Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Includes bibliographical references (leaves 26-29). Also available via the Internet.

No description available.

Este trabalho descreve a utilização dos programas do sistema especialista denominado SISTEMAT, avaliando a sua eficiência para auxiliar os pesquisadores da área de Produtos Naturais no processo de determinação estrutural de sesquiterpenos, a partir de dados de RMN 13C. Os principais sistemas especialistas em determinação estrutural operam, basicamente, combinando fragmentos estruturais, chamados \"restrições estruturais\", obtidos a partir de dados espectroscópicos. Ocorre que para moléculas complexas (com mais do que 15 átomos), o número de propostas estruturais geradas é muito grande, sendo necessária a ajuda do químico para eliminar estruturas improváveis. Este fato demonstra a necessidade de grandes restrições estruturais para o bom funcionamento do programa gerador, como por exemplo, a definição de classe e esqueleto, que foram utilizadas no desenvolvimento do SISTEMAT. O SISTEMAT foi criado especificamente para determinação estrutural de substâncias de origem natural, sendo desenvolvidas técnicas para obtenção de regras heurísticas, a partir de dados de RMN13C, que permitam a identificação de esqueletos de produtos naturais. Estes serão usados como grandes restrições pelo gerador de estruturas, evitando-se, assim, a explosão combinatória e a geração de propostas estruturais incompatíveis. Para a realização deste trabalho foi criado um banco de dados contendo os deslocamentos químicos e multiplicidades de 2306 espectros de sesquiterpenos, distribuídos entre substâncias pertencentes a 288 tipos de esqueletos. Estes dados são analisados pelos vários programas aplicativos do SISTEMAT, sendo fornecidos os esqueletos mais prováveis para uma substância-problema e grandes subestruturas compatíveis com o espectro analisado. Para avaliar o desempenho do sistema foram realizados testes com dados de RMN 13C de 60 sesquiterpenos. A aplicação do SISTEMAT na identificação de sesquiterpenos em misturas, como por exemplo, em óleos essenciais, também foi investigada pela primeira vez, com resultados promissores. / The present work describes the use of the expert system programs called SISTEMAT, evaluating their efficacy at helping Natural Products researchers to determine the structure of sesquiterpenes, using 13C-NMR spectroscopy data. The major expert systems for structural determination operate by combining structural fragments called \"structural restrictions\", obtained from spectroscopic data. For complex molecules (bearing more than 15 atoms), the number of proposed structures becomes too large, hence the imposition of external chemical knowledge is required, in order to exclude improbable structures. This fact demonstrates the need of large structural restrictions to be imposed to get acceptable results output by the generator program. The definition of class and skeleton, which were used during the development of SISTEMAT, are examples of such restrictions. SISTEMAT was created specially for natural products structural determination and methods were developed to obtain heuristic rules, mainly from 13C-NMR data, which allow the identification of natural products skeletal types. These will be used as large restrictions by the generator of structures, in order to avoid a combinatory explosion process at the generation step of the system. To reach the purpose of this work a data base was created with 2306 13C-NMR spectra of sesquiterpenes, distributed in 288 skeletal types. Those data are used by the set of SISTEMAT programs which propose the most probable skeleton for the unknown sesquiterpene together with some large substructures compatible with the analysed spectrum. To evaluate the efficacy of the system, tests were carried out with the RMN 13C data from 60 sesquiterpenes. The application of SISTEMAT in the identification of sesquiterpenes in neat essential oils was also investigated for the first time with promising results.

O estudo fitoquímico do extrato etanólico de caules adultos de Araucaria angustifólia resultou no isolamento e identificação da vanilina, p-hidroxibenzaldeído, coniferaldeído, dois isoflavonóides (cabreuvina e irisolidona), quatro lignanas (pinoresinol, eudesmina, lariciresinol e 9\'-O-acetato de lariciresinol) e β-sitosterol. Foi desenvolvido um protocolo para a obtenção de calos, a partir de caules de plântulas estioladas, dos quais foram isolados e caracterizados mistura de isômeros E e Z do p-cumarato de octadecila e do ferulato de octadecila. / Phytochemical investigations carried out on ethanolic extract from woods of Araucaria angustifolia resulted on the isolation and identification of vanillin, p-hydroxybenzaldehyde, coniferaldehyde; two isoflavones (cabreuvine and irisolidone); four lignans (pinoresinol, eudesmine, lariciresinol and 9\'-O-lariciresinolacetate), and β-sitosterol. Its callus culture was showed to accumulate mixtures of isomers E and Z of octadecyl p-cumarate and of octadecyl ferulate.

