• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 4
  • 1
  • Tagged with
  • 7
  • 7
  • 7
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 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

Synthetic studies towards manzamine A

Townsend, Robert J. January 1999 (has links)
No description available.
2

Studies on the Natural Products from the Taiwanese Soft Corals Clavularia viridis, Xenia florida, Cespitularia taeniata, Cespitularia hypotentaculata, and Sarcophyton stolidotum

Cheng, Yuan-Bin 16 July 2007 (has links)
This dissertation mainly discussed the investigation of five different soft corals collected in Green Island and one soft coral collected in Kenting. They were identified as Clavularia viridis, Xenia florida, Cespitularia taeniata, Cespitularia hypotentaculata, and Sarcophyton stolidotum. In the isolation of these corals, there were sixty natural products discovered, including twenty night new compounds and three new derivatives. The research of soft coral Clavularia viridis has result in the isolation of six new prostanoids, designated as 4-deacetoxyl-12-O-deacetylclavulone I (1), 4-deacetoxyl-12-O-deacetylclavulone II (2), bromovulone II (3), iodovulone II (4), 4-deacetoxyl-12-O-deacetylclavuloneIII (5), and bromovulone III (6), together with seven known prostanoids, identified as clavulone I (33), clavulone II (34), chlorovulone II (35), 4-deacetoxylclavulone II (36), clavulone III (37), chlorovulone III (38), and 7-acetoxy-7,8-dihydroiodovulone I (39). In the investigation of the soft coral Xenia florida, three new compounds called florxenilides A-C (7-9), has been purified. The research also obtained seven xenicane-type diterpenes, xeniafaraunol A (40), xeniafaraunol B (41), florlide A (42), florlide C (43), florlide D (44), 9-deoxyxeniolide A (45), and 9-deoxyxeniolide B (46) in addition to two cadinene-type sesquiterpenes, xenitorins A (47) and B (48). Florxenilides A and C also treated with some chemical reagents to afford three new derivatives, 10-benzoylflorxenilide A (10), Florxenilide C monoacetate (11), and 10-dehydroflorxenilide A (12). Otherwise, the study in Cespitularia taeniata has afforded ten new nitrogen-containing compounds, cespitulactams D-K (13-20) and taenialactams A-B (21-22), in addition to four known compounds, atractylenolactam (49), cespitulactam A (50), cespitulactam B (51), and cespitularin F (52). Moreover, there were three new compounds, namely cespihypotins E, F, and H (23, 24, 25) have been discovered from another soft coral Cespitularia hypotentaculata. The study of this coral also observed seven known components called cespihypotin G (53), cespitulactone A (54), cespitularin F (52), cespitularin D (56), cespihypotins A-C (55, 57, 58). Investigation of the non-polar extract of the soft coral Sarcophyton stolidotum collected in Kenting resulted in the isolation of seven new 14-membered carbocyclic cembranes, sarcostolides A-G (26-32), together with two known cembranes isosarcophytoxide (59) and isosarcophine (60). All the structures of above metabolites were elucidated by physical and spectroscopic analyses including IR, Mass, UV, NMR, and optical rotation, and by compared with published data in many previous papers. The stereochemistry of these compounds as determined by NOESY experiments, CD spectroscopic data, and Mosher¡¦s methods. Cytotoxicity tests were measured by Dr. Kuo Yao-Haur and Dr. Guh Jih-Hwa. Isolated marine prostanoids showed potent activities against human prostate carcinoma (PC-3) and colon adenocarcinoma (HT-29) cells. Among them bromovulone III (6) had the most potent cytotoxicity against both cell lines at IC50 0.5
3

Studies towards the total synthesis of madeirolide A

Yip, Adam Christopher Loy January 2018 (has links)
Madeirolide A (1) is a structurally novel polyketide natural product first isolated from the deep-sea sponge Leiodermatium sp. by Wright in 2009. Initial biological investigations of madeirolide A revealed potent inhibition of the fungal pathogen Candida albicans but failed to determine any appreciable cytotoxicity when tested against a limited range of cancer cell lines. The unusual bioactivity of madeirolide A coupled with uncertainty over the true stereostructure of the natural product makes it a compelling target for synthesis. This thesis discloses synthetic efforts towards the total synthesis of madeirolide A with an emphasis on the construction of the all-cis C21 - C27 eastern tetrahydropyran. Chapters 1 and 2 provide an introduction to the importance of natural products in drug discovery and outline the context of this project with details of the isolation and biological activity of madeirolide A. Previous synthetic efforts are also reviewed including those from within the group which formed the basis of the present studies. Chapter 3 describes the synthesis of a fully elaborated C1 - C11 fragment, building upon previously published work in the group. Specifically, it details the successful completion of a modified approach designed to avoid some of the major challenges previously encountered such as undesired migration of protecting groups and challenges in selectively installing an (E)-vinyl iodide. Chapter 4 discusses ongoing efforts towards the challenging C12 - C27 fragment of madeirolide A. The stereocontrolled synthesis of several linear C19 - C27 precursors is outlined, followed by details of screening reactions conducted to affect the desired oxy- Michael cyclisation. Additionally, extensive computational studies have been undertaken in an attempt to rationalise the frustrating lack of reactivity observed with the goal of developing a substrate suitably elaborated to cyclise. Finally, the asymmetric synthesis of the C13 - C17 subfragment is outlined, which will provide eventual access to the eastern tetrahydrofuran. Chapter 5 summarises the synthetic work carried out thus far and explores potential strategies for the future completion of the natural product with a focus on alternative disconnections of the eastern tetrahydropyran.
4

