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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

Cloning and biochemical characterization of the hectochlorin biosynthetic gene cluster from the marine cyanobacterium Lyngbya majuscula

Ramaswamy, Aishwarya V. 02 June 2005 (has links)
Cyanobacteria are rich in biologically active secondary metabolites, many of which have potential application as anticancer or antimicrobial drugs or as useful probes in cell biology studies. A Jamaican isolate of the marine cyanobacterium, Lyngbya majuscula was the source of a novel antifungal and cytotoxic secondary metabolite, hectochlorin. The structure of hectochlorin suggested that it was derived from a hybid PKS/NRPS system. Unique features of hectochlorin such as the presence of a gem dichloro functionality and two 2,3-dihydroxy isovaleric acid prompted efforts to clone and characterize the gene cluster involved in hectochlorin biosynthesis. Initial attempts to isolate the hectochlorin biosynthetic gene cluster led to the identification of a mixed PKS/NRPS gene cluster, LMcryl, whose genetic architecture did not substantiate its involvement in the biosynthesis of hectochlorin. This gene cluster was designated as a cryptic gene cluster because a corresponding metabolite remains as yet unidentified. The expression of this gene cluster was successfully demonstrated using RT-PCR and these results form the basis for characterizing the metabolite using a novel interdisciplinary approach. A 38 kb region putatively involved in the biosynthesis of hectochlorin has also been isolated and characterized. The hct gene cluster consists of eight open reading frames (ORFs) and appears to be colinear with regard to hectochlorin biosynthesis. An unusual feature of this gene cluster includes the presence of a ketoreductase domain in an NRPS module and appears to be the first report of such an occurrence in a cyanobacterial secondary metabolite gene cluster. Other tailoring enzymes present in the gene cluster are two cytochrome P450 monooxygenases and a putative halogenase. The juxtaposition of two ORF's with identical modular organization suggests that this gene cluster may have resulted from a gene duplication event. Furthermore, biochemical characterization of two adenylation domains from this cluster strengthens its involvement in the biosynthesis of hectochlorin. / Graduation date: 2006
2

Structure elucidation and biosynthetic investigations of marine cyanobacterial secondary metabolites

Nogle, Lisa Marie 06 August 2002 (has links)
This thesis details my investigations of marine cyanobacterial natural products that resulted in the discovery of thirteen new secondary metabolites, the isolation of over fifteen previously reported metabolites and the biosynthetic investigation of two additional cyanobacterial compounds. Two novel lipopeptides were identified from a Lyngbya majuscula and Schizothrix sp. assemblage collected in the Fiji Islands. Somamide A is a depsipeptide consisting of a hexanoate moiety extended by seven amino acids, including two nonstandard units characteristic of cyanobacterial peptides. In contrast, somocystinamide A is a unique linear disulfide dimer displaying potent cytotoxicity against a mammalian neuroblastoma cell line. The organic extract from a Puerto Rican L. majuscula proved remarkably rich in chemistry, producing twelve known compounds as well as four new secondary metabolites. Among these new isolates were the novel sodium channel blocker antillatoxin B, a new chlorinated quinoline derivative and the new ��-pyrone malyngamide T. A collection of L. majuscula from Antany Mora, Madagascar, led to the isolation of the previously reported antineoplastic agent dolastatin 16 and the discovery of a new series of lipopeptides, the antanapeptins. These new molecules are characterized by the presence of the unique ��-hydroxy acid 3-hydroxy-2-methyloctynoate, or its reduced double- or single-bond equivalent. Wewakazole is a novel cyclic dodecapeptide isolated from a Papua New Guinea collection of L. majuscula. This large molecule contains both a methyloxazole and two oxazoles, residues rarely observed in marine cyanobacterial metabolites. Extensive utilization of 1D and 2D NMR techniques were required to elucidate the structure of this distinctive peptide. Biosynthetic investigations of two halogenated cytotoxins were also conducted on a cultured L. majuscula strain originally isolated from Hector Bay, Jamaica. Stable isotope feeding experiments demonstrated that both jamaicamide A and hectochlorin derive from mixed PKS and NRPS biosynthetic origins but are comprised of primary precursors unique to each molecule. / Graduation date: 2003
3

Marine algal secondary metabolites of unique structure and biomedicinal or agrichemical potential

