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  • 151. Casillo, Angela
    et al.
    Ståhle, Jonas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Parrilli, Ermenegilda
    Sannino, Filomena
    Mitchell, Daniel E.
    Pieretti, Giuseppina
    Gibson, Matthew I.
    Marino, Gennaro
    Lanzetta, Rosa
    Parrilli, Michelangelo
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tutino, Maria L.
    Corsaro, Maria M.
    Structural characterization of an all-aminosugar-containing capsular polysaccharide from Colwellia psychrerythraea 34H2017In: Antonie van Leeuwenhoek. International Journal of General and Molecular Microbiology, ISSN 0003-6072, E-ISSN 1572-9699, Vol. 110, no 11, p. 1377-1387Article in journal (Refereed)
    Abstract [en]

    Colwellia psychrerythraea strain 34H, a Gram-negative bacterium isolated from Arctic marine sediments, is considered a model to study the adaptation to cold environments. Recently, we demonstrated that C. psychrerythraea 34H produces two different extracellular polysaccharides, a capsular polysaccharide and a medium released polysaccharide, which confer cryoprotection to the bacterium. In this study, we report the structure of an additional capsular polysaccharide produced by Colwellia grown at a different temperature. The structure was determined using chemical methods, and one- and two-dimensional NMR spectroscopy. The results showed a trisaccharide repeating unit made up of only amino-sugar residues: N-acetyl-galactosamine, 2,4-diacetamido-2,4,6-trideoxy-glucose (bacillosamine), and 2-acetamido-2-deoxyglucuronic acid with the following structure: -> 4)-beta-d-GlcpNAcA-(1 -> 3)-beta-d-QuipNAc4NAc-(1 -> 3)-beta-d-GalpNAc-(1 ->. The 3D model, generated in accordance with H-1,H-1-NOE NMR correlations and consisting of ten repeating units, shows a helical structure. In contrast with the other extracellular polysaccharides produced from Colwellia at 4 A degrees C, this molecule displays only a low ice recrystallization inhibition activity.

  • 152. Castro, Vasco
    et al.
    Dvinskikh, Sergey V.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sandström, Dick
    Maliniak, Arnold
    NMR studies of membranes composed of glycolipids and phospholipids2007In: Biochimica et Biophysica Acta, Vol. 1768, no -, p. 2432-2437Article in journal (Refereed)
  • 153. Chassagne, Pierre
    et al.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Guerreiro, Catherine
    Gauthier, Charles
    Phalipon, Armelle
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mulard, Laurence A.
    Structural Studies of the O-Acetyl-Containing O-Antigen from a Shigella flexneri Serotype 6 Strain and Synthesis of Oligosaccharide Fragments Thereof2013In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 19, p. 4085-4106Article in journal (Refereed)
    Abstract [en]

    Extensive analysis by NMR spectroscopy of the delipidated lipopolysaccharide of Shigella flexneri serotype 6 strain MDC 2924-71 confirmed the most recently reported structure of the O-antigen repeating unit as {4)--D-GalpA-(13)--D-GalpNAc-(12)--L-Rhap3Ac/4Ac-(12)--L-Rhap-(1}, and revealed the non-stoichiometric acetylation at O-3C/4C. Input from the CASPER program helped to ascertain the fine distribution of the three possible patterns of O-acetylation. The non-O-acetylated repeating unit (ABCD) corresponded to about 2/3 of the population, while 1/4 was acetylated at O-3C (3AcCDAB), and 1/10 at O-4C (4AcCDAB). Di- to tetrasaccharides with a GalpA residue (A) at their reducing end were synthesized as their propyl glycosides following a multistep linear strategy relying on late-stage acetylation at O-3C. Thus, the 3C-O-acetylated and non-O-acetylated targets were synthesized from common protected intermediates. Rhamnosylation was most efficiently achieved by using imidate donors, including at O-4 of a benzyl galacturonate acceptor. In contrast, a thiophenyl 2-deoxy-2-trichloroacetamido-D-galactopyranoside precursor was preferred for chain elongation involving residue B. Final Pd/C-mediated deprotection ensured O-acetyl stability. All of the target molecules represent parts of the O-antigen of S. flexneri 6, a prevalent serotype. Non-O-acetylated oligosaccharides are also fragments of the Escherichia coli O147 O-antigen.

