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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.
11

Atividade biolÃgica das lectinas de sementes de erythrina fusca e velutina, de algas marinhas hypnea musciformes, bryothamnion seaforthii e triquetrum e do produto natural diterpeno casbano, em culturas de pseudomonas aeruginosa / Biological activity of lectins from Erythrina velutina and fusca, seaweed Hypnea musciformes, bryothamnion seaforthii and triquetrum and casbano diterpene natural product, in cultures of Pseudomonas aeruginosa

Ricardo Hideo Togashi 24 February 2010 (has links)
FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Neste trabalho avaliamos a atividade biolÃgica de lectinas de sementes de Erythrina fusca e velutina, de algas marinhas Hypnea musciformes, Bryothamnion seaforthii e triquetrum e do diterpeno casbano, um produto natural isolado de Croton nepetaefolius, sobre Pseudomonas aeruginosa ATCC 10145. Foi comparada a aÃÃo in vitro das 5 lectinas e do diterpeno casbano, sobre colÃnias de P. aeruginosa, em placas de poliestireno. Investigada a aÃÃo das lectinas de alga marinha H.musciforme, de sementes de Erythrina velutina, e do diterpeno casbano, no processo de formaÃÃo do biofilme bacteriano de P.aeruginosa, em placas de poliestireno; e identificado entre as lectinas de E.velutina, H.musciforme e diterpeno casbano, aquele com maior potencial de aplicaÃÃo no controle do crescimento de colÃnias de P. aeruginosa. As lectinas testadas nÃo foram capazes de inibir o crescimento e a formaÃÃo de biofilme de Pseudomonas aeruginosa nas condiÃÃes experimentadas. Por outro lado, diterpeno casbano, na concentraÃÃo de 500 μg/mL em 18 horas, foi capaz de inibir o crescimento de P. aeruginosa em 40%, comparado ao controle positivo. Esta inibiÃÃo foi observada atà uma concentraÃÃo de 125 μg/mL. Entretanto, nÃo foi observada inibiÃÃo da formaÃÃo do biofilme da P. aeruginosa nas concentraÃÃes utilizadas neste estudo. / In this study the biological activity of seeds lectins from Erythrina velutina and fusca, marine algae Hypnea musciformis, Bryothamnion seaforthii and triquetrum and the diterpene casbane, a natural product isolated from Croton nepetaefolius was evaluated upon Pseudomonas aeruginosa ATCC 10145. We compared the in vitro effect of lectins and diterpene casbane on colonies of P. aeruginosa in microtiter plates. Investigated the action of lectins from marine algae H. musciforme of seeds of Erythrina velutina, and diterpeno casbano in the process of formation of P. aeruginosa biofilm on polystyrene plates, and identified among lectins: E. velutina, H. musciforme and diterpene casbane, the one with greater potential for application in controlling the growth of colonies of P. aeruginosa. The lectins tested were able to inhibit growth and biofilm formation of P. aeruginosa in the studied conditions. Moreover, diterpene casbane at a concentration of 500 mg/mL in 18 hours, was able to inhibit the growth of P. aeruginosa in 40%, compared to positive control. This inhibition was observed until a concentration of 125 mg/mL. However, the inhibition of biofilm formation of P. aeruginosa there was no observed at the concentrations used in this study.
12

AvaliaÃÃo in vitro da interferÃncia de lectinas vegetais e do diterpeno casbano isolado de Croton nepataefolius sobre o crescimento de formas planctÃnicas e biofilmes de Pseudomonas aeruginosa / In vitro evaluation of the interference of plant lectins and the diterpene isolated from Croton casbano nepataefolius on the growth of planktonic forms and biofilms of Pseudomonas aeruginosa