Milligan, Kenneth Edward 10 October 2001 (has links)
This thesis describes investigations of marine algal secondary metabolites, with particular interest in their biomedical and agrichemical potential. Invaluable in such pursuits have been the access and application of advanced spectroscopic techniques, such as NMR, and the ability to assess the biological activity of the algal samples in a variety of diverse protocols, through in-house evaluation and industrial collaborations. As an in-house bioassay, a survey of algal extracts for molluscicidal activity has led to the isolation of the previously reported chondrocole C (Portieria hornemanni), tanikolide (Lyngbya majuscula), and debromoaplysiatoxin (L majuscula). Debromoaplysiatoxin is 100 times more potent than niclosamide, the commercially utilized molluscicide. Such activity may make debromoaplysiatoxin an attractive agent for molluscan biological control to prevent the spread of schistosomiasis in artificial waterways such as irrigation channels and rice paddies. The isolation of chondrocole C led to further chemical investigations of P. hornemanni. A total of six related polyhalogenated monoterpenes were isolated from this collection. While four of these compounds were previously reported, taviochtodene represents the newest member of this class of secondary metabolites. Previously, this alga has yielded compounds with great potential anticancer utility, but naturally and synthetically elusive. The discovery of this class of chemistry potentially locates new geographic territory to search for such anticancer metabolites. While there has been little reported biological activity attributed to the malyngamides, they form the most prevalent class of secondary metabolites isolated from Lyngbya majuscula. To this list we have added malyngamides L, Q, and R. Of particular note, malyngamides Q and R were the first malyngamides to have been reported with altered stereochemistry at the vinyl chloride carbon. Subsequently, and in part stimulated by this finding, this alternate stereochemistry has been defined for some newly reported malyngamides. Also from L majuscula, tortugin and lyngbyabellin B were isolated as toxic cyclic depsipeptides. Both of these compounds displayed relatively potent biological activity (brine shrimp and antifungal). Each possessing particular structural motifs previously seen in invertebrate secondary metabolites, they lend further evidence for cyanobacteria as the producer of many of the polyhalogenated compounds often attributed to de novo invertebrate biosynthesis. / Graduation date: 2002
4

Biosynthetic investigations of two secondary metabolites from the marine cyanobacterium Lyngbya majuscula

Rossi, James V. 06 March 1997 (has links)
Marine cyanobacteria have been shown to produce a variety of biologically active and stucturally diverse secondary metabolites. These compounds are of interest to natural products researchers mainly because of their potential application as biomedicinals, biochemical probes, and agrichemicals. The metabolic pathways utilized by the cyanobacterium Lyngbya majuscula to generate curacin A, a potent antimitotic and its cometabolite, the molluscicidal barbamide, have been studied. Application of methods including radioisotope and stable isotope labeling have revealed the role of acetate and the amino acids methionine, valine, cysteine, and leucine as potential precursors in the biosynthesis of curacin and barbamide. An analytical technique based upon GC-EIMS methodology has also been developed to monitor the production levels of curacin A from cultures of Lyngbya majuscula with respect to growth. This method which makes use of the thiazole analog of curacin A, curazole as an internal standard, has also been preliminarily applied to the curacin A production in response to environmental factors associated with changes in geographical locations at or near sites where the original collections of the cyanophyte were made in Curacao, Netherlands Antillies. This was performed by a series of transplantation experiments envolving high and trace curacin A producing strains of L. majuscula. Interest in the bioactive profile of curacin A prompted a pilot scale up of the cultured tissue for isolation of the metabolite. These efforts provided a framework of methods that can be used industrially to obtain large quantites of the compound to meet possible future pharmaceutical or dignostics demands. / Graduation date: 1997
5

Isolation of marine metabolites from S̲y̲m̲b̲i̲o̲d̲i̲n̲i̲u̲m̲ species of dinoflagellates /

Drainville-Higgins, Katherine Evelyn. January 2004 (has links)
Thesis (Ph. D.)--University of Rhode Island, 2004. / Typescript. Includes bibliographical references (leaves 339-347).
6

Pyrroloiminoquinone metabolites from South African Latrunculid sponges /

Antunes, Edith Martins. January 2003 (has links)
Thesis (Ph. D. (Chemistry))--Rhodes University, 2003.
7

Studies toward the synthesis of halichlorine and pinnaic acid /

Korf, Eric A. January 1900 (has links)
Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references. Also available on the World Wide Web.
8

Natural Product Studies of Marine Organisms from the Western Atlantic

Unknown Date (has links)
The projects described in this dissertation are focused on compounds derived from marine organisms collected from the western Atlantic marine environment. Chapter 1 provides an introduction to the study of natural products chemistry, marine natural products, and overview of the research undertaken from natural product chemists. Chapter 2 describes the isolation and structure elucidation of a series of rare diterpenoids from the gorgonian Briareum asbestinum, together with their conformational analysis and biosynthetic interconversions. These rare diterpenes from Briareum asbestinum are linked by an unusual transannular oxa-6π electrocyclization which is described in detail and this work demonstates the biomimetic hemisynthesis of briareolate esters L (19) to B (22) achieved via an intermediary, briareolate ester G (2), through a controlled set of photoinduced isomerizations and a unique photochromic transannular oxa-6π electrocyclization. This work focuses largely on the mechanistic understanding of the photochemical production of these briarane diterpenoids and illustrates a unique UVA/UVC, photochromic switch which induces a transannular oxa- 6π electrocyclization. Chapter 3 describes the assay-guided isolation of marine antioxidants. This chapter focuses on the screening of marine organism extracts using the Ferric Reducing Antioxidant Power (FRAP) assay for antioxidant activity guided isolation of marine natural products. The chapter concludes with the activity guided isolation and structural elucidation of 1-O-palmitoyl-2-O-myristoyl-3-O-(6-sulfo-α-D-quinovopyranosyl)- glycerol (40) to show direct antioxidant potential through FRAP analysis. Chapter 4 describes the isolation, structural elucidation and pharmacological evaluation of the novel secondary metabolites iso-PsA(45), Iso-PsC (46), iso-PsD (47) as well as known Pseudopterosins A(41), B(42), C(43), D(44), K(48), K2’OAc(49), K2’OAc(50). These secondary metabolites were evaluated for both cytotoxicity. The chapter concludes with the screening of these compounds as αβ-amyloid fibril modulators utilizing atomic force microcopy (AFM). / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection
9

