Change search
Refine search result
123456 101 - 150 of 257
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 101.
    Kalek, Marcin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of C(sp2)-P bonds by palladium-catalyzed reactions: Mechanistic investigations and synthetic studies2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on synthetic and mechanistic aspects of palladium-catalyzed C(sp2)-P bond-forming reactions, with the aim to develop mild and efficient methods for the synthesis of biologically active phosphorus compounds, e.g. DNA analogs.

    The first part of the thesis is devoted to detailed mechanistic investigations of the palladium-catalyzed C-P cross-coupling reaction, in order to fully understand the underlying chemistry and by rational design of the reaction conditions, improve the overall efficiency of the process and broaden its applicability. In particular influence of palladium coordination by different anions on the rate of ligand substitution and reductive elimination steps of the reaction was studied. It was found that coordination of acetate ion results in unprecedented acceleration of both of the mechanistic steps, what leads to remarkable shortening of the overall reaction times. In-depth kinetic investigations enabled to ascribe the observed effects to ability of the acetate ion to act as a bidentate ligand for palladium. This causes considerable alternation of the reaction mechanism, comparing to the reaction involving halide-containing complexes, and results in significant rate increase.

    Based on the above mechanistic studies an efficient method for the synthesis of arylphosphonates, using substoichiometric amounts of inorganic acetate additive and reduced amount of catalyst, was developed.

    In the next part of the thesis, efforts to further enhance the palladium-catalyzed cross-coupling efficiency by using a microwave-assisted synthesis are described. These explorations resulted in a successful development of two protocols, one for a cross-coupling of H-phosphonates and the other for H,H-phosphinates, under the microwave heating conditions. Application of this energy source resulted in extremely short reaction times, measured in minutes.

    The final chapter of this thesis deals with studies on palladium-catalyzed SN2’ propargylic substitution reaction with phosphorus nucleophiles, which leads to allene products. Efficient procedure for the synthesis of allenylphosphonates and related compounds was developed. The method enables full control of stereochemistry in the allene moiety and at the asymmetric phosphorus center. Some conclusions on the mechanism of the reaction were also drawn.

  • 102.
    Kapla, Jon
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Engström, Olof
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wohlert, Jakob
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Molecular dynamics simulations and NMR spectroscopy studies of trehalose-lipid bilayer systems2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 34, p. 22438-22447Article in journal (Refereed)
    Abstract [en]

    The disaccharide trehalose (TRH) strongly affects the physical properties of lipid bilayers. We investigate interactions between lipid membranes formed by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and TRH using NMR spectroscopy and molecular dynamics (MD) computer simulations. We compare dipolar couplings derived from DMPC/TRH trajectories with those determined (i) experimentally in TRH using conventional high-resolution NMR in a weakly ordered solvent (bicelles), and (ii) by solid-state NMR in multilamellar vesicles (MLV) formed by DMPC. Analysis of the experimental and MD-derived couplings in DMPC indicated that the force field used in the simulations reasonably well describes the experimental results with the exception for the glycerol fragment that exhibits significant deviations. The signs of dipolar couplings, not available from the experiments on highly ordered systems, were determined from the trajectory analysis. The crucial step in the analysis of residual dipolar couplings (RDCs) in TRH determined in a bicelle-environment was access to the conformational distributions derived from the MD trajectory. Furthermore, the conformational behavior of TRH, investigated by J-couplings, in the ordered and isotropic phases is essentially identical, indicating that the general assumptions in the analyses of RDCs are well founded.

  • 103.
    Karlsson, Erik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalysts for Oxygen Production and Utilization: Closing the Oxygen Cycle: From Biomimetic Oxidation to Artificial Photosynthesis2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the development and study of catalysts for redox reactions, which either utilize oxygen or hydrogen peroxide for the purpose of selectively oxidizing organic substrates, or produce oxygen as the necessary byproduct in the production of hydrogen by artificial photosynthesis.

    The first chapter gives a general introduction about the use of environmentally friendly oxidants in the field of organic synthesis, and about the field of artificial photosynthesis. The second chapter describes a computational study of the mechanism of palladium-catalyzed oxidative carbohydroxylation of allene-substituted conjugated dienes. The proposed mechanism, which was supported by DFT calculations, involves an unusual water attack on a (π-allyl)palladium complex. The third chapter describes a computational study of the oxidation of unfunctionalized hydrocarbons, ethers and alcohols with hydrogen peroxide, catalyzed by methyltrioxorhenium (MTO). The mechanism was found to proceed via rate-limiting hydride abstraction followed by hydroxide transfer in a single concerted, but highly asynchronous, step as shown by intrinsic reaction coordinate (IRC) scans. The fourth chapter describes the use of a new hybrid (hydroquinone-Schiff base)cobalt catalyst as electron transfer mediator (ETM) in the palladium-catalyzed aerobic carbocyclization of enallenes. Covalently linking the two ETMs gave a fivefold rate increase compared to the use of separate components. The fifth chapter describes an improved synthetic route to the (hydroquinone-Schiff base)cobalt catalysts. Preparation of the key intermediate 5-(2,5-hydroxyphenyl)salicylaldehyde was improved by optimization of the key Suzuki coupling and change of protecting groups from methyl ethers to easily cleaved THP groups. The catalysts could thus be prepared in good overall yield from inexpensive starting materials.

    Finally, the sixth chapter describes the preparation and study of two catalysts for water oxidation, both based on ligands containing imidazole groups, analogous to the histidine residues present in the oxygen evolving complex (OEC) and in many other metalloenzymes. The first, ruthenium-based, catalyst was found to catalyze highly efficient water oxidation induced by visible light. The second catalyst is, to the best of our knowledge, the first homogeneous manganese complex to catalyze light-driven water oxidation.

  • 104.
    Kerdphon, Sutthichat
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    NHC,P- and N,P-Iridium Catalysts for Hydrogenations and Hydrogen Transfer Reactions2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work described in this thesis is focused on hydrogenation and hydrogen transfer reactions using iridium catalysts. The first part concerns the use of N-heterocyclic carbene-phosphine iridium complexes in alkylation reactions (Chapters 2 and 3) and the hydrogenation of ketones (Chapter 4). A number of N-heterocyclic carbene-phosphine iridium complexes have been prepared and evaluated as catalysts for C-N bond formation of amides using alcohols as the electrophile. This catalytic system can be used with a wide range of substrates at low catalyst loading (only 0.5 mol%) to furnish the desired products in up to 98% isolated yield. The achiral N-heterocyclic carbene-phosphine iridium complexes were also found to catalyze the methylation of ketones with methanol under mild conditions to afford the mono-methylated products in up to 98% isolated yield with low catalyst loading (1.0 mol%). Additionally, several chiral N-heterocyclic carbene-phosphine iridium complexes were synthesized and evaluated in asymmetric hydrogenation of ketones. The reactions were carried out at room temperature under base-free conditions to obtain the chiral alcohols in up to 96% ee in 30 minutes.

    The second part of this thesis (Chapter 5) details the preparation of new N,P-iridium complexes which were found to be highly efficient catalysts for the asymmetric hydrogenation of challenging tetrasubstituted olefins. This catalytic system results in optically active compounds of high enantiomeric excess (up to 98% ee) as the single diasteroisomer.

  • 105.
    Kerdphon, Sutthichat
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Xu, Quan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Parihar, Vijay Singh
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    C-N Coupling of Amides with Alcohols Catalyzed by N-Heterocyclic Carbene-Phosphine Iridium Complexes2015In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 80, no 22, p. 11529-11537Article in journal (Refereed)
    Abstract [en]

    N-heterocyclic carbene-phosphine iridium complexes (NHC-Ir) were developed/found to be a highly reactive catalyst for N-monoalkylation of amides with alcohols via hydrogen transfer. The reaction produced the desired product in high isolated yields using a wide range of substrates with low catalyst loading and short reaction times.

