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  • 351.
    Gustafson, Karl P. J.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Görbe, Tamás
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    de Gonzalo-Calvo, Gonzalo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yuan, Ning
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Swedish University of Agricultural Sciences, Sweden.
    Schreiber, Cynthia L.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Shchukarev, Andrey
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Persson, Ingmar
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Chemoenzymatic Dynamic Kinetic Resolution of Primary Benzylic Amines using Pd-0-CalB CLEA as a Biohybrid Catalyst2019In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 25, no 39, p. 9174-9179Article in journal (Refereed)
    Abstract [en]

    Herein, we report on the use a biohybrid catalyst consisting of palladium nanoparticles immobilized on cross-linked enzyme aggregates of lipase B of Candida antarctica (CalB CLEA) for the dynamic kinetic resolution (DKR) of benzylic amines. A set of amines were demonstrated to undergo an efficient DKR and the recyclability of the catalysts was studied. Extensive efforts to further elucidate the structure of the catalyst are presented.

  • 352.
    Gustafson, Karl P. J.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lihammar, Richard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Engström, Karin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Chemoenzymatic Dynamic Kinetic Resolution of Primary Amines Using a Recyclable Palladium Nanoparticle Catalyst Together with Lipases2014In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 79, no 9, p. 3747-3751Article in journal (Refereed)
    Abstract [en]

    A catalyst consisting of palladium nanoparticles supported on amino-functionalized siliceous mesocellular foam (Pd-AmP-MCF) was used in chemoenzymatic dynamic kinetic resolution (DKR) to convert primary amines to amides in high yields and excellent ee's. The efficiency of the nanocatalyst at temperatures below 70 degrees C enables reaction conditions that are more suitable for enzymes. In the present study, this is exemplified by subjecting 1-phenylethylamine (1a) and analogous benzylic amines to DKR reactions using two commercially available lipases, Novozyme-435 (Candida antartica Lipase B) and Amano Lipase PS-C1 (lipase from Burkholderia cepacia) as biocatalysts. The latter enzyme has not previously been used in the DKR of amines because of its low stability at temperatures over 60 degrees C. The viability of the heterogeneous Pd-AmP-MCF was further demonstrated in a recycling study, which shows that the catalyst can be reused up to five times.

  • 353.
    Gustafson, Karl P. J.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Shatskiy, Andrey
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kärkäs, Markus D.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Schluschass, Bastian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johnston, Eric V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Water oxidation mediated by ruthenium oxide nanoparticles supported on siliceous mesocellular foam2017In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 7, no 1, p. 293-299Article in journal (Refereed)
    Abstract [en]

    Artificial photosynthesis is an attractive strategy for converting solar energy into fuel. In this context, development of catalysts for oxidation of water to molecular oxygen remains a critical bottleneck. Herein, we describe the preparation of a well-defined nanostructured RuO2 catalyst, which is able to carry out the oxidation of water both chemically and photochemically. The developed heterogeneous RuO2 nanocatalyst was found to be highly active, exceeding the performance of most known heterogeneous water oxidation catalysts when driven by chemical or photogenerated oxidants.

  • 354.
    Gustafsson, Mikaela
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bartoszewicz, Agnieszka
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhao, Tony
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Li, Zhongyue
    Zhu, Guangshan
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    A family of highly stable lanthanide metal-organic frameworks: structural evolution and catalytic activity2010In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 22, no 11, p. 3316-3322Article in journal (Refereed)
    Abstract [en]

    A family of homeotypic porous lanthanide metal−organic frameworks (MOFs), [Ln(btc)(H2O)]·guest (Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Ho (6), Er (7), and Yb (8); guest: DMF or H2O) was synthesized. The structures of the as-synthesized compounds are tetragonal and contain 1D channels with accessible lanthanide ions. In situ single crystal X-ray diffraction shows that 1 undergoes a single-crystal to polycrystalline to single-crystal transformation from room temperature to 180 °C. During the release of DMF and water molecules from the channels by evacuation and subsequent heating, the structures of 1 and 7 transformed from tetragonal to monoclinic, and then to tetragonal, while the structure of 8 remained tetragonal. The transformation between the monoclinic and the low temperature tetragonal phases is reversible. The Ln(btc) MOFs are stable to at least 480 °C and are among the most thermally stable MOFs. The Ln(btc) MOFs act as efficient Lewis acid catalysts for the cyanosilylation of aldehydes yielding cyanohydrins in high yields within short reaction times. 1 also catalyzes the cyanosilylation of less reactive substrates, such as ketones at room temperature. The Ln(btc) MOFs could be recycled and reused without loss of their crystallinity and activity.

  • 355. Gustafsson, Nina M. S.
    et al.
    Färnegårdh, Katarina
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Science for Life Laboratory (SciLifeLab). Kancera AB, Sweden.
    Bonagas, Nadilly
    Ninou, Anna Huguet
    Groth, Petra
    Wiita, Elisee
    Jönsson, Mattias
    Hallberg, Kenth
    Lehto, Jemina
    Pennisi, Rosa
    Martinsson, Jessica
    Norström, Carina
    Hollers, Jessica
    Schultz, Johan
    Andersson, Martin
    Markova, Natalia
    Marttila, Petra
    Kim, Baek
    Norin, Martin
    Olin, Thomas
    Helleday, Thomas
    Targeting PFKFB3 radiosensitizes cancer cells and suppresses homologous recombination2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 3872Article in journal (Refereed)
    Abstract [en]

    The glycolytic PFKFB3 enzyme is widely overexpressed in cancer cells and an emerging anticancer target. Here, we identify PFKFB3 as a critical factor in homologous recombination (HR) repair of DNA double-strand breaks. PFKFB3 rapidly relocates into ionizing radiation (IR)-induced nuclear foci in an MRN-ATM-gamma H2AX-MDC1-dependent manner and co-localizes with DNA damage and HR repair proteins. PFKFB3 relocalization is critical for recruitment of HR proteins, HR activity, and cell survival upon IR. We develop KAN0438757, a small molecule inhibitor that potently targets PFKFB3. Pharmacological PFKFB3 inhibition impairs recruitment of ribonucleotide reductase M2 and deoxynucleotide incorporation upon DNA repair, and reduces dNTP levels. Importantly, KAN0438757 induces radiosensitization in transformed cells while leaving non-transformed cells unaffected. In summary, we identify a key role for PFKFB3 enzymatic activity in HR repair and present KAN0438757, a selective PFKFB3 inhibitor that could potentially be used as a strategy for the treatment of cancer.

