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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.
1

Molecular probes for the evaluation of three isomerase enzyme mechanisms in secondary metabolism /

Nasomjai, Pitak. January 2010 (has links)
Thesis (Ph.D.) - University of St Andrews, January 2010.
2

Secondary metabolites from selected marine organisms

Pathirana, Induruwa Charles January 1986 (has links)
Marine organisms are known to produce secondary metabolites which have novel structures and are often biologically active. Chemical studies of biologically active metabolites from three different marine organisms led to the discovery of six new compounds and six previously known compounds. The brown alga Dictyota binghamiae is fairly abundant in British Columbia coastal waters. A chemical study of this alga yielded ten diterpenoids of which four are new compounds. All the new compounds, dictyoxide A (66), dictyol G acetate (68), dictyotriol A diacetate (69), and epidictyol B acetate (70) contain a perhydroazulene carbon skeleton first encountered in the algal metabolite pachydictyol A (29). Dictyoxide A (66) appears to be an artifact of isolation. The acetates 68, 69, 70 were found to be antibacterial and antifungal. Six previously known compounds pachydictyol A (29), dictyol C (32), dictyoxide (35), acetyldictyolal (49) and the acetals 61a and 61b were also isolated from this alga. Chemical studies on an Agelas sp. of sponge collected in Sri Lanka yielded the antimicrobial metabolite desbromooroidin (79). An interesting interaction between the starfish Dermasterias imbricata and the sea anemone Stompia coccinea was observed a long time ago. When contacted by the starfish, the anemone displays an unusual "swimming" response which was, according to other subsequent studies, caused by a single chemical substance in the starfish. A study conducted to elucidate the structure of this starfish metabolite led to the isolation of imbricatine (91), a unique benzyltetrahydroisoquinoline alkaloid. Imbricatine (91) induced S. coccinea swimming response at a very low concentration and also exhibited antitumor activity. Structures of all the new metabolites were determined by spectral analysis, and chemical degradations and chemical interconversions. / Science, Faculty of / Chemistry, Department of / Graduate
3

Novel bioactive secondary metabolites from the marine cyanobacterium Lyngbya majuscula

Wu, Min, 1963- 13 September 1996 (has links)
Marine algae have been recognized as a rich resource of new and unusual organic molecules with diverse biological properties. The current need to develop new antifungal, anticancer, antibiotic and antiviral drugs has led to an intense research effort into the discovery, isolation and structure determination of potential medicinal agents from marine algae. In the past two years, I have participated in a drug discovery program designed for antitumor, antifungal and other agents of potential pharmaceutical utility from the marine cyanobacterium Lyngbya majuscula. This research utilized modern chromatographic and spectrochemical techniques including 2D NMR spectroscopy. Brine shrimp toxicity guided the fractionation that led to the discovery of the biologically active compound kalkitoxin from a Curacao Lyngbya majuscula extract. The structure of this new thiazoline ring-containing lipid was determined spectroscopically by interpretation of 2D-NMR experiments, including heteronuclear multiple quantum coherence (HMQC), heteronuclear multiple-bond coherence spectroscopy (HMBC) and ��H-��H COSY at room temperature and elevated temperature. Kalkitoxin shows modest molluscicidal toxicity, good brine shrimp toxicity and extremely potent ichthyotoxicity. From the same extract of Lyngbya majuscula, I also isolated two other secondary metabolites, malyngamide J and malyngamide L. The structures of these new compounds, including stereochemistry, were determined by spectroscopic techniques including 2D-NMR experiments and by comparison with other known malyngamides. / Graduation date: 1997
4

Structure and synthesis of Gunnera perpensa secondary metabolites.

