In recent years, N-hetereocyclic carbenes (NHCs) have received considerable attention as organocatalysts due to their unusual ability to induce a reversal of reactivity (Umpolung) in aldehydes. Indeed, NHCs unique properties have been applied to the efficient and metal-free synthesis of organic compounds that have proven elusive using traditional approaches.<p> My Masters research program has been focused on the use of NHCs as organocatalysts in ring expansion reactions and their applications to cascade reactions.<p> During my Masters studies, an NHC-catalyzed efficient ring expansion of 4-, 5-, and 6-membered oxacycloalkane-2-carboxaldehydes to generate the corresponding lactone derivatives was developed. This reaction provides access to a variety of lactones using readily available NHCs under mild conditions.<p> Then, the ring-expansion lactonization has been successfully extended to an efficient lactamization using azacycloalkane-carboxaldehydes, which could provide functionalized lactams in moderate yields under mild conditions.<p> In addition, intrigued by the possibility of effecting the Umpolung of electron-poor dienes using NHC catalysts, the ring-expansion lactonization was applied to an attempted Diels-Alder-ring expansion cascade reaction. Though no cascade reactions were observed, some very interesting results were obtained, and those results will guide future investigations in this area.

Microbiologists have long focused on transcription as a main source of physiological regulation in bacterial adaptation. However, the time scale on which certain cellular responses must be coordinated dictates that a more rapid system be in place to deal with sudden environmental stresses. In eukaryotes, understanding the proteasome and ubiquitin-tagging has led to an appreciation for protein turnover as a mechanism for rapid adaptation. Like eukaryotes, bacteria possess several proteolytic complexes that degrade proteins into smaller polypeptides and amino acids. These enzymes were discovered as maintainers of protein quality control, through recognition of aberrant protein products, but recent studies have suggested that they play an active role in regulation of cell processes through degradation of endogenous proteins. Surprisingly, a genome wide screen for essential genes in Mycobacterium tuberculosis (Mtb) found numerous proteases to be essential for growth, providing evidence that degradative regulation may be critical for survival. One essential complex, Clp protease, was intriguing as it appeared to have a divergent structure in Mtb, and was largely dispensable for growth in most other organisms. In order to study the importance of protein turnover and degradative regulation in Mtb, I chose to study Clp as a model. I confirmed that Clp was required for normal growth in mycobacteria through targeted genetic engineering, and demonstrated that depletion of Clp was bactericidal. We hypothesized that a protease would be essential because it might prevent accumulation of toxic proteins or repressors of vital processes. To understand why Clp protease was so critical, I conducted proteomic analysis comparing wildtype and Clp-depleted cells to identify substrates of the protease. In line with our hypothesis, I identified WhiB1, a redox-sensitive transcriptional repressor. Blocking degradation of WhiB1 by Clp resulted in death, suggesting that the importance of Clp can be partially explained by its action on the repressor. Finally, taking advantage of known Clp-specific inhibitors in S. aureus, we showed that Clp could be targeted with small molecules in Mtb. The elucidation of novel drug targets and small molecules active against Mtb is crucial due to the overwhelming prevalence of the disease and rises in drug resistant forms.

No description available.

β-Lactones are a class of structurally unique compounds. The versatile reactivity patterns offered by β-lactones have enable chemists to utilize them as powerful synthetic vehicles in complex molecule synthesis. In the total syntheses of the naturally occurring, α-glucosidase inhibitors schulzeines B & C, a readily available trichloromethyl β-lactone was used as a versatile masked surrogate for bishomoserine aldehyde, which led to a highly efficient construction of the core structures through a pivotal Pictet-Spengler condensation and a Corey-Link reaction. The first total synthesis of (+)-omphadiol was achieved in ten steps from (R)-carvone. This synthesis features a three-step synthesis of a bicyclic β-lactone, which constitutes the key intermediate for the highly stereocontrolled introduction of the six contiguous stereogenic centers in the natural product. In efforts toward the total syntheses of scabrolides A & B and sinulochmodin C via transannular C-H insertions, β-lactones served as the key intermediates for the synthesis of complex macrocyclic model substrates. These model studies provided valuable insights into the reactivity and selectivity issues for transannular C-H insertion reactions.

