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Strategies for the synthesis of benzyltetrahydroisoquinoline alkaloids.Sonopo, Molahlehi Samuel. January 2011 (has links)
The objectives of this project were to investigate the application of new
methodologies for the preparation of benzyltetrahydroisoquinoline monomers and
secondly, to synthesise the bisbenzyltetrahydroisoquinoline neferine and its
analogues. Neferine was isolated from the roots of Nelumbo nucifera. This
compound has been reported to exhibit important biological activities, which
include anti-arrhymia, anti-platelet aggregation, anti-thrombosis, anti-cancer as
well as anti-HIV activities. Moreover, neferine showed lower cytotoxicity compared
to other isoquinolines. However, the total synthesis of this compound has not been
reported.
Two methodolologies based on the intramolecular hydroamination of
aminostilbenes and aminoalkynes were investigated for the preparation of
benzyltetrahydroisoquinolines with different oxygenation patterns. In these
strategies, the aminostilbene and aminoalkyne precursors were successfully
synthesised by the Heck and Sonogashira coupling reactions, respectively. The
attempts to cyclise the aminostilbenes into the corresponding
tetrahydroisoquinolines under base-catalysed, metal-catalysed and acid-catalysed
conditions were unsuccessful. On the other hand, cyclisation of aminoalkynes into
dihydroisoquinolines was achieved with the aid of titanium catalysts. Different
titanium catalysts were tested for this hydroaminationation reaction. Optimum
results were obtained with bis-(cyclopentadienyl)dimethyl titanium(IV) catalyst,
albeit the yields were inconsistent when the reaction was performed on a larger
scale.
Induction of the desired stereochemistry on the dihydroisoquinolines prepared by
the hydroamination of aminoalkynes was attempted with the chiral BINOL
phosphoric acid catalyst without success. The catalyst was prepared in good
yields and high enantiomeric excess from cheap and readily-available starting
materials. Had this reaction been successful, this would have been a breakthrough
in the stereoselective reduction of dihydroisoquinolines as most chiral catalysts,
which are currently employed are expensive, difficult to prepare and some are air
and moisture-sensitive.
Although the first objectives of this project are not fully met, the results obtained in
the synthesis of benzyltetrahydroisoquinolines by the hydroamination of
aminostilbenes and aminoalkynes contribute greatly to the prevailing literature on
the synthesis of benzyltetrahydroisoquinolines by these reactions. Presently, there
is limited literature on the synthesis of benzyltetrahydroisoquinolines by these
methods. Moreover, there is a need for the development of new synthetic
strategies that would render benzyltetrahydroisoquinolines in minimum steps and
good yields.
It was planned that, upon successful synthesis of benzyltetrahydroisoquinolines
from aminostilbene and aminoalkyne precursors, these modern methodologies
would be applied in the synthesis of the two benzyltetrahydroisoquinoline scaffolds
of neferine. However, these routes could not be pursued due to failure to ringclose
the aminostilbenes and irreproducibility of results in the preparation of
dihydroisoquinolines from aminoalkynes. Therefore, classical procedures were
employed for the preparation of benzylisoquinoline nuclei of neferine.
Three different synthetic routes were followed for the synthesis of neferine and its
analogues. The first two methods were based on the Ullmann coupling reaction for
the formation of the diaryl ether bond. The first method entailed an early
construction of the ether link and late construction of the two isoquinoline rings on
the ether bridge. The second method involved synthesis of the two isoquinoline
nuclei, and coupling of the two units by the Ullmann reaction in the late stages of
the synthesis. In the last synthetic strategy, the diaryl ether bridge was constructed
by the nucleophilic aromatic substitution reaction. In all the three methods, the two
isoquinoline rings were formed by the Bischler-Napieralski cyclisation reaction.
In the first route, we succeeded in preparing the two major building blocks, which
were N-(3,4-dimethoxyphenylethyl)-4-benzyloxy-3-iodophenylacetamide and [2-
(4’-hydroxy-3’-methoxyphenyl)ethyl]carbamic acid tert-butyl ester. The Ullmann
coupling of the two compounds afforded the diphenyl ether N-(3,4-
dimethoxyphenylethyl)-4-benzyloxy-3-(4-(3-methoxyphenoxy)ethyl-tertbutylcarbamate)
phenylacetamide, albeit in low yields. Although N-(3,4-
dimethoxyphenylethyl)-4-benzyloxy-3-(4-(3-methoxyphenoxy)ethyl-tertbutylcarbamate)
phenylacetamide was obtained in low yields, the successful
formation of the diaryl ether bond from electron-rich haloacetamide and
hydroxyphenethylamine is a great advancement in the synthesis of
bisbenzyltetrahydroisoquinolines. In the second approach, the two
benzyltetrahydroisoquinoline precursors for the Ullmann coupling reaction were
successfully synthesised. These were the 7-hydroxybenzyltetrahydroisoquinoline
and the 3’-iodobenzyltetrahydroisoquinoline. The Ullmann coupling reaction of the
two isoquinolines did not give any fruitful results. In the last synthetic strategy, the
formation of the diaryl ether bridge was based on the nucleophilic aromatic
substitution reaction. In this route, we managed to synthesise the two coupling
partners for the nucleophilic aromatic substitution reaction leading to Omethylneferine.