  • 356.
    Gustafsson, Robert
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Jemth, Ann-Sofie
    Gustafsson, Nina M. S.
    Färnegårdh, Katarina
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Loseva, Olga
    Wiita, Elisée
    Bonagas, Nadilly
    Dahllund, Leif
    Llona-Minguez, Sabin
    Häggblad, Maria
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Henriksson, Martin
    Andersson, Yasmin
    Homan, Evert
    Helleday, Thomas
    Stenmark, Pal
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Crystal Structure of the Emerging Cancer Target MTHFD2 in Complex with a Substrate-Based Inhibitor2017In: Cancer Research, ISSN 0008-5472, E-ISSN 1538-7445, Vol. 77, no 4, p. 937-948Article in journal (Refereed)
    Abstract [en]

    To sustain their proliferation, cancer cells become dependent on one-carbon metabolism to support purine and thymidylate synthesis. Indeed, one of the most highly upregulated enzymes during neoplastic transformation is MTHFD2, a mitochondrial methylenetetrahydrofolate dehydrogenase and cyclohydrolase involved in one-carbon metabolism. Because MTHFD2 is expressed normally only during embryonic development, it offers a disease-selective therapeutic target for eradicating cancer cells while sparing healthy cells. Here we report the synthesis and preclinical characterization of the first inhibitor of human MTHFD2. We also disclose the first crystal structure of MTHFD2 in complex with a substrate-based inhibitor and the enzyme cofactors NAD(+) and inorganic phosphate. Our work provides a rationale for continued development of a structural framework for the generation of potent and selective MTHFD2 inhibitors for cancer treatment.

  • 357.
    Guđmundsson, Arnar
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gustafson, Karl P. J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mai, Binh Khanh
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hobiger, Viola
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Diastereoselective Synthesis of N-Protected 2,3-Dihydropyrroles via Iron-Catalyzed Cycloisomerization of alpha-Allenic Sulfonamides2019In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 9, no 3, p. 1733-1737Article in journal (Refereed)
    Abstract [en]

    Herein, we report the synthesis of 2,3-dihydropyrroles via an iron-catalyzed intramolecular nucleophilic cyclization of alpha-allenic sulfonamides. A highly diastereoselective variant of the reaction was also developed with the use of 1,2-disubstituted allenamides, which afforded 2,3-dihydropyrroles with diastereomeric ratios of >98:2. Insight into the mechanism was gained through a detailed DFT study, which elucidates the reaction mechanism and rationalizes the high chemoselectivity and diastereoselectivity.

  • 358.
    Görbe, Tamás
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gustafson, Karl P. J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kervefors, Gabriella
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zheng, Haoquan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Johnston, Eric V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Design of a Pd(0)-CalB CLEA Biohybrid Catalyst and Its Application in a One-Pot Cascade Reaction2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 3, p. 1601-1605Article in journal (Refereed)
    Abstract [en]

    Herein, a design of a biohybrid catalyst is described, consisting of Pd nanoparticles and a cross-linked network of aggregated lipase B enzyme of Candida antarctica (CalB CLEA) functioning as an active support for the Pd nanoparticles. Both entities of the hybrid catalyst showed good catalytic activity. The applicability was demonstrated in a one-pot reaction, where the Pd-catalyzed cycloisomerization of 4-pentynoic acid afforded a lactone that serves as an acyl donor in a subsequent selective enzymatic kinetic resolution of a set of sec-alcohols. The catalyst proved to be robust and could be recycled five times without a significant loss of activity.

  • 359.
    Görbe, Tamás
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lihammar, Richard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Heterogeneous Acid-Catalyzed Racemization of Tertiary Alcohols2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 1, p. 77-80Article in journal (Refereed)
    Abstract [en]

    Tertiary alcohols are important structural motifs in natural products and building blocks in organic synthesis but only few methods are known for their enantioselective preparation. Chiral resolution is one of these approaches that leaves one enantiomer (50% of the material) unaffected. An attractive method to increase the efficiency of those resolutions is to racemize the unaffected enantiomer. In the present work, we have developed a practical racemization protocol for tertiary alcohols. Five different acidic resin materials were tested. The Dowex 50WX8 was the resin of choice since it was capable of racemizing tertiary alcohols without any byproduct formation. Suitable solvents and a biphasic system were investigated, and the optimized system was capable of racemizing differently substituted tertiary alcohols.

  • 360. Hafrén, Jonas
    et al.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Direct Bronsted acid-catalyzed derivatization of cellulose with poly(L-lactic acid) and D-mandelic acid2007In: Nordic Pulp and Paper Research Journal, ISSN 0283-2631, Vol. 22, no 2, p. 184-187Article in journal (Refereed)
  • 361. Hakkarainen, Birgit
    et al.
    Kenne, Lennart
    Lahmann, Martina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Oscarson, Stefan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sandström, Corine
    Spectral assignments and reference data: NMR study of hydroxy protons of di- and trimannosides, substructures of Man-92007In: Magnetic Resonance in Chemistry, ISSN 0749-1581, Vol. 45, no 12, p. 1076-1080Article in journal (Refereed)
  • 362.
    Hamark, Christoffer
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Berntsson, Ronnie P. -A.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Masuyer, Geoffrey
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Henriksson, Linda M.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Gustafsson, Robert
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Stenmark, Pål
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Glycans Confer Specificity to the Recognition of Ganglioside Receptors by Botulinum Neurotoxin A2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 1, p. 218-230Article in journal (Refereed)
    Abstract [en]

    The highly poisonous botulinum neurotoxins, produced by the bacterium Clostridium botulinum, act on their hosts by a high-affinity association to two receptors on neuronal cell surfaces as the first step of invasion. The glycan motifs of gangliosides serve as initial coreceptors for these protein complexes, whereby a membrane protein receptor is bound. Herein we set out to characterize the carbohydrate minimal binding epitope of the botulinum neurotoxin serotype A. By means of ligand-based NMR spectroscopy, X-ray crystallography, computer simulations, and isothermal titration calorimetry, a screening of ganglioside analogues together with a detailed characterization of various carbohydrate ligand complexes with the toxin were accomplished. We show that the representation of the glycan epitope to the protein affects the details of binding. Notably, both branches of the oligosaccharide GD la can associate to botulinum neurotoxin serotype A when expressed as individual trisaccharides. It is, however, the terminal branch of GD1a as well as this trisaccharide motif alone, corresponding to the sialyl-Thomsen-Friedenreich antigen, that represents the active ligand epitope, and these compounds bind to the neurotoxin with a high degree of predisposition but with low affinities. This finding does not correlate with the oligosaccharide moieties having a strong contribution to the total affinity, which was expected to be the case. We here propose that the glycan part of the ganglioside receptors mainly provides abundance and specificity, whereas the interaction with the membrane itself and protein receptor brings about the strong total binding of the toxin to the neuronal membrane.

