 3-destigloyl-6-deoxyswietenine, 3-destigloyl-6- deoxy-3ß-acetoxyswietenine, 3ß-dihydrocarapin, and 3-destigloyl-6- deoxy-3ß, 12ß-diacetoxyswietenine. Others prepared before, but isolated as natural products for the first time include deoxy- andirobin, and 6-deoxyswietenolide. In addition two substances, A and B from K. ivorensis root-bark have structures proposed for them which are still to be confirmed, while not much is known of the structures of a few others especially methyl senegalensate. Most of these extracts contain glycosides and steroids, ß-sitosterol in particular. Of these only the steroid hormone 20ß-acetoxy-3-oxopregn-4-ene, a new compound, was sufficiently studied to be assigned a structure which was confirmed. The structural elucidation of these compounds have depended almost entirely on their spectral properties including those of their Chemical transformation products. Obviously physical properties played a great part especially in confirming a known compound by comparison of data. The co-occurence of some of these compounds have strengthened the argument for the biogenesis proposed. The chemotaxonomic implication was also discussed. A number of interesting reactions including some rearrangements are discussed and mechanism for some of them have been suggested.
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    SYNTHETIC STUDIES ON STEROIDAL ALKALOIDS
    (1966) ADEGOKE, E. A.
    In the first part of this thesis, a brief survey of the chemistry of veratramine viz. its occurrence, isolation and structural diagnosis is given. This part also includes a review of recent work on the stereochemistry and the synthetic work of other workers on the alkaloid. The main section describes three approaches to the synthesis of the C-Nor-D-homo ring system of the veratrum alkaloids. Howell and Taylor’s acetate diester 6(β-acetoxy-1 β:2αdi (methoxy carbonyl methyl)-9β-methyl-trans decalin prepared from 2:3:4:9:10:12- hexahydro-6-methoxy-12-methyl-2-oxophenanthrene was successfully cyclised to the potential intermediate 6(β -acetoxy-1 β:2α-( cyclopen- tan-3-one)-9-methyl-trans decalin. The pentanone was ring extended to give a solid substance which certainly contained the steroidal ring system of veratramine but which could not be obtained in the pure form. Attempts aimed at an easier preparation of the pentanone acetate by alkylating 1-oxo-6-ethoxy-8a-methyl-1,2,3,7,8, 8a hexahydro naphthalene with different alkylating agents were unsuccessful, the starting material being recovered in each case. In a second approach, 1-(2-cyanoethyl)-2-hydroxy naphthalene was converted to 2:3:4:9:10:12-hexahydro-6-methoxy-7-(3-bromo- propyl)-12-methyl-2-oxophenanthrene and 8-oxo-10a-methyl-1,2,3,4,5,6,8,9,10,10a-decahydro-1-oxa chrysene. The benzene nucleus of either intermediate was resistant to reduction and so they could not be used for further work. In the last attempt, 2-benzoyloxy-1,2,3,4,5,6,7,9,10,11,12,13 dodecahydro-12-methyl-7-oxophenanthrene was prepared starting with 2-naphthol and the tricyclic enone was successfully condensed with 2,2-ethylenedioxy-5-bromo pentan-2-one in the presence of potassium t-butoxide in t-butanol. The adduct was successively reduced, reacted with methyl magnesium bromide, deketalized y acetylated, ozonised and cyclised to give an oily substance which contained the veratramine steroidal nucleus as revealed by its U.V. spectrum. The oil did not crystallize. An oil which should probably crystallize more readily could be obtained if complete reduction of the original ansaturated adduct could be accomplished in the attempts some new compounds were prepared. These were mainly naphthalene, phenanthrene and hydrochrysene compounds. I.R U.V, or N.M.R. spectroscopic data were recorded for all the new compounds and for most of the known ones. Some structural formulae are repeated in the script, so as to aid the reader’s comprehension.