One of the building blocks was the natural
benzyltetrahydroisoquinoline, hydroxylaudanidine, and its coupling partner was N-
[2-(4-fluoro-3-nitrophenyl)ethyl]-2-(4-methoxyphenyl)-N-methylacetamide. The
major challenges in this route were encountered in the preparation the
fluoroacetamide, which involved several low-yielding synthetic steps and tedious
chromatographic purifications. The nucleophilic aromatic substitution reaction of
the two precursors was attempted in vain.
Even though the total synthesis of neferine could not be accomplished, it is
strongly believed that the developed synthetic routes will enable us to complete
the synthesis of the targeted compound and other naturally-occurring
bisbenzyltetrahydroisoquinolines. The results obtained herein represent a
significant advance considering the importance of the
bisbenzyltetrahydroisoquinolines as biologically active compounds. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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Synthesis and characterization of divinyl monomers for styrene-based reaction injection moldingSanchez, John Lawrence, January 2003 (has links) (PDF)
Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.
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The synthesis of precursors to conjugated polymers /Davis, Heather, January 1998 (has links)
Thesis (M.Sc.), Memorial University of Newfoundland, 1999. / Bibliography: p.125-131.
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Synthesis of biodegradable polymers for delivery of diagnostic agentsMatthews, Susan Elizabeth January 1995 (has links)
No description available.
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The nature of the base polymer and the properties of N.B.R. gum vulcanizatesKiroski, Dusko January 1995 (has links)
No description available.
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Avaliação morfológica, físico-química e mecânica longitudinal de adesivo dental experimental manipulado com diferentes concentrações de água / Morphological, physical - chemical and mecanical analysis a long term of dental adhesive formulated with different water contentEsteves, Stella Renata Machado Silva 02 February 2018 (has links)
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Previous issue date: 2018-02-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo desse estudo foi avaliar um adesivo experimental com diferentes concentrações de água, bem como sua degradação morfológica, química, física e mecânica. A primeira etapa envolveu a manipulação do adesivo experimental contendo 45/55% de HEMA e BisGMA, 0.5% de canforoquinona, 0.5% EDMAB e 1% de DPIHP. Foram incorporadas diferentes concentrações de água a partir dessa formulação adesiva (0, 10 e 16%). Os modelos adesivos foram fotopolimerizados e as análises iniciais realizadas: Morfológicas (Estereomicroscopio e Micro-xct); Físicas (Rugosidade-Ru, Sorção-Sor, Solubilidade-Sol); Químicas (Grau de conversão-GC, Mapeamento do espécime com 16% de água e os monômeros liberados pela CLAE); Mecânicas (Resistência flexural-RF, Módulo de elasticidade-ME e Resistência a compressão-RC). Em seguida os espécimes foram divididos conforme a solução de envelhecimento (água, etanol e acetona). Foram realizadas novas análises após o envelhecimento por 2 e 84 dias. Os testes estatísticos ANOVA e Tukey (5%) foram realizados. Os resultados iniciais, sem o envelhecimento, mostraram que as diferentes concentrações de água influenciam as propriedades dos adesivos. Na análise morfológica notou-se a presença de bolhas no espécime com 16% de água. Para a Ru e GC os maiores valores foram encontrados para os espécimes com mais água em sua composição e os menores para 0%. Já nas análises mecânicas, para RF e ME os espécimes com 10% de água foram mais resistentes; e em RC os espécimes com 16% foram menos resistentes. Após o envelhecimento notou-se trincas nos espécimes 0% e 16% na solução de acetona. Nos testes físicos, os espécimes com 16% absorveram mais solução; o etanol mostrou menores valores de solubilidade; Para Ru a água e a acetona diferiram em todas as concentrações e períodos, o mesmo ocorrendo para as concentrações 0 e 16%. Nos testes químicos o GC não foi alterado pelo envelhecimento. O mapeamento na amostra com 16% de água mostrou que inicialmente perto do poro o GC é menor e a quantidade de HEMA é maior; longe do poro a relação é inversa. Porém, após o envelhecimento, o GC próximo ao poro se tornou similar ao distante do poro. Através da CLAE observou-se uma maior liberação de componentes do espécime com 0% de água que os espécimes com 10% e 16%. Os testes mecânicos mostraram que o envelhecimento em acetona foi mais prejudicial que em água. Para a RF e ME os espécimes com 0% de água foram mais