  • 363.
    Hamark, Christoffer
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Landström, Jens
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ethyl 3,6-di-O-benzyl-2-deoxy-N-phthalimido-1-thio-β-D-glucopyranoside2010In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. E66, p. o3250-o3251Article in journal (Refereed)
    Abstract [en]

    In the title compound, C30H31NO6S, the plane of the N-phthalimido group is nearly orthogonal to the least-squares plane of the sugar ring (defined by atoms C2, C3, C5 and O5 using standard glucose nomenclature), making a dihedral angle of 72.8 (1)°. The thioethyl group has the exo-anomeric conformation. The hydroxy group forms an intermolecular hydrogen bond to the O atom in the sugar ring, generating [100] chains. There are four close - contacts with centroid-centroid distances less than 4.0 Å, all with dihedral angles between the interacting systems of only 8°, supporting energetically favourable stacking interactions

  • 364.
    Hamark, Christoffer
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Landström, Jens
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ethyl 4,6-O-benzylidene-2-deoxy-N-phthalimido-1-thio-β-D-glucopyranoside2010In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. E66, p. o3249-Article in journal (Refereed)
  • 365.
    Hamark, Christoffer
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Landström, Jens
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    SEAL by NMR: Glyco-Based Selenium-Labeled Affinity Ligands Detected by NMR Spectroscopy2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 43, p. 13905-13908Article in journal (Refereed)
    Abstract [en]

    We report a method for the screening of interactions between proteins and selenium-labeled carbohydrate ligands. SEAL by NMR is demonstrated with selenoglycosides binding to lectins where the selenium nucleus serves as an NMR-active handle and reports on binding through Se-77 NMR spectroscopy. In terms of overall sensitivity, this nucleus is comparable to C-13 NMR, while the NMR spectral width is ten times larger, yielding little overlap in Se-77 NMR spectroscopy, even for similar compounds. The studied ligands are singly selenated bioisosteres of methyl glycosides for which straightforward preparation methods are at hand and libraries can readily be generated. The strength of the approach lies in its simplicity, sensitivity to binding events, the tolerance to additives and the possibility of having several ligands in the assay. This study extends the increasing potential of selenium in structure biology and medicinal chemistry. We anticipate that SEAL by NMR will be a beneficial tool for the development of selenium-based bioactive compounds, such as glycomimetic drug candidates.

  • 366.
    Hamark, Christoffer
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Landström, Jens
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dotson Fagerström, Alexandra
    Sandgren, Mats
    Ståhlberg, Jerry
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Enantioselective Binding of Propranolol and Analogues Thereof to Cellobiohydrolase Cel7A2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 68, p. 17975-17985Article in journal (Refereed)
    Abstract [en]

    At the catalytic site for the hydrolysis of cellulose the enzyme cellobiohydrolase Cel7A binds the enantiomers of the adrenergic beta-blocker propranolol with different selectivity. Methyl-to-hydroxymethyl group modifications of propranolol, which result in higher affinity and improved selectivity, were herein studied by H-1,H-1 and H-1,C-13 scalar spin-spin coupling constants as well as utilizing the nuclear Overhauser effect (NOE) in conjunction with molecular dynamics simulations of the ligands per se, which showed the presence of all-antiperiplanar conformations, except for the one containing a vicinal oxygen-oxygen arrangement governed by the gauche effect. For the ligand-protein complexes investigated by NMR spectroscopy using, inter alia, transferred NOESY and saturation-transfer difference (STD) NMR experiments the S-isomers were shown to bind with a higher affinity and a conformation similar to that preferred in solution, in contrast to the R-isomer. The fact that the S-form of the propranolol enantiomer is pre-arranged for binding to the protein is also observed for a crystal structure of dihydroxy-(S)-propranolol and Cel7A presented herein. Whereas the binding of propranolol is entropy driven, the complexation with the dihydroxy analogue is anticipated to be favored also by an enthalpic term, such as for its enantiomer, that is, dihydroxy-(R)-propranolol, because hydrogen-bond donation replaces the corresponding bonding from hydroxyl groups in glucosyl residues of the natural substrate. In addition to a favorable entropy component, albeit lesser in magnitude, this represents an effect of enthalpy-to-entropy compensation in ligand-protein interactions.

  • 367. Hammar, Peter
    et al.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Density functional theory study of the stereoselectivity in small peptide-catalyzed intermolecular aldol reactions2008In: Tetrahedron: Asymmetry, ISSN 0957-4166, Vol. 19, no 13, p. 1617-1621Article in journal (Refereed)
  • 368. Hammarström, Lars G. J.
    et al.
    Harmel, Robert K.
    Granath, Mikael
    Ringom, Rune
    Gravenfors, Ylva
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Färnegårdh, Katarina
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Svensson, Per H.
    Wennman, David
    Lundin, Göran
    Roddis, Ylva
    Kitambi, Satish S.
    Bernlind, Alexandra
    Lehmann, Fredrik
    Ernfors, Patrik
    The Oncolytic Efficacy and in Vivo Pharmacokinetics of [2-(4-Chlorophenyl)quinolin-4-yl](piperidine-2-yl)methanol (Vacquinol-1) Are Governed by Distinct Stereochemical Features2016In: Journal of Medicinal Chemistry, ISSN 0022-2623, E-ISSN 1520-4804, Vol. 59, no 18, p. 8577-8592Article in journal (Refereed)
    Abstract [en]

    Glioblastoma remains an incurable brain cancer. Drugs developed in the past 20 years have not improved the prognosis for patients, necessitating the development of new treatments. We have previously reported the therapeutic potential of the quinoline methanol Vacquinol-1 (1) that targets glioblastoma cells and induces cell death by catastrophic vacuolization. Compound 1 is a mixture of four stereoisomers due to the two adjacent stereogenic centers in the molecule, complicating further development in the preclinical setting. This work describes the isolation and characterization of the individual isomers of 1 and shows that these display stereospecific pharmacokinetic and pharmacodynamic features. In addition, we present a stereoselective synthesis of the active isomers, providing a basis for further development of this compound series into a novel experimental therapeutic for glioblastoma.