  • 106.
    Kjellgren, Johan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Employment of Palladium Pincer Complex Catalysts and Lewis Acids for Synthesis and Transformation of Organometallic Compounds2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is mainly focused on the development of new palladium catalyzed transformations using so-called “pincer” complexes. These complexes were applied as catalysts in two important areas of organometallic chemistry: substitution of propargylic substrates by dimetallic reagents; and allylation of aldehydes and imines by allylstannanes. In addition, this thesis includes studies on Lewis acid mediated cyclization reactions of allylsilanes with aldehydes.

    Pincer complex catalyzed substitution of various propargylic substrates could be achieved under mild conditions using tin and silicon based dimetallic reagents to obtain propargyl- and allenylstannanes and silanes. The regioselectivity of the substitution reaction strongly depends on the steric and electronic effects of the propargylic substrate. According to our mechanistic studies the key intermediate of the reaction is an organostannane (or silane) coordinated pincer complex. DFT modeling studies on the transfer of the trimethylstannyl functionality to the propargylic substrate revealed a novel mechanism, which is based on the unique topology of the pincer-complex catalysts.

    Our further studies showed that palladium pincer complexes can be employed as efficient catalysts for electrophilic allylic substitution of allylstannanes with aldehyde and imine substrates. In contrast to previous applications for electrophilic allylic substitutions via bis-allylpalladium complexes, this reaction involves mono-allylpalladium intermediates which were observed by 1H-NMR spectroscopy.

    The last chapter of this thesis is focused on Lewis-acid mediated cyclization of hydroxy functionalized allylsilanes, which afford tetrahydropyran derivatives with a high stereoselectivity.

  • 107.
    Krajangsri, Suppachai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Development of Asymmetric Iridium Catalysed Hydrogenation Reactions2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The focus of the work presented in this thesis is the development of iridium-catalysed asymmetric hydrogenation reactions.

    The first part of this thesis covers the development of dynamic kinetic resolution in asymmetric hydrogenation of chiral, racemic secondary allylic alcohols, which are converted to chiral saturated alcohols with high dr and ee. In this study, a wide range of substrates was successfully hydrogenated to give good results, with up to 95:5 dr and 99% ee. Moreover, a number of different allylic alcohol derivatives were also investigated and found to undergo the DKR of hydrogenation with good results.

    The second part of this thesis is directed towards the development of regioselective asymmetric mono-hydrogenation of 1,4- and 1,5-disubstituted 1,4-cyclohexadienes. Under optimized hydrogenation conditions, high yield of regioselective mono-hydrogenated products and excellent enantioselectivity were observed in most cases. The usefulness of the reaction was demonstrated in the preparation of important chiral α,β-unsaturated ketones in good yield and excellent ee of up to 96%. Our novel method provides a general route to this important class of compounds.

    The third part concerns the development of asymmetric hydrogenation of β-hydroxy silanes. It was observed that under hydrogenation conditions, β-hydroxy silanes undergo Peterson olefination to form terminal olefins which are then hydrogenated using an Ir catalyst. A new class of Ir-N,P catalysts were prepared and provided high yield with excellent ee in up to 99%. In addition, the reaction was highly chemoselective and could be tuned to hydrogenate either an olefin or a β-hydroxy silane depending on the choice of catalyst and reaction conditions.

    The final part describes the asymmetric hydrogenation of enamides. A variety of oxazolidinone-enamides were prepared and evaluated in this reaction. High yields, (up to 99%) and excellent ee, (up to 99%) were obtained.

  • 108.
    Kullberg, Martin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Studies on nucleoside H-phosphonoselenoate chemistry and chalcogen exchange reaction between P(V) and P(III) compounds2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, the chemistry of compounds containing P-Se bonds has been studied. As a new addition to this class of compounds, H-phosphonoselenoate monoesters, have been introduced and two synthetic pathways for their preparation have been developed.

    The reactivity of H-phosphonoselenoate monoesters towards a variety of condensing agents has been studied. From these, efficient conditions for the synthesis of H-phosphonoselenoate diesters have been developed. The produced diesters have subsequently been used in oxidative transformations, which gave access to the corresponding P(V) compounds, e.g. dinucleoside phosphoroselenoates or dinucleoside phosphoroselenothioates.

    Furthermore, a new selenizing agent, triphenyl phosphoroselenoate, has been developed for selenization of P(III) compounds. This reagent has high solubility in organic solvents and was found to convert phosphite triesters and H-phosphonate diesters efficiently into the corresponding phosphoroselenoate derivatives.

    The selenization of P(III) compounds with triphenyl phosphoroselenoate proceeds through a selenium transfer reaction. A computational study was performed to gain insight into a mechanism for this reaction. The results indicate that the transfer of selenium or sulfur from P(V) to P(III) compounds proceeds most likely via an X-philic attack of the P(III) nucleophile on the chalcogen of the P(V) species. For the transfer of oxygen, the reaction may also proceed via an edge attack on the P=O bond.

  • 109. Küpper, Frithjof C.
    et al.
    Feiters, Martin C.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kaiho, Tatsuo
    Yanagida, Shozo
    Zimmermann, Michael B.
    Carpenter, Lucy J.
    Luther, George W.
    Lu, Zunli
    Jonsson, Mats
    Kloo, Lars
    Purple fumes: the importance of iodine2013In: Science in School, ISSN 1818-0353, E-ISSN 1818-0361, no 27, p. 10p. 45-53Article in journal (Other academic)
  • 110.
    Laine, Tanja M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Development of Ruthenium Catalysts for Water Oxidation2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    An increasing global energy demand requires alternative fuel sources. A promising method is artificial photosynthesis. Although, the artificial processes are different from the natural photosynthetic process, the basic principles are the same, i.e. to split water and to convert solar energy into chemical energy. The energy is stored in bonds, which can at a later stage be released upon combustion. The bottleneck in the artificial systems is the water oxidation. The aim of this research has been to develop catalysts for water oxidation that are stable, yet efficient. The molecular catalysts are comprised of organic ligands that ultimately are responsible for the catalyst structure and activity. These ligands are often based on polypyridines or other nitrogen-containing aromatic compounds. This thesis describes the development of molecular ruthenium catalysts and the evaluation of their ability to mediate chemical and photochemical oxidation of water. Previous work from our group has shown that the introduction of negatively charged groups into the ligand frameworks lowers the redox potentials of the metal complexes. This is beneficial as it makes it possible to drive water oxidation with [Ru(bpy)3]3+-type oxidants (bpy = 2,2’-bipyridine), which can be photochemically generated from the corresponding [Ru(bpy)3]2+ complex. Hence, all the designed ligands herein contain negatively charged groups in the coordination site for ruthenium.

    The first part of this thesis describes the development of two mononuclear ruthenium complexes and the evaluation of these for water oxidation. Both complexes displayed low redox potentials, allowing for water oxidation to be driven either chemically or photochemically using the mild one-electron oxidant [Ru(bpy)3]3+.

    The second part is a structure–activity relationship study on several analogues of mononuclear ruthenium complexes. The complexes were active for water oxidation and the redox potentials of the analogues displayed a linear relationship with the Hammet σmeta parameter. It was also found that the complexes form high-valent Ru(VI) species, which are responsible for mediating O–O bond formation.

    The last part of the thesis describes the development of a dinuclear ruthenium complex and the catalytic performance for chemical and photochemical water oxidation. It was found that the complex undergoes O–O bond formation via a bridging peroxide intermediate, i.e. an I2M–type mechanism.

  • 111.
    Larsson, Andreas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis, structure and conformation of oligo- and polysaccharides2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Carbohydrates are a complex group of biomolecules with a high structural diversity. Their almost omnipresent occurrence has generated a broad field of research in both biology and chemistry. This thesis focuses on three different aspects of carbohydrate chemistry, synthesis, structure elucidation and the conformational analysis of carbohydrates.