Discovery of cytotoxic natural products from South African marine sponges

Lerata, Mookho Sylvia January 2018 (has links)
Magister Pharmaceuticae - Mpharm / Cancer is a major health problem worldwide and killing millions of people each year. The use of natural products as chemotherapeutic agents is well established, however, many of the currently available drugs are associated with undesirable side effects and high toxicity. Furthermore, the development of drug resistant cancers makes the search for anticancer lead compounds a priority. In this study a library of prefractionated marine sponge extracts was established and used to prioritise samples for isolation of bioactive metabolites. From the generated library, two of the sponges of genera Ircinia sp. and Latrunculid sp. resulted in isolation of furanosesterterpenes (7E,12Z,20Z,18S-variabilin) and pyrroloiminoquinone (tsitsikammamine A and tsitsikammamine N-18 oxime) alkaloids respectively. The structures of these compounds were elucidated by analysis of 1D and 2D NMR data. These compounds displayed moderate to potent cytotoxicity against MCF-7, PC-3, U-87 and HEK-293 cells lines through apoptosis, with lack of selectivity for cancer cell lines.
5

Chemical and biological evaluation of palythoa tuberculosa collected from the red sea

Elbagory, Abdulrahman Mohammed January 2015 (has links)
Masters of Science / A chemical study on the total extract of the zoanthid Palythoa tuberculosa, collected from the Red Sea, resulted in the isolation of seven polyhydroxylated sterols viz: palysterols A-G, six of which are new. Their chemical structures were elucidated on the basis of their 1D and 2D NMR and MS spectroscopic data. Palysterols B and G demonstrated cytotoxic activity on three human cancer cell lines (MCF-7, HeLa, and HT- 29). Palysterol G, in particular, was able to induce apoptosis in breast adenocarcinoma(MCF-7) cells
6

Synergizing Microbial Culturing, Whole Genome Sequencing, Asymmetric Synthesis and Tandem MS for Reconstruction of Polyketide and Alkaloid Natural Product Biosynthesis in Marine Actinomycete Nocardiopsis sp CMB- M0232

Alqahtani, Norah Faihan 03 June 2015 (has links)
No description available.
7

The distribution, biosynthetic origin and functional significance of Tyrian purple precursors in the Australian muricid Dicathais orbita (Neogastropoda: Muricidae)