  • 369. Harper, James K.
    et al.
    Tishler, Derek
    Richardson, David
    Lokvam, John
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Solid-State NMR Characterization of the Molecular Conformation in Disordered Methyl alpha-L-Rhamnofuranoside2013In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 117, no 26, p. 5534-5541Article in journal (Refereed)
    Abstract [en]

    A combination of solid-state C-13 NMR tensor data and DFT computational methods is utilized to predict the conformation in disordered methyl alpha-L-rhamnofuranoside. This previously uncharacterized solid is found to be crystalline and consists of at least six distinct conformations that exchange on the kHz time scale. A total of 66 model structures were evaluated, and six were identified as being consistent with experimental C-13 NMR data. All feasible structures have very similar carbon and oxygen positions and differ most significantly in OH hydrogen orientations. A concerted rearrangement of OH hydrogens is proposed to account for the observed dynamic disorder. This rearrangement is accompanied by smaller changes in ring conformation and is slow enough to be observed on the NMR time scale due to severe steric crowding among ring substituents. The relatively minor differences in non-hydrogen atom positions in the final structures suggest that characterization of a complete crystal structure by X-ray powder diffraction may be feasible.

  • 370. Harvey, Jeremy N.
    et al.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Maseras, Feliu
    Perrin, Lionel
    Scope and Challenge of Computational Methods for Studying Mechanism and Reactivity in Homogeneous Catalysis2019In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 9, no 8, p. 6803-6813Article in journal (Refereed)
    Abstract [en]

    Computational methods based on quantum mechanical modeling are increasingly used to provide insight into mechanistic aspects of homogeneous catalysis. While the potential and value of such methods are obvious, it is also clear that it remains challenging to obtain reliable and predictive mechanistic insights from modeling. In this Perspective, we assess the various factors influencing the quality of computational studies. While the type of electronic structure theory methodology used is of course of great importance, we argue that many other aspects can play a large role also. The other factors emphasized here include the treatment of entropic effects, solvation, the choice of the structural model, conformational complexity, the translation of computed relative Gibbs energies into a kinetic model, and the high demands required for the prediction of selectivity.

  • 371. Hatcher, Elizabeth
    et al.
    Säwén, Elin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    MacKerell, Jr., Alexander D.
    Conformational properties of methyl β-maltoside and methyl α- and β-cellobioside disaccharides2011In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 115, no 3, p. 597-608Article in journal (Refereed)
    Abstract [en]

    An investigation of the conformational properties of methyl β-maltoside, methyl α-cellobioside, and methyl β-cellobioside disaccharides using NMR spectroscopy and molecular dynamics (MD) techniques, is presented. Emphasis is placed on validation of a recently presented force field for hexopyranose disaccharides followed by elucidation of the conformational properties of two different types of glycosidic linkages, α-(1 → 4) and β-(1 → 4). Both gas-phase and aqueous-phase simulations are performed to gain insight into the effect of solvent on the conformational properties. A number of transglycosidic J-coupling constants and proton−proton distances are calculated from the simulations and are used to identify the percent sampling of the three glycosidic conformations (syn, anti-, and anti-ψ) and, in turn, describe the flexibility around the glycosidic linkage. The results show the force field to be in overall good agreement with experiment, although some very small limitations are evident. Subsequently, a thorough hydrogen bonding analysis is performed to obtain insights into the conformational properties of the disaccharides. In methyl β-maltoside, competition between HO2′−O3 intramolecular hydrogen bonding and intermolecular hydrogen bonding of those groups with solvent leads to increased sampling of syn, anti-, and anti-ψ conformations and better agreement with NMR J-coupling constants. In methyl α- and β-cellobioside, O5′−HO6 and HO2′−O3 hydrogen bonding interactions are in competition with intermolecular hydrogen bonding involving the solvent molecules. This competition leads to retention of the O5′−HO3 hydrogen bond and increased sampling of the syn region of the /ψ map. Moreover, glycosidic torsions are correlated to the intramolecular hydrogen bonding occurring in the molecules. The present results verify that in the β-(1 → 4)-linkage intramolecular hydrogen bonding in the aqueous phase is due to the decreased ability of water to successfully compete for the O5′ and HO3 hydrogen bonding moieties, in contrast to that occurring between the O5′ and HO6 atoms in this α-(1 → 4)-linkage.

  • 372. Hayashi, Yukiko
    et al.
    Santoro, Stefano
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Azuma, Yuki
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ohshima, Takashi
    Mashima, Kazushi
    Enzyme-Like Catalysis via Ternary Complex Mechanism: Alkoxy-Bridged Dinuclear Cobalt Complex Mediates Chemoselective O-Esterification over N-Amidation2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 16, p. 6192-6199Article in journal (Refereed)
    Abstract [en]

    Hydroxy group-selective acylation in the presence of more nucleophilic amines was achieved using acetates of first-row late transition metals, such as Mn, Fe, Co, Cu, and Zn. Among them, cobalt(II) acetate was the best catalyst in terms of reactivity and selectivity. The combination of an octanuclear cobalt carboxylate cluster [Co-4(OCOR)(6)O](2) (2a: R = CF3, 2b: R = CH3, 2c: R = Bu-t) with nitrogen-containing ligands, such as 2,2'-bipyridine, provided an efficient catalytic system for transesterification, in which an alkoxide-bridged dinuclear complex, Co-2((OCOBu)-Bu-t)(2)-(bpy)(2)(mu(2)-OCH2-C6H4-4-CH3)(2) (10), was successfully isolated as a key intermediate. Kinetic studies and density functional theory calculations revealed Michaelis-Menten behavior of the complex 10 through an ordered ternary complex mechanism similar to dinuclear metallo-enzymes, suggesting the formation of alkoxides followed by coordination of the ester.