  • 154.
    Chen, Hong
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Deng, Youqian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yu, Zhengbao
    Zhao, Huishuang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yao, Qingxia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    3D Open-Framework Vanadoborate as a Highly Effective Heterogeneous Pre-catalyst for the Oxidation of Alkylbenzenes2013In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 25, no 24, p. 5031-5036Article in journal (Refereed)
    Abstract [en]

    Three three-dimensional (3D) open-framework vanadoborates, denoted as SUT-6-Zn, SUT-6-Mn, and SUT-6-Ni, were synthesized using diethylenetriamine as a template. SUT-6-Zn, SUT-6-Mn, and SUT-6-Ni are isostructural and built from (VO)(12)O-6 B18O36(OH)(6) clusters bridged by ZnO5, MnO6, and NiO6 polyhedra, respectively, to form the 3D frameworks. SUT-6 is the first vanadoborate with a 3D framework. The framework follows a semiregular hxg net topology with a 2-fold interpenetrated diamond-like channel system. The amount of template used in the synthesis played an important role in the dimensionality of the resulting vanadoborate structures. A small amount of diethylenetriamine led to the formation of this first 3D vanadoborate framework, while an increased amount of diethylenetriamine resulted in vanadoborates with zero-dimensional (0D) and one-dimensional (1D) structures. SUT-6-Zn was proved to be an efficient heterogeneous precatalyst for the oxidation of alkylbenzenes.

  • 155. Chen, Mo
    et al.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Brady, John W.
    Wohlert, Jakob
    Molecular Dynamics Simulations of the Ionic Liquid 1-n-Butyl-3-Methylimidazolium Chloride and Its Binary Mixtures with Ethanol2014In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 10, no 10, p. 4465-4479Article in journal (Refereed)
    Abstract [en]

    Room temperature ionic liquids (ILs) of the imidazolium family have attracted much attention during the past decade for their capability to dissolve biomass. Besides experimental work, numerous compuational studies have been concerned with the physical properties of both neat ILs and their interactions with different solutes, in particular, carbohydrates. Many classical force fields designed specifically for ILs have been found to yield viscosities that are too high for the liquid state, which has been attributed to the fact that the effective charge densities are too high due to the lack of electronic polarizability. One solution to this problem has been uniform scaling of the partial charges by a scale factor in the range 0.6-0.9, depending on model. This procedure has been shown to improve the viscosity of the models, and also to positively affect other properties, such as diffusion constants and ionic conductivity. However, less attention has been paid to how this affects the overall thermodynamics of the system, and the problems it might create when the IL models are combined with other force fields (e.g., for solutes). In the present work, we employ three widely used IL force fields to simulate 1-n-buty1-3-methyl-imidazolium chloride in both the crystal and the liquid state, as well as its binary mixture with ethanol. Two approaches are used: one in which the ionic charge is retained at its full integer value and one in which the partial charges are uniformly reduced to 85%. We investigate and calculate crystal and liquid structures, molar heat capacities, heats of fusion, self-diffusion constants, ionic conductivity, and viscosity for the neat IL, and ethanol activity as a function of ethanol concentration for the binary mixture. We show that properties of the crystal are less affected by charge scaling compared to the liquid. In the liquid state, transport properties of the neat IL are generally improved by scaling, whereas values for the heat of fusion are unaffected, and results for the heat capacity are ambiguous. Neither full nor reduced charges could reproduce experimental ethanol activities for the whole range of compositions.

  • 156. Chen, Shi-Lu
    et al.
    Blomberg, Margareta R. A.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    An investigation of possible competing mechanisms for Ni-containing methyl-coenzyme M reductase2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 27, p. 14029-14035Article in journal (Refereed)
    Abstract [en]

    Ni-containing methyl-coenzyme M reductase (MCR) is capable of catalyzing methane formation from methyl-coenzyme M (CH3-SCoM) and coenzyme B (CoB-SH), and also its reverse reaction (methane oxidation). Based on extensive experimental and theoretical investigations, it has turned out that a mechanism including an organometallic methyl-Ni(III)F-430 intermediate is inaccessible, while another mechanism involving a methyl radical and a Ni(II)-SCoM species currently appears to be the most acceptable one for MCR. In the present paper, using hybrid density functional theory and an active-site model based on the X-ray crystal structure, two other mechanisms were studied and finally also ruled out. One of them, involving proton binding on the CH3-SCoM substrate, which should facilitate methyl-Ni(III)F-430 formation, is demonstrated to be quite unfavorable since the substrate has a much smaller proton affinity than the F-430 cofactor. Another one (oxidative addition mechanism) is also shown to be unfavorable for the MCR reaction, due to the large endothermicity for the formation of the ternary intermediate with side-on C-S (for CH3-SCoM) or C-H (for methane) coordination to Ni.

  • 157. Chen, Shi-Lu
    et al.
    Liao, Rong-Zhen
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Phosphate Monoester Hydrolysis by Trinuclear Alkaline Phosphatase; DFT Study of Transition States and Reaction Mechanism2014In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 11, p. 2321-2330Article in journal (Refereed)
    Abstract [en]

    Alkaline phosphatase (AP) is a trinuclear metalloenzyme that catalyzes the hydrolysis of a broad range of phosphate monoesters to form inorganic phosphate and alcohol (or phenol). In this paper, by using density functional theory with a model based on a crystal structure, the AP-catalyzed hydrolysis of phosphate monoesters is investigated by calculating two substrates, that is, methyl and p-nitrophenyl phosphates, which represent alkyl and aryl phosphates, respectively. The calculations confirm that the AP reaction employs a ping-pong mechanism involving two chemical displacement steps, that is, the displacement of the substrate leaving group by a Ser102 alkoxide and the hydrolysis of the phosphoseryl intermediate by a Zn2-bound hydroxide. Both displacement steps proceed via a concerted associative pathway no matter which substrate is used. Other mechanistic aspects are also studied. Comparison of our calculations with linear free energy relationships experiments shows good agreement.

  • 158. Chojnacka, Kinga
    et al.
    Santoro, Stefano
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Awartani, Radi
    Richards, Nigel G. J.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Aponick, Aaron
    Synthetic studies on the solanacol ABC ring system by cation-initiated cascade cyclization: implications for strigolactone biosynthesis2011In: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 9, no 15, p. 5350-5353Article in journal (Refereed)
    Abstract [en]

    We report a new method for constructing the ABC ringsystem of strigolactones, in a single step from a simple linearprecursor by acid-catalyzed double cyclization. The reactionproceeds with a high degree of stereochemical control, whichcan be qualitatively rationalized usingDFT calculations. Ourconcise synthetic approach offers a new model for thinkingabout the (as yet) unknown chemistry that is employed in thebiosynthetic pathways leading to this class of plant hormones.

  • 159. Chow, Winnie W. Y.
    et al.
    Herwik, Stanislav
    Kisban, Sebastian
    Ruther, Patrick
    Neves, Herc
    Oscarsson, Sven
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gothelid, Emmanuelle
    Influence of bio-coatings on the recording performance of neural electrodes2014In: Biomedizinische Technik (Berlin. Zeitschrift), ISSN 1862-278X, E-ISSN 0013-5585, Vol. 59, no 4, p. 315-322Article in journal (Refereed)
    Abstract [en]

    Neural probes are complex devices consisting of metallic (often Pt based) electrodes, spread over an insolating/dielectric backbone. Their functionality is often limited in time because of the formation of scaring tissues around the implantation tracks. Functionalization of the probes surface can be used to limit the glial scar reaction. This is however challenging, as this treatment has to be equally efficient on all probe surfaces (metallic as well as dielectric) and should not influence the electrodes performances. This paper presents a novel technique to functionalize recording neural probes with hyaluronic acid (HyA), a major component of the extracellular matrix (ECM). HyA and the probe surface are both modified to make the reaction feasible: HyA is chemically functionalized with SS-pyridine groups while the probe surfaces are silanized. The thiol groups thus introduced on the probe surface can then react with the HyA SS-pyridine group, resulting in a covalent bonding of the latter on the former. The electrodes are protected by introducing a pretreatment step, namely an additional hyaluronic acid layer on the platinum electrode, prior to the silanization process, which was found to be effective in reducing electrode impedance under optimized conditions.

  • 160. Chow, Winnie W. Y.
    et al.
    Herwik, Stanislav
    Ruther, Patrick
    Gothelid, Emmanuelle
    Oscarsson, Sven
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bio-polymer coatings on neural probe surfaces: Influence of the initial sample composition2012In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 258, no 20, p. 7864-7871Article in journal (Refereed)
    Abstract [en]

    This paper presents the results of the study of hyaluronic acid (HyA) coating on two structural materials, silicon oxide (dielectric) surface and platinum (Pt) surface used for fabrication of probes developed for neurological investigations in the framework of the EU-project NeuroProbes. The silicon-based neural probes consist of multiple Pt electrodes on the probe shafts for neural recording applications. HyA coatings were proposed to apply on the probe surfaces to enhance the biocompatibility [1]. This study aims at understanding the influence of the initial composition of the probe surface on the structure and morphology of HyA coating. HyA was chemically functionalized by SS-pyridin using (N-Succinimidyl 3-[2-pyridyldithio]-propionate) (SPDP) and was immobilized on the surfaces via a covalent bond. The dielectric and Pt surfaces were derivatized by use of (3-mercaptopropyl) methyldimethoxysilane (MPMDMS). The silanol groups in MPMDMS bind to the dielectric surface, leaving the thiol groups at the uppermost surface and the thiol groups then bind covalently to the functionalized HyA. On the Pt surface, it is the thiol group which binds on the Pt surface. The coated surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). A well-defined HyA layer was observed on both dielectric and Pt surfaces. The coating of two molecular weights (340 kDa and 1.3 MDa) of HyA was examined. The influence of the silanized layer on the HyA coating was also investigated.

  • 161. Chowdhury, Sugata
    et al.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Russo, Nino
    Sicilia, Emilia
    Mechanistic investigation of the hydrogenation of O2 by a transfer hydrogenation catalyst2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 12, p. 4178-4190Article in journal (Refereed)
  • 162. Closson, Adam
    et al.
    Johansson, Mikael
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Ionic liquid-immobilized catalytic system for biomimetic dihydroxylation of olefins2004In: Chemical Communication, ISSN 0366-5607, no 13, p. 1494-1495Article in journal (Refereed)
  • 163.
    Colas, Kilian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martín-Montero, Raúl
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mendoza, Abraham
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Intermolecular Pummerer Coupling with Carbon Nucleophiles in Non-Electrophilic Media2017In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 56, no 50, p. 16042-16046Article in journal (Refereed)
    Abstract [en]

    A new Pummerer-type C-C coupling protocol is introduced based on turbo-organomagnesium amides, which unlike traditional Pummerer reactions, does not require strong electrophilic activators, engages a broad range of C(sp(3))-, C(sp(2))-, and C(sp)-nucleophiles, and seamlessly integrates with C-H and C-X magnesiation. Given the central character of sulfur compounds in organic chemistry, this protocol allows access to unrelated carbonyls, olefins, organometallics, halides, and boronic esters through a single strategy.

  • 164. Coll, Mercedes
    et al.
    Ahlford, Katrin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pamies, Oscar
    Adolfsson, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dieguez, Montserrat
    Modular Furanoside Pseudodipeptides and Thioamides, Readily Available Ligand Libraries for Metal-Catalyzed Transfer Hydrogenation Reactions: Scope and Limitations2012In: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 354, no 2-3, p. 415-427Article in journal (Refereed)
    Abstract [en]

    Two new highly modular carbohydrate-based, pseudodipeptide and thioamide ligand libraries have been synthesized for the rhodium- and ruthenium-catalyzed asymmetric transfer hydrogenation (ATH) of prochiral ketones. These series of ligands can be prepared efficiently from easily accessible D-xylose and D-glucose. The ligand libraries contain two main ligand structures (pseudodipeptide and thioamide) that have been designed by making systematic modifications to one of the most successful ligand families developed for the ATH. As well as studying the effect of these two ligand structures on the catalytic performance, we also evaluated the effect of modifying several of the ligand parameters. We found that the effectiveness of the ligands at transferring the chiral information in the product can be tuned by correctly choosing the ligand components (ligand structure and ligand parameters). Excellent enantioselectivities (