• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 143
  • 40
  • 17
  • 15
  • 5
  • 5
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 284
  • 88
  • 61
  • 54
  • 41
  • 40
  • 35
  • 31
  • 21
  • 21
  • 21
  • 20
  • 20
  • 19
  • 19
  • 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.
231

D-glucosamine as "green" substrate in synthesis of ligands for asymetric catalysis

Wojcik, Karolina 22 October 2012 (has links) (PDF)
Several ligands derived from D-glucosamine, designed for different catalytic reactions havebeen synthesized. The ligands for homogeneous catalysis based on 1,2-glucodiamine wereprepared, and used in reactions of allylic alkylation, hydrogenation and Michael addition.Supported Aqueous Phase Catalyst (SAPC) system was prepared from D-glucosamine anduse with very good results in Suzuki Miyaura cross coupling reactions. Catalyst was alsorecycled. Attempt to prepare ligands grafted on SBA-silica matrix were made as well asligands containing poly(ethylene) glycol moiety.
232

Towards the synthesis of monoterpenoids indole alkaloids of the aspidospermatan and strychnan type / Nouvelles voies d'accés aux alcaloides d'Aspidosperma

Dawood, Dawood Hosni 17 December 2010 (has links)
L'objectif de ce travail était d'accéder au squelette des alcaloïdes de type Aspidosperma et Strychnos à partir d'arylcyclohexa-2,5-diènes. Ces derniers sont d'abord synthétisés par réaction de Birch alkylante, puis ont été désymétrisés dans un premier temps par des réactions de Michael. Cette réaction fournit la cétone de Büchi, le noyau tétracyclique des alcaloïdes Aspidosperma en seulement en 6 étapes et un rendement global de 17%. Dans un second temps, la réaction d'amination oxydante catalysée par des métaux (Pd, Cu) a été développée. Cette réaction a permis un accès rapide au squelette pentacyclique d’aza-aspidospermanes et au squelette tétracycliques des alcaloïdes de type Strychnos. En parallèle, nous avons décrit une approche vers le squelette pentacyclique de la mossambine et la strychnine. / The aim of this work was to access the skeleton of the Aspidosperma and the Strychnos alkaloids using arylcyclohexa-2,5-dienes as common synthetic precursors. Initially, these arylcyclohexadienes were synthesized through Birch reductive alkylation reactions. The desymmetrization of these cyclohexadienes was developed via the Michael addition reaction, providing the Büchi ketone, the tetracyclic core of Aspidosperma alkaloids, in only 6 steps and 17% overall yield. On the other hand, we described the oxidative amination reaction catalyzed by metals (Pd, Cu). The palladium oxidative amination reaction allowed a fast access to the pentacyclic framework of aza-aspidospermanes and the tetracyclic framework of the strychnos. In parallel, we have described an approach toward the pentacyclic skeleton of mossambine and strychnine.
233

Development of catalytic enantioselective C-C bond-forming and cascade transformations by merging homogeneous or heterogeneous transition metal catalysis with asymmetric aminocatalysis

Afewerki, Samson January 2014 (has links)
Chiral molecules play a central role in our daily life and in nature, for instance the different enantiomers or diastereomers of a chiral molecule may show completely different biological activity. For this reason, it is a vital goal for synthetic chemists to design selective and efficient methodologies that allow the synthesis of the desired enantiomer. In this context, it is highly important that the concept of green chemistry is considered while designing new approaches that eventually will provide more environmental and sustainable chemical synthesis.The aim of this thesis is to develop the concept of combining transition metal catalysis and aminocatalysis in one process (dual catalysis). This strategy would give access to powerful tools to promote reactions that were not successful with either transition metal catalyst or the organocatalyst alone. The protocols presented in this thesis based on organocatalytic transformations via enamine or iminium intermediates or both, in combination with transition metal catalysis, describes new enantioselective organocatalytic procedures that afford valuable compounds with high chemo- and enantioselectivity from inexpensive commercial available starting materials. In paper I, we present a successful example of dual catalysis: the combination of transition metal activation of an electrophile and aminocatalyst activation of a nucleophile via enamine intermediate. In paper II, the opposite scenario is presented, here the transition metal activates the nucleophile and the aminocatalyst activates the electrophile via an iminium intermediate. In paper III,we present a domino Michael/carbocyclisation reaction that is catalysed by a chiral amine (via iminium/enamine activation) in combination with a transition metal catalysts activation of an electrophile. In paper IV, the concept of dual catalysis was further extended and applied for the highly enantioselective synthesis of valuable structural scaffolds, namely poly-substituted spirocyclic oxindoles. Finally, in paper V the concept of dual catalysis was expanded, by investigating more challenging and environmentally benign processes, such as the successful combination of a heterogeneous palladium and amine catalysts for the highly enantioselective synthesis of functionalised cyclopentenes, containing an all carbonquaternary stereocenter, dihydrofurans and dihydropyrrolidines.
234