afetados que os espécimes com 10% e 16% em 2 e 84 dias. Para a RC após 2 dias o espécime com 16% foi mais afetado que 0 e 10%, no entanto, após 84 dias o espécime com 0% foi mais afetado pelo envelhecimento. Pode-se constatar que a quantidade de água e o tipo de envelhecimento afetam as propriedades dos sistemas adesivos baseados na composição 45/55% HEMA/BisGMA. / The aim of this study was evaluated an experimental adhesive with different water content, as well the degradation morphological, physical, chemical and mechanical. Firstly the dental adhesive was manipulated with 45/55% of HEMA and BisGMA, 0.5% of CQ, 0.5% EDMAB e 1% of DPIHP. Was added different water content (0, 10 and 16%). The adhesive model was cured and the analysis was done: Morphological (Stereomicroscope and Micro-xct); Physical (Surface Roughness), Sorption, Solubility); Chemical (Degree of convertion, Map of the pore on 16% water content sample and the released monomers- HPLC); Mechanicals (Flexural strength, Modulus of elasticity and Compressive strength). After the these analyzes, the samples were divided to each evaluation into 3 groups according to solution for performed ageing (water, ethanol and acetone). Further analyzes were performed after aging for 2 and 84 days. Statistical tests of ANOVA and Tukey (5%) were performed. Initial results, without aging, showed that the different water content influence adhesive properties. In the morphological analysis, bubbles were present on the sample with 16% water. For Ru and DC all specimens differed from each other, with the highest values for the specimens with 16% and the lowest to 0%. In the mechanical analyzes, for RF and ME the specimens with 10% water were more resistant; and in RC the specimens with 16% were less resistant. After aging it is possible notice cracks on the border of specimens 0% and 16% in the acetone. In the physical tests, the specimens with 16% absorbed more solution; ethanol showed lower values of solubility; For Ru, water and an acetone are differed in all concentrations and periods, the same for the concentration 0 and 16%. In the chemical tests DC was not altered by aging. The mapping in the sample with 16% of water showed that near to the pore the DC is smaller and a quantity of HEMA is larger; far from the pore this relation is inverse. However, after aging solutions, the DC near the pore became similar to the far from pore. Through HPLC was possible observed that release more components of the sample with 0% than 10% and 16%. The mechanical tests showed that the acetone damage more samples than water. For an RF and ME the specimens 0% were more affected than 10% and 16% after 2 and 84 days. For a RC after 2 days the sample with 16% was more affected than 0 and 10%, however, after 84 days the specimen with 0% was more affected by aging. It can be seen that the amount of water and the type of aging affect the adhesive properties of the database systems based on the 45/55% HEMA / BisGMA composition.
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Some studies on the monomer-dimer problemMenon, V. V. January 1968 (has links)
No description available.
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Thermo-Catalytic Polymerisation in WoodJuneja, Subhash Chander 10 1900 (has links)
<p> An experimental investigation of polymerisation of several monomers in wood was performed using free radical initiators such as benzoyl peroxide and 2-azo-bis-isobutyronitrile. The most promising comonomer system appeared to be styrene and acrylonitrile. As a result of copolymerisation of styrene and acrylonitrile in the cell cavities of wood, many improvements in physical properties of wood resulted. The improvement in physical properties of wood containing thermo-catalytically copolymerised styrene and acrylonitrile was found to be better than those of radiation initiated graft copolymerised wood. Thermo-catalytically produced wood polymer combinations showed as much improvement in physical properties as shown by those produced by radiation initiation without the use of swelling agents.</p> / Thesis / Master of Science (MSc)
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Towards organic ferromagnets via high-spin polyradicals : the synthesis of azo functionalised polymersGoodwin, Neil John January 1998 (has links)
No description available.
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Upscale synthesis of symmetrical and unsymmetrical monomers towards bridge trifluoromethylated poly (p-phenylenevinylene) and theoretical NMR studiesPinto, Jean Pierre. January 2008 (has links)
Thesis (M.S.)--Rutgers University, 2008. / "Graduate Program in Chemistry." Includes bibliographical references (p. 63-64).
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