    The first paper describes the synthesis of a penta- and a tetrasaccharide related to the highly branched capsular polysaccharide from Streptococcus pneumoniae type 37. In the second paper, the structure of the O-antigenic repeating unit from the lipopolysaccharide of E. coli 396/C1 was determined along with indications of the structure of the biological repeating unit. In addition, its structural and immunological relationship with E. coli O126 is discussed. In the third paper, partially protected galactopyranosides were examined to clarify the origin of an intriguing 4JHO,H coupling, where a W-mediated coupling pathway was found to operate. In the fourth paper, the conformation of methyl a-cellobioside is studied with a combination of molecular dynamics simulations and NMR spectroscopy. In addition to the expected syn-conformation, detection and quantification of anti-ø and anti-ψ conformers was also possible.

  • 112.
    Larsson, Johanna M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Transition metal-catalyzed allylic and vinylic functionalization: Method development and mechanistic investigations2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The use of small molecule building blocks in, for example, pharmaceutical research and new material development, creates a need for new and improved organic synthesis methods. The use of transition metals as mediators and catalysts opens up new reaction pathways that have made the synthesis of completely new compounds possible as well as greatly improved the synthetic routes to known compounds.

    Herein, the development of new metal-mediated and catalyzed reactions for construction of vinylic and allylic carbon-carbon and carbon-heteroatom bonds is described.  The use of iodonium salts as coupling partners in Pd-catalyzed Heck type reactions with alkenes is shown to improve the current substrate scope. Results from a mechanistic study indicate that the reaction proceeds via high oxidation state palladium intermediates.

    The use of IIII reagents is also believed to facilitate a PdII/PdIV catalytic cycle in allylic silylation of alkenes using (SiMe3)2, which, to the best of our knowledge, is the first method developed for metal-catalyzed allylic C-H silylation.

    The same silyl-source, (SiMe3)2, has previously been used in a Pd-catalyzed allylic substitution reaction in which allylic silanes are formed from allylic alcohols. A detailed mechanistic investigation of this reaction is described in which by-products as well as intermediates, including the resting state of the catalyst, are identified using 1H, 11B, 19F and 29Si NMR spectroscopy. Kinetic experiments are performed that give information about the turn-over limiting step and the mechanism of the analogous borylation using B2pin2 is also investigated. Insights from this study further made it possible to improve the stereoselectivity of this reaction.

    Additionally, a new method for Cu-mediated trifluoromethylation of allylic halides is presented in which linear products are formed exclusively from both linear and branched allylic substrates at room temperature.  Identification of allylic fluorides as by-products during the reaction also led to the development of a similar Cu-mediated reaction for the fluorination of allylic halides.

  • 113. Li, Jia-Qi
    et al.
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry. University of KwaZulu-Natal, South Africa.
    Room temperature and solvent-free iridium-catalyzed selective alkylation of anilines with alcohols2013In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 49, no 55, p. 6131-6133Article in journal (Refereed)
    Abstract [en]

    A bidentate iridium NHC-phosphine complex has been developed and applied to the N-monoalkylation of aromatic amines with a wide range of primary alcohols and to the N-heterocyclization of amino alcohols. This reaction resulted in high isolated product yields, even at room temperature and under solvent-free conditions.

  • 114. Li, Jia-Qi
    et al.
    Liu, Jianguo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Krajangsri, Suppachai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Chumnanvej, Napasawan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Singh, Thishana
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Asymmetric Hydrogenation of Allylic Alcohols Using Ir-N,P-Complexes2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 12, p. 8342-8349Article in journal (Refereed)
    Abstract [en]

    In this study, a series of gamma,gamma-disubstituted and beta,gamma-disubstituted allylic alcohols were prepared and successfully hydrogenated using suitable N,P-based Ir complexes. High yields and excellent enantioselectivities were obtained for most of the substrates studied. This investigation also revealed the effect of the acidity of the N,P-Ir-complexes on the acid sensitive allylic alcohols. DFT Delta pK(a) calculations were used to explain the effect of the N,P-ligand on the acidity of the corresponding Ir-complex. The selectivity model of the reaction was used to accurately predict the absolute configuration of the hydrogenated alcohols.

  • 115.
    Liao, Rongzhen
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Quantum Chemical Cluster Modeling of Enzymatic Reactions2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Quantum chemical cluster approach has been shown to be quite powerful and efficient in the modeling of enzyme active sites and reaction mechanisms. In this thesis, the reaction mechanisms of several enzymes have been investigated using the hybrid density functional B3LYP. The enzymes studied include four dinuclear zinc enzymes, namely dihydroorotase, N-acyl-homoserine lactone hydrolase, RNase Z, and human renal dipeptidase, two trinuclear zinc enzymes, namely phospholipase C and nuclease P1, two tungstoenzymes, namely formaldehyde ferredoxin oxidoreductase and acetylene hydratase, aspartate α-decarboxylase, and mycolic acid cyclopropane synthase. The potential energy profiles for various mechanistic scenarios have been calculated and analyzed. The role of the metal ions as well as important active site residues has been discussed.

      In the cluster approach, the effects of the parts of the enzyme that are not explicitly included in the model are taken into account using implicit solvation methods.

      For all six zinc-dependent enzymes studied, the di-zinc bridging hydroxide has been shown to be capable of performing nucleophilic attack on the substrate. In addition, one, two, or even all three zinc ions participate in the stabilization of the negative charge in the transition states and intermediates, thereby lowering the barriers.

      For the two tungstoenzymes, several different mechanistic scenarios have been considered to identify the energetically most feasible one. For both enzymes, new mechanisms are proposed.

      Finally, the mechanism of mycolic acid cyclopropane synthase has been shown to be a direct methyl transfer to the substrate double bond, followed by proton transfer to the bicarbonate.

      From the studies of these enzymes, we demonstrate that density functional calculations are able to solve mechanistic problems related to enzymatic reactions, and a wealth of new insight can be obtained.

  • 116.
    Lihammar, Richard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Enzyme- and Transition Metal-Catalyzed Asymmetric Transformations: Application of Enzymatic (D)KR in Enantioselective Synthesis2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dynamic kinetic resolution (DKR) is a powerful method for obtaining compounds with high optical purity. The process relies on the combination of a kinetic resolution with an in situ racemization. In this thesis, a combination of an immobilized hydrolase and a transition metal-based racemization catalyst was employed in DKR to transform racemic alcohols and amines into enantioenriched esters and amides, respectively.

    In the first part the DKR of 1,2-amino alcohols with different rings sizes and N-protecting groups is described. We showed that the immobilization method used to support the lipase strongly influenced the stereoselectivity of the reaction.

    The second part deals with the DKR of C3-functionalized cyclic allylic alcohols affording the corresponding allylic esters in high yields and high ee’s. The protocol was also extended to include carbohydrate derivatives, leading to inversion of a hydroxyl substituted chiral center on the carbohydrate.

    The third part focuses on an improved method for obtaining benzylic primary amines. By using a novel, recyclable catalyst composed of Pd nanoparticles on amino-functionalized mesocellular foam, DKR could be performed at 50 °C. Moreover, Lipase PS was for the first time employed in the DKR of amines.

    In the fourth part DKR was applied in the total synthesis of Duloxetine, a compound used in the treatment of major depressive disorder. By performing a six-step synthesis, utilizing DKR in the enantiodetermining step, Duloxetine could be isolated in an overall yield of 37% and an ee >96%.

    In the final part we investigated how the enantioselectivty of reactions catalyzed by Candida Antarctica lipase B for δ-substituted alkan-2-ols are influenced by water. The results showed that the enzyme displays much higher enantioselectivity in water than in anhydrous toluene. The effect was rationalized by the creation of a water mediated hydrogen bond in the active site that helps the enzyme form enantiodiscriminating binding modes.