Synthèse, pharmacomodulation et évaluation biologique de nouveaux dérivés de quinazoline à visées antiparasitaire et anticancéreuse / Synthesis, pharmacomodulation and biological evaluation of new quinazoline derivatives as potential antiparasitic and anticancer agents

Kabri, Youssef 12 March 2010 (has links)
Ce travail est consacré à la synthèse, pharmacomodulation et évaluation de nouveaux dérivés de quinazoline à visées antiparasitaire et anticancéreuse sous irradiation micro-ondes. Dans un premier chapitre, nous indiquons les principales méthodes d’accès au noyau quinazoline, les propriétés pharmacologiques associées aux principes actifs comportant ce motif et nous présentons les données bibliographiques actualisées sur la réaction de SRN1. Lors du second chapitre, la synthèse et la réactivité avec les anions nitronates et sulfinates de la 2-chlorométhyl-3-méthylquinazolin-4(3H)-one sont successivement décrites. Une étude mécanistique permet de démontrer le mécanisme radicalaire en chaîne SRN1 concernant la réaction avec les anions nitronates et un mécanisme de type SN2 avec les anions sulfinates. Par la suite, nous nous sommes intéressés à la préparation de nouvelles quinazolines, sous irradiation micro-ondes, en étudiant les réactions de SNAr puis de couplage de Suzuki-Miyaura en série 4-chloroquinazoline. A partir de ces résultats, nous avons développé la réaction régiosélective de Suzuki-Miyaura, sur la 4,7-dichloro-2-(2-méthylprop-1-ényl)-6-nitroquinazoline, et préparé toute une série de 4,7-diarylquinazolines hautement fonctionnalisées. Enfin, l’évaluation biologique des produits issus des réactions de SNAr a révélé des activités antipaludiques, anti-Leishmania et inhibitrices d’EGFR1 prometteuses, détaillées dans le dernier chapitre. / This work focuses on the synthesis of new bioactive quinazoline derivatives under microwave irradiation. In the first chapter, we indicate the main methods for preparing the quinazoline ring, the pharmacological properties associated to the quinazoline-derivated drug compounds and we present the SRN1 reaction updated bibliography. In the second chapter, the synthesis and reactivity of 2-chloromethyl-3-methylquinazolin-4(3H)-one with nitronate and sulfinate anions are successively described. A mechanistic study permits to demonstrate the SRN1 radical chain mechanism for the reaction with nitronate anions and a SN2 one for sulfinate anions. Afterwards, we prepared new original quinazolines, under microwave irradiation, by studying SNAr and Suzuki-Miyaura coupling reactions in 4-chloroquinazoline series. From these results, we have developed a regioselective Suzuki-Miyaura reaction on the 4,7-dichloro-2-(2-methylprop-1-enyl)-6-nitroquinazoline and prepared a new series of highly functionalized 4,7-diarylquinazolines. Finally, the biological evaluation of the products prepared by SNAr, showed interesting antiplasmodial and anti-leishmania activities along with EGFR1 inhibition properties.
235

Réaction de Michael et de Mannich appliquées à des arylcyclohexa-2,5-diènes en vue de la synthèse d'alcaloïdes de type aspidosperma et morphinanes

Dunet, Julie 27 November 2009 (has links)
L’objectif de cette thèse était d’accéder au squelette de deux grandes familles d’alcaloïdes, les aspidosperma et les morphinanes, avec pour but, l’utilisation de précurseurs communs, les arylcyclohexa-2,5-diènes. Dans un premier temps, ces arylcyclohexa-2,5-diènes, obtenus par réaction de Birch alkylante, ont été désymétrisés par application de la réaction de Michael. Les substrats ainsi obtenus ont été diversement fonctionnalisés jusqu’à obtention du squelette pentacyclique des aspidosperma. Dans un second temps, plusieurs méthodologies utilisant des réactions de type Mannich ont été développées. Ces méthodologies ont permis d’atteindre une base tricyclique de la famille des morphinanes. Plusieurs transformations ont ensuite été examinées afin d’accéder au squelette tétracyclique avancé de cette famille d’alcaloïdes. / The objective of this work was to access the skeleton of two families of alkaloids, the aspidosperma and the morphinan, using arylcyclohexa-2,5-dienes as common synthetic precursors. In one hand, these arylcyclohexadienes, synthesized by reductive Birch alkylation, were desymmetrized via the Michael reaction. The resulting compounds were then functionalized to give the pentacyclic skeleton of aspidosperma alkaloids. On the other hand, several methodologies were developed using Mannich type reactions. These methodologies allowed an access to the tricyclic framework of the morphinan family. Several transformations were then examined to attain the tetracyclic skeleton of this family of alkaloids.
236

Stereoselective intramolecular Michael addition reactions of pyrrole and their application to natural product syntheses

Beck, Daniel Antony Speedie, beckautomatic@gmail.com January 2006 (has links)
Chapter one; “(-)-Rhazinilam and (-)-Rhazinal: Alkaloids with Anti-mitotic Properties Derived from Kopsia teoi”, provides the background information behind the motives that initiated this research project. The plant alkaloid (-)-rhazinilam [(-)-1] and its naturally-occurring derivative (-)-rhazinal [(-)-13] both exhibit potent anti-mitotic activities and, as such, are interesting targets for total synthesis. Chapter one is a review of the literature regarding these two compounds and discusses the occurrence, proposed biosynthetic origins, structural elucidation and biological activites of compound (-)-1 and that of its analogues including alkaloid (-)-13. Previous total syntheses of these two compounds are then examined, concluding with the only reported total synthesis of compound (-)-13. Developed within the Banwell research group, this total synthesis produced the racemic modification of alkaloid (-)-13 due to a lack of any stereocontrol in the key intramolecular Michael addition step. This unprecedented key step, involving cyclisation of the C2 of pyrrole onto an N-tethered and ?,?-disubstituted acrylate to produce a quaternary-carbon stereogenic centre, would be of greatly enhanced utility if it could be achieved in a catalytic-enantioselective fashion. The realisation of this goal is the central aim of the research conducted within this thesis. ¶ Chapter two; “Investigating Asymmetric Induction in the Intramolecular Michael Addition of pyrrole to N-Tethered Acrylates and Related Species”, introduces the model study used to direct research towards achieving the goal of asymmetric induction in the title process. The model is a somewhat simplified version of the original process used in the total synthesis of compound (-)-13 involving cyclisation of the C2 of pyrrole onto an N-tethered and ?-monosubstituted Michael acceptor, to produce a tertiary-carbon stereogenic centre. This simplification allows the rapid synthesis of a broad range of potential substrates for use in the title process, thus enabling the investigation of various different approaches to inducing asymmetry therein. High levels of asymmetric induction are observed with the use of chiral substrates or catalysts, facilitating the synthesis of both 6- and 7-membered rings annulated to pyrrole with construction of the relevant tertiary-carbon stereogenic centre in enantio-enriched form. For the reactions producing a 6-membered ring annulated to pyrrole, unambiguous proof of the absolute sense of asymmetric induction observed in the intramolecular Michael addition event is established using a chemical correlation study involving elaboration of a key indolizine-type cyclisation product, to the plant alkaloid of known absolute stereochemistry, (-)-tashiromine [(-)-75]. For the reaction producing a 7-membered ring annulated to pyrrole, the same information is obtained via X-ray crystallographic analyses of a dibrominated derivative of a key pyrroloazepine-type cyclisation product. ¶ Chapter three “An Enantioselective Total Synthesis of the Alkaloid (-)-Rhazinal: An Anti-mitotic Agent Isolated from Kopsia teoi.”, focuses on the application of methodology developed in the previous chapter, to the original goal of inducing asymmetry in the intramolecular Michael addition reaction, involving cyclisation of the C2 of pyrrole onto an N-tethered and ?,?-disubstituted acrylate to produce a quaternary-carbon stereogenic centre. This is ultimately achieved in a catalytic-enantioselective fashion, resulting in the first such total synthesis of the anti-mitotic alkaloid (-)-rhazinal [(-)-13]. ¶ Chapter four “Extending the Reaction Manifold to the Syntheses of Related Natural Products: A Formal Total Synthesis of (+)-Aspidospermidine and Syntheses of (-)-Rhazinilam and (-)-Leuconolam from (-)-Rhazinal”, describes three extensions to the reaction manifold used in the enantioselective total synthesis of alkaloid (-)-13: The acquisition in an enantioselective manner, of an intermediate previously obtained in racemic form, en route to the racemic modification of the natural product (±)-aspidospermidine [(±)-134], constitutes a formal and enantioselective total synthesis of (+)-aspidospermidine [(+)-134]. The direct deformylation of (-)-rhazinal [(-)-13], is carried out, to produce the parent alkaloid (-)-rhazinilam [(-)-1]. The pyrrole ring present in (-)-rhazinilam [(-)-1] is oxidised, to produce the related natural product (-)-Leuconolam [(-)-12] which has not, hitherto, been prepared by total synthesis. ¶Chapter five contains the experimental procedures and characterisation data associated with compounds described in chapters two to four.
237