O estudo fitoquímico do extrato etanólico de caules adultos de Araucaria angustifólia resultou no isolamento e identificação da vanilina, p-hidroxibenzaldeído, coniferaldeído, dois isoflavonóides (cabreuvina e irisolidona), quatro lignanas (pinoresinol, eudesmina, lariciresinol e 9\'-O-acetato de lariciresinol) e β-sitosterol. Foi desenvolvido um protocolo para a obtenção de calos, a partir de caules de plântulas estioladas, dos quais foram isolados e caracterizados mistura de isômeros E e Z do p-cumarato de octadecila e do ferulato de octadecila. / Phytochemical investigations carried out on ethanolic extract from woods of Araucaria angustifolia resulted on the isolation and identification of vanillin, p-hydroxybenzaldehyde, coniferaldehyde; two isoflavones (cabreuvine and irisolidone); four lignans (pinoresinol, eudesmine, lariciresinol and 9\'-O-lariciresinolacetate), and β-sitosterol. Its callus culture was showed to accumulate mixtures of isomers E and Z of octadecyl p-cumarate and of octadecyl ferulate.

(+)-9,10-Dibromocamphor 3̲7̲, prepared in three steps from (+)-3-e̲n̲d̲o̲-bromocamphor 1̲5̲a̲, was found to undergo facile ring cleavage to provide the cyclopentanoid ring systems 1̲5̲8̲, 1̲5̲9̲ and 1̲6̲1̲. The bromoacid 1̲5̲9̲ was readily lactonised to provide 1̲6̲0̲ in high yield. The hydroxyacid 1̲6̲1̲ was converted into the hydrindenone 1̲9̲0̲ in three steps and a further six steps were required to complete the total enantiospecific synthesis of (-)-estrone e̲n̲t̲4̲1̲. Studies directed toward the synthesis of vitamin D₃ (2̲1̲3̲) and metabolites have shown that diastereoselective alkylation of lactone 1̲6̲0̲ and ester 2̲8̲3̲ (derived from 1̲6̲1̲) can be accomplished in high yield and with almost complete stereoselectivity. As a result, diol 3̲2̲2̲, representing the structural sub-unit of ring D and side chain of vitamin D₃, has been synthesised. Ring cleavage of the bromoketone 3̲5̲0̲ (derived from 1̲5̲9̲) gave 3̲5̲2̲ which was transformed into the aldehyde 3̲3̲2̲ and the trienols 3̲4̲0̲a̲ and 3̲4̲0̲b̲ to complete a formal synthesis of 3̲2̲7̲a̲, one of the components of the California Red Scale pheromone. Methylation of camphor 1̲0̲ yielded the 3-e̲x̲o̲-methyI derivative 3̲6̲2̲b̲ as the major product. The thermodynamically most stable epimer was found to be 3-e̲n̲d̲o̲-methylcamphor 3̲6̲2̲a̲. In contrast, 3-methylcamphor 3̲6̲2̲a.̲b̲ undergoes preferential endo alkylation. The factors governing these results are discussed. (+)-3- e̲n̲d̲o̲-Bromocamphor 1̲5̲a̲ and (+)-3- e̲n̲d̲o̲-9-dibromocamphor 1̲8̲a̲ were found to rearrange to provide (-)-6- e̲n̲d̲o̲-bromocamphor 1̲7̲2̲ and (-)-6- e̲n̲d̲o̲-9-dibromocamphor 2̲6̲. Dehalogenation of 1̲7̲2̲ provided optically pure (-)-camphor e̲n̲t̲1̲0̲ while dehydrohalogenation gave (+)-5,6-dehydrocamphor 1̲7̲3̲.[formula omitted] / Science, Faculty of / Chemistry, Department of / Graduate