Peter, Xolani Kevin. January 2007 (has links)
The project focused on the isolation, characterization and synthesis of secondary metabolites of Gunnera perpensa L. (Gunneraceae), a South African medicinal plant used by many South African women to induce or augment labour and as an antenatal medication to tone the uterus. From the methanol extracts of the rhizomes we have isolated the compounds Z-venusol, methyl lespedezate, 4-6>-/?-D-glucopyranosyl-3,3',4'-tri-0- methylellagic acid and punicallagin. Structural elucidation of the compounds was performed using NMR spectroscopy. The presence of ellagic acid derivatives and hydrolysable tannins have not previously been reported from the family Gunneraceae. The study also focuses on the development of an HPLC analytical method to fingerprint the crude extracts of G perpensa. This method was used to determine the chemical composition of the rhizomes of the G. perpensa collected in different parts of South Africa. It is clear from the HPLC study that the rhizomes contain large concentrations of the hydrolysable tannin punicalagin and the second most abundant metabolite was Z-venusol. However, it was observed from plants collected in different regions that the ratio between punicalagin and Z-venusol differs substantially in the different extracts. An ellagic acid derivative isolated from G. perpensa contains a biaryl structure derived from gallic acid. The synthesis described in this thesis focused on reaction methods to access unsymmetrical biaryls and two synthetic routes were investigated - one that relies on the Ullmann reaction and the second that uses the Heck coupling reaction. Success of this coupling reaction towards the formation of ellagic acid derivatives was accomplished by the Heck coupling reaction method. One of the most important considerations towards the synthesis was the manipulation of hydroxyl groups of gallic acid by selective protection reactions that provide entry to the aforementioned preparation of unsymmetrical ellagic acid derivatives. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.
5

Novel secondary metabolites from selected British Columbian marine invertebrates

Ayer, Stephen William January 1985 (has links)
Marine organisms show potential as sources for novel, biologically and pharmacologically active, secondary metabolites. Examination of three nudibranch and one bryozoan species for biologically active metabolites has led to the isolation and structural elucidation of nine new and two known secondary metabolites. The structures of all the compounds were determined by using a combination of spectral analysis, chemical interconversion, synthesis, and single-crystal X-ray diffraction analysis. The British Columbian dorid nudibranch Acanthodoris nanaimoensis yielded three new sesquiterpenoids. The structures of nanaimoal (61) , acanthodoral (64) , and isoacanthodoral (65) represent novel sesquiterpenoid carbon skeletons. The natural mixture of aldehydes 61, 64, and 65 exhibited antibacterial and antifungal activity. From Aldisa cooperi, two ∆⁴-3-ketosteroidal acids 23 and 24, and glycerol ether 25 were isolated. Acid 23 showed feeding deterrent activity against fish. The dendronotid nudibranch Meli be leonina gave 2,6-dimethy1-5-heptenal 53 and 2,6-dimethyl-5-heptenoic acid 54. The aldehyde 53 was responsible for the "grapefruit like" odour of the nudibranch. The bryozoan Phidolopora pacifica was examined in an attempt to correlate the absence of surface fouling, in the field, with the presence of biologically active secondary metabolites. The purine alkaloids 179 and 180, which contain the rare naturally occurring nitro functionality, were responsible for much of the antifungal and antialgal activity of the crude extracts. Three nitrophenols 181, 189, and 209 were also isolated from P. pacifica. Nitrophenol 181 had been previously shown to inhibit chloroplast development both in green plants and in the unicellular algae Euglena sp. / Science, Faculty of / Chemistry, Department of / Graduate
6

Structure and stereochemistry of compounds from Cassipourea species.

Taylor, Craig William. January 1993 (has links)
Abstract available in pdf file.
7

Screening, in-vitro propagation and bioaugmentation of Ceratotheca triloba for the production of secondary metabolites