  • 117.
    Lihammar, Richard
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Rönnols, Jerk
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Epimerization of Glycal Derivatives by a Cyclopentadienylruthenium Catalyst: Application to Metalloenzymatic DYKAT2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 45, p. 14756-14762Article in journal (Refereed)
    Abstract [en]

    Epimerization of a non-anomeric stereogenic center in carbohydrates is an important transformation in the synthesis of natural products. In this study an epimerization procedure of the allylic alcohols of glycals by cyclopentadienylruthenium catalyst 1 is presented. The epimerization of 4,6-O-benzylidene-D-glucal 4 in toluene is rapid, and an equlibrium with its D-allal epimer 5 is established within 5min at room temperature. Exchange rates for allal and glucal formation were determined by 1D H-1 EXSY NMR experiments to be 0.055s(-1) and 0.075s(-1), respectively. For 4-O-benzyl-L-rhamnal 8 the epimerization was less rapid and four days of epimerization was required to achieve equilibration of the epimers at room temperature. The epimerization methodology was subsequently combined with acylating enzymes in a dynamic kinetic asymmetric transformation (DYKAT), giving stereoselective acylation to the desired stereoisomers 12, 13, and 15. The net effect of this process is an inversion of a stereogenic center on the glycal, and yields ranging from 71% to 83% of the epimer were obtained.

  • 118.
    Lind, Maria E. S.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Quantum Chemical Modeling of Asymmetric Enzymatic Reactions2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Computational methods are very useful tools in the study of enzymatic reactions, as they can provide a detailed understanding of reaction mechanisms and the sources of various selectivities. In this thesis, density functional theory has been employed to examine four different enzymes of potential importance for biocatalytic applications. The enzymes considered are limonene epoxide hydrolase, soluble epoxide hydrolase, arylmalonate decarboxylase and phenolic acid decarboxylase. Besides the reaction mechanisms, the enantioselectivities in three of these enzymes have also been investigated in detail. In all studies, quite large quantum chemical cluster models of the active sites have been used. In particular, the models have to account for the chiral environment of the active site in order to reproduce and rationalize the experimentally observed selectivities.

    For both epoxide hydrolases, the calculated enantioselectivities are in good agreement with experiments. In addition, explanations for the change in stereochemical outcome for the mutants of limonene epoxide hydrolase, and for the observed enantioconvergency in the soluble epoxide hydrolase are presented.

    The reaction mechanisms of the two decarboxylases are found to involve the formation of an enediolate- or a quinone methide intermediate, supporting thus the main features of the proposed mechanisms in both cases. For arylmalonate decarboxylase, an explanation for the observed enantioselectivity is also presented.

    In addition to the obtained chemical insights, the results presented in this thesis demonstrate that the quantum chemical cluster approach is indeed a valuable tool in the field of asymmetric biocatalysis.

  • 119.
    Lindberg, Bo G.
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Merritt, Eleanor A.
    Rayl, Melanie
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Liu, Chenxiao
    Parmryd, Ingela
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Faye, Ingrid
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Immunogenic and Antioxidant Effects of a Pathogen-Associated Prenyl Pyrophosphate in Anopheles gambiae2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 8, p. e73868-Article in journal (Refereed)
    Abstract [en]

    Despite efficient vector transmission, Plasmodium parasites suffer great bottlenecks during their developmental stages within Anopheles mosquitoes. The outcome depends on a complex three-way interaction between host, parasite and gut bacteria. Although considerable progress has been made recently in deciphering Anopheles effector responses, little is currently known regarding the underlying microbial immune elicitors. An interesting candidate in this sense is the pathogen-derived prenyl pyrophosphate and designated phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), found in Plasmodium and most eubacteria but not in higher eukaryotes. HMBPP is the most potent stimulant known of human V gamma 9V delta 2 T cells, a unique lymphocyte subset that expands during several infections including malaria. In this study, we show that V(Y)9V delta 2 T cells proliferate when stimulated with supernatants from intraerythrocytic stages of Plasmodium falciparum cultures, suggesting that biologically relevant doses of phosphoantigens are excreted by the parasite. Next, we used Anopheles gambiae to investigate the immune-and redox-stimulating effects of HMBPP. We demonstrate a potent activation in vitro of all but one of the signaling pathways earlier implicated in the human V(Y)9V delta 2 T cell response, as p38, JNK and PI3K/Akt but not ERK were activated in the A. gambiae 4a3B cell line. Additionally, both HMBPP and the downstream endogenous metabolite isopentenyl pyrophosphate displayed antioxidant effects by promoting cellular tolerance to hydrogen peroxide challenge. When provided in the mosquito blood meal, HMBPP induced temporal changes in the expression of several immune genes. In contrast to meso-diaminopimelic acid containing peptidoglycan, HMBPP induced expression of dual oxidase and nitric oxide synthase, two key determinants of Plasmodium infection. Furthermore, temporal fluctuations in midgut bacterial numbers were observed. The multifaceted effects observed in this study indicates that HMBPP is an important elicitor in common for both Plasmodium and gut bacteria in the mosquito.

  • 120.
    Lindstedt, Erik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Metal-Free O- and C-Arylation with Diaryliodonium Salts2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns the development of metal-free applications using diaryliodonium salts. The first project describes an arylation protocol of allylic and benzylic alcohols in aqueous media. The method proceeds under mild conditions and the ether products were obtained in moderate to good yields. The methodology was also expanded to include arylation of phenols, giving diaryl ethers in good to excellent yields. In the second project, an arylation method that included a wider range of aliphatic alcohols was developed. The scope of accessible alkyl aryl ethers was studied and included a comparative study of phenylation and nitrophenylation of various alcohols. Finally, a formal metal-free synthesis of butoxycain was performed, illustrating the applicability of the developed method.

    The third project focused on the limitations and side reactions occurring in Chapter 2 and 3. First, an approach to access symmetric diaryl ethers via arylation of hydroxide was presented. This reaction gave rise to a number of side products, which we hypothesized to originate from aryne-type intermediates. A mechanism for the formation of these side products was suggested, supported by trapping and deuterium labeling experiments.

    Oxidation of the alcohol to the corresponding ketone was also observed and the mechanism of this interesting side reaction was investigated. The latter was suggested to proceed via an intramolecular oxidation without the involvement of radicals or arynes.

    The fourth project covers a method to synthesize highly sterically congested alkyl aryl ethers via arylation of tertiary alcohols using diaryliodonium salts. The method displayed a broad scope of tertiary alcohols and was also suitable for fluorinated alcohols.

    The final project detailed in this thesis deals with C-arylation with diaryliodonium salts, showcasing nitroalkanes as well as a nitro ester as suitable nucleophiles for metal-free arylation. 

  • 121.
    Lindstedt, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ghosh, Raju
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Metal-Free Synthesis of Aryl Ethers in Water2013In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 15, no 23, p. 6070-6073Article in journal (Refereed)
    Abstract [en]

    The first arylation of allylic and benzylic alcohols with diaryliodonium salts is reported. The reaction yields alkyl aryl ethers under mild and metal-free conditions. Phenols are arylated to diaryl ethers in good to excellent yields. The reaction employs diaryliodonium salts and sodium hydroxide in water at low temperature, and excess amounts of the coupling partners are avoided.

  • 122.
    Lindstedt, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Reitti, Marcus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    One-Pot Synthesis of Unsymmetric Diaryliodonium Salts from Iodine and Arenes2017In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 82, no 22, p. 11909-11914Article in journal (Refereed)
    Abstract [en]

    The first synthesis of unsymmetric diaryliodonium salts directly from iodine and arenes is presented. The methodology provides diaryliodonium salts with the trimethoxyphenyl (TMP) moiety as dummy group. The protocol avoids the customary use of iodoarenes, which can be both expensive and toxic. Excess reagents are not required, and the reactions are performed under mild conditions. O-Arylations with these TMP salts were demonstrated to be highly chemoselective.

  • 123.
    Lindstedt, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stridfeldt, Elin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mild Synthesis of Sterically Congested Alkyl Aryl Ethers2016In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 18, no 17, p. 4234-4237Article in journal (Refereed)
    Abstract [en]

    An efficient and transition-metal-free method is presented to access tertiary alkyl aryl ethers by arylation of tertiary alcohols with ortho-substituted diaryliodonium salts. The scope covers cyclic and acyclic aliphatic, benzylic, allylic, and propargylic tertiary alcohols as well as primary and secondary fluorinated alcohols. The methodology gives access to alkyl aryl ethers of previously unprecedented steric congestion. Furthermore, the versatility of the developed procedure was demonstrated by arylation of the pro-drug mestranol.