  • 373. He, Xibing
    et al.
    Hatcher, Elizabeth
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    MacKerell, Alexander D., Jr.
    Bifurcated Hydrogen Bonding and Asymmetric Fluctuations in a Carbohydrate Crystal Studied via X-ray Crystallography and Computational Analysis2013In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 117, no 25, p. 7546-7553Article in journal (Refereed)
    Abstract [en]

    The structure of the O-methyl glycoside of the naturally occurring 6-O-[(R)-1-carboxyethyl]-alpha-D-galactopyranose, C10H18O8, has been determined by X-ray crystallography at 100 K, supplementing the previously determined structure obtained at 293 K (Acta Crystallogr. 1996, C52, 2285-2287). Molecular dynamics simulations of this glycoside were Performed in the crystal environment with different numbers of units cells included in the primary simulation system at both 100 and 293 K. The Calculated unit cell Parameters and the intramolecular geometries (bonds, angles, and dihedrals) agree well with experimental results. Atomic fluctuations, including B-factors and anisotropies, are in good agreement with respect to the relative values on an atom-by-atom basis. In addition, the fluctuations increase with increasing simulation system size, with the simulated values converging to values lower than those observed experimentally indicating that the simulation model is not accounting for all possible contributions to the experimentally observed B-factors, which may be related to either the simulation time scale or size. In the simulation's, the hydroxyl group of O7 is found to from bifurcated hydrogen bonds with O6 and O8 of an adjacent molecule, with the interactions dominated by the interaction HO7-O6 interaction. Quantum mechanical calculations support this observation.

  • 374.
    Henry, Jeffrey L.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Posevins, Daniels
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Bin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Qiu, Youai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Highly Selective Olefin-Assisted Pd-II-Catalyzed Oxidative Alkynylation of Enallenes2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 33, p. 7896-7899Article in journal (Refereed)
    Abstract [en]

    An olefin-assisted, palladium-catalyzed oxidative alkynylation of enallenes for regio- and stereoselective synthesis of substituted trienynes has been developed. The reaction shows a broad substrate scope and good tolerance for various functional groups on the allene moiety, including carboxylic acid esters, free hydroxyls, imides, and alkyl groups. Also, a wide range of terminal alkynes with electron-donating and electron-withdrawing aryls, heteroaryls, alkyls, trimethylsilyl, and free hydroxyl groups are tolerated.

  • 375. Hernández-Toribio, Jorge
    et al.
    Gómez Arrayás, Ramón
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Carretero, Juan C.
    Catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides with α,β-unsaturated ketones2009In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 11, no 2, p. 393-396Article in journal (Refereed)
  • 376.
    Heshmat, Mojgan
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Vrije Universiteit Amsterdam, The Netherlands.
    Unraveling the Origin of Solvent Induced Enantioselectivity in the Henry Reaction with Cinchona Thiourea as Catalyst2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 40, p. 7974-7982Article in journal (Refereed)
    Abstract [en]

    In this work, we report an energy decomposition and electronic structure analysis using DFT calculations for the C-C coupling step in the Henry reaction with cinchona thiourea as catalyst and DMF solvent to unravel the origin of enantioselectivity. We found that the conformation of flexible thiourea moiety is affected by the solvent, and in the preferred conformation of thiourea in strong Lewis basic DMF solvent, the N-H sites are in the opposite direction, i.e., in trans conformation. Hence, the thiourea moiety acts via single hydrogen bonding with substrates. The conformation of the substrates with respect to the forming C-C bond plays critical role to increase orbital interaction between two substrates and enhances hydrogen bond strength between substrates and catalyst, which in turn stabilizes the positive charge developing on the catalyst at the transition state for one of the enantiomers (S). Thus, the enantioselectivity has electronic structure origin. The stronger H-bond formation in the S enantiomer has been confirmed by the calculated IR spectra and is in agreement with thus far experimental and computational results.

  • 377.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    A Prediction of Proton-Catalyzed Hydrogenation of Ketones in Lewis Basic Solvent through Facile Splitting of Hydrogen Molecules2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 5, p. 1036-1039Article in journal (Refereed)
    Abstract [en]

    A ketone's carbonyl carbon is electrophilic and harbors a part of the lowest unoccupied molecular orbital of the carbonyl group, resembling a Lewis acidic center; under the right circumstances it exhibits very useful chemical reactivity, although the natural electrophilicity of the ketone's carbonyl carbon is often not strong enough on its own to produce such reactivity. Quantum chemical calculations predict that a proton shared between a ketone and the Lewis basic solvent molecule (dioxane or THF) activates carbonyl carbon to the point of enabling a facile heterolytic splitting of H-2. Proton-catalyzed hydrogenation of a ketone in Lewis basic solvent is the result. The mechanism involves the interaction of H-2 with the enhanced Lewis acidity of a carbonyl carbon and the free Lewis basic solvent molecule polarizes H-2 and enables the hydride-type attack on carbonyl carbon, which is very strongly influenced by the proton shared between a ketone and solvent. The hydride-type attack on carbon is reminiscent of the splitting of H-2 by singlet carbenes except that, in this case, a Lewis base from the surrounding environment (solvent) is necessary for polarization of H-2 and acceptance of the proton resulting from the heterolytic splitting of H-2.

  • 378.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Carbonyl Activation by Borane Lewis Acid Complexation: Transition States of H-2 Splitting at the Activated Carbonyl Carbon Atom in a Lewis Basic Solvent and the Proton-Transfer Dynamics of the Boroalkoxide Intermediate2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 38, p. 9098-9113Article in journal (Refereed)
    Abstract [en]

    By using transition-state (TS) calculations, we examined how Lewis acid (LA) complexation activates carbonyl compounds in the context of hydrogenation of carbonyl compounds by H-2 in Lewis basic (ethereal) solvents containing borane LAs of the type (C6F5)(3)B. According to our calculations, LA complexation does not activate a ketone sufficiently enough for the direct addition of H-2 to the O = C unsaturated bond; but, calculations indicate a possibly facile heterolytic cleavage of H-2 at the activated and thus sufficiently Lewis acidic carbonyl carbon atom with the assistance of the Lewis basic solvent (i.e., 1,4-dioxane or THF). For the solvent-assisted H-2 splitting at the carbonyl carbon atom of (C6F5)(3)B adducts with different ketones, a number of TSs are computed and the obtained results are related to insights from experiment. By using the Born-Oppenheimer molecular dynamics with the DFT for electronic structure calculations, the evolution of the (C6F5)(3)B-alkoxide ionic intermediate and the proton transfer to the alkoxide oxygen atom were investigated. The results indicate a plausible hydrogenation mechanism with a LA, that is, (C6F5)(3)B, as a catalyst, namely, 1) the step of H-2 cleavage that involves a Lewis basic solvent molecule plus the carbonyl carbon atom of thermodynamically stable and experimentally identifiable (C6F5)(3)B-ketone adducts in which (C6F5)(3)B is the Lewis acid promoter, 2) the transfer of the solvent-bound proton to the oxygen atom of the (C6F5)(3)B-alkoxide intermediate giving the (C6F5)(3)B-alcohol adduct, and 3) the S(N)2-style displacement of the alcohol by a ketone or a Lewis basic solvent molecule.

