The isolation, characterisation and chemotaxonomic significance of secondary metabolites from selected South African Laurencia spp. Rhodophyta
- Authors: Fakee, Jameel
- Date: 2015
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/64696 , vital:28593
- Description: Bioprospection of marine organisms as a potential source for lead drugs is becoming increasingly popular. The secondary metabolome of these organisms consists of structurally diverse molecules possessing unprecedented carbon skeletons, the biosynthesis of which occurs via complex metabolomic pathways driven by specialist enzymes. This structural novelty is highly influential on the favourable bioactivity these compounds display. A prominent example of such a compound is trabectedin marketed as Yondelis®. Registered for the treatment of soft tissue sarcomas, this marine drug was developed from extracts of the tunicate Ecteinascidia turbinata. South Africa is renowned for possessing a highly diverse marine biota including several endemic species of marine red algae belonging to the Laurencia sensu stricto genus, which falls within the Laurencia complex. Despite having a good reputation for fascinating secondary metabolites, the taxonomy of Laurencia natural products is proving challenging for reasons including the presence of cryptic species, as well as individual species displaying morphological variability. The aim of this study was thus to isolate secondary metabolites from various South African Laurencia spp. and subsequently assess their chemotaxonomic significance by analysis of a parallel plastid rbcL phylogeny study of Laurencia spp. This study reports the first phycochemical investigation into Laurencia natalensis Kylin, Laurencia cf. corymbosa J.Agardh, Laurencia complanata (Suhr) Kützing, Laurencia sodwaniensis Francis, Bolton, Mattio and Anderson submitted, Laurencia multiclavata Francis, Bolton, Mattio and Anderson submitted, and a South African specimen of Laurenciella marilzae Gil-Rodríguez, Sentíes, Díaz-Larrea, Cassano and M.T. Fujii (basionym: Laurencia marilzae) originally described from Spain. Additionally, the chemical profiles of previously explored species Laurencia flexuosa Kützing and Laurencia glomerata Kützing were re-investigated. The organic extracts of the above species afforded 31 compounds belonging to a wide array of structural classes including halo-chamigranes, linear C15 acetogenins, indole alkaloids, cuparanes and cyclic bromo-ethers. A new tri-cyclic keto-cuparane (4.4) was isolated from L.cf. corymbosa alongside the new cuparanes 4.1 and 4.7. Algoane (5.9), a unique marker compound isolated from L. natalensis, was previously only reported from a sea-hare. Such marker compounds which are exclusive to an individual algal species increase the ease of their subsequent identification. The feasibility of chemotaxonomy as an additional tool to classify Laurencia spp. Was established as broad predictions of a specimen’s phylogeny, based on representatives of its secondary metabolome, proved viable. The study specimens were shown to possess similar chemical profiles to their sister species e.g. L. complanata, L. sodwaniensis and L. multiclavata produced similar metabolites to their sister species as inferred by an rbcL phylogeny tree. Finally, a 1H NMR profiling study on the crude organic extracts of various Laurencia spp. generated distinctive, reproducible spectra, exposing the value of NMR spectroscopy as a rudimentary species discernment tool.
- Full Text:
- Date Issued: 2015
“Watch-dogs for an Economy” : a determination of the origins of the South African Public Accountants' and Auditors' Board – as the Regulator of the Profession – principally through an analysis of the debates and related reports to the House of Assembly of the Parliament of the Union of South Africa in the period 1913–1940
- Authors: Lancaster, Jonathan Charles Swinburne
- Date: 2014
- Subjects: Public Accountants' and Auditors' Board (South Africa) , Accounting -- Law and legislation -- South Africa , Accounting -- South Africa -- History , Accounting -- Standards -- South Africa , South Africa -- Economic conditions -- 1918-1961 , South Africa -- Politics and government -- 1909-1948
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:922 , http://hdl.handle.net/10962/d1020876
- Description: This thesis concentrates upon a new field of research in South African accounting scholarship – this being, in general terms, accounting history and more specifically an analysis of the origins of the Public Accountants’ and Auditors’ Board as watch-dog in relation to: ● the South African economy in the period 1913–1940; and ● the changing political framework (also in the period 1913–1940). The integration of economy, politics and personal ambition on the part of early 20th Century accounting societies, led to a variety of responses, counter proposals, stalemates and unfocused activity which caused the process of accountants’ registration to extend over 38 years in South Africa. This confusion was in strong contrast to the process of speedy registration of accountants in New Zealand and Australia. The final unification of South African accounting societies in 1951 created the Public Accountants’ and Auditors’ Board. Its creation, at long last, suggested an overarching control and regulation which was mirrored in the final political unification and economic stability of a South Africa dominated by Afrikaner Nationalists. One further element was interwoven into the fabric of the thesis – this being the application of institutional economic theory and its impact upon the accounting concepts of “material irregularity” and “reportable irregularity”.
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- Date Issued: 2014