Fabiano Fazanaro 26 February 2010 (has links)
FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Este trabalho mostra as atividades biolÃgicas de lectinas isoladas de sementes de Vatairea macrocarpa e de Vatairea guianensis e do composto vegetal diterpeno casbano, isolado do Croton nepetaefolius, sobre o crescimento de Pseudomonas aeruginosa (ATCC 9027), causadora de otite externa. Comparou-se a aÃÃo in vitro das duas lectinas e do composto vegetal diterpeno casbano sobre culturas de P. aeruginosa em placas de poliestireno. As cÃlulas bacterianas foram testadas tanto em sua forma planctÃnica como na de biofilme. As lectinas testadas nÃo foram capazes de inibir o crescimento da forma planctÃnica e a formaÃÃo de biofilme da P. aeruginosa nas condiÃÃes experimentais. Por outro lado, o diterpeno casbano foi capaz de inibir o crescimento de P. aeruginosa na forma planctÃnica, nas concentraÃÃes de 500, 250 e 125 Âg/mL. Entretanto, nÃo foi observada inibiÃÃo da formaÃÃo do biofilme da P. aeruginosa nas concentraÃÃes utilizadas neste estudo. O diterpeno casbano isolado de Croton nepetaefolius poderà ser utilizado, apÃs a realizaÃÃo de outros estudos, como ferramenta biotecnolÃgica antimicrobiana sobre as formas planctÃnicas de P. aeruginosa / This work shows the biological activities of lectins isolated from Vatairea macrocarpa and Vatairea guianensis seeds and the vegetable compound diterpen casban, isolated from Croton nepetaefolius on the growth of Pseudomonas aeruginosa (ATCC 9027) that causes otites externa. The in vitro activity of the two lectins and vegetable compound casbane diterpene were compared on cultures of P. aeruginosa in polystyrene microplates. The bacterial cells were tested such in planktonic as in biofilm forms. The lectins tested were not capable to inhibit the growth and biofilm production of P. aeruginosa in the experimental conditions. On the other hand, the casbane diterpene was capable to inhibit the growth of planctonic forms of P. aeruginosa at the concentrations of 500, 250 and 125 Âg/mL. However, the inhibition of biofilm production was not observed at the same concentrations. The casbane diterpene isolated from Croton nepetaefolius can be used, after the realization of other studies, as an antibiotic biotechnological tool on planktonic forms of P. aeruginosa
13

Efeito do diterpeno Manool sobre a função vascular de ratos normotensos e hipertensos / The effect of diterpene Manool on vascular function of normotensive and hypertensive rats