  • 124.
    Lindström, Ulf M.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Somfai, Peter
    Microwave-assisted aminolysis of vinylepoxides1999In: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 40, no 52, p. 9273-9276Article in journal (Refereed)
    Abstract [en]

    Di- and trisubstituted vinyl epoxides in NH4OH were subjected to microwave irradn. affording the corresponding vicinal amino alcs. in high yields. The reaction is stereospecific and highly regioselective for addn. at the allylic carbon. [on SciFinder(R)]

  • 125.
    Lindén, Auri
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Flavins as Biomimetic Catalysts for Sulfoxidation by H2O2: Catalyst Immobilization in Ionic Liquid for H2O2 Oxidations2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the development of catalytic oxidation reactions utilizing hydrogen peroxide as terminal oxidant. The main focus has been to find flavin catalysts that are easy to handle and stable to store but still able to perform the desired reaction. A variety of dihydroflavins were prepared and the electrochemical oxidation potentials were measured and compared with their catalytic activity.

    A flavin catalyst was applied in the sulfoxidation of allylic and vinylic sulfides by H2O2. This transformation was highly chemoselective and the sulfoxides were obtained without formation of other oxidation products. The scope of the reaction was demonstrated by applying the method on substrates with a wide range of functional groups such as a tertiary amine. Another flavin catalyst was immobilized in the ionic liquid [BMIm]PF6 and used for sulfoxidations by H2O2. The chemoselectivity was maintained in this system and the catalyst-ionic liquid system could be recycled several times.

    Finally two bimetallic catalyst systems for the dihydroxylation of alkenes by H2O2 were immobilized in the ionic liquid. These systems employed either vanadium acetylacetonate VO(acac)2 or methyl trioxorhenium (MTO) as co-catalysts together with the substrate-selective osmium catalyst. Good to excellent yields of the diols were obtained.

  • 126.
    Liu, Jianguo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Iridium Catalysed Asymmetric Hydrogenation of Olefins and Dynamic Kinetic Resolution in the Asymmetric Hydrogenation of Allylic Alcohols2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work described in this thesis is focused on exploring the efficacy of iridium-catalysed asymmetric hydrogenation of precursors to chiral alcohols and chiral cyclohexanes. A range of allylic alcohols including γ,γ-dialkyl allylic alcohols and (Z)-allylic alcohols were prepared and evaluated in the asymmetric hydrogenation using iridium catalysts resulting in chiral alcohols in high yields and excellent enantioselectivity. This methodology was applied in the formal synthesis of Aliskiren, an efficient renin inhibitor drug, using the asymmetric hydrogenation of an allylic alcohol as a key-step. Another project concerned the dynamic kinetic resolution of racemic secondary allylic alcohols using Ir-N,P catalysts under hydrogenation conditions. A range of secondary allylic alcohols and protected alcohols were evaluated in the asymmetric hydrogenation via dynamic kinetic resolution using Ir-N,P catalysts. The corresponding chiral saturated alcohols were formed in good yield with excellent diastereoselectivites (up to 95/5) and enantioselectivities (>99% ee). The last part of this thesis is directed towards the development of highly regio- and enantioselective asymmetric hydrogenation of 1,4-cyclohexadienes and its application in the preparation of useful chiral cyclohexenone intermediates. Non-functionalised, functionalised and heterocycle-containing cyclohexadienes were evaluated. Good yield of regioselectively mono-hydrogenated silyl protected enol ethers were obtained in most cases with excellent enantioselectivity. 

  • 127.
    Liu, Jianguo
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Krajangsri, Suppachai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Singh, Thishana
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    De Seriis, Giulia
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Chumnanvej, Napasawan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Wu, Haibo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Regioselective Iridium-Catalyzed Asymmetric Monohydrogenation of 1,4-Dienes2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 41, p. 14470-14475Article in journal (Refereed)
    Abstract [en]

    A highly efficient regio- and enantioselective monohydrogenation of 1,4-dienes has been realized using an iridium catalyst with a chiral N,P-ligand under mild conditions. The substrate scope was studied and included both unfunctionalized as well as functionalized substituents on the meta- or para-position. Substrates having substituents with functionalities such as silyl protected alcohols or ketals were monohydrogenated in high regioselectivity and high enantiomeric excess (up to 98% ee).

  • 128.
    Lundberg, Helena
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Group (IV) Metal-Catalyzed Direct Amidation: Synthesis and Mechanistic Considerations2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The amide unit constitutes the backbone of proteins, and it is present in a large number of pharmaceutically active molecules, polymeric materials such as nylon and Kevlar, as well as in food additives like aspartame. Amides are produced in enormous amounts every year, thus, environmentally friendly and selective methods for their formation are of great importance. This thesis deals with the direct formation of amides from non-activated carboxylic acids and amines with the aid of group (IV) metal complexes. Water is the only by-product of this environmentally benign process. This fact stands in contrast to the most common methods for amide formation to date, which involve the use of waste-intensive, expensive and often toxic coupling reagents. The catalytic protocols presented herein use titanium, zirconium and hafnium complexes under mild reaction conditions to produce amides in good to excellent yields. Furthermore, carbamates are demonstrated to be suitable sources of gaseous amines for the formation of primary and tertiary amides under catalytic conditions. In addition, preliminary results from on-going mechanistic investigations of the zirconium- and hafnium-catalyzed processes are presented.

  • 129.
    Lundberg, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tinnis, Fredrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selander, Nicklas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Adolfsson, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic amide formation from non-activated carboxylic acids and amines2014In: Chemical Society Reviews, ISSN 0306-0012, E-ISSN 1460-4744, Vol. 43, no 8, p. 2714-2742Article, review/survey (Refereed)
    Abstract [en]

    The amide functionality is found in a wide variety of biological and synthetic structures such as proteins, polymers, pesticides and pharmaceuticals. Due to the fact that synthetic amides are still mainly produced by the aid of coupling reagents with poor atom-economy, the direct catalytic formation of amides from carboxylic acids and amines has become a field of emerging importance. A general, efficient and selective catalytic method for this transformation would meet well with the increasing demands for green chemistry procedures. This review covers catalytic and synthetically relevant methods for direct condensation of carboxylic acids and amines. A comprehensive overview of homogeneous and heterogeneous catalytic methods is presented, covering biocatalysts, Lewis acid catalysts based on boron and metals as well an assortment of other types of catalysts.

  • 130.
    Lundborg, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Computer-Assisted Carbohydrate Structural Studies and Drug Discovery2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Carbohydrates are abundant in nature and have functions ranging from energy storage to acting as structural components. Analysis of carbohydrate structures is important and can be used for, for instance, clinical diagnosis of diseases as well as in bacterial studies. The complexity of glycans makes it difficult to determine their structures. NMR spectroscopy is an advanced method that can be used to examine carbohydrates at the atomic level, but full assignments of the signals require much work. Reliable automation of this process would be of great help. Herein studies of Escherichia coli O-antigen polysaccharides are presented, both a structure determination by NMR and also research on glycosyltransferases which assemble the polysaccharides. The computer program CASPER has been improved to assist in carbohydrate studies and in the long run make it possible to automatically determine structures based only on NMR data.

    Detailed computer studies of glycans can shed light on their interactions with proteins and help find inhibitors to prevent unwanted binding. The WaaG glycosyltransferase is important for the formation of E. coli lipopolysaccharides. Molecular docking analyses of structures confirmed to bind this enzyme have provided information on how inhibitors could be composed. Noroviruses cause gastroenteritis, such as the winter vomiting disease, after binding human histo-blood group antigens. In one of the projects, fragment-based docking, followed by molecular dynamics simulations and binding free energy calculations, was used to find competitive binders to the P domain of the capsid of the norovirus VA387. These novel structures have high affinity and are a very good starting point for developing drugs against noroviruses. The protein targets in these two projects are carbohydrate binding, but the techniques are general and can be applied to other research projects.

