|
|
Conjugate Addition Coupled with Enolate Oxidation in the Total Synthesis of Natural Polyphenols
Mašek, Tomáš ; Jahn, Ullrich (advisor) ; Pospíšil, Jiří (referee) ; Švenda, Jakub (referee)
1 ABSTRACT This thesis describes the development of the concept of C-C bond forming conjugate addition/oxidative cyclisation reactions and their application in the total synthesis of natural polyphenols. The first part deals with the development of methodology for conjugate addition of main- group organometallic reagents to unsaturated carbonyl compounds coupled with in situ single electron transfer oxidation. The resulting radical undergoes stereoselective cyclisation, that can be followed by a second SET oxidation, leading to further cationic cyclisation. This methodology is ideally suited for the synthesis of furoindane stilbenolignans (FIS), a neglected and structurally distinct class of natural polyphenols. Using this process, racemic synthesis of a derivative of kompasinol A was achieved, confirming the relative configuration of FISs. In an effort to develop asymmetric route to FISs, an unprecedented direct conjugate addition of aryllithiums to ylidenemalonates mediated by diethers and diamines was discovered, leading to asymmetric synthesis of gnetifolin F and 11- deoxykompasinol A. Based on X-ray evidence, a related annulation methodology consisting of direct conjugate addition/epoxide opening was shown to result in bridged lactones, instead of isomeric FISs. This finding led to an approach for the...
|
|
|
Synthesis of selagibenzophenone C and derivatives for confirmation of the stucture of the natural product.
Kunák, Dominik ; Rýček, Lukáš (advisor) ; Matoušová, Eliška (referee)
5 Abstract This bachelor's thesis deals with the preparation of selagibenzophenone C. The natural product was prepared in a six-step synthesis, where subsequent analysis and comparison of the spectrum of the synthetic substance with the spectra described for the isolated product verified whether the structure of the isolated natural product was deciphered correctly. Furthermore, it was verified that intermediates in the synthesis of selagibenzophenone C can undergo cyclization reactions to form a fluorene core. Analogous cyclization is the main step in the biosynthesis of selaginpulvilins from the corresponding selaginellins. The obtained fluorene derivatives will therefore be used as standards in the following studies to determine whether these substances obtained by us are also natural compounds. Key words Total synthesis, natural product, polyphenols, natural fluorene derivates, selagibenzophenones
|
|
|
Synthesis and Properties of Neuroactive Steroids
Kapras, Vojtěch
Herein is reported the synthesis of molecular probes for action of neuroactive steroids in vitro and in living organisms. In the first part, preparation of enantiomeric pregnane steroids is investigated, ultimately resulting into the total synthesis of ent-progesterone. The chirality of the target molecule is introduced by a highly effective organocatalytic asymmetric Robinson annulation. A new method for the sequential construction of five-membered carbocyclic ring is introduced as the key step. This is composed of substrate-controlled copper-catalyzed conjugate addition followed by radical oxygenation and subsequent thermal cyclization employing the persistent radical effect. The synthesis of truncated neurosteroid analogs is described and their biological activity at the NMDA receptor is compared with the native hormone. In the second part, methodology for specific deuterium labeling of both angular methyls of the 5β-pregnane steroid core is explored. Special attention was paid to the Barton-McCombie deoxygenation as the tool for introduction of the last deuterium atom into the methyl group. Both positions were labelled with total of three deuterium atoms in high isotopic purity.
|
|
|
Asymmetric Tandem Lithium Amide Conjugate Addition/Radical Reactions and Their Application in the Total Synthesis of Natural Products
Hidasová, Denisa ; Jahn, Ullrich (advisor) ; Kočovský, Pavel (referee) ; Míšek, Jiří (referee)
This thesis deals with single-electron transfer (SET) radical processes mediated by ferrocenium hexafluorophosphate and TEMPO and their application in the total synthesis of natural products. Asymmetric aminooxygenation methodology for the synthesis of anti-β-amino-α-hydroxy acid derivatives has been developed by utilizing a highly diastereoselective aza-Michael addition of chiral lithium amides to various α,β-unsaturated esters or amides/SET oxidation/radical α-oxygenation. The potential of this methodology was demonstrated in short total syntheses of the anti-β-amino-α-hydroxy acid fragments of the macrocyclic (depsi)peptides perthamide C and largamide H, and (-)-cytoxazone, which is a selective modulator of TH2 cytokine secretion. The SET-catalyzed asymmetric tandem lithium amide conjugate addition/5-exo radical cyclization/oxygenation reactions were applied in the synthesis of highly substituted pyrrolidines, azabicyclo[n.3.0]alkanes and spiropyrrolidines. An enantioselective total synthesis of the pyrrolidine alkaloid (-)-α-kainic acid was accomplished by employing the SET-catalyzed 5-exo radical cyclization/oxygenation.
|
|
|
New Thermal and Oxidative Radical Cyclization Methodology and Application to the Total Synthesis of Bridged Diketopiperazine Alkaloids
Amatov, Tynchtyk ; Jahn, Ullrich (advisor) ; Pour, Milan (referee) ; Cibulka, Radek (referee)
This thesis describes the development of new thermal and oxidative radical cyclization methodologies and their application to the total syntheses of alkaloids, particularly to bridged diketopiperazine (DKP) alkaloids. A practical solvent free approach to diverse DKPs and quinazolines is described. The methodology proceeds by thermal silica gel mediated deprotection of the Boc protecting group and intramolecular condensation of the resulting free dipeptides and tripeptides. It was applied to the total syntheses of alkaloids glyantrypine and ardeemin. A major part of the thesis concerns with the discovery and applications of novel diketopiperazine derived alkoxyamines. Their propensity to undergo facile thermal C-O bond homolysis to generate captodative DKP radicals and persistent TEMPO radical allowed using them as radical surrogates. The methodology takes advantage of the persistent radical effect (PRE). The methodology based on PRE was applied in an asymmetric approach to the alkaloid asperparaline C. An asymmetric synthesis of a very advanced precursor to asperparaline C, 8- oxoasperparaline C, was accomplished in 11 steps and 15% overall yield. The key steps of the synthesis include a direct oxidative cyclization of DKPs, regioselective furan dearomatization with singlet oxygen and a reductive...
|
|
|
Synthesis and Properties of Neuroactive Steroids
Kapras, Vojtěch ; Chodounská, Hana (advisor) ; Pour, Milan (referee) ; Drašar, Pavel (referee)
Herein is reported the synthesis of molecular probes for action of neuroactive steroids in vitro and in living organisms. In the first part, preparation of enantiomeric pregnane steroids is investigated, ultimately resulting into the total synthesis of ent-progesterone. The chirality of the target molecule is introduced by a highly effective organocatalytic asymmetric Robinson annulation. A new method for the sequential construction of five-membered carbocyclic ring is introduced as the key step. This is composed of substrate-controlled copper-catalyzed conjugate addition followed by radical oxygenation and subsequent thermal cyclization employing the persistent radical effect. The synthesis of truncated neurosteroid analogs is described and their biological activity at the NMDA receptor is compared with the native hormone. In the second part, methodology for specific deuterium labeling of both angular methyls of the 5β-pregnane steroid core is explored. Special attention was paid to the Barton-McCombie deoxygenation as the tool for introduction of the last deuterium atom into the methyl group. Both positions were labelled with total of three deuterium atoms in high isotopic purity.
|
|
|
Synthesis and Properties of Neuroactive Steroids
Kapras, Vojtěch
Herein is reported the synthesis of molecular probes for action of neuroactive steroids in vitro and in living organisms. In the first part, preparation of enantiomeric pregnane steroids is investigated, ultimately resulting into the total synthesis of ent-progesterone. The chirality of the target molecule is introduced by a highly effective organocatalytic asymmetric Robinson annulation. A new method for the sequential construction of five-membered carbocyclic ring is introduced as the key step. This is composed of substrate-controlled copper-catalyzed conjugate addition followed by radical oxygenation and subsequent thermal cyclization employing the persistent radical effect. The synthesis of truncated neurosteroid analogs is described and their biological activity at the NMDA receptor is compared with the native hormone. In the second part, methodology for specific deuterium labeling of both angular methyls of the 5β-pregnane steroid core is explored. Special attention was paid to the Barton-McCombie deoxygenation as the tool for introduction of the last deuterium atom into the methyl group. Both positions were labelled with total of three deuterium atoms in high isotopic purity.
|
|
|
Preparation of biologically active compounds using organocatalysis
Šimek, Michal ; Veselý, Jan (advisor) ; Kočovský, Pavel (referee)
This diploma thesis deals with the use of organocatalysis in an asymmetric allylic substitution reaction of Morita-Baylis-Hillman carbonates by aniline derivatives leading to enantiomerically enriched allylic amines. The first part of the thesis is focused on optimizing the reaction conditions in the organocatalytic reaction with respect to the yields and enantiomeric excesses of the products. In the second part of the thesis prepared enantiomerically enriched allylic amines are used in the cyclization step to give β-lactame cycles that serve as the key intermediates in the total synthesis of Ezetimib as is demonstrated in the final part of the diploma thesis.
|
guest ::
