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Development of catalytic systems suitable for the enantioselective synthesis of heterocycles
Dočekal, Vojtěch ; Veselý, Jan (advisor) ; Cibulka, Radek (referee) ; Pospíšil, Jiří (referee)
The development of novel methodologies and synthetic strategies for the preparation of complex 3D heterocyclic compounds with the well-defined spatial arrangement of functional groups represents one of the most studied research problems in current synthetic chemistry. Nowadays, organocatalysis (beside transition-metal catalysis and biocatalysis) became the most popular tool, because of usage small chiral organic compound for asymmetric induction and acceleration of reaction. In this thesis, the development of novel organocatalytic methodologies for the preparation of various heterocyclic compounds is described. The utility of novel methodologies is demonstrated by easy access to chiral building block molecules or products with valuable physical or biological properties. In the first part, a novel [4+2] cycloaddition reaction of sulfur-containing heterocyclic electron-deficient alkenes with allenic compounds catalyzed by chiral tertiary amine is described. Organocatalytic cycloaddition reaction of 3-benzylidene benzo[b]thiophenones with allenoates was investigated and optimized. Dihydro-2H-pyranes were obtained in high isolated yields (up to 92%) and optical purities (up to 99% ee). The robustness and synthetic utility of the developed methodology was demonstrated by a simple work-up of...
Electrochemistry of Nitrocalixarenes
Liška, Alan ; Vojtíšek, Pavel (advisor) ; Cibulka, Radek (referee)
In this diploma thesis a detailed investigation of the step-by-step reduction mechanism of cone-mono-, di-, tri and tetranitrocalix[4]arenes (in non-aqueous DMF) is presented. The intramolecular interaction of reducible (and reduced) centers and its consequences for the geometry of the starting molecule was discussed including the character of radicalic intermediates and their spin state. It was found, that the electrochemically generated radical anions of nitrogroups (unlike their starting electroneutral state) can act as ligands. Therefore, a study of complex formation equilibria of cone-tetranitrocalix[4]arenes with alkali metal cations followed. The possible use of a "stereoelectrochemical" approach (the relationship between geometry or conformation of the molecule and its electrochemical data) was demonstrated in describing and explaining conformational and electrochemical differences between two isomeric dinitrocalix[4]arenes. Finally, a new series of 1,3-alt-tetranitrothiacalix[4]arenes was electrochemically characterized and compared with the "classic" calixarene derivatives. Key words: electrochemistry, calixarenes, stereochemistry
Electrochemistry of Calixarenes
Liška, Alan ; Ludvík, Jiří (advisor) ; Zima, Jiří (referee) ; Cibulka, Radek (referee)
In the present thesis, both the published and the "ready-to-be-submitted" results concerning electrochemistry of calixarenes are summarized. The main focus is given to the detailed interpretation of experimental data, acquired during a systematic study of electroactive calixarene derivatives. The experiments were conducted under aprotic conditions (DMF) on mercury electrodes (mainly cyclic voltammetry and DC-polarography). It is demonstrated that electrochemistry should not serve only for redox characterization of studied compounds, but it offers a great number of other valuable information. The subject matter of the study are the calix[4]arenes (prevalently in the cone-conformation) which bear one to four reducible or oxidizable substituents ("redox probes") at various positions in order to be electrochemically investigable. Nitro- and nitroso compounds together with aldehydes, ketones, nitriles, aldoximes, carboxylic acids and corresponding esters, sulphones and esters of sulphonic acids are the most discussed compound series. Their relationship between structure and electrochemical response is presented in new connections ("stereoelectrochemistry"), in other words, how the redox probe position on the benzene ring (para-/meta-), bridging groups, or adjacent vs. opposite aromatic units...