  • 131.
    Lundborg, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ali, Eunus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    An in silico virtual screening study for the design of norovirus inhibitors: fragment-based molecular docking and binding free energy calculations2013In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 378, p. 133-138Article in journal (Refereed)
    Abstract [en]

    Gastrointestinal infections caused by noroviruses may be prevented by the inhibition of their binding to histo-blood group carbohydrate antigens. A fragment-based virtual screening approach was used, employing docking followed by molecular dynamics simulations in order to enable binding free energy calculations using the linear interaction energy method. The resulting structures, composed of high-affinity fragments, can be a good starting point for lead optimizations and four molecules that pass both REOS and SYLVIA filters, which can remove known toxic features and assess the synthetic accessibility, respectively, are proposed as inhibitors.

  • 132. Mahanti, Bani
    et al.
    González Miera, Greco
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martínez-Castro, Elisa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bedin, Michele
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ott, Sascha
    Thapper, Anders
    Homogeneous Water Oxidation by Half-Sandwich Iridium(III) N-Heterocyclic Carbene Complexes with Pendant Hydroxy and Amino Groups2017In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 10, no 22, p. 4616-4623Article in journal (Refereed)
    Abstract [en]

    Herein, we report three (IrCp)-Cp-III* complexes with hydroxy-or amino-functionalized N-heterocyclic carbene (NHC) ligands that catalyze efficient water oxidation induced by addition of ceric ammonium nitrate (CAN). The pendant hydroxy or amino groups are very important for activity, and the complexes with heteroatom-functionalized NHC ligands show up to 15 times higher rates of oxygen evolution in CAN-induced water oxidation than a reference (IrCp)-Cp-III* complex without heteroatom functionalization. The formation of molecular high-valent Ir intermediates that are presumably involved in the rate-determining step for water oxidation is established by UV/Vis spectroscopy and ESI-MS under turnover conditions. The hydroxy groups on the NHC ligands, as well as chloride ligands on the iridium center are proposed to structurally stabilize the highvalent species, and thereby improve the catalytic activity. The Ir-III complex with a hydroxy-functionalized NHC shows the highest catalytic activity with a TON of 2500 obtained in 3 h and with >90% yield relative to the amount of oxidant used.

  • 133. Mally, Manuela
    et al.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    LeibundGut-Landmann, Salome
    Laacisse, Lamia
    Fan, Yao-Yun
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Aebi, Markus
    Glycoengineering of host mimicking type-2 LacNAc polymersand Lewis X antigens on bacterial cell surfaces2013In: Molecular Microbiology, ISSN 0950-382X, E-ISSN 1365-2958, Vol. 87, no 1, p. 112-131Article in journal (Refereed)
    Abstract [en]

    Bacterial carbohydrate structures play a central role in mediating a variety of host-pathogen interactions. Glycans can either elicit protective immune response or lead to escape of immune surveillance by mimicking host structures. Lipopolysaccharide (LPS), a major component on the surface of Gram-negative bacteria, is composed of a lipid A-core and the O-antigen polysaccharide. Pathogens like Neisseria meningitidis expose a lipooligosaccharide (LOS), which outermost glycans mimick mammalian epitopes to avoid immune recognition. Lewis X (Gal beta 1-4(Fuc alpha 1-3)GlcNAc) antigens of Helicobacter pylori or of the helminth Schistosoma mansoni modulate the immune response by interacting with receptors on human dendritic cells. In a glycoengineering approach we generate human carbohydrate structures on the surface of recombinant Gram-negative bacteria, such as Escherichia coli and Salmonella enterica sv. Typhimurium that lack O-antigen. A ubiquitous building block in mammalian N-linked protein glycans is Gal beta 1-4GlcNAc, referred to as a type-2 N-acetyllactosamine, LacNAc, sequence. Strains displaying polymeric LacNAc were generated by introducing a combination of glycosyltransferases that act on modified lipid A-cores, resulting in efficient expression of the carbohydrate epitope on bacterial cell surfaces. The poly-LacNAc scaffold was used as an acceptor for fucosylation leading to polymers of Lewis X antigens. We analysed the distribution of the carbohydrate epitopes by FACS, microscopy and ELISA and confirmed engineered LOS containing LacNAc and Lewis X repeats by MALDI-TOF and NMR analysis. Glycoengineered LOS induced pro-inflammatory response in murine dendritic cells. These bacterial strains can thus serve as tools to analyse the role of defined carbohydrate structures in different biological processes.

  • 134.
    Malmgren, Joel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Iodonium Salts: Preparation, Chemoselectivity and Metal-Catalyzed Applications2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns the preparation and use of diaryliodonium salts. In Project I various unsymmetrical diaryliodonium salts were reacted with three different nucleophiles in order to study the chemoselectivity of the reactions of the salts. The main focus of this project was to gain a deeper understanding of the underlying factors that affect the chemoselectivity in transition metal-free arylation reactions. They were found to be very nucleophile-dependent. Some nucleophiles were very sensitive to electronic effects, whereas others were sensitive to steric factors. Ultimately, some arenes are never transferred. A very interesting scrambling reaction was also observed under the reaction conditions, where unsymmetrical diaryliodonium salts form symmetrical salts in situ.

    Project II details the preparation of N-heteroaryliodonium salts via a one-pot procedure. The salts were designed so that the N-heteroaryl moiety was selectively transferred in applications both with and without transition metals. The chemoselectivity was demonstrated by selective transfer of the pyridyl group onto two different nucleophiles.

    The third project in the thesis discusses the synthesis of alkynyl(aryl)iodonium salts and alkynylbenziodoxolones from arylsilanes. This protocol could potentially be a very useful complement to the existing procedures, in which boronic acids are used.

    The last part of the thesis (Project IV) describes a C-2 selective arylation of indoles where diaryliodonium salts were used in combination with hetero-geneous palladium catalysis. This transformation was performed in water at ambient temperature to 50 °C, and tolerated variations of both the indole and the diaryliodonium salt. Importantly, several N-H indoles could be arylated. The MCF-supported Pd-catalyst showed very little leaching and it was demonstrated that the main part of the reaction occurred via heterogeneous catalysis.

  • 135.
    Malmgren, Joel
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nagendiran, Anuja
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    C-2 Selective Arylation of Indoles with Heterogeneous Nanopalladium and Diaryliodonium Salts2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 42, p. 13531-13535Article in journal (Refereed)
    Abstract [en]

    A simple and efficient method to prepare synthetically useful 2-arylindoles is presented, using a heterogeneous Pd catalyst and diaryliodonium salts in water under mild conditions. A remarkably low leaching of metal catalyst was observed under the applied conditions. The developed protocol is highly C-2 selective and tolerates structural variations both in the indole and in the diaryliodonium salt. Arylations of both NH indoles and N-protected indoles with ortho-substituted, electron-rich, electron-deficient, or halogenated diaryliodonium salts were achieved to give the desired products in high to excellent isolated yields within 6 to 15 h at room temperature or 40 °C.

  • 136.
    Malmgren, Joel
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Santoro, Stefano
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jalalian, Nazli
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Arylation with Unsymmetrical Diaryliodonium Salts: A Chemoselectivity Study2013In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 19, no 31, p. 10334-10342Article in journal (Refereed)
    Abstract [en]

    Phenols, anilines, and malonates have been arylated under metal-free conditions with twelve aryl(phenyl)iodonium salts in a systematic chemoselectivity study. A new “anti-ortho effect” has been identified in the arylation of malonates. Several “dummy groups” have been found that give complete chemoselectivity in the transfer of the phenyl moiety, irrespective of the nucleophile. An aryl exchange in the diaryliodonium salts has been observed under certain arylation conditions. DFT calculations have been performed to investigate the reaction mechanism and to elucidate the origins of the observed selectivities. These results are expected to facilitate the design of chiral diaryliodonium salts and the development of catalytic arylation reactions that are based on these sustainable and metal-free reagents.