  • 379.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Computational Elucidation of a Role That Bronsted Acidification of the Lewis Acid-Bound Water Might Play in the Hydrogenation of Carbonyl Compounds with H-2 in Lewis Basic Solvents2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 48, p. 11489-11493Article in journal (Refereed)
    Abstract [en]

    Bronsted acidification of water by Lewis acid (LA) complexation is one of the fundamental principles in chemistry. Using transition-state calculations (TS), herein we investigate the role that Bronsted acidification of the LA-bound water might play in the mechanism of the hydrogenation of carbonyl compounds in Lewis basic solvents under non-anhydrous conditions. The potential energy scans and TS calculations were carried out with a series of eight borane LAs as well as the commonly known strong LA AlCl3 in 1,4-dioxane or THF as Lewis basic solvents. Our molecular model consists of the dative LA-water adduct with hydrogen bonds to acetone and a solvent molecule plus one additional solvent molecule that participates is the TS structure describing the cleavage of H-2 at acetone's carbonyl carbon atom. In all the molecular models applied here, acetone (O=CMe2) is the archetypical carbonyl substrate. We demonstrate that Bronsted acidification of the LA-bound water can indeed lower the barrier height of the solvent-involving H-2-cleavage at the acetone's carbonyl carbon atom. This is significant because at present it is believed that the mechanism of the herein considered reaction is described by the same mechanism regardless of whether the reaction conditions are strictly anhydrous or non-anhydrous. Our results offer an alternative to this belief that warrants consideration and further study.

  • 380.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    H-2 Cleavage by Frustrated Lewis Pairs Characterized by the Energy Decomposition Analysis of Transition States: An Alternative to the Electron Transfer and Electric Field Models2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 36, p. 7202-7211Article in journal (Refereed)
    Abstract [en]

    Knowing that the Papai's electron transfer (ET) and the Grimme's electric field (EF) models draw attention to somewhat different physical aspects, we are going to systematically (re)examine interactions in the transition states (TSs) of the heterolytic H-2-cleavage by the Frustrated Lewis Pairs (FLPs). Our main vehicle is the quantitative energy decomposition analysis (EDA), a powerful method for elucidation of interactions, plus the analysis of molecular orbitals (MOs). Herein, the Lewis acid (LA) is B(C6F5)(3) and the Lewis bases (LBs) are tBu(3)P, (o-C6H4Me)(3)P, 2,6-lutidine, 2,4,6-lutidine, MeN=C(Ph)Me imine, MeN(H)-C(H)PhMe amine, THF, 1,4-dioxane, and acetone. For a series of the phosphorus-, nitrogen-, and oxygen-bearing LBs plus B(C6F5)(3), we will show that (i) neither the electrostatic nor the orbital interactions dominate but instead both are essential alongside the Pauli repulsion and (ii) the frontier molecular orbitals (FMOs) of a TS can arise not only from the push-pull molecular orbital scheme by Papai et al., which directly involves the occupied sigma and the empty sigma* MOs of H-2, but also from a more intricate but energetically more fitting orbital interactions which have escaped notice thus far.

  • 381.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structurally Flexible Oxocarbenium/Borohydride Ion Pair: Dynamics of Hydride Transfer on the Background of Conformational Roaming2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 23, p. 5098-5106Article in journal (Refereed)
    Abstract [en]

    We apply Born-Oppenheimer molecular dynamics to the practically significant [dioxane-H(+)-acetone]-[(C6F5)(3)B-H(-)] and [Et2O-H(+)-OCPr2][(C6F5)(3)B-H(-)] ion pair intermediates. Dynamics of hydride transfer in cation/anion ion pair takes place on the background of large amplitude configurational changes. Geometry of oxocarbenium/borohydride ion pairs is flexible, meaning that we uncover significant actual structural disorder at a finite temperature. Therefore, although the starting structure can be fairly close to the configurational area of the hydride transfer transition state (TS) and despite a low potential energy barrier (ca. 1.5 kcal/mol, according to the literature), already at T approximate to 325 K the system can remain ignorant of the TS region and move round and about (roam) in the configurational space for a period of time in the range between 10 and 100 ps. This indicates structural flexibility of oxocarbenium/borohydride ion pair on apparently a flat potential energy landscape of cation/anion interaction, and this has not been taken into consideration by the free energy estimations in static considerations made thus far. The difference between the dynamics-based representation of the system versus the static representation amounts to the difference between quasi-bimolecular versus unimolecular descriptions of the hydride transfer step.

  • 382.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Surprisingly Flexible Oxonium/Borohydride Ion Pair Configurations2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 15, p. 3713-3727Article in journal (Refereed)
    Abstract [en]

    We investigate the geometry of oxonium/borohydride ion pairs [ether-H(+) ether] [LA-H(-)] with dioxane, THF, and Et2O as ethers and B(C6F5)(3) as the Lewis acid (LA). The question is about possible location of the disolvated proton [ether -H(+) -ether], with respect to the hydride of the structurally complex [LA -H(-)] anion. Using Born Oppenheimer molecular dynamics and a comparison of the potential and free energies of the optimized configurations, we show that herein considered ion pairs are much more flexible geometrically than previously thought. Conformers with different locations of cations with respect to anions are governed by a flat energy -landscape. We found a novel configuration in which oxonium is below [LA-11((-))], with respect to the direction of borane -> hydride vector, and the proton -hydride distance is ca. 6 A. With calculations of the vibrational spectra of [ether-H(+)-ether][(C6F5)(3)B-H(-)] for dioxane, THF, and Et2O as ethers, we investigate the manifestation of SSLB-type (short, strong, low -barrier) hydrogen bonding in the OHO motif of an oxonium cation.