Ariadne Santana e Neves Monteiro 09 May 2016 (has links)
Introdução: A hipertensão arterial sistêmica (HAS) é uma condição clínica multifatorial caracterizada por níveis elevados e sustentados de pressão arterial. Nos últimos anos, estudos demonstraram o efeito cardiovascular de diversos metabólitos originados de várias espécies de plantas. O diterpeno é um exemplo, o qual age por meio de diversos mecanismos farmacológicos. Sabendo que o Manool pertence a esta classe de compostos, isso o torna uma substância com potencial uso no tratamento da HAS, motivo pelo qual se propôs o desenvolvimento deste trabalho. Objetivos: 1) Avaliar in vivo o possível efeito vasodilatador de diferentes doses do Manool e o efeito sobre os níveis plasmáticos de óxido nítrico (NO), em animais normotensos e hipertensos e; 2) Verificar in vitro os mecanismos endoteliais envolvidos na resposta de relaxamento, em anéis de aorta de ratos. Material e métodos: Os animais foram divididos aleatoriamente em dois grupos: hipertenso e normotenso. Os animais do grupo hipertenso foram submetidos ao procedimento cirúrgico 2R1C para indução de hipertensão, enquanto os animais do grupo normotenso foram sham-operados. A pressão arterial (PA) não-invasiva, foi mensurada utilizando-se um manguito, conectado a um sensor para registro de PA, colocado em torno da cauda do animal. Para identificar os efeitos in vivo do composto, três doses do composto foram aplicadas nos animais, a monitorização invasiva da PA foi realizada por meio do MP System 100 A. Para a medida do óxido nítrico (NO) plasmático, foi utilizada a técnica de quimiluminescência NO/ozônio (O3). Com intuito de observar os mecanismos envolvidos no relaxamento induzido pelo composto, curvas concentração-resposta para o Manool, foram obtidas em anéis de aorta com e sem endotélio, na presença e ausência de L-NAME e ODQ. Resultados: Os resultados sobre a ?PAS mostrou que o Manool, promoveu redução da PAS tanto em normotensos quanto hipertensos. Os resultados das curvas dose-resposta mostraram que o manool promoveu relaxamento Resumo dependente do endotélio e este foi inibido na presença de L-NAME e ODQ. Não foi observado diferença na dosagem de NOx. Conclusão: Em resposta aos objetivos propostos para a presente investigação pode-se concluir que o Manool é uma droga hipotensora, possivelmente dependente em grande parte da função endotelial via NO/cGMP. / Introduction: Systemic hypertension (SH) is a multifactorial clinical condition characterized by high and sustained levels of blood pressure. In recent years, studies have demonstrated the cardiovascular effect of various metabolites derived from many plant species. The diterpene is an example, which acts through different pharmacological mechanisms. The Manool belongs to this class of compounds, that makes a substance with potential use in the treatment of SH, which let us to propose the development of this work. Objectives: 1) To evaluate in vivo the possible vasodilator effect of different doses of Manool and the effect on the plasma levels of nitric oxide (NO) in normotensive and hypertensive animals; 2) Evaluate in vitro endothelial mechanisms involved in the relaxation response in rat aortic rings. Material and methods: The animals were randomly divided in two groups: normotensive and hypertensive. The animals of the hypertensive group underwent the surgical procedure 2K1C for hypertension induction, while the animals of the normotensive group were sham-operated. The blood pressure (BP) non-invasive, was measured using a cuff, connected to a sensor for registration BP, placed around the animal\'s tail. To identify the in vivo effects of the compound, three doses of the compound were applied in animals, invasive BP monitoring was performed using the System MP 100 A. For the measurement of NO plasma, we used the technique of chemiluminescence NO/ozone (O3). In order to observe the mechanisms involved in the relaxation induced by compound concentration-response curves for Manool were obtained in the aorta rings with and without endothelium in the presence and absence of L-NAME and ODQ. Results: The results on variation of systolic blood pressure (?SBP) showed that Manool, decreases the SBP in both normotensive as hypertensive. The results of the dose-response curves showed that the Manool promoted endothelium dependent relaxation and this was inhibited in the presence of L-NAME and ODQ. There was no difference in NOx dosage. Conclusion: In response to the proposed Abstract objectives for the present investigation may conclude that the Manool is a hypotensive drug, possibly dependent in large part on endothelial function NO / cGMP pathway.
14

Approaches towards a total synthesis of the phomactins

Irshad, Abdur Rehman January 2011 (has links)
Within this thesis are described synthetic approaches towards the phomactins which are novel platelet activating factor antagonists. The synthesis of known alcohol 162 is described, the two key intermediates being aldehyde 160 and vinyl iodide 161. The key step of the synthesis of aldehyde 160 is a [2,3]-Wittig-Still rearrangement of stannane 159 which introduces the hindered C1-C2 bond present in the phomactins. The vinyl iodide 161 is made in four steps from 4-pentyn-1-ol. Addition of the vinyl ytterbium species derived from the vinyl iodide to aldehyde 160 gave secondary alcohol 162. Subsequent transformations furnished the bisprotected macrocyclic sulfone 174 in four steps from alcohol 162 to give the C2 SEM protected macrocycle. Elaboration of the macrocycle to ketoaldehyde 206 was made possible by the TPAP oxidation/rearrangement reaction. Reduction with DIBAL-Hgave diol 175. Attempts at removing the sulfone appendage proved difficult so the diol was protected as the bis-acetate to attempt a selective epoxidation of the D3,4 olefin in the presence of the D1,15 olefin. Although this looked promising with the formation of the mono-epoxide 213, the inefficiency of removing the SEM group at C2 prior to the epoxidation meant the route was not viable. Removing both protecting groups from macrocycle 174 was possible with refluxing TBAF and after incorporating the epoxide of the D3,4 olefin, the macrocycle was elaborated to the benzyl ether 217. Applying the TPAP oxidation/DIBAL-H reduction sequence furnished advanced intermediate 179 which has the full carbon skeleton found in phomactin A and also had oxygen functionality at all the required positions.
15