Mohanlall, Viresh January 2010 (has links)
Submitted in fulfillment for the Degree of Doctor of Technology: Biotechnology, Durban University of Technology, 2010. / Ceratatheca triloba (Bernh.) E. Mey. Ex Hook. f. is one of four species that is common to the summer rainfall areas in South Africa, especially the grasslands. It is used in traditional medicine to treat stomach cramps, nausea, fever and diarrhea. Like many other plants used in the traditional medicine system, these uses are not justified through scientific investigations. This study was undertaken to characterize the functionality of the main bioactive compounds from Ceratatheca triloba. This was achieved by isolating and identifying predominant chemicals from the non polar extracts using conventional chromatography techniques. Once identified the crude extracts and identified compounds were tested for their antimicrobial, anti-oxidant activity, anti-inflammatory activity and anticancer activity. This was followed by investigating the safety of the crude extracts and the purified compounds by the Brine shrimp lethality assay, and its toxicity to HepG2 cells and the Salmonella mutagenecity test. For large scale production, we set up a protocol to produce 9, 10 anthracenedione in a cell suspension culture system. Following the complete chemical profile of the roots, stems, flowers and leaves the predominant compounds were isolated, characterized and identified by UV-Vis, IR, EI-LCMS and NMR (COSY, HMQC, HMBC and DEPT). Three anthraquinone derivatives and one steroid, 9, 10 anthracenedione, 1-hydroxy-4-methylanthraquinone, 5, 8-dimethoxy-2, 3, 10, 10a-tetrahydro-1H-phenanthrene-4, 9-dione and androst-5-ene-3, 17, 19-triol were determine by analysis of spectral data (UV, 1H NMR, 13C NMR and EI-LC-MS) 9, 10 anthracenedione and 1 hydroxy-4-methylanthraquinone showed antibacterial activity against S.aureus, M. luteus, B cureus and E. coli. Due to the synergistic effect of the individual compounds, the crude extract exhibited good potency (>500) against S.aureus and M. luteus, medium potency against E. coli. and S. typhimurium (<100) and very low potency against B cureus (<10). Although a similar trend was observed for 9, 10 anthracenedione and 1 hydroxy-4-methylanthraquinone unlike the crude extract. A very low potency against S.aureus for 9, 10 anthracenedione and a high potency for 1 hydroxy-4-methylanthraquinone. Thus 9, 10 anthracenedione is an effective drug against E. coli and S. typhimurium and 1 hydroxy-4-methylanthraquinone is effective against S.aureus and M. luteus. The crude root extracts and 9, 10 anthracenedione, 1 hydroxy-4-methylanthraquinone, 8-dimethoxy-2, 3, 10, 10a-tetrahydro-1H-phenanthrene-4 showed a ± 50% reduction of the free radicals. No anti-inflammatory activity was observed. The purified extracts showed moderate toxicity against HepG2 cells at high concentrations and no toxicity was observed against brine shimp larvae. No mutagenecity was observed with the crude extracts using the Ames test. All purified and crude extracts showed potent inhibition of the human topoisomerase II enzyme. In conclusion, although this study does not indicate any relationship to its traditional usage it provides valuable information that paves a way for commercial exploitation of C. triloba. 9, 10 anthracenedione and 1 hydroxy-4-methylanthraquinone can be used as antibacterial agents. Their antioxidative potential can be exploited for anti-cancer as in many cancers reactive oxygen species are implicated in the aetiology of these cancers. Furthermore, in this study 9, 10 anthracenedione was produced from both callus cultures and cell suspension cultures. This compound demonstrates potent anti-topoisomerase II activity which is vital to cancer treatment. Thus, the synergistic effect of 9, 10 anthracenedione and 1 hydroxy-4-methylanthraquinone as antibacterial, anti-oxidative and anti-cancer compounds demonstrate the importance of C. triloba. / Centre for Research Capacity Development ; National Research Foundation
8

Genetic transformation of Ceratotheca triloba for the production of anthraquinones from hairy root cultures