Fifteen naphthylisoquinoline (NIQ) alkaloids including four new compounds, the 5,8'-coupled ancistroyafungines A-C, and the 5,1'-linked ancistroyafungine D, as well as eleven known NIQs were isolated from the stem bark of an unidentified Ancistrocladus (Ancistrocladaceae) liana recently discovered in the North-Central region of the Democratic Republic of the Congo. Most of the isolated alkaloids were S-configured at C-3, and possessed an oxygen function at C-6 in the isoquinoline portion, which is characteristic to the subclass of “Ancistrocladaceae-type” alkaloids. This finding was geo- and chemotaxonomically interesting since, except for one other Ancistrocladus species found in the Central Congo Basin, only Southeast Asian and East African Ancistrocladaceae are known to exclusively produce naphthylisoquinolines with these structural features. Moreover, the alkaloid pattern of this Congolese liana clearly differentiates this plant from all other Ancistrocladus taxa that have so far been botanically described, which suggests that it might represent a new species or subspecies. The new ancistroyafungines displayed strong preferential cytotoxic activities (with PC50 7.6 to 22.7 µM) towards human PANC-1 pancreatic cancer cells in nutrient-deprived medium, without showing toxicity in normal, nutrient-rich conditions. Along with the above described naphthylisoquinoline alkaloids, nine other analytes including four flavonoids: quercetin, kaempferol, hyperoside, and isoquercetin, and five lignans: justicidins A and B, 6-methoxyjusticidin A, chinensinaphthol, and retrochinensinaphthol methyl ether were isolated from Monsonia angustifolia and Monsonia glauca plants collected in South Africa. The extracts, the fractions, and compounds of M. angustifolia and M. glauca plants were screened for the first time for their Nrf2 activity. M. angustifolia sequential extracts exhibited superior Nrf2 activation with three active extracts, n-hexane, methanol, and aqueous extracts showing 169.0, 236.1, and 130.0% increase relative to the control. The methanol extract of M. angustifolia showed the strongest increase, better than that of sulforaphane (170.0%) used as positive control. Seven fractions collected from the column chromatography of the methanol extract of M. angustifolia exhibited a good Nrf2 activation with percentage increase ranging from 106.0 to 199.0% relative to the control. The isolated flavonoids from these fractions were screened for Nrf2 activity but the tests were inconclusive as the compounds may have decomposed in DMSO during the lengthy storage process, nevertheless, these compounds have been previously reported to be Nrf2 modulators. Based on this, they are in all likelihood responsible of the good activity of the methanol extracts of both Monsonia species. This study was the first to report the presence of isolated flavonoids in M. angustifolia. The isolated lignans were inactive against the human PANC-1 pancreatic cancer cell but they displayed strong to moderate activities against the HeLa cervical cancer cell. Justicidin B was the most potent compound of the isolated lignans with the IC50 value of 1.2 µM. The UPLC-MS chromatograms of the two species showed them to be different, as justicidin B was mainly found in M. glauca while justicidin A and 6-methoxyjusticidin A were predominant in M. angustifolia. To the best of our knowledge, this is the first report on the presence of justicidin B in Monsonia glauca, as well as its phytochemical properties and its bioactivities. / Thesis PhD (Chemistry))--University of Pretoria, 2019. / The Deutsche Forschungsgemeinschaft (Project Br 699/14-2; SFB 630 “Agents against Infectious Diseases”) The Excellence Scholarship Program BEBUC (www. foerderverein-uni-kinshasa.de), The South African Department of Science and Technology (DST) The National Research Foundation (NRF)/South Africa and The University of Pretoria / Chemistry / PhD (Chemistry) / Unrestricted

No description available.

