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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Actinomycetes and fungi associated with marine invertebrates : a potential source of bioactive compounds : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Microbiology at the University of Canterbury /

Mahyudin, Nor Ainy. January 1900 (has links)
Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). "January 2008." Includes bibliographical references (leaves 201-215). Also available via the World Wide Web.

Structure elucidation of bioactive natural products from Madagascar marine algae and cyanobacteria /

Andrianasolo, Eric Hajaniriana. January 1900 (has links)
Thesis (Ph. D.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 223-233). Also available on the World Wide Web.

Investigations of the type II intramolecular Diels-Alder reaction directed toward natural product synthesis : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at the University of Canterbury /

Muscroft-Taylor, Andrew Clive. January 1900 (has links)
Thesis (Ph. D.)--University of Canterbury, 2006. / Typescript (photocopy). "February 2006." Includes bibliographical references. Also available via the World Wide Web.

Marine anti-malarial isonitriles : a synthetic and computational study

Adendorff, Matthew Ralph 17 May 2010 (has links)
The development of Plasmodium falciparum malarial resistance to the current armoury of anti-malarial drugs requires the development of new treatments to help combat this disease. The marine environment is a well established source of potential pharmaceuticals. Of interest to us are isonitrile, isocyanate and isothiocyanate compounds isolated from marine sponges and molluscs which have exhibited nano-molar anti-plasmodial activities. Through quantitative structure-activity relation studies (QSAR), a literature precedent exists for a pseudoreceptor model from which a pharmacophore for the design of novel anti-malarial agents was proposed. The current theory suggests that these marine compounds exert their inhibitory action through interfering with the heme detoxification pathway in P. falciparum. We propose that the computational methods used to draw detailed conclusions about the mode of action of these marine compounds were inadequate. This thesis addresses this problem using contemporary computational methodologies and seeks to propose a more robust method for the rational design of new anti-malarial drug compounds that inhibit heme polymerization to hemozoin. In order to investigate the interactions of the marine compounds with their heme targets, a series of modern computational procedures were formulated, validated and then applied to theoretical systems. The validations of these algorithms, before their application to the marine compound-heme systems, were achieved through two case studies. The first was used to investigate the applicability of the statistical docking algorithm AutoDock to be used for the exploration of conformational space around the heme target. A theoretical P. falciparum 1-deoxy-D-xylulose-5-phosphate reductoisomerase (PfDXR) enzyme model, constructed by the Biochemistry Department at Rhodes University, provided the ideal model to validate the AutoDock program. The protein model was accordingly subjected to rigorous docking simulations with over 30 different ligand molecules using the AutoDock algorithm which allowed for the docking algorithm’s limitations to be ascertained and improved upon. This investigation facilitated the successful validation of the protein model, which can now be used for the rational design of new PfDXR-inhibiting anti-plasmodial compounds, as well as enabling us to propose an improvement of the docking algorithm for application to the heme systems. The second case study was used to investigate the applicability of an ab initio molecular dynamics algorithm for simulation of bond breaking/forming events between the marine compounds and their heme target. This validation involved the exploration of intermolecular interactions in a naturally occurring nonoligomeric zipper using the Car-Parrinello Molecular Dynamics (CPMD) method. This study allowed us to propose a model for the intermolecular forces responsible for zipper self-assembly and showcased the CPMD method’s abilities to simulate and predict bond forming/breaking events. Data from the computational analyses suggested that the interactions between marine isonitriles, isocyanates and isothiocyanates occur through bond-less electrostatic attractions rather than through formal intermolecular bonds as had been previously suggested. Accordingly, a simple bicyclic tertiary isonitrile (5.14) was synthesized using Kitano et al’s relatively underutilized isonitrile synthetic method for the conversion of tertiary alcohols to their corresponding isonitriles. This compound’s potential for heme detoxification inhibition was then explored in vitro via the pyridine-hemochrome assay. The assay data suggested that the synthesized isonitrile was capable of inhibiting heme polymerization in a similar fashion to the known inhibitor chloroquine. Attempts to synthesize tricyclic analogues of 5.14 were unsuccessful and highlighted the limitation of Kitano et al’s isonitrile synthetic methodology.

Studies in marine quinone chemistry

Sunassee, Suthananda Naidu January 2011 (has links)
This thesis is divided into two parts and the rationale of the research conducted is based on the cytotoxicity of the prenylated quinones 1.24-1.29, isolated from the South African nudibranch Leminda millecra, against oesophageal cancer cells. The first part (Chapters 2 and 3) of the thesis initially documents the distribution of cytotoxic and antioxidant prenylated quinones and hydroquinones in the marine environment. We have been able to show, for the first time, that these compounds can be divided into eight structural classes closely related to their phyletic distribution. Secondly, we attempted to synthesize the two marine natural products 1.24 and 1.26 in an effort to contribute to an ongoing collaborative search with the Division of Medical Biochemistry at the University of Cape Town for new compounds with anti-oesophageal cancer activity. Accordingly, we followed the published synthetic procedure for 1.26 and, although we were unable to reproduce the reported results, we have generated five new prenylated quinone analogues 3.53-3.55, 3.63 and 3.71, which are a potentially viable addition to our ongoing structure-activity relationship (SAR) studies. Moreover, we embarked on a 7Li NMR mechanistic study for the synthesis of 3.2 from 3.1 which rewarded us with an improved and reproducible methodology for this crucial reaction that is detailed in Chapter 3. The second part of this thesis (Chapters 4 and 5) is concerned with a synthetic, structural, electrochemical and biological exploration of the 1,4-naphthoquinone nucleus as a primary pharmacophore in our search for new chemical entities which can induce apoptosis in oesophageal cancer cells, thus contributing to our overall ongoing SAR study in this class of compounds. Seven new naphthoquinone derivatves (4.19, 4.30, 4.31, 4.33 and 4.46-4.48) of the natural products 2-deoxylapachol (2.44), lapachol (4.1) and β-lapachone (5.2) were synthesized and 2-(1`-hydroxy-`-phenylmethyl)-1,4-naphthoquinone (4.29) was found to be the most cytotoxic (IC50 1.5 μM) against the oesophageal cancer cell line WHCO1, while 5.2, which is currently in phase II clinical trials as an anticancer drug, was found to be similarly active (IC50 1.6 μM). Electrochemical investigations of the redox properties of the benzylic alcohol derivatives 4.29-4.31 indicated a higher reduction potential compared to their oxidized counterparts 4.45-4.48, and this finding has been correlated to the increased activity of 4.29-4.31 against the WHCO1 cell line. Additionally, 4.29 is synthetically more accessible than either 1.26 or 5.2 and potentially a lead compound in our search for new and more effective chemotherapeutic agents against oesophageal cancer

Effects of stressors on differential gene expression and secondary metabolites by Axinella corrugata

Unknown Date (has links)
Sponges are an important source of bioactive marine natural products, or secondary metabolites. The common Caribbean reef sponge, Axinella corrugata, produces an antitumor and antibacterial chemical, stevensine. This study determined whether environmental stressors, such as elevated temperature and exposure to Amphibalanus amphitrite larvae, affect the production of stevensine by A.corrugata and if the stressors caused A.corrugata to exhibit differential gene expression. Temperature stress resulted in no significant change in the production of stevensine; only two genes were significantly differentially expressed, including hsp70. Larval stressed resulted in increased production of stevensine and significant differential gene expression (more than seventy genes). This study suggests that A.corrugata may be resilient to elevations in temperature and that one of stevensine's roles in nature is as an antifoulant. / by Jennifer Grima. / Thesis (M.S.)--Florida Atlantic University, 2013 / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Isolation and Structural Elucidation of Novel Bioactive Natural Products from Marine Organisms of the Western Atlantic Ocean