  • 383.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Theory-Based Extension of the Catalyst Scope in the Base-Catalyzed Hydrogenation of Ketones: RCOOH-Catalyzed Hydrogenation of Carbonyl Compounds with H-2 Involving a Proton Shuttle2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 72, p. 18193-18202Article in journal (Refereed)
    Abstract [en]

    As an extension of the reaction mechanism describing the base-catalyzed hydrogenation of ketones according to Berkessel et al., we use a standard methodology for transition-state (TS) calculations in order to check the possibility of heterolytic cleavage of H-2 at the ketone's carbonyl carbon atom, yielding one-step hydrogenation path with involvement of carboxylic acid as a catalyst. As an extension of the catalyst scope in the base-catalyzed hydrogenation of ketones, our mechanism involves a molecule with a labile proton and a Lewis basic oxygen atom as a catalyst-for example, R-C(= O) OH carboxylic acids-so that the heterolytic cleavage of H-2 could take place between the Lewis basic oxygen atom of a carboxylic acid and the electrophilic (Lewis acidic) carbonyl carbon of a ketone/aldehyde. According to our TS calculations, protonation of a ketone/aldehyde by a proton shuttle (hydrogen bond) facilitates the hydride-type attack on the ketone's carbonyl carbon atom in the process of the heterolytic cleavage of H-2. Ketones with electron-rich and electron-withdrawing substituents in combination with a few carboxylic and amino acids-in total, 41 substrate-catalyst couples-have been computationally evaluated in this article and the calculated reaction barriers are encouragingly moderate for many of the considered substrate-catalyst couples.

  • 384.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Water and a Borohydride/Hydronium Intermediate in the Borane-Catalyzed Hydrogenation of Carbonyl Compounds with H-2 in Wet Ether: A Computational Study2018In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, no 38, p. 8952-8962Article in journal (Refereed)
    Abstract [en]

    We have computationally evaluated water as an active Lewis base (LB) and introduced the borohydride/hydronium intermediate in the mechanism of B(C6F5)(3)-catalyzed hydrogenation of carbonyl compounds with H-2 in wet/moist ether. Our calculations extend the known frustrated Lewis pair mechanism of this reaction toward the inclusion of water as the active participant in all steps. Although the definition of the zero-energy point interweaves in comparison of the scenarios with and without water, we will be able to show that (i) water (hydrogen bonded to its molecular environment) can, in principle, act as a reasonably viable LB in cooperation with the borane Lewis acid such as B(C6F5)(3) but relatively a strong borane-water complexation can be the hindering factor; (ii) the herein-proposed borohydride/hydronium intermediates with the hydronium cation having three OH center dot center dot center dot ether hydrogen bonds or a combination of the OH center dot center dot center dot ether/OH center dot center dot center dot ketone hydrogen bonds appear to be as valid as the previously considered borohydride/oxonium or borohydride/oxocarbenium intermediates; (iii) the proton-coupled hydride transfer from the borohydride/hydronium to a ketone (acetone) has a reasonably low barrier. Our findings could be useful for better mechanistic understanding and further development of the aforementioned reaction.

  • 385.
    Hiresova, Renata
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stawinski, Jacek
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nucleoside H-phosphonates, XXII: Synthesis and properties of new nucleotide analogues - H-phosphonothiolate diesters2007In: Synlett, ISSN 0936-5214, no 17, p. 2748-2752Article in journal (Refereed)
  • 386.
    Hoben, Christine E.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kanupp, Lisa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Practical chemoenzymatic dynamic kinetic resolution of primary amines via transfer of a readily removable benzyloxycarbonyl group2008In: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 49, no 6, p. 977-979Article in journal (Refereed)
  • 387.
    Horváth, Attila
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mild and Efficient Palladium(II)-Catalyzed Racemization of Allenes2004In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 8, p. 964-965Article in journal (Refereed)
    Abstract [en]

    Allenes undergo racemization in the presence of catalytic amounts of Pd(OAc)2/LiBr under mild conditions; the reaction proceeds via a bromopalladation–debromopalladation sequence and tolerates various functional groups.

     

  • 388.
    Horváth, Attila
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Palladium(II)-Catalyzed SN2' Reactions of α-Allenic Acetates: Stereoconvergent Synthesis of (Z,E)-2-Bromo-1,3-dienes2001In: Journal of Organic Chemistry, Vol. 66, no 24, p. 8120-8126Article in journal (Refereed)
  • 389.
    Horváth, Attila
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Benner, Jessica
    Simple, Enantiocontrolled Synthesis of 3-Pyrrolines from α-Amino Allenes2004In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, Vol. 2004, no 15, p. 3240-3243Article in journal (Refereed)
    Abstract [en]

    Cyclization of -amino allenes in the presence of N-bromosuccinimide afforded pyrrolines in good yields. The products were obtained with high enantiomeric excesses when optically active allenes were used as substrates. The synthesis of a 2,5-dehydroprolinol derivative is also presented.

  • 390.
    Horváth, Attila
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jonasson, Catrin
    Bäckvall, Jan-Erling
    Intramolecular Palladium(II)-Catalyzed 1,2-Addition to Allenes2000In: Journal of the American Chemical Society, ISSN 0002-7863, Vol. 122, no 40, p. 9600-9609Article in journal (Refereed)
  • 391. Huang, Genping
    et al.
    Diner, Colin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanism and Stereoselectivity of the BINOL-Catalyzed Allylboration of Skatoles2017In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 19, no 21, p. 5904-5907Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations have been performed to investigate the binaphthol-catalyzed allylboration of skatoles. The high stereoselectivity observed for the reaction is reproduced well by the calculations and was found to be mainly a result of steric repulsions in the corresponding Zimmerman-Traxler transition states. The role of the additive MeOH in enhancing the stereoselectivity was also investigated and is suggested to promote the formation of less reactive allylboronic ester intermediates, thereby suppressing the formation of allylboroxine species, which undergo the facile racemic background reaction.