Enantioselective allylation of dienals and their application in tiacumicin synthesis
Koukal, Petr ; Kotora, Martin (advisor) ; Cibulka, Radek (referee) ; Pour, Milan (referee)
The current methodologies of catalytic enantioselective allylation of aldehydes were studied on conjugated dienals and later on haloacrylaldehydes as the substrates. The resulting enantioenriched homoallylalcohols were prepared by reactions promoted either by commercial Brønsted acid catalysts or by Lewis base catalysts developed by our group, often with high enantio- and diastereoselectivities. Subsequently, the methodology was expanded on catalytic enantioselective crotylation and pentenylation reactions, practically unknown not only with these substrates. The applicability of this synthetic approach was demonstrated on preparation of several natural products or their intermediates.
Synthesis and application of new bipyridine ligands
Bednářová, Eva ; Kotora, Martin (advisor) ; Cibulka, Radek (referee) ; Michelet, Véronique (referee)
2,2'-Bipyridines and their appropriate N,N'-dioxides form a significant class of heteroaromatic compounds, which has found application in various fields of chemistry and predominantly in asymmetric catalysis. One of the most powerful methods for their synthesis is cocyclotrimerization of alkynes with nitriles. A new variant of cyclotrimerization reaction - cocyclotrimerization of halodiynes with nitriles, which results in the formation of 2- and 3-halopyridines, has been developed. The reaction was studied on a wide range of substrates providing the pyridine products in good isolated yields. Formation of an unexpected product of halogen exchange reaction was observed during the course of the study and its origin was elucidated by experimental studies. The prepared 2-halopyridines were used as starting materials for syntheses of new chiral 2,2'-bipyridine ligands. The crucial step of their synthesis turned out to be the reductive dimerization of 2-halopyridines to the corresponding 2,2'-bipyridines. Application of the formed bipyridine ligands was then tested in various metal-catalyzed asymmetric reactions, namely Mukaiyama aldol reaction, hydroxymethylation, conjugate addition, C-H activation of indole and desymmetrization of meso-epoxides, in which one of the bipyridine ligands showed...
Synthesis of Neuraminidase binders suitable for theranostics
Berenguer Albiñana, Carlos ; Machara, Aleš (advisor) ; Cibulka, Radek (referee) ; Soural, Miroslav (referee)
Influenza viruses cause respiratory illnesses which can vary in severity depending on the strain of the virus, as well as the age and health condition of the host. Influenza remains a major threat to public health due to its nature prone to suffer mutations. As a result, vaccines have to be reformulated annually and new strains may cause sporadic global pandemics. Furthermore, the recent emergence of resistant strains of the virus against the current standard of care (oseltamivir and zanamivir) underlines the need of novel anti-influenza therapeutics. The aim of this dissertation work is to contribute to the discovery of new anti-influenza inhibitors either by rational drug-design and optimization of oseltamivir structure, or by developing screening assays suitable for the discovery of novel inhibitors of the enzymes neuraminidase or RNA-polymerase. Scheme 1. Overview of the strategy used for the development of new anti-influenza therapeutics. The dashed arrows indicate the inhibitors that were converted into probes and their corresponding target enzymes Two main modification points were explored for the improvement of oseltamivir properties (Scheme 1); modifications at carbon C-3 aimed to overcome oseltamivir resistance caused by common mutations like H274Y, meanwhile modifications at carbon C-5...
Preparation of Influenza Neuraminidase and Polymerase Inhibitors
Zima, Václav ; Machara, Aleš (advisor) ; Cibulka, Radek (referee) ; Soural, Miroslav (referee)
Influenza is an infectious disease caused by the influenza virus. This virus causes a severe viral infection that spreads easily from person to person in yearly pandemics. Vaccination is the most effective way to prevent the infection, however, due to the high rate in mutations of the virus, the vaccine needs to be often reformulated. Another option to combat influenza is based on administration of antiviral drugs. Clinical studies of isolated influenza strains ("avian flu" H5N1, 2004; "swine flu" H1N1, 2009) revealed resistance towards known influenza neuraminidase inhibitors (zanamivir, oseltamivir). The resistance is caused by structural changes close to the enzymatic site. This calls for the development of new neuraminidase inhibitors as well for development of inhibitors targeting different influenza enzymes. This Thesis is focused on design and synthesis of new inhibitors of influenza neuraminidase and RNA-dependent RNA polymerase, namely PA subunit and the assembly of PA-PB1 heterodimer enzymes (Scheme 1). Influenza neuraminidase inhibitors were prepared by C-5 derivatization of oseltamivir followed by subsequent extension of its structure with binders of 150-cavity. Binding potencies of new oseltamivir derivatives against two influenza strains were determined. The next part contributed to...