Cell-type specificity and herbivore-induced responses of primary and terpene secondary metabolism in Arabidopsis roots

Zhang, Jingyu 02 September 2013 (has links)
Plants employ diverse defense mechanisms to combat attack by harmful organisms. For instance, plants produce constitutive physical barriers or use chemical compounds such as specialized secondary metabolites to resist herbivore or pathogen invasion. Considering the cost-efficiency and energy balance between defense, growth and reproduction, defense reactions in plants have to be regulated temporally and spatially. As more cost-efficient strategies, plants may induce their defense response only in the presence of the attacker or restrict constitutive defenses to specific tissues or cells. In this study, we investigated aspects of the spatial regulation and induced changes of primary and secondary metabolism in roots of Arabidopsis thaliana. Roots represent important organs for anchoring plants in the soil and taking up water and nutrients. Hence, it is assumed that roots are as well protected as aerial tissues by different defense mechanisms. The first part of this work is focused on the cell-type-specific biosynthesis of volatile terpenes in Arabidopsis roots. Terpenes are the most abundant specialized metabolites in plants and play an important role in plant defense against pathogens or herbivores. Terpene biosynthetic enzyme activities are often coordinated in specific tissues and cellular compartments. Fine-scale transcriptome maps of Arabidopsis roots have shown that terpene biosynthesis is restricted to particular cell types. However, the reasons and significance of this cell-type specificity are not well understood. We hypothesized that the formation of terpene metabolites is not restricted to specific cells but can be supported by different cell types. We, therefore, probed the plasticity of the cell-specific formation of terpenes by swapping the expression of the terpene synthase (TPS) genes, TPS08, TPS13 and TPS25, between different root cell types in the respective mutant background. To investigate the ectopic expression of TPSs at different levels, quantitative real-time PCR (qRT-PCR), confocal microscopy, and gas chromatography-mass spectrometry (GC-MS) were performed. We found that terpene synthase TPS08, which produces the diterpene rhizathalene and is normally expressed in the root vascular tissue, is functionally active when expressed in the epidermis or cortex, although at substantially lower levels compared to the wild type. We did not find an obvious correlation between the volatile emission level and gene transcript level of TPS08, which may be attributed to a reduced activity of the expressed TPS08-yellow fluorescent protein (YFP) fusion protein. When expression of TPS13 (producing the sesquiterpene (Z)-"-bisabolene) was directed from the cortex to the epidermis or stele, TPS13 gene expression and (Z)-"-bisabolene formation was supported by these cell types although to varying levels in comparison to wild type. TPS13-YFP fluorescent signal driven by the epidermal WER and GL3 promoters was primarily detected at the root tip. Terpene production was also observed for the (E)-"-farnesene sesquiterpene synthase TPS25 when its expression was switched from the endodermis and non-hair producing epidermal cells to hair producing epidermal cells although only a weak fluorescent signal was detected from the expressed TPS25-mGFP protein. Together, the results provide preliminary evidence for a relaxed cell specificity of terpene biosynthesis in Arabidopsis roots and suggest that tissue-specific terpene metabolite patterns could change depending on different selective pressures in rhizosphere. In the second part of this study, we performed global gene transcript profiling and primary metabolite analysis of Arabidopsis roots upon feeding by the generalist root herbivore, Bradysia (fungus gnat). In a microarray analysis, we identified 451 of 22,810 genes that were up-regulated more than 2-fold. Gene ontology (GO) analysis showed that 26% of those genes with predicted or known functions play a role in primary or secondary metabolism, while 24% are involved in cell signaling or in responses to stimulating factors, such as jasmonic acid (JA), ethylene, wounding, and oxidative stress. At the metabolite level, we observed only marginal changes of amino acid, sugar and carboxylic acid relative levels over a time course of 4 days of Bradysia feeding. There was a trend for increased levels of amino acids and the relative levels of sucrose were increased significantly ("=0.05) at the fourth day of feeding. In conclusion, the study provided evidence for the induction of genes related to primary and secondary metabolism and stress responses in Arabidopsis roots, but showed only marginal changes at the primary metabolite level. In addition, the work indicated that the formation of terpene-specialized metabolites in Arabidopsis roots is not restricted to specific cells, but can be supported by different cell types. / Master of Science
16