  • 392.
    Huang, Genping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kalek, Marcin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanism and Selectivity of Rhodium-Catalyzed 1:2 Coupling of Aldehydes and Allenes2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 20, p. 7647-7659Article in journal (Refereed)
    Abstract [en]

    The rhodium-catalyzed highly regioselective 1:2 coupling of aldehydes and allenes was investigated by means of density functional theory calculations. Full free energy profiles were calculated, and several possible reaction pathways were evaluated. It is shown that the energetically most plausible catalytic cycle is initiated by oxidative coupling of the two allenes, which was found to be the rate-determining step of the overall reaction. Importantly, Rh allyl complexes that are able to adopt both eta(3) and eta(1) configurations were identified as key intermediates present throughout the catalytic cycle with profound implications for the selectivity of the reaction. The calculations reproduced and rationalized the experimentally observed selectivities and provided an explanation for the remarkable alteration in the product distribution when the catalyst precursor is changed from [RhCl(nbd)](2) (nbd = norbornadiene) to complexes containing noncoordinating counterions ([Rh(cod)(2)X]; X = OTf, BF4, PF6; cod = 1,5-cyclooctadiene). It turns out that the overall selectivity of the reaction is controlled by a combination of the inherent selectivities of several of the elementary steps and that both the mechanism and the nature of the selectivity-determining steps change when the catalyst is changed.

  • 393.
    Huang, Genping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kalek, Marcin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Liao, Rong-Zhen
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanism, reactivity, and selectivity of the iridium-catalyzed C(sp(3))-H borylation of chlorosilanes2015In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 6, no 3, p. 1735-1746Article in journal (Refereed)
    Abstract [en]

    The iridium-catalyzed C(sp(3))-H borylation of methylchlorosilanes is investigated by means of density functional theory, using the B3LYP and M06 functionals. The calculations establish that the resting state of the catalyst is a seven-coordinate Ir(V) species that has to be converted into an Ir(III)tris(boryl) complex in order to effect the oxidative addition of the C-H bond. This is then followed by a C-B reductive elimination to yield the borylated product, and the catalytic cycle is finally completed by the regeneration of the active catalyst over two facile steps. The two employed functionals give somewhat different conclusions concerning the nature of the rate-determining step, and whether reductive elimination occurs directly or after a prior isomerization of the Ir(V) hydride intermediate complex. The calculations reproduce quite well the experimentally-observed trends in the reactivities of substrates with different substituents. It is demonstrated that the reactivity can be correlated to the Ir-C bond dissociation energies of the corresponding Ir(V) hydride intermediates. The effect of the chlorosilyl group is identified to originate from the alpha-carbanion-stabilizing effect of the silicon, which is further reinforced by the presence of an electron-withdrawing chlorine substituent. Furthermore, the source of selectivity for the borylation of primary over secondary C(sp(3))-H can be explained on a steric basis, by repulsion between the alkyl group and the Ir/ligand moiety. Finally, the difference in the reactivity between C(sp(3))-H and C(sp(2))-H borylation is investigated and rationalized in terms of distortion/interaction analysis.

  • 394. Huang, Ping
    et al.
    Högblom, Joakim
    Anderlund, Magnus F.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    Magnuson, Ann
    Styring, Stenbjörn
    Light-indused multistep oxidation of dinuclear manganese complexes for artificial photosyntesis2004In: Journal of Inorganic Biochemistry, ISSN 0162-0134, Vol. 98, no 5, p. 733-745Article in journal (Refereed)
  • 395. Huang, Yong
    et al.
    Gao, Weiming
    Åkermark, Torbjörn
    Li, Mingrun
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    An Air-Stable Fe3S4 Complex with Properties Similar to Those of the HOXair State of the Diiron Hydrogenases2012In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 27, p. 4259-4263Article in journal (Refereed)
    Abstract [en]

    A Fe3S4 complex bridged by azapropanedithiolate (adt), complex 6, was prepared as a potential model of the HOXair state of [FeFe]-hydrogenases. Complex 6 was characterized by IR and 1H NMR spectroscopy, and its structure was determined by X-ray crystallography. The electrochemical studies show that complex 6 is redox-active under acidic conditions, which provides insight into the catalytic mechanism. Hydrogen evolution, driven by visible light, was observed in CH3CN/D2O solution by online mass spectroscopy.

  • 396. Hughes, Arwel
    et al.
    Patel, Dhilon S.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Klauda, Jeffery B.
    Clifton, Luke A.
    Im, Wonpil
    Physical Properties of Bacterial Outer Membrane Models: Neutron Reflectometry & Molecular Simulation2019In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 116, no 6, p. 1095-1104Article in journal (Refereed)
    Abstract [en]

    The outer membrane (OM) of Gram-negative bacteria is an asymmetric bilayer having phospholipids in the inner leaflet and lipopolysaccharides in the outer leaflet. This unique asymmetry and the complex carbohydrates in lipopolysaccharides make it a daunting task to study the asymmetrical OM structure and dynamics, its interactions with OM proteins, and its roles in translocation of substrates, including antibiotics. In this study, we combine neutron reflectometry and molecular simulation to explore the physical properties of OM mimetics. There is excellent agreement between experiment and simulation, allowing experimental testing of the conclusions from simulations studies and also atomistic interpretation of the behavior of experimental model systems, such as the degree of lipid asymmetry, the lipid component (tail, head, and sugar) profiles along the bilayer normal, and lateral packing (i.e., average surface area per lipid). Therefore, the combination of both approaches provides a powerful new means to explore the biological and biophysical behavior of the bacterial OM.

  • 397. Ibrahem, Ismail
    et al.
    Breistein, Palle
    Cordova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    One-Pot Three-Component Highly Selective Synthesis of Homoallylboronates by Using Metal-Free Catalysis2012In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 18, no 17, p. 5175-5179Article in journal (Refereed)
  • 398. Ibrahem, Ismail
    et al.
    Breistein, Palle
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    One-Pot Three-Component Catalytic Enantioselective Synthesis of Homoallylboronates2011In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 50, no 50, p. 12036-12041Article in journal (Refereed)
  • 399.
    Ibrahem, Ismail
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Casas, Jesus
    Cordova, Armando
    Direct Catalytic Enantioselective a-aminomethylation of ketones2004In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 43, p. 6528-Article in journal (Refereed)
  • 400.
    Ibrahem, Ismail
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dziedzic, Pawel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Organocatalytic asymmetric alpha-aminomethylation of cyclohexanones2006In: Synthesis, ISSN 0039-7881, no 23, p. 4060-4064Article in journal (Refereed)
567891011 351 - 400 of 1217
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