  • 137.
    Manta, Bianca
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Quantum Chemical Studies of Enzymatic Reaction Mechanisms2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Computer modeling of enzymes is a valuable complement to experiments. Quantum chemical studies of enzymatic reactions can provide a detailed description of the reaction mechanism and elucidate the roles of various residues in the active site. Different reaction pathways can be analyzed, and their feasibility be established based on calculated energy barriers.

    In the present thesis, density functional theory has been used to study the active sites and reaction mechanisms of three different enzymes, cytosine deaminase (CDA) from Escherichia coli, ω-transaminase from Chromobacterium violaceum (Cv-ωTA) and dinitrogenase reductase-activating glycohydrolase (DraG) from Rhodospirillum rubrum. The cluster approach has been employed to design models of the active sites based on available crystal structures. The geometries and energies of transition states and intermediates along various reaction pathways have been calculated, and used to construct the energy graphs of the reactions.

    In the study of CDA (Paper I), two different tautomers of a histidine residue were considered. The obtained reaction mechanism was found to support the main features of the previously proposed mechanism. The sequence of the events was established, and the residues needed for the proton transfer steps were elucidated.

    In the study of Cv-ωTA (Paper II and Paper III), two active site models were employed to study the conversion of two different substrates, a hydrophobic amine and an amino acid. Differences and similarities in the reaction mechanisms of the two substrates were established, and the role of an arginine residue in the dual substrate recognition was confirmed.

    In the study of DraG (Paper IV), two different substrate-binding modes and two different protonation states of an aspartate residue were considered. The coordination of the first-shell ligands and the substrate to the two manganese ions in the active site was characterized, and a possible proton donor in the first step of the proposed reaction mechanism was identified.

  • 138.
    Marcos, Rocio
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Combined Enzyme and Transition-Metal Catalysis for Dynamic Kinetic Resolutions2012In: Israel Journal of Chemistry, ISSN 0021-2148, Vol. 52, no 7, p. 639-652Article, review/survey (Refereed)
    Abstract [en]

    The preparation of optically pure alcohols, axially chiral allenes, and amine derivatives by using enzymes and transition-metal catalysts through dynamic kinetic resolution (DKR) is reviewed. After a general introduction into enzymatic kinetic resolutions and racemizations catalyzed by transition-metal complexes, selected examples of DKRs are presented, from early work to more recent outstanding contributions, and also applications of this approach.

  • 139.
    Margarita, Cristiana
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Evolution and Prospects of the Asymmetric Hydrogenation of Unfunctionalized Olefins2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 4, p. 1346-1356Article in journal (Refereed)
    Abstract [en]

    The catalytic enantioselective hydrogenation of prochiral olefins is a key reaction in asymmetric synthesis. Its relevance applies to both industry and academia as an inherently direct and sustainable strategy to induce chirality. Here we briefly recount the early breakthroughs concerning the asymmetric hydrogenation of largely unfunctionalized olefins, from the first reports to the advent of chiral Crabtree-like catalysts. The mechanism and its implications on the enantioselectivity are shortly discussed. The main focus of this Perspective lies on the more recent advances in the field, such as the latest developed classes of ligands and the opportunity to employ more Earth-abundant metals. Therefore, separate sections consider iridium N,P-, NHC-, P,S-, and O,P catalysts, and rhodium, palladium, cobalt, and iron catalysts. Finally, the remaining unsolved challenges are examined, and the potential directions of forthcoming research are outlined.

  • 140.
    Martinez-Erro, Samuel
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bermejo Gómez, Antonio
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Vazquez-Romero, Ana
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Erbing, Elis
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    2,2-Diiododimedone: a mild electrophilic iodinating agent for the selective synthesis of alpha-iodoketones from allylic alcohols2017In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 53, no 71, p. 9842-9845Article in journal (Refereed)
    Abstract [en]

    2,2-Diiodo-5,5-dimethylcyclohexane-1,3-dione is reported as a new electrophilic iodinating agent that selectively iodinates electron-rich aromatics. In contrast to other common electrophilic iodinating reagents, its mild nature allows it to be used for the selective synthesis of alpha-iodinated carbonyl compounds from allylic alcohols through a 1,3-hydrogen shift/iodination process catalyzed by iridium(III) complexes.

  • 141.
    Martinez-Erro, Samuel
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sanz-Marco, Amparo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bermejo Gómez, Antonio
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Vazquez-Romero, Ana
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ahlquist, Mårten S. G.
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Base-Catalyzed Stereospecific Isomerization of Electron-Deficient Allylic Alcohols and Ethers through Ion-Pairing2016In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 138, no 40, p. 13408-13414Article in journal (Refereed)
    Abstract [en]

    A mild base-catalyzed strategy for the isomerization of allylic alcohols and allylic ethers has been developed. Experimental and computational investigations indicate that transition metal catalysts are not required when basic additives are present. As in the case of using transition metals under basic conditions, the isomerization catalyzed solely by base also follows a stereospecific pathway. The reaction is initiated by a rate-limiting deprotonation. Formation of an intimate ion pair between an allylic anion and the conjugate acid of the base results in efficient transfer of chirality. Through this mechanism, stereochemical information contained in the allylic alcohols is transferred to the ketone products. The stereospecific isomerization is also applicable for the first time to allylic ethers, yielding synthetically valuable enantioenriched (up to 97% ee) enol ethers.

  • 142.
    Mendoza, Abraham
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Colas, Kilian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Suarez-Pantiga, Samuel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Götz, Daniel C. G.
    Johansson, Magnus J.
    Chemical Innovation through Ligand Total Synthesis2016In: Synlett: Accounts and Rapid Communications in Synthetic Organic Chemistry, ISSN 0936-5214, E-ISSN 1437-2096, Vol. 27, no 12, p. 1753-1759Article in journal (Refereed)
    Abstract [en]

    Natural products are an abundant source of synthetic challenges that foster crucial breakthroughs in organic chemistry. Despite the superior complexity of these targets, ligand total synthesis can inspire solutions to unsolved chemical problems and provide access to creative catalyst designs. This Synpacts article presents a comparative analysis of natural and ligand total synthesis to provide a context for our recent research and motivate the importance of future undertakings in this area.

  • 143. Mensch, Carl
    et al.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johannessen, Christian
    Studying the Glycan Moiety of RNase B by Means of Raman and Raman Optical Activity2014In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 11, p. 2252-2254Article in journal (Refereed)
    Abstract [en]

    Raman and Raman optical activity (ROA) spectroscopy are used to study the solution-phase structure of the glycan moiety of the protein ribonuclease B (RNase B). Spectral data of the intact glycan moiety of RNase B is obtained by subtracting high-quality spectral data of RNase A, the non-glycosylated form of the RNase, from the spectra of the glycoprotein. The remaining difference spectra are compared to spectra generated from Raman and ROA data of the constituent disaccharides of the RNase glycan, achieving convincing spectral overlap. The results show that ROA spectroscopy is able to extract detailed spectral data of the glycan moieties of proteins, provided that the non-glycosylated isoform is available. Furthermore, good comparison between the full glycan spectrum and the regenerated spectra based on the disaccharide data lends great promise to ROA as a tool for the solution-phase structural analysis of this structurally elusive class of biomolecules.

  • 144.
    Merritt, Eleanor A.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Malmgren, Joel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Klinke, Felix J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of diaryliodonium triflates using environmentally benign oxidizing agents2009In: Synlett: Accounts and Rapid Communications in Synthetic Organic Chemistry, ISSN 0936-5214, E-ISSN 1437-2096, no 14, p. 2277-2280Article in journal (Refereed)
  • 145.
    Merritt, Eleanor A.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    α-Functionalization of carbonyl compounds using hypervalent iodine reagents2011In: Synthesis (Stuttgart), ISSN 0039-7881, E-ISSN 1437-210X, no 4, p. 517-538Article in journal (Refereed)
    Abstract [en]

    α-Functionalized carbonyl compounds are versatile intermediates in organic synthesis. A broad range of both carbon and heteroatom substituents can be introduced into the α-position of carbonyl compounds using hypervalent iodine reagents. Herein we summarize the use of these environmentally benign reagents with particular emphasis on catalytic and asymmetric methodology developed over the past decade.