Synthèse de ligands du récepteu de l'Urotensine II et des récepteurs de la Mélatonine. Composés à noyau pyrido[2,3-d]pyrimidine ou imidazo[1,2-a]pyridine

Griffon Du Bellay, Amaury 05 December 2008 (has links) (PDF)
L'Urotensine II est un peptide vasoactif que l'on retrouve chez toutes les espèces étudiées. Elle présente une partie N-terminale linéaire variable selon l'espèce et une partie C-terminale hexocyclique constante et responsable de l'activité. Parmi les ligands développés, le Palosuran, un inhibiteur sélectif du récepteur de l'Urotensine II, présente un intérêt dans le traitement de l'insuffisance rénale du patient diabétique voire dans certaines pathologies ischémiques. Dans la première partie de ce travail de thèse, une série de composés à noyau pyrido[2,3-d]pyrimidine a été développée, tout d'abord, par analogie aux structures brevetées par Takeda puis sur le modèle du Palosuran.<br />La Mélatonine est une hormone à noyau indolique produite pendant la nuit par la glande pinéale et qui présente de nombreuses propriétés dont la plus importante est la synchronisation de l'horloge biologique avec le cycle jour-nuit. L'Agomélatine, analogue mélatoninergique à noyau naphtalénique développé par les Laboratoires Servier pour le traitement de la dépression, est un agoniste des récepteurs MT1 et MT2 et un antagoniste du récepteur 5HT2c. C'est sur ce modèle, qu'ont été développés des ligands à noyau pyrido[2,3-d]pyrimidine par substitution des sommets 2, 4 et 6, soit par alkylation, soit par couplages palladiés. La ramification de la chaîne latérale de l'Agomélatine ayant conduit à des composés actifs, il a été envisagé la synthèse d'analogues possédant la même chaîne en série pyrido[2,3-d]pyrimidine d'une part puis imidazo[1,2-a]pyridine d'autre part.
238

Asymmetric Synthesis of C-Glycosylated Amino Acids : Incorporation in Collagen Glycopeptides and Evaluation in a Model for Rheumatoid Arthritis

Gustafsson, Tomas January 2005 (has links)
<p>This thesis describes stereoselective syntheses of four amino acids, three of which are C-glycosidic analogues of glycosylated amino acids. The overall goal of the project was to probe the interactions between MHC molecules, glycopeptide antigens and T cell receptors, that are essential for development of collagen induced arthritis. Collagen induced arthritis is a frequently used mouse model for rheumatoid arthritis, an autoimmune disease that attacks joint cartilage and leads to a painful and eventually crippling condition.</p><p>The thesis is based on four studies. The first study describes the synthesis of hydroxylysine, an amino acid that is found in collagen and is an important constituent of the glycopeptide proposed as an antigen in collagen induced arthritis. During the synthesis of hydroxylysine some new insight into the mechanism of the reductive opening of <i>p</i>-methoxybenzylidene acetals was obtained.</p><p>The remaining three studies deals with the synthesis of C-glycosidic analogues of glycosylated amino acids, hydroxy norvaline, threonine and hydroxylysine.The synthesis of each amino acid required control of several stereogenic centra and utilizes a variety of approaches such as use of stereoselective reactions, chiral auxilaries, chiral templates and asymmetric catalysis.</p><p>The C-glycosidic analogues of galactosylated hydroxynorvaline and hydroxylysine were incorporated in glycopeptides from type II collagen and evaluated in T cell response assays. It was found that the T cells were stimulated by the C-glycopeptides, but that higher concentrations were required than for the native O-glycopeptide</p>
239