Synthesis and reactivity of hypervalent sulfur fluorides
Ajenjo, Javier ; Beier, Petr (advisor) ; Jahn, Ullrich (referee) ; Cibulka, Radek (referee)
The pentafluorosulfanyl (SF5) group displays remarkable and unique properties, including large dipole moment, high electronegativity, high thermal and chemical stability, as well as high lipophilicity. However, only a few synthetic methods for the preparation of aromatic pentafluorosulfanyl building blocks have been developed to date. This work aims at improving availability and accessibility of aryl sulfurpentafluoride building blocks. In the first part of the work, the synthesis of aryl sulfurpentafluorides by the direct fluorination of diaryl disulfides with elemental fluorine is described. Nowadays, this synthetic strategy is used by industry on a multi-kilogram scale. However, the scope of the reaction is only limited to 3- and 4- nitro-1-(pentafluorosulfanyl)benzenes. In this work, the synthesis of various para-, meta- and ortho-substituted-(pentafluorosulfanyl)benzenes following the same approach was carried out. In the second part, the derivatization of aryl sulfurpentafluoride building blocks was investigated. Direct fluorination of 3-nitro-1-(pentafluorosulfanyl)benzene afforded 3-fluoro-5-nitro-1- (pentafluorosulfanyl)benzene. The titled compound was derivatized by two different processes: nucleophilic aromatic substitution (SNAr) of fluorine and vicarious nucleophilic substitution of...
Synthesis and application of new bipyridine ligands
Bednářová, Eva ; Kotora, Martin (advisor) ; Cibulka, Radek (referee) ; Michelet, Véronique (referee)
2,2'-Bipyridines and their appropriate N,N'-dioxides form a significant class of heteroaromatic compounds, which has found application in various fields of chemistry and predominantly in asymmetric catalysis. One of the most powerful methods for their synthesis is cocyclotrimerization of alkynes with nitriles. A new variant of cyclotrimerization reaction - cocyclotrimerization of halodiynes with nitriles, which results in the formation of 2- and 3-halopyridines, has been developed. The reaction was studied on a wide range of substrates providing the pyridine products in good isolated yields. Formation of an unexpected product of halogen exchange reaction was observed during the course of the study and its origin was elucidated by experimental studies. The prepared 2-halopyridines were used as starting materials for syntheses of new chiral 2,2'-bipyridine ligands. The crucial step of their synthesis turned out to be the reductive dimerization of 2-halopyridines to the corresponding 2,2'-bipyridines. Application of the formed bipyridine ligands was then tested in various metal-catalyzed asymmetric reactions, namely Mukaiyama aldol reaction, hydroxymethylation, conjugate addition, C-H activation of indole and desymmetrization of meso-epoxides, in which one of the bipyridine ligands showed...
Enantioselective allylation of dienals and their application in tiacumicin synthesis
Koukal, Petr ; Kotora, Martin (advisor) ; Cibulka, Radek (referee) ; Pour, Milan (referee)
The current methodologies of catalytic enantioselective allylation of aldehydes were studied on conjugated dienals and later on haloacrylaldehydes as the substrates. The resulting enantioenriched homoallylalcohols were prepared by reactions promoted either by commercial Brønsted acid catalysts or by Lewis base catalysts developed by our group, often with high enantio- and diastereoselectivities. Subsequently, the methodology was expanded on catalytic enantioselective crotylation and pentenylation reactions, practically unknown not only with these substrates. The applicability of this synthetic approach was demonstrated on preparation of several natural products or their intermediates.

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