  • 146.
    Moa, Sara
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Quantum chemical modelling of enantioselectivity in alcohol dehydrogenase2017Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Biocatalytic methods of synthesis are becoming increasingly important in industry. Using enzymes as catalysts allows highly selective reactions to be performed under milder physical conditions and in a more environmentally benign fashion than most corresponding chemical catalysts.

    Enzymes have in general evolved to perform one type of reaction on a limited set of molecules, and hence there is often a need to alter the specificity of an enzyme to suit a desired process. Understanding the details of enzymatic catalysis at a quantum mechanical level enables the intelligent redesign of these macromolecules. For this purpose, density functional theory (DFT) has been shown to epitomise a suitable balance of accuracy and computational cost. Thus, this thesis describes the quantum chemical rationalisation of the reaction mechanism and sources of selectivity of the bacterial alcohol dehydrogenase TbSADH – an enzyme highly suited to modification for industrial processes.

    ADHs catalyse reversibly the interconversion of alcohols and ketones or aldehydes. Herein, the general ADH reaction mechanism was shown to be viable for this enzyme. In addition, the experimental enantiopreference of the enzyme was reproduced, and thus the reversal of selectivity seen with the slight increase in substrate size was captured. The main determinant of selectivity was found to be a fine balance of repulsive steric interactions and attractive dispersion effects between the substrate and the hydrophobic binding pockets. The ability of the modelling methodology to capture effects such as these represents further evidence of its usefulness as a complement to experimental work in designing the biocatalysts of the future.

    The development of protocols to allow quantum mechanical investigation of the production of large and industrially interesting axially chiral alcohols is also presented. The work described has showed that quantum chemical models of many hundreds of atoms are now within our grasp, and although they were unable to correctly describe the selectivity for the large 4-(bromomethylene)cyclohexan-1-one in TbSADH, the protocols devised can be very useful for future investigations of enzymatic catalysis.

  • 147.
    Mobarak, Hani
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis and analysis of carbohydrates related to bacterial polysaccharides2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The outer surface of bacteria is composed of around 75% carbohydrates, which are vital for the bacteria to survive and communicate with the host biological system. The thesis discusses different properties of carbohydrates that are essential for understanding the bacterial behavior in biological systems. The first three chapters give an overview of carbohydrates.

    The fourth chapter discusses the synthesis of four amide-substituted 3,6-dideoxy-α-D-galactopyranosides, namely, methyl α-3,6-dideoxy-3-formamido-, acetamido-, (R)-3-hydroxybutyramido-, and (4-hydroxybutyramido)-D-galactopyranoside. These sugars were found as components of some bacterial O-antigens; the study is a step toward the synthesis of oligosaccharides that contain them. The fifth chapter describes the exchange kinetics of the formyl and acetyl derivatives that were synthesized. Both of them have two conformational states for the amide side-chain. 13C-NMR saturation transfer experiments are utilized for these measurements to reveal more about their properties in solution.

    In chaptr six, NMR and conformational analysis of oligosaccharides related to the O-antigen of Yersinia enterocolitica O:3 bacteria were carried out to obtain more information regarding their 3D structure.

    Chapter seven is focusing on the development of CASPER, a program for rapid assignment of 1H- and 13C-NMR chemical shifts of bacterial lipopolysaccharides, by adding more sugars into its database and testing it for naturally occurring LPS as well as extending the scope for synthetic carbohydrates, which is planned to be developed further in the future.

  • 148.
    Nagendiran, Anuja
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic reactions with palladium supported on mesocellular foam: Applications in hydrogenation, isomerization, and C-C bond forming reactions2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The major part of this thesis concerns the development of catalytic methodologies based on palladium nanoparticles immobilized on aminopropyl-functionalized siliceous mesocellular foam (Pd0-AmP-MCF). The catalytic activity of the precursor to the nanocatalyst, PdII-AmP-MCF is also covered by this work.

    In the first part the application of Pd0-AmP-MCF in Suzuki-Miyaura cross-coupling reactions and transfer hydrogenation of alkenes under microwave irradiation is described. Excellent reactivity was observed and a broad range of substrates were tolerated for both transformations. The Pd0-AmP-MCF exhibited high recyclability as well as low metal leaching in both cases.

    The aim of the second part was to evaluate the catalytic efficiency of the closely related PdII-AmP-MCF for cycloisomerization of various acetylenic acids. The catalyst was able to promote formation of lactones under mild conditions using catalyst loadings of 0.3 - 0.5 mol% at temperatures of up to 50 oC in the presence of Et3N. By adding 1,4-benzoquinone to the reaction, the catalyst could be recycled four times without any observable decrease in the activity.

    The selective arylation of indoles at the C-2 position using Pd-AmP-MCF and symmetric diaryliodonium salts is presented in the third part. These studies revealed that Pd0-AmP-MCF was more effective than PdII-AmP-MCF for this transformation. Variously substituted indoles as well as diaryliodonium salts were tolerated, giving arylated indoles in high yields within 15 h at 20 - 50 oC in H2O. Only very small amounts of Pd leaching were observed and in this case the catalyst exhibited moderate recyclability.

    The final part of the thesis describes the selective hydrogenation of the C=C in different α,β-unsaturated systems. The double bond was efficiently hydrogenated in high yields both under batch and continuous-flow conditions. High recyclability and low metal leaching were observed in both cases.

  • 149.
    Nagendiran, Anuja
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pascanu, Vlad
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bermejo Gómez, Antonio
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    González Miera, Greco
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mild and Selective Catalytic Hydrogenation of the C=C Bond in a,b-Unsaturated Carbonyl Compounds Using Supported Palladium Nanoparticles2016In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 22, no 21, p. 7184-7189Article in journal (Refereed)
    Abstract [en]

    Chemoselective reduction of the C=C bond in a variety of α,β-unsaturated carbonyl compounds using supported palladium nanoparticles is reported. Three different heterogeneous catalysts were compared using 1 atm of H2: 1) nano-Pd on a metal–organic framework (MOF: Pd0-MIL-101-NH2(Cr)), 2) nano-Pd on a siliceous mesocellular foam (MCF: Pd0-AmP-MCF), and 3) commercially available palladium on carbon (Pd/C). Initial studies showed that the Pd@MOF and Pd@MCF nanocatalysts were superior in activity and selectivity compared to commercial Pd/C. Both Pd0-MIL-101-NH2(Cr) and Pd0-AmP-MCF were capable of delivering the desired products in very short reaction times (10–90 min) with low loadings of Pd (0.5–1 mol %). Additionally, the two catalytic systems exhibited high recyclability and very low levels of metal leaching.

  • 150.
    Nagendiran, Anuja
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Haller, Clemence
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johnston, Eric V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Cycloisomerization of Acetylenic Acids to gamma-Alkylidene Lactones using a Palladium(II) Catalyst Supported on Amino-Functionalized Siliceous Mesocellular Foam2014In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 79, no 3, p. 1399-1405Article in journal (Refereed)
    Abstract [en]

    Cycloisomerization of various gamma-acetylenic acids to their corresponding gamma-alkylidene lactones by the use of a heterogeneous Pd(II) catalyst supported on amino-functionalized siliceous mesocellular foam is described. Substrates containing terminal as well as internal alkynes were cyclized in high to excellent yields within 2-24 h under mild reaction conditions. The protocol exhibited high regio- and stereoselectivity, favoring the exo-dig product with high Z selectivity. Moreover, the catalyst displayed excellent stability under the employed reaction conditions, as demonstrated by its good recyclability and low leaching.

123456 101 - 150 of 257
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf