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In order to compare the pyrrolizidine alkaloid content of two closely related species, Senecio chrysocoma and S. paniculatus, nine populations of plants distributed between the two species, were examined. Three novel pyrrolizidine alkaloids, 7ß-angelyl-l-methylene-8∝-pyrrolizidine, 7ß-angelyl-l-methylene-8∝-pyrrolizidine and 7ß-angelyl-l-methyleneSO!-pyrrolizidine-4-oxide, as well as eight known pyrrolizidine alkaloids, 7-angelylhastanecine, 9-angelylhastanecine, 7-angelylplatynecine, 9-angelylplatynecine, 9-angelylplatynecine-4-oxide, sarracine, neosarracine and retrorsine, were isolated and identified by NMR and GC-MS techniques. Traces of five tiglyl isomers, 9-tiglylplatynecine, 9-tigl ylplatynecine-4-oxide, 7ß-tiglyl-l-methylene-8∝-pyrrolizidine, sarranicine and neosarranicine, were also isolated and tentatively identified; however, these compounds could have been artefacts of the extraction and analytical procedures. While both species of plant investigated, S. chrysocoma and S. paniculatus, were found to be morphologically different, their pyrrolizidine alkaloid content was, in fact, very similar. The presence of retrorsine in S. paniculatus plant extracts, but not in those from S. chrysocoma plants, was the only major chemical difference observed. It is perhaps significant that retrorsine was the only macrocyclic pyrrolizidine to be identified. A comprehensive, computerised database of physical data for pyrrolizidine alkaloids has been compiled, which has facilitated the identification of new pyrrolizidines and the examination of trends in proton and carbon-13 NMR data for pyrrolizidine alkaloids. A stereospecific synthesis of 7ß-angelyl-l-methylene-8∝-pyrrolizidine was undertaken toconfirm the absolute stereochemistry of the product isolated from S. chrysocoma and S. paniculatus. An inseparable 5:2 mixture of 7ß-angelyl-l-methylene-8∝-pyrrolizidine and 7ß-angelyl-l,2-didehydro-l-methyl-8∝-pyrrolizidine, together with a small amount of tiglyl isomer, was finally synthesised. The application of various chiral differentiating chromatographic and spectroscopic techniques confirmed that both the natural and synthetic products had the same stereochemistry, permitting the natural alkaloid to be identified as 7ß-angelyl-methylene-8∝-pyrrol izidine

The ability to construct C-N bonds is of great importance to organic chemists as exemplified by the vast number of natural products, pharmaceutical agents and fine chemicals that contain such linkages. An atom efficient C-N bond forming reaction namely hydroamination has attracted much interest to date due to its ability in forming amine, imine and enamine functionality. The scope of this project involved the attempted synthesis of a biologically active and nitrogen containing pyrrolizidine alkaloid isolated from cryptic thief ants and poison dart frogs namely 223H (xenovenine). The method of hydroamination was utilized as the pivotal ring forming step and was established as being a valuable synthetic tool towards the construction of 223H (xenovenine). The stereoselective synthesis resulted in the successful formation of ethyl (3R)-5-heptyl-3-methyl-2,3-dihydro-lH-pyrrolizine-7-carboxylate 74, a novel, and structurally analogous precursor to 223H (xenovenine) over 10 synthetic steps from (S)-pyroglutamic acid. The following research also resulted in the synthesis of two other novel compounds namely ethyl 3-[(2R)-2-methyl-5-thioxotetrahydro-lH-pyrrol-l-yl]propanoate 86 and ethyl 3-{(5R)-2-[(E)-2-ethoxy-2-oxoethylidene]-5-methyltetrahydro-lH-pyrrol-l-yl}propanoate 87. A catalytic hydroamination study on the conversion of C-propargyl vinylogous amides into pyrroles demonstrated that transition metal salts of groups 11 and 12 serve as effective hydroamination catalysts. The oxide, acetate, chloride and nitrate derivatives of group 11 and 12 metals namely Cu(II), Ag(I), Zn(II), Cd(II) and Hg(II) were employed as potential hydroamination catalysts in the oxidation states provided. The Zn(II) catalyst series with the exception ZnO provided the greatest hydroamination yields under mild reaction conditions owing to their high Lewis acidities however the Ag(I) and Hg(II) catalyst series also provided excellent yields of product under more forcing reaction conditions. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Bacterial cultures enriched from sheep rumen fluid have demonstrated the ability to detoxify pyrrolizidine alkaloids (seneciphylline and jacobine) in tansy ragwort (Senecio jacobaea). The microbes are difficult to isolate using classical anaerobic techniques, therefore, microbes from two different enrichment cultures demonstrating similar degradation activity were identified using their 16S ribosomal RNA genes. Gene sequences from a rich medium enrichment were matched to Clostridium bifermentans, Prevotella ruminicola, Escherichia coif, and from a minimal medium enrichment to, C. clostridiiforme, C. aminophilum, Streptococcus bovis, and Butyrivibrio fibrosolvens. There were no identical organisms between the two libraries, but the common genus was Clostridium. / Graduation date: 1998