Naicker, Leeann January 2012 (has links)
Submitted in complete fulfillment for the Degree of Master of Technology: Biotechnology, Durban University of Technology, 2012. / Many secondary metabolites that have been extracted from medicinal plants have been used as source of clinical drugs. However, the concentration of the active metabolites in plants is generally low. An attractive alternative for producing these important secondary metabolites is via plant tissue culture technology. More particularly, the genetic transformation of a plant tissue by Agrobaterium rhizogenes has been employed for producing high yields of secondary metabolites. In a previous study, three structurally similar anthraquinones: 9,10-Anthracenedione, 1-Hydroxy-4-methylanthraquinone and 5,8-Dimethoxy-2,3,10,10a-tetrahydro-1H,4aH-phenanthrene-4,9-dione, and one steroid; Androst-5-ene-3, 17, 19-triol were isolated from the root extracts of C. triloba. The anthraquinones have shown to exhibit the anticancer mechanism which involves the inhibition of the activity of the human topoisomerase II enzyme that transforms supercoiled DNA to linear DNA. However, these anthraquinones were found in very low concentrations. Therefore, in this study we used plant cell and tissue culture systems (cell suspension, shoot and hairy root cultures) of C. triloba to increase the production of anthraquinones. Since the establishment of C. triloba in vitro plant systems required a source sterile explants, a protocol that involved the use of NaCIO was optimized for the sterilization and subsequent germination of C. triloba seeds which were micro-propagated into shoot cultures. These cultures provided a source explants for the induction of callus and hairy root cultures. The biomass of these plant cell and tissue cultures were subsequently bulked up for the extraction for anthraquinones and the yields were compared followed by fractionation and identification of the major compounds. The bioactivity of the fractions was evaluated by testing their cytotoxicity on cancer cells and anti-topoisomerase activity. The sterilization protocol that provided sterile seeds was found to be a solution of 30% NaCIO at an exposure time of 10 minutes. From the sterilized seeds shoot cultures were established on MS medium. The leaf explants of the shoot cultures were then used to induce callus cultures which subsequently were transferred to liquid medium whereby the total biomass of suspension cultures increased from 4 g to 134.18 g (wet weight). Also hairy roots cultures were established from stem explants with a low cell density inoculum of A. rhizogenes at a transformation efficiency of 73%. The growth of these hairy roots was slow in hormone free medium. This was overcomed with the use NAA and IAA which increased the xvii biomass from 1.03 g in the control culture (without hormone) to 23.91 g and 46.13 g respectively. An evaluation of the anthraquinones in the field root and hairy root, cell suspension and shoot culture extracts was carried out by using their Thin Layer Chromatography profiles and the High Performance Liquid Chromatography profiles as well as the standards, 9,10-Anthracenedione and 1-Hydroxy-4-methylanthaquinone. TLC analysis showed that the RF values of the fractions CT01 and CT02 matched the RF values of anthraquinones standards while HPLC analysis revealed that hairy root cultures supplemented with IAA (125.03 μg.mg-1) or NAA (98.25 μg. mg-1) produced a higher concentration of anthraquinones than the control culture (without hormone) (13.33 μg.mg-1), the field roots (33.51 μg. mg-1) and the shoot (3.23 μg.mg-1) and cell suspension cultures (13.17 μg.mg-1). Due to co-elution of the compounds in HPLC analysis, six fractions were isolated by Preparative Thin Layer Chromatography from the hairy root extract (obtained from the culture supplemented with NAA) and were coded as CT01, CT02, CT03, CT04, CT05 and CT06. The compounds in these fractions were identified by Electron Ionization-Liquid chromatography-Mass Spectroscopy and it was found that the hairy roots produced one acridone derivative; 5-Methoxy-2-nitro-10H-acridin-9-one, one naphthoquinone derivative; 2H-Naphto[2,3-b]pyran-5,10-dione,3,4-dihydro-2,2-dimethyl- and seven anthracenedione derivatives. These were: i) 5,8-Dimethoxy-2,3,10,10a-tetrahydro-1H,4aH-phenanthrene-4,9-dione, ii) 9,10-Anthracenedione, 2-methyl-, iii) 1-Hydroxy-4-methylanthraquinone, iv) 9,10-Anthracenedione, 2-ethyl-, v) 1,5-Diaminoanthraquinone, vi) Phenanthrene, 3,6-dimethoxy-9-methyl-, vii) 9,10-Anthracenedione, 1,4-dimethyl-. Fractions CT01 (5,8-Dimethoxy-2,3,10,10a-tetrahydro-1H,4aH-phenanthrene-4,9-dione, 9,10-Anthracenedione, 2-methyl- and 1-Hydroxy-4-methylanthraquinone) and CT02 (9,10- Anthracenedione, 2-ethyl-) were cytotoxic to the DU-145 cancer cell line at concentrations of 125 μg.mg-1 to 1000 μg.mg-1. These fractions also showed anti-topoisomerase activity as they inhibited the conversion of supercoiled DNA into linear DNA. In conclusion this is the first study that describes the transformation of C. triloba by A. rhizogenes mediated transformation and compares the production of anthraquinones in C. triloba hairy roots to the field roots, shoot and cell suspension cultures. This study has xviii indicated that hairy root cultures is a high-yielding production system for anthraquinones (5,8-Dimethoxy-2,3,10,10a-tetrahydro-1H,4aH-phenanthrene-4,9-dione, 1-Hydroxy-4-methylanthraquinone, 9,10-Anthracenedione, 2-methyl- and 9,10- Anthracenedione, 2-ethyl-) which could have the potential to be used in cancer therapy. In addition the discovery of C. triloba hairy roots having the biosynthetic capacity to synthesize five valuable anthraquinone derivatives that are not found the field roots has also been revealed. / National Research Foundation.
9

The biosynthesis and production of hypoxoside in Hypoxis hemerocallidea Fisch. and Mey. in vivo and in vitro.