Antimicrobial resistance is a human health issue that demands development of new antibiotics with unique mechanisms of action to combat antibiotic failure in the clinic. Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a particular resistant pathogen associated with high levels of incidence and mortality. Isolation and structural elucidation of the antibiotic natural products armeniaspirols A-C was first reported in 2012 by Sanofi. Armeniaspirol possess an unprecedented scaffold and novel multiple mechanisms of action. For these reasons the armeniaspirols were an ideal scaffold to investigate for the development of antibiotics effective against current resistant pathogens. A series of focused derivatives were synthesized and evaluated for antibiotic activity against clinically relevant pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus. Replacement of the N-methyl with N-hexyl and various N-benzyl substituents lead to a substantial increase in antibiotic activity and potency for inhibition of both ClpYQ and ClpXP, the intracellular targets of armeniaspirol. Armeniaspirol is also known to disrupt the proton motive force (PMF) in bacteria, though initial work by the Brönstrup lab suggested this was via shuttling of protons across the membrane. With a library of analogues in hand from our previous study, we sought to characterize their disruption of the PMF. Using a voltage sensitive dye-based assay and checkerboard synergy-based assay we demonstrated that armeniaspirols disrupt the proton motive force by dissipating the electrical potential (ΔΨ) of the PMF, correcting the previous literature, which suggested they disrupted the transmembrane proton gradient (ΔpH). Lastly, our efforts toward the total synthesis of armeniaspirol A using an oxidative chlorination transformation led to a constitutional isomer of armeniaspirol by an unexpected Lewis acid mediated rearrangement in the penultimate step. We characterized the scope of carbonyl derivatives that could undergo successful oxidation generating the key α,β-dichloro-α,β-unsaturated lactam of the armeniaspirol scaffold. Our work led to a mechanistic study demonstrating how simple ketones undergo decomposition via acylium ion formation whereas esters and amides are effectively oxidized to the desired product. Overall, the research presented here lays the foundation for the future work to confirm safety, efficacy, and toxicity of the armeniaspirols and to synthesize new analogues with improved drug like characteristics. In addition, this thesis previews an evolution-based link between armeniaspirol and its biosynthetic precursor that suggests mid- to late-stage biosynthetic intermediates are likely to possess biological activity but via a different mechanism of action as compared to the parent natural products. Furthermore, this analysis suggests that the intermediate is likely to synergize with the natural product, increasing the fitness of the producing organism as the pathway evolves.

Microbial natural products have been an invaluable resource for providing clinically relevant therapeutics for almost a century, including most of the commonly used antibiotics that are still in medical use today. In more recent decades, the need for new biotherapeutics has begun to grow, as multi-drug resistant pathogens continue to emerge, putting into question the long-term efficacy of many drugs that we routinely depend on to combat infectious diseases. To affect this growing medical crisis, new efforts are being applied to computationally mine the genomes of microorganisms for biosynthetic gene clusters that code for molecules possessing anti-microbial activities that circumvent known resistance mechanisms. To this end, cutting-edge software platforms have been developed that can identify, with high predictive accuracy, microbial genomes that code for natural products of potential interest. However, with such analyses comes the need to thoroughly vet each predicted gene cluster, to identify those high-value candidate molecules that are not associated with known resistance mechanisms. In this work, a new strategy was developed that involved cataloguing all known ‘self-resistance’ mechanisms encoded by natural product producing microorganisms, which protect the producer from the highly toxic effects of their secreted anti-microbial agents. This collection of resistance data was leveraged and used to engineer an automated software-based pipeline that interrogates biosynthetic gene clusters and relates them to previously identified resistance mechanisms. Gene clusters that are revealed to be independent of known resistance mechanisms can then be flagged for further chemical and biological study in the laboratory. Such in-depth interrogations of microbial genomes aim to help reveal the full biological repertoire of antibiotics yet to be discovered from microorganisms, and will lead to the development of the next generation of biotherapeutics to quell the growing medical crisis of antibiotic-resistance among human pathogenic organisms. / Thesis / Master of Science (MSc) / It would be hard to imagine a world where we could no longer use the antibiotics we are routinely being prescribed for common bacterial infections. Currently, we are in an era where this thought could become a reality. Although we have been able to discover antibiotics in the past from soil dwelling microbes, this approach to discovery is being constantly challenged. At the same time, the bacteria are getting smarter in their ways to evade antibiotics, in the form of resistance, or self-protection mechanisms. As such is it essential to devise methods which can predict the potential for resistance to the antibiotics we use early in the discovery and isolation process. By using what we have learned in the past about how bacteria protect themselves for antibiotics, we can to stay one step ahead of them as we continue to search for new sources of antibiotics from bacteria.