Diterpene Synthases of the Rice Blast Fungus: Phylogenetic Analysis and Biochemical Characterization

Shahi, Ayousha 13 May 2022 (has links) (PDF)
Plant-pathogenic fungi harbor various specialized metabolites including diterpenoids that function as hormones and virulence factors. The fungus Magnaporthe oryzae is the causal agent of rice blast disease and can infect over 50 grass species. We demonstrate that the rice blast fungus encodes two diterpene synthases that produce normal pimara-8,15-diene and manoyl oxide scaffolds. Phylogenetic analysis of diterpene synthases among rice blast pathotypes showed functional conservation of the two core diterpene synthases amongst all pathotypes and suggests further expansion in select grass species. These insights into the blast fungal terpenome may inform efforts to counteract deleterious phytopathogens in crucial food crops.
17

Molecular and Functional Characterization of Terpene Chemical Defense in Arabidopsis Roots in Interaction with the Herbivore Bradysia spp. (fungus gnat)

Vaughan, Martha Marie 18 June 2010 (has links)
Roots and leaves are integrated structural elements that together sustain plant growth and development. Insect herbivores pose a constant threat to both above- and belowground plant tissues. To ward off herbivorous insects, plants have developed different strategies such as direct and indirect chemical defense mechanisms. Research has primarily focused on visible aboveground interactions between plants and herbivores. Root-feeding insects, although often overlooked, play a major role in inducing physical and physiological changes in plants. However, little is known about how plants deploy chemical defense against root herbivores. We have developed an Arabidopsis aeroponic culture system based on clay granulate, which provides access to root tissue and accommodates subterranean insect herbivores. Using this system, feeding performance and plant tissue damage by the root herbivore Bradysia (fungus gnat) were evaluated. Larval feeding was found to reduce Arabidopsis root biomass and water uptake. Furthermore, we have characterized a root-specific terpene synthase AtTPS08, which is responsible for the constitutive formation of the novel volatile diterpene compound, rhizathalene, in Arabidopsis roots. Rhizathalene synthase is a class I diterpene synthase that has high affinity for the substrate geranylgeranyl diphosphate (GGPP) and is targeted to the root leucoplast. Expression of the β-glucuronidase (GUS) reporter gene fused to the upstream genomic region of AtTPS08 demonstrated constitutive promoter activity in the root vascular tissue and root tips. Using the established bioassay with Arabidopsis and Bradysia larvae, in aeroponic culture we could show that roots deficient in rhizathalene synthesis were more susceptible to herbivory. Our work provides in vivo-evidence that diterpene compounds are involved in belowground direct defense against root-feeding insects. Future work is still required to improve our understanding of plant root defense. This study has provided a basis for future investigations on the biochemistry, molecular regulation and defensive function of Arabidopsis root chemicals in interaction with both above- and belowground herbivores (and pathogens). / Ph. D.
18

Viridiofungins and xeniolide F: target oriented synthesis using different rearrangement reactions of a common substrate class / Xeniolid F und Viridiofungine: Unterschiedliche Umlagerungsreaktionen führen ausgehend von einer gemeinsamen Substratklasse zu sehr verschiedenen Bausteinen für die Naturstoffsynthese