Unknown Date (has links)
The aim of this dissertation was to elaborate the exploration of biologically active secondary metabolites from the marine sponge Cacospongia cf. linteiformis collected from the Bahamas and the soft coral Briareum asbestinum collected from two different sites in Florida State, Boca Raton and Dry Tortugas. In chapter one, a review on previous chemical and biological studies of the marine sponge C. cf. linteiformis and soft coral B. asbestinum is provided. Particular attention is given to spongianolides and briarellins, two important classes of compounds isolated from C. cf. linteiformis and B. asbestinum, respectively, and their structural features and diverse bioactivities. In chapter two, the isolation and relative configuration determination of four epimeric sesterterpenoids, spongianolides E & F (18c, 18d, 19c, 19d) from C. cf. linteiformis collected from the Bahamas are discussed. Thanks to chemical modification (acetylation), diastereomeric 18c&18d and 19c&19d, respectively, were able to be isolated using chromatographic techniques for the first time, and then the relative configurations of 18c, 18d, 19c, 19d were determined based on NOESY NMR experiments. The bioactivity of mixture of compounds 18c, 18d, 19c, 19d were tested and it exhibited inhibition against Schnurri-3 (a regulator of postnatal bone mass). In chapter three, the isolation and structural elucidation of four new compounds, florellins A-D (49-52), from B. asbestinum collected off the coast of Boca Raton, FL are discussed. The molecular structures of these compounds were established by spectroscopic analysis. Compounds 49-52 are the first briarellins containing an acyl group at C-13, while 49 and 50 are the first briarellins possessing acylation at C-15. Florellins A–C (49-51) were screened and found cytotoxic against three human cell lines, BT474, WM266−4 and HEK293. In chapter four, the isolation and structural elucidation of four new compounds, florellins E-H (57-60), from B. asbestinum collected in Dry Tortugas, FL are discussed. The molecular structures of these compounds were established by spectroscopic analysis. Florellins F (58) and H (60) were screened against three human cell lines, BT474, WM266−4 and HEK293, but no cytotoxicity was exhibited. In chapter five, all the experimental procedures are described, including analytical instruments, animal materials, extraction and isolation processes, spectroscopic data and protocols of bioassays. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

A study of plocamium corallorhiza secondary metabolites and their biological activity

Mkwananzi, Henry Bayanda January 2005 (has links)
Seaweeds of the genus Plocamium are known to produce a variety of halogenated monoterpenes. In addition to their ecological role as feeding deterrents, biological activities reported for these compounds include antibacterial, antialgal, antifungal and anticancer activities. An investigation of the non-polar extracts of the seaweed Plocamium corallorhiza resulted in the isolation of six known halogenated monoterpene compounds, 4-bromo-5-bromomethyl-1-chlorovinyl-2, 5-dichloro-methylcyclohexane (2.68), 1,4,8-tribromo-3 ,7-dichloro-3, 7-dimethyl-1,5-octadiene (2.67), 8-bromo-1 ,3,4,7-tetrachloro-3, 7-dimethyl-1,5-octadiene (2.66), 4,6-dibromo-1,1-dichloro-3,7-dimethyl-2,7-octadiene (2.64), 4,8-dibromo-1,1,7-trichloro-3,7-dimethyl-2,5-octadiene (2.65) and 3,4 ,6,7-tetrachloro-3, 7-dimethyl-1-octene (2.63) as well as eight new compounds, including five halogenated monoterpene aldehydes. The new compounds were identified by 1D and 2D NMR spectroscopic techniques as: 8-Bromo-6,7-dichloro-3,7-dimethyl-octa-2,4-dienal (2.72), 8-Bromo-1,1,2,7-tetrachloro-3,7-dimethyl-octa-3,5-diene (2.70), 4,8-Dichloro-3,7-dimethyl-octa-2,4,6-trienal (2.74), 4-Bromo-8-chloro-3, 7-di methyl-octa-2, 6-dienal (2 76), 8-Bromo-4-chloro-3, 7-dimethyl-octa-2,4 ,6-trienaI (2.75), 4-Bromo-1,3,6,7-tetrachloro-3 ,7-dimethyl-octa-1,4-diene (2.71), 8-Bromo-1,3,4,7-tetrachloro-3,7-dimethyl-octa-1,5-diene (2.69), 4,6-Dibromo-3,7 -dimethyl-octa-2,7-dienal (2.73). All compounds were screened for antimicrobial activity, brine shrimp lethality and cytotoxicity towards oesophageal cancer cells. Compound 2.68 was toxic to brine shrimp larvae at a concentration of 50 μ/mL. It also showed promising activity towards oesophageal cancer cells with an IC₅₀, of 2 μg/mL.