Cyclic peroxides are abundant in Nature and synthetic manipulation of the peroxide linkage and alkene portion of 1,2-dioxines has established 1,2-dioxines as important compounds as both chemical building blocks and bioactive compounds. Much of the chemistry performed thus far utilizing 1,2-dioxines involves the initial rearrangement of 1,2-dioxines to γ-hydroxyenones allowing for the generation of structural motifs such as cyclopropanes, THF’s, THP’s, 1,4-diketones and natural sugars. Herein describes the synthesis of novel 1,2-dioxines with a variety of tethered functionalities and their transformations to afford novel cyclic compounds whilst maintaining the peroxide linkage intact. Chapter two outlines the intramolecular cyclisations of tethered hydroxyl and carboxylic acid moieties onto the olefin of 1,2- dioxines to generate both tetrahydrofurans and dihydrofuran-2(3H)-ones, whilst maintaining the peroxide linkage. This work presents the first examples of syn fused cyclic peroxide furans through intramolecular cyclisation of tethered hydroxyl groups. Improved methods for the oxidation of hydroxyl tethered 1,2-dioxines to carboxylic acid moieties are also reported. In addition, improved methods for intramolecular cyclisation of carboxylic acid moieties where developed to afford syn fused cyclic peroxide lactones. Furthermore, reduction of the peroxide bond enabled generation of functionalized tetrahydrofurans and dihydrofuran-2(3H)-ones which have previously been utilized as synthetic building blocks for several natural products. Chapter three reports the first examples of carbenoid insertion into the peroxide linkage of 1,2-dioxines allowing for the generation of novel bicyclic hemiacetals. Alternatively novel tricyclic cyclopropyl peroxides where generated through insertion into the olefin whilst maintaining the peroxide linage intact. Additionally, the attempted intramolecular cyclisation of diazoketone tethered bicyclic 1,2-dioxines was also probed. Furthermore, the attempted intermolecular insertion of diazoketones onto 1,2-dioxines are presented within this chapter. Finally, Chapter four outlines the intramolecular cyclisations of bromo-alkyl tethered 1,2-dioxines to furnish novel cyclic cyclopentyl peroxides whilst maintaining the peroxide linkage intact. The work presented in this chapter represents the first examples of the synthesis of syn fused cyclic cyclopentyl peroxides. In summary, this thesis outlines methodology towards the synthesis of novel cyclic peroxides from 1,2-dioxines containing tethered functional groups. / Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2009

Thesis (M. Sc.)(Chemistry)--University of Pretoria, 2005. / Includes bibliographical references. Available on the Internet via the World Wide Web.

Made available in DSpace on 2015-04-09T12:28:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-06-09Bitstream added on 2015-04-09T12:47:39Z : No. of bitstreams: 1 000816587.pdf: 400325 bytes, checksum: fe57a4f95b8cfd93f1cdf6d5195f67d6 (MD5) / As mudanças nos controles internacionais dos alimentos visando sua inocuidade se efetivaram com a mudança de século, tendo como base a Análise de Riscos e a Análise de Perigos e Pontos Críticos de Controle. Para os resíduos químicos, apesar de problema pré-existente, a situação só ganhou notoriedade a partir de 2010 com a detecção da presença de resíduos de avermectinas em produtos cárneos brasileiros exportados para os Estados Unidos e União Europeia. A partir de então, várias medidas de mitigação foram inseridas no conjunto rotineiro de autocontroles pelas empresas processadoras. Neste trabalho objetivou-se verificar a praticidade e eficácia dessas medidas para o controle efetivo dos processos, segregando animais abatidos que pudessem contribuir para níveis inaceitáveis do perigo, com base na monitoração de resíduos de avermectinas em duas matrizes amostrais, fígado e músculo de bovinos abatidos. Para a matriz músculo foram analisados 81.565 lotes de animais, com 1,41% desses ou 1.153 lotes que apresentaram resíduos de avermectinas superiores ao LMR de 10μg/kg durante os anos de 2010 e 2011. A partir de 2012 utilizou-se a matriz fígado, sendo analisadas 77.056 amostras. Dessas, 29.267 ou 37,98% apresentaram positividade para resíduos, sendo que 4.602 ou 5,97% foram superiores ao LMR de 100μg/kg. Os resultados analíticos demonstram, até agora, agravamento do problema no elo primário da produção de carne bovina brasileira / Changes in international food controls aiming their safety occurred with the change of the century, based on the Risk Analysis and Hazard Analysis and Critical Control Points. For chemical residues, although a pre-existing problem, the situation only gained notoriety after 2010, with the presence of avermectin residues in Brazilian meat products exported to the United States and European Union. Since then, several mitigation measures were incorporated in the routine set of self-controls the processing companies.This work aimed to verify the practicality and effectiveness of these measures for effective control of processes, segregating slaughtered animals that could contribute to unacceptable levels of risk, based on monitoring of avermectins residues in two sample matrices, liver and muscle of cattle slaughtered. For the muscle matrix were analyzed 81,565 batches of animals, with 1,153 or 1.41% batches whose residues were above the avermectin MRL (Maximum Residue Level) of 10μg/kg during the years 2010 and 2011. from 2012 was used the liver matrix , with 77,056 samples being analyzed. Of these, 29,267 or 37.98% were positive for residues, with 4,602 or 5.97% above the MRL of 100μg/kg. The analytical results shown so far, the aggravation of problems at the primary link of the production chain of Brazilian beef