Bayley, Arlene Diane. January 1989 (has links)
Hypoxoside, a phenolic diglucoside, with a diarylpentane-type structure, is thought to be the medicinally active constituent of corm extracts of Hypoxis hemerocallidea Fisch. & Mey. which are reputed to alleviate the symptoms of prostate hypertrophy and urinary infections. The biosynthes is and production of this unique phytochemical were investigated in H. hemerocallidea using both in vivo and in vitro systems. It was found, in root-producing callus, that [l4]C-phenylalanine and [14]C-t-cinnamic acid were efficient precursors for hypoxoside in comparison to [14]C-sodium acetate and [14]C-acetyl coenzyme-A, which were not incorporated into the phenolic compound. Thus, at least one aryl moiety of hypoxoside was derived, via phenylalanine and t-cinnamic acid, from the shikimate pathway. The acetate pathway did not appear to be involved in the biosynthetic process. The data supports the hypothesis that the molecule is formed from two cinnamate units with the loss of a carbon atom, in opposition to the proposal that the molecule is derived from head-to-tail condensation of acetate units onto a propenylic moiety. Despite the structural similarities between hypoxoside and caffeic and p-coumaric acids, these two hydroxycinnamic acids were not efficient precursors for hypoxoside in vivo or in vitro. A number of reasons are put forward to explain this finding. It was found that the greatest concentration of hypoxoside was located in the corms of intact plants. The major biosynthetic site of the molecule was also found to be located in this organ. Since the roots did accumulate the phytochemical to a small extent, the biosynthetic potential of these organs has not been disregarded. That of the leaves has been, however. The report by PAGE (1984) that the upper region of the corm contained a greater con cent ration of hypoxoside than the lower portion, is substantiated in this study, where this region was found to be more biosynthetically active than the lower half. Light microscopic and electron microscopic studies revealed that starch storing cells, which accumulated phenolics in their vacuoles, contained seemingly synthetically active tubular endoplasmic reticulum in their cytoplasm. A greater number of these cells were concentrated in the upper region as opposed to the lower half of the corm. It is postulated that these cells are the site for biosynthesis and accumulation of hypoxoside. The shikimate pathway, from which the precursors for hypoxoside are derived, was found, through the exposure of intact plants to [14]C-carbon dioxide, to be located mainly in the leaves. It is postulated from the above study and one in which [14]C-phenylalanine, [14]C-t-cinnamic acid, [14]C-p-coumaric acid and [14]C-caffeic acid were applied to intact plants, that phenylalanine and/or cinnamic acid are the transported form of the shi kimate derivatives. p-Coumaric and caffeic acids, which are metabolically more stable, are envisaged to be the sequestering forms. The investigation of the seasonal production of hypoxoside revealed that most of the synthesis and accumulation occurred after the corms had broken winter dormancy and after the flush of leaf growth had slowed down. During dormancy the production of hypoxoside appeared to cease. The in vjtro studies, where the effects of light, temperature, nutrients, plant growth regulators and supply of potential precursors, on hypoxoside production by root-producing callus were investigated, indicate that this metabolite is not simply a "shunt" metabolite. A number of factors other than precursor availability enhanced, or reduced the jn vjtro production of this phytochemical. Furthermore, production of the phytochemical and growth were not always antagonistic. Hypoxoside, the biosynthesis of which requires a more thorough investigation, is, however, according to this investigation, a typical secondary metabolite in many respects. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1989.
10

Isolation and identification of novel compounds from indigenous plants.

Sehlapelo, Bethuel (Tiny) Matshene. January 1993 (has links)
Abstract available in pdf file.

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