Pollex, Annett 10 October 2006 (has links) (PDF)
The present dissertation covers the total synthesis of viridiofungin triesters and studies toward the total synthesis of xeniolide F. In both cases, sigmatropic rearrangements of α-allyloxy substituted α,β-unsaturated esters are employed: for the viridiofungin ester synthesis a [2,3]-Wittig rearrangement and for the xeniolide F synthesis a catalytic asymmetric Claisen rearrangement CAC. For both rearrangement reactions the historical development, main characteristic and important variations are discussed. The viridiofungin triester synthesis represents a convergent and highly flexible route toward these natural products. The [2,3]-Wittig rearrangement allowed the diastereoselective synthesis of the polar head group with two adjacent stereogenic centers. The E-configured double bond was formed by a Julia-Kocienski olefination. During the studies toward the total synthesis of xeniolide F a new, diastereoselective strategy for the generation of allyl vinyl ethers with E-configured vinyl ether double bond was established employing rhodium catalyzed OH-insertion and an E-selective Horner-Wadsworth-Emmons olefination. Under the conditions of the catalytic asymmetric Claisen rearrangement (CAC) this highly substituted allyl vinyl ether rearranged diastero- and enantioselectively to the corresponding a-keto ester. This example clearly illustrates the high potential of the CAC as synthetic tool for natural product synthesis. / In der vorliegenden Arbeit wird die Totalsynthese von Tirestern der Viridiofungine A, A2 und A4 sowie die Synthese eines Schlüsselintermediates für die Totalsynthese von Xeniolid F dargestellt. In beiden Fällen wird ausgehend von einem α-allyloxysubstituierten α,β-ungesättigten Ester eine Umlagerungsreaktion als Schlüsselschritt eingesetzt: im Falle der Viridiofunginester eine diastereoselektive [2,3]-Wittig-Umlagerung, bei den Arbeiten zur Totalsynthese von Xeniolid F eine diastero- und enantioselektive, katalytische Claisenumlagerung. Für beide Umlagerungsreaktionen werden ausführlich die theoretischen Hintergründe sowie die historische Entwicklung und wichtige Varianten besprochen. Mit der Viridiofungintriestersynthese wird eine konvergente und bezüglich der lipophilen Seitenkette sehr flexible Syntheseroute vorgestellt. Die [2,3]-Wittig-Umlagerung konnte dabei erfolgreich für die diastereoselektive Synthese der hochsubstituierten, polaren Kopfgruppe der Viridiofunginester mit zwei benachbarten stereogenen Zentren (davon eines quartär) eingesetzt werden. Zur Bildung der E-konfigurierten Doppelbindung wurde die Julia-Kocienskie-Olefinierung ausgenutzt. Bei den Arbeiten zur Totalsynthese von Xeniolid F wurde eine neuartige Strategie zur diastereoselektiven Synthese eines Allylvinylethers mit E-konfigurierter Vinyletherdoppelbindung eingesetzt. Die Horner-Wadsworth-Emmons-Olefinierung (HWE-Olefinierung) generierte dabei E-selektiv die Vinyletherdoppelbindung. Das für die HWE-Olefinierung benötigte Phosphonat wurde durch rhodiumkatalysierte OH-Insertion aus einem Allylalkohol und einem Diazaphosphonoacetat hergestellt. Der hochsubstituierte Allylvinylether wurde unter den Bedingungen der katalytisch asymmetrischen Claisenumlagerung umgesetzt und führte mit exzellenter Diastereo- und Enantioselektivität zum entsprechenden α-Ketoester. Anhand dieses Beispiels konnte das Potential der katalytisch asymmetrischen Claisenumlagerung zum Aufbau von hochfunktionalisierten Bausteinen für die Naturstoffsynthese verdeutlicht werden.
19

Viridiofungins and xeniolide F: target oriented synthesis using different rearrangement reactions of a common substrate class