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Made available in DSpace on 2014-10-09T12:33:51Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:59Z (GMT). No. of bitstreams: 1 16497.pdf: 92708 bytes, checksum: 7ccf16810b03dfc8aa4c309390f8b21a (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Esta tese de doutorado aborda alguns aspectos do estudo de plantas medicinais e de princípios ativos naturais. Os procedimentos experimentais incluíram o estudo fitoquímico de uma planta medicinal da família Asteraceae, o desenvolvimento de um método analítico com validação das análises empregadas e o estudo de atividades biológicas relativas ao processo inflamatório. A primeira etapa compreendeu o estudo fitoquímico da planta medicinal Smallanthus sonchifolius (Asteraceae), envolvendo o isolamento de metabólitos secundários da classe dos terpenóides. Do extrato de lavagem foliar foram isoladas as seguintes lactonas sesquiterpênicas (LSTs): enidrina, uvedalina, sonchifolina, fluctuanina, polimatina B, (1Z,4E)-8&#946;-metacriloilóxi-9&#945;-acetoilóxi-germacra-1(10),4,11(13)-trien-6&#945;,12-olido-14-oato de metila, (1Z,4E)-8&#946;-angeloilóxi-14-oxo-germacra-1(10),4,11(13)-trien-6&#945;,12-olido, (1Z,4E)-8&#946;-metacriloilóxi-germacra-1(10),4,11(13)-trien-6&#945;,12-olido-14-oato de metila, ácido (1Z,4E)-8&#946;-angeloilóxi-germacra-1(10),4,11(13)-trien-6&#945;,12-olido-14-óico e (1Z)-3&#945;,4&#946;-epóxi-8&#946;-[(1Z,4E)-(2S,3R)-2-hidróxi-3-óxi-(8&#946;-angeloilóxi-germacra-1(10),4,11(13)-trien-6&#945;,12-olido)]-9&#945;-acetoilóxi-germacra-1(10),11(13)-dien-6&#945;,12-olido-14-oato de metila. A segunda etapa tratou do desenvolvimento de método e validação das análises para controle de qualidade químico de S. sonchifolius em cromatografia líquida de alta eficiência (CLAE). Além disso, foi realizada a quantificação do principal metabólito secundário isolado nos extratos glandulares e de lavagem foliar, a LST enidrina. Esta substância compõe 0,97 % do peso seco das folhas de S. sonchifolius. A terceira etapa refere-se às atividades biológicas, as quais foram avaliadas empregando-se diversos ensaios. Também foi realizada a otimização de método para avaliação da secreção de elastase por neutrófilos humanos e o estudo da estimulação basal de neutrófilos. Ainda foram investigados os efeitos de produtos fitoterápicos, como gel de Arnica montana e extrato de Harpagophytum procumbens, e de metabólitos secundários, como LSTs e alcalóides, na atividade enzimática de elastase, na secreção de elastase por neutrófilos, na ativação do fator de transcrição NF-&#954;B via EMSA, na produção de luciferase por meio de reporter gen assay e de interleucina-8 via ELISA. Com exceção de dois alcalóides, todas as substâncias e produtos testados apresentaram atividades de inibição dos processos inflamatórios investigados. / This Ph.D. thesis deals with some aspects of the study of medicinal plants and their biologically active natural compounds. The experimental procedures comprised the phytochemical study of a plant from the family Asteraceae, the development of an analytical method with validation of the employed analysis and the study of the biological activities related to the inflammatory process. The first step comprised the phytochemical study of the medicinal plant Smallanthus sonchifolius (Asteraceae) and the isolation of secondary metabolites. From the leaf rinse extract were isolated the sesquiterpene lactones (STLs) enhydrin, uvedalin, sonchifolin, fluctuanin, polymatin B, methyl (1Z,4E)-8&#946;-metacryloyloxy-9&#945;-acetoyloxy-germacra-1(10),4,11(13)-trien-6&#945;,12-olide-14-ate, (1Z,4E)-8&#946;-angeloyloxy-14-oxo-germacra-1(10),4,11(13)-trien-6&#945;,12-olide, methyl (1Z,4E)-8&#946;-metacryloyloxy-germacra-1(10),4,11(13)-trien-6&#945;,12-olide-14-ate, (1Z,4E)-8&#946;-angeloyloxy-germacra-1(10),4,11(13)-trien-6&#945;,12-olide-14-oic acid, methyl (1Z)-3&#945;,4&#946;-epoxy-8&#946;-[(1Z,4E)-(2S,3R)-2-hydroxy-3-oxy-(8&#946;-angeloyloxy-germacra-1(10),4,11(13)-trien-6&#945;,12-olide)]-9&#945;-acetoyloxy-germacra-1(10),11(13)-dien-6&#945;,12-olide-14-ate. The second part was related to the development and validation of a chromatographic method for the chemical quality control of S. sonchifolius using high performance liquid chromatography (HPLC). Furthermore, the quantification of the main secondary metabolite, the STL enhydrin on glandular and leaf rinse extracts was also performed. This compound comprises 0,97 % of dried leaves weight of the plant. The third part deals with biological activities, which were investigated through different assays. One method for the study of the elastase release from human neutrophils was evaluated and the basal stimulation of neutrophils was studied. The effects of phytoterapeutic agents, like Arnica montana gel and Harpagophytum procumbens extract, and of the secondary metabolites, like LSTs and alkaloids, on the enzymatic activity of elastase, on elastase release from neutrophils, on the activation of the transcription factor NF-&#954;B through EMSA, on luciferase production through reporter gene assay and on interleucina-8 production through ELISA were also carried out. Both phytoterapeutic agents as well as the great majority of the tested compounds showed some inhibitory activity over the investigated inflammatory processes.