Asymmetric Synthesis of C-Glycosylated Amino Acids : Incorporation in Collagen Glycopeptides and Evaluation in a Model for Rheumatoid Arthritis

Gustafsson, Tomas January 2005 (has links)
This thesis describes stereoselective syntheses of four amino acids, three of which are C-glycosidic analogues of glycosylated amino acids. The overall goal of the project was to probe the interactions between MHC molecules, glycopeptide antigens and T cell receptors, that are essential for development of collagen induced arthritis. Collagen induced arthritis is a frequently used mouse model for rheumatoid arthritis, an autoimmune disease that attacks joint cartilage and leads to a painful and eventually crippling condition. The thesis is based on four studies. The first study describes the synthesis of hydroxylysine, an amino acid that is found in collagen and is an important constituent of the glycopeptide proposed as an antigen in collagen induced arthritis. During the synthesis of hydroxylysine some new insight into the mechanism of the reductive opening of p-methoxybenzylidene acetals was obtained. The remaining three studies deals with the synthesis of C-glycosidic analogues of glycosylated amino acids, hydroxy norvaline, threonine and hydroxylysine.The synthesis of each amino acid required control of several stereogenic centra and utilizes a variety of approaches such as use of stereoselective reactions, chiral auxilaries, chiral templates and asymmetric catalysis. The C-glycosidic analogues of galactosylated hydroxynorvaline and hydroxylysine were incorporated in glycopeptides from type II collagen and evaluated in T cell response assays. It was found that the T cells were stimulated by the C-glycopeptides, but that higher concentrations were required than for the native O-glycopeptide
240

Chiral Pyridine-Containing Ligands for Asymmetric Catalysis. Synthesis and Applications

Rahm, Fredrik January 2003 (has links)
This thesis deals with the design and syntheses of chiral,enantiopure pyridinecontaining ligands and their applicationsin asymmetric catalyis. Chiral pyridyl pyrrolidine ligands and pyridyl oxazolineligands were synthesized and employed in thepalladium-catalysed allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate. Theinfluence of the steric properties of the ligands wereinvestigated. Ditopic ligands, containing crown ether units as structuralelements, were synthesized and some of the ligands were used asligands in the palladiumcatalysed allylic alkylation of1,3-diphenyl-2-propenyl acetate with dimethyl malonate. A smallrate enhancement was observed, compared with analogous ligandslacking the crown ether unit, when these ditopic ligands wereused in dilute systems. A modular approach was used to synthesize chiralenantiomerically pure pyridyl alcohols and C2-symmetric2,2’-bipyridines, with the chirality originating from thechiral pool. Electronic and steric properties of the compoundswere varied and they were used as ligands in theenantioselective addition of diethylzinc to benzaldehyde. Thesense of asymmetric induction was found to be determined by theabsolute configuration of the carbinol carbon atom. Theelectronic properties of the ligands had a minor influence onthe levels of enantioselectivity induced by the ligands. Chiral pyridyl phosphinite ligands and pyridyl phosphiteligands were synthesized from the pyridyl alcohols andevaluated as ligands in palladiumcatalysed allylic alkylations.With the phosphinite ligands, the sense of chiral induction wasfound to be determined by the absolute configuration of theformer carbinol carbon atom. A kinetic resolution of theracemic starting material was observed with one of thephosphite ligands. Moderate enantioselectivities wereachieved. <b>Kewords:</b>asymmetric catalysis, chiral ligand, chiralpool, oxazoline, crownether, ditopic receptor, bipyridine,pyridyl alcohol, modular approach, P,Nligand, diethylzinc,allylic alkylation.

Page generated in 0.1307 seconds