Pollex, Annett 22 September 2006 (has links)
The present dissertation covers the total synthesis of viridiofungin triesters and studies toward the total synthesis of xeniolide F. In both cases, sigmatropic rearrangements of α-allyloxy substituted α,β-unsaturated esters are employed: for the viridiofungin ester synthesis a [2,3]-Wittig rearrangement and for the xeniolide F synthesis a catalytic asymmetric Claisen rearrangement CAC. For both rearrangement reactions the historical development, main characteristic and important variations are discussed. The viridiofungin triester synthesis represents a convergent and highly flexible route toward these natural products. The [2,3]-Wittig rearrangement allowed the diastereoselective synthesis of the polar head group with two adjacent stereogenic centers. The E-configured double bond was formed by a Julia-Kocienski olefination. During the studies toward the total synthesis of xeniolide F a new, diastereoselective strategy for the generation of allyl vinyl ethers with E-configured vinyl ether double bond was established employing rhodium catalyzed OH-insertion and an E-selective Horner-Wadsworth-Emmons olefination. Under the conditions of the catalytic asymmetric Claisen rearrangement (CAC) this highly substituted allyl vinyl ether rearranged diastero- and enantioselectively to the corresponding a-keto ester. This example clearly illustrates the high potential of the CAC as synthetic tool for natural product synthesis. / In der vorliegenden Arbeit wird die Totalsynthese von Tirestern der Viridiofungine A, A2 und A4 sowie die Synthese eines Schlüsselintermediates für die Totalsynthese von Xeniolid F dargestellt. In beiden Fällen wird ausgehend von einem α-allyloxysubstituierten α,β-ungesättigten Ester eine Umlagerungsreaktion als Schlüsselschritt eingesetzt: im Falle der Viridiofunginester eine diastereoselektive [2,3]-Wittig-Umlagerung, bei den Arbeiten zur Totalsynthese von Xeniolid F eine diastero- und enantioselektive, katalytische Claisenumlagerung. Für beide Umlagerungsreaktionen werden ausführlich die theoretischen Hintergründe sowie die historische Entwicklung und wichtige Varianten besprochen. Mit der Viridiofungintriestersynthese wird eine konvergente und bezüglich der lipophilen Seitenkette sehr flexible Syntheseroute vorgestellt. Die [2,3]-Wittig-Umlagerung konnte dabei erfolgreich für die diastereoselektive Synthese der hochsubstituierten, polaren Kopfgruppe der Viridiofunginester mit zwei benachbarten stereogenen Zentren (davon eines quartär) eingesetzt werden. Zur Bildung der E-konfigurierten Doppelbindung wurde die Julia-Kocienskie-Olefinierung ausgenutzt. Bei den Arbeiten zur Totalsynthese von Xeniolid F wurde eine neuartige Strategie zur diastereoselektiven Synthese eines Allylvinylethers mit E-konfigurierter Vinyletherdoppelbindung eingesetzt. Die Horner-Wadsworth-Emmons-Olefinierung (HWE-Olefinierung) generierte dabei E-selektiv die Vinyletherdoppelbindung. Das für die HWE-Olefinierung benötigte Phosphonat wurde durch rhodiumkatalysierte OH-Insertion aus einem Allylalkohol und einem Diazaphosphonoacetat hergestellt. Der hochsubstituierte Allylvinylether wurde unter den Bedingungen der katalytisch asymmetrischen Claisenumlagerung umgesetzt und führte mit exzellenter Diastereo- und Enantioselektivität zum entsprechenden α-Ketoester. Anhand dieses Beispiels konnte das Potential der katalytisch asymmetrischen Claisenumlagerung zum Aufbau von hochfunktionalisierten Bausteinen für die Naturstoffsynthese verdeutlicht werden.
20

ENGINEERING NOVEL TERPENE PRODUCTION PLATFORMS IN THE YEAST SACCHAROMYCES CEREVISIAE

ZHUANG, XUN 01 January 2013 (has links)
The chemical diversity and biological activities of terpene and terpenoids have served in the development of new flavors, fragrances, medicines and pesticides. While terpenes are made predominantly by plants and microbes in small amounts and as components of complex mixtures, chemical synthesis of terpenes remains technically challenging, costly and inefficient. In this dissertation, methods to create new yeast lines possessing a dispensable mevalonate biosynthetic pathway wherein carbon flux can be diverted to build any chemical class of terpene product are described. The ability of this line to generate diterpenes was next investigated. Using a 5.5 L fed bath fermentation system, about 569 mg/L kaurene and approximately 207 mg/L abietadiene plus 136 mg/L additional isomers were achieved. To engineer more highly modified diterpenes might have greater industrial, agricultural or medicinal applications, kaurenoic acid production reached 514 mg/L with byproduct kaurene and kaurenal at 71.7mg/L and 20.1mg/L, respectively, in fed batch fermentation conditions. Furthermore, ZXM lines for engineer monoterpene and ZXB lines for engineer triterpene were generated by additional specific genomic modification, 84.76 ±13.2 mg/L linalool, 20.54±3.8 mg/L nerolidol and 297.7mg/L squalene were accumulate in ZXM144 line ana ZXB line, respectively, in shake flask conditions.

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