Biosynthesis, production and structural studies of secondary metabolites in cultured marine cyanobacteria

Vulpanovici, Florina Alexandra 23 July 2003 (has links)
This thesis details investigations of marine cyanobacterial secondary metabolism, with emphasis on a strain of Phormidium sp. collected in Indonesia. These studies assessed the effects of nineteen putative elicitor compounds on the growth and metabolite production of five species of marine cyanobacteria, biosynthetic investigation of an intriguing secondary metabolite, phormidolide, and the discovery of one novel halogenated peptide, phormidamide. The growth, biomass production and the ratio of the components of the extract were affected by some of the elicitors in most of the cyanobacterial species tested. However, production of a novel secondary metabolite or a significant change in the bioactivity of the extracts was not observed. Biosynthetic investigations of a brominated brine shrimp toxic polyketide, phormidolide, were conducted on a cultured Phormidium sp. strain originally isolated from Indonesia. Stable isotope feeding experiments confirmed its polyketide nature and established a new example of a general trend in cyanobacterial metabolism where both S-adenosyl methionine and C2 of acetate contribute to the biogenesis of pendant methyl groups. At the same time, feedings with deuterated acetate provided insight into the HMG-CoA synthase-like mechanism by which addition of pendant methyl groups from C2 of acetate takes place. Studies of phormidolide production in bromine-depleted medium showed that two analogs are produced, debromophormidolide with a terminal olefin in place of the vinyl bromide, and iodophormidolide, introducing iodine in place of bromine from the trace amounts present in the medium. Supplementation of the bromine-depleted culture medium with iodine resulted in a 10-fold increase of iodophormidolide production, while bromine supplementation resulted in a more moderate (2.5 fold) enhancement in phormidolide yield. A novel halogenated cytotoxic peptide, phormidamide, was isolated and a planar structure is proposed, pending confirmation by X-ray crystallographic analysis. Phormidamide contains a unique bromophenylalanine functionality, three chlorine atoms, and a very high number of quaternary carbon atoms which have hindered structural elucidation efforts through spectroscopic methods. / Graduation date: 2004
10

Structure and biosynthesis of marine cyanobacterial natural products : development and application of new NMR methods

Marquez, Brian L. 29 June 2001 (has links)
This thesis is an account of my explorations into the field of natural products chemistry. These investigations led to the discovery of several novel secondary metabolites isolated from the marine cyanobacterium Lyngbya majuscula. In addition, biosynthetic investigations were undertaken using stable isotope-labeled precursors. The dominant role that NMR spectroscopy plays in the field of natural products chemistry has led to the development of several novel pulse sequences. Hectochlorin was discovered during a phytochemical investigation of a cultured L. majuscula originally collected off the coast of the Caribbean Island, Jamaica. The absolute stereochemistry was determined by X-ray crystallography. Through a series of biological evaluations, this compound was found to stimulate actin polymerization. The jamaicamide class of compound was isolated from the same organism that yielded hectochlorin. The structures were elucidated utilizing a variety of NMR methods, including a newly developed pulse sequence. Because the producing organism was in culture, a biosynthetic pathway investigation ensued to elucidate the carbon framework in jamaicamide A. The marine natural product barbamide is intriguing due to the incorporation of a trichloromethyl group into its molecular constitution. Further investigation into the timing of the chlorination reaction has been pursued. In addition, the isolation of dechlorobarbamide and the determination of the absolute stereochemistry assignment of barbamide was accomplished. A reevaluation of the stereochemistry of antillatoxin necessitated a correction in the original assignment. Four antillatoxin stereoisomers were obtained from a collaborator and found to possess differing levels of biological activity. The three dimensional solution structures of these isomers were evaluated in an effort to understand the role these stereochemical features play in the observed bioactivity. The structures were determined utilizing NMR-derived constraints applied to molecular modeling calculations. The development of two new pulse sequences for the determination of long-range heteronuclear coupling constants was also accomplished. The 1,1 ADEQUATE experiment was modified to yield an ACCORDIAN experiment which can be optimized to observe of a wide range of ��J[subscript cc] couplings. This new experiment is demonstrated for a model compound as well as for the new marine natural product jamaicamide A. / Graduation date: 2002

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