Westley, Chantel Barbara, chantel.westley@flinders.edu.au January 2008 (has links)
Information on the biosynthetic origin and functional advantage of marine mollusc natural products is not only essential to our understanding of chemical ecology, but to the development and responsible production of therapeutic agents. As demonstrating in situ activity is methodologically hindered, functions inferred by in vitro activity have been assumed for many secondary metabolites. The anatomical and ontogenetic distribution of natural products can not only provide information on the biosynthesis and storage of metabolites, but identify selective pressures likely to affect survivorship at a specific life stage. Thus, dissection and chemical analysis of distinct tissues, in combination with histochemistry may offer a valuable approach. Marine gastropods of the Muricidae are renowned for the ancient dye Tyrian purple, which evolves from choline esters of bromoindoxyl sulphate in the hypobranchial gland through a series of enzymatic and photo-oxidative reactions. Prochromogen hydrolysis by arylsulphatase liberates neuromuscular active choline esters and cytotoxic bromoindole precursors, which also occur in muricid egg masses. Although visual accounts of dye pigments in the muricid gonoduct suggest precursors may be incorporated into egg masses from a maternal source, their biosynthetic origin and the evolutionary significance of the hypobranchial gland is unknown. Thus, the Muricidae, and in particular Dicathais orbita upon which most previous research has been focused, is an ideal model for this novel approach to natural product research. To confirm observations of dye pigments in muricid gonoducts and gain an understanding of their anatomical distribution, a liquid chromatography-mass spectrometry (LC-MS) method was developed to simultaneously quantify pigments, precursors and the prochromogen, tyrindoxyl sulfate. The prochromogen was not only detected in albumen and capsule gland extracts, but bioactive intermediates and the dye 6,6’-dibromoindigo were also present in the latter. These findings provided preliminary evidence for the maternal provision of prochromogens in egg masses of D. orbita and identified regions within which to conduct histochemical investigations. Tyrindoxyl sulphate was also detected in male prostate gland extracts, along with the dibromoindigo isomer, 6,6’-dibromoindirubin and its oxidative precursor, 6-bromoisatin. This not only implies physiological differences exist between male and female gonoducts, but that these secondary metabolites are not solely intended for egg masses and may hold significance throughout the life cycle. Histomorphological inspection of the pallial gonoduct-hypobranchial gland complex was conducted over the annual cycle to determine a mechanism for precursor transfer between these structures. Although an anatomical connection was not detected, the secretions of two hypobranchial cell types thought to be involved in Tyrian purple synthesis were of remarkable biochemical similarity to those of various capsule and albumen gland lobes. Together these findings implied the potential for natural product synthesis within the pallial gonoduct of D. orbita. To establish the role of these glandular lobes in the incorporation of intracapsular fluid and capsule laminae, identical histochemical techniques were applied to transverse capsule wall sections. Biochemical correlations not only provided a simple method of deciphering the complex process of encapsulation in neogastropods, but effectively identified the destination of gonoduct secretions in egg capsules of D. orbita. Comparisons of capsule and gonoduct biochemistry revealed that the intracapsular fluid and inner capsule wall are secreted by the posterior capsule gland lobe, the middle lamina by the lateral lobes and the outer layers by the dorsal lobe, albumen and pedal glands. Investigation into the location of regulatory enzymes and precursors was conducted to establish the biosynthetic origin of Tyrian purple prochromogens and mechanisms governing bioactive precursor synthesis. Novel histochemical techniques for the localization of bromoperoxidase, the enzyme thought to facilitate prochromogen bromination, and tyrindoxyl sulphate were developed and applied to gonoduct, hypobranchial gland, and encapsulated larvae sections. Standard staining reactions for the indole precursor, tryptophan, and arylsulphatase were also applied. The histochemical approach adopted revealed that tyrindoxyl sulphate is de novo biosynthesized through the post-translational bromination of dietary derived tryptophan. Two biosynthetic sites were identified, one related to hypobranchial secondary metabolism and the second of significance to the presence of bioactive precursors in muricid egg masses. Tryptophan is stored within secretory cells of the lateral hypobranchial epithelium and once exocytosed, is united with bromoperoxidase from supportive cells to form tyrindoxyl sulphate. Prochromogen synthesis also occurs in the subepithelial vascular sinus for storage and secretion by medial hypobranchial secretory cells. Bioactive precursor synthesis on the epithelial surface is regulated by the liberation of arylsulphatase from adjacent supportive cells. These findings not only provide evidence for de novo biosynthesis of Tyrian purple precursors, but are first account of natural product biosynthesis within the gastropod hypobranchial gland. Together these findings imply a naturally selected function for the synthesis of bioactive indoles in hypobranchial gland secretions of the Muricidae and Gastropoda. Tyrindoxyl sulphate is also transported within the vascular sinus to lateral and dorsal capsule gland lobes where bromoperoxidase and arylsulphatase also occur. Arylsulphatase was also detected within the albumen gland, which along with the posterior capsule gland lobe, acts as a storage site for dietary tryptophan. Thus, tyrindoxyl sulphate and the constituents for prochromogen and precursor biosynthesis are introduced to intracapsular fluid and capsule laminae by the capsule gland. Histochemistry in combination with LC-MS revealed an identical biosynthetic profile within larval vitellus, which is elaborated during oogenesis and may also receive secretions from the albumen gland. Due to the absence of a hypobranchial gland in veligers, it appears that pelagic larvae rely on vitelline natural products until settlement and metamorphous. These findings together with the in situ antimicrobial activity of bromoindoles suggest Tyrian purple precursors are incorporated into muricid egg masses as a maternal investment in larval defence against pathogens. The results of this investigation clearly highlight the benefits of adopting a histochemical approach to natural product research. This novel alternative to radioisotopes and in situ demonstration of bioactivity, can not only aid in the elucidation of secondary metabolic pathways and chemically mediated interactions, but identify mechanisms of metabolite regulation and differentiate between biosynthetic and storage tissues. Apart from providing insight into the ecological significance of muricid secondary metabolites, the biosynthetic information provided is valuable to our understanding of chemical phylogeny and biosynthetic enzyme sequencing for the environmentally sound development of natural products as biomedical agents.

Page generated in 0.113 seconds