Synthetic and bioactivity studies of antiplasmodial and antibacterial marine natural products / Synthetic and bioactivity studies of antiplasmodial and anti-bacterial marine natural products

Young, Ryan Mark January 2012 (has links)
This thesis is divided into two parts, assessing marine and synthetic compounds active firstly against Plasmodium falciparum (Chapter 3 and 4) and secondly active against methicillin resistant Staphylococcus aureus (MRSA, Chapter 5). In Chapter 3 the synthesis of nine new tricyclic podocarpanes (3.203-3.207 and 3.209-3.212) from the diterpene (+)-manool is described. Initial SAR study of synthetic podocarpanes concluded that the most active compound was a C-13 phenyl substituted podocarpane (3.204, IC₅₀ 6.6 μM). By preparing analogues with varying halogenated substituents on the phenyl ring (3.209-3.212) the antiplasmodial activity was improved (IC₅₀ 1.4 μM), while simultaneously decreasing the haemolysis previously reported for this class of compounds. Inspired by the antiplasmodial activity of Wright and Wattanapiromsakul’s tricycle marine isonitriles (2.16-2.21 and 2.24-2.27) an unsuccessfully attempt was made to convert tertiary alcohol moieties to isonitrile functionalities in compounds 3.188, 3.204-3.207 and 3.209-3.212. Over a decade ago Wright et al. proposed a putative antiplasmodial mechanism of action for marine isonitriles (2.4, 2.9, 2.15, 2.19 and 2.35) and isothiocyanate (2.34) which involved interference in haem detoxification by P. falciparum thus inhibiting the growth of the parasite. In Chapter 4 we describe how we successfully managed to scale down Egan’s β-haematin inhibition assay for the analyses of small quantities of marine natural products as potential β-haematin inhibitors. Our modified assay revealed that the most active antiplasmodial marine isonitrile 2.9 (IC₅₀ 13 nM) showed total β-haematin inhibition while 2.15 (IC₅₀ 81 nM) and 2.19 (IC₅₀ 31 nM) showed partial inhibition at three equivalents relative to haem. Using contempary molecular modelling techniques the charge on the isonitrile functionality was more accurately describe and the modified charge data sets was used to explore docking of marine isonitriles to haem using AutoDock. In Chapter 5 we describe how a lead South African marine bisindole MRSA pyruvate kinase inhibitor (5.8) was discovered in collaboration with colleagues at the University of British Columbia (UBC) and how this discovery inspired us to design a synthetic route to the dibrominated bisindole, isobromotopsentin (5.20) in an attempt to increase the bioactivity displayed by 5.8. We devised a fast and high yielding synthetic route using microwave assited organic synthesis. We first tested this synthesis using simple aryl glyoxals (5.27-5.32) as precursors to synthesize biphenylimidazoles (5.21-5.26), which later allowed us to synthesize the ascidian natural product 5.111. This method was sucessfully extended to the synthesis of deoxytopsentin (5.33) from an N-Boc protected indole methyl ketone (5.89). We subsequently were able to effectively remove the carbamate protection via thermal decomposition by heating the protected bisindole imidazole (5.90) in a microwave reactor for 5 min under argon. The synthesis of 5.20 resulted in an inseparable mixture of monoprotected and totally deprotected topsentin products, and due to time constraints we were not able to optimise this synthesis. Nonetheless our synthesis of the marine natural product 5.33 which was faster and higher yielding than previously reported routes could be extended to the synthesis of other topsentin bisindoles (5.138-5.140). Work towards this goal continues in our laboratory.

Biomimetic apporaches to the synthesis of polyketide derived marine natural products (-)-Maurenone and the spiculoic acids /

Crossman, Julia Stephanie, January 2007 (has links)
Thesis (Ph.D.)--Flinders University, Dept. of Chemistry. / Typescript bound. Includes bibliographical references: (p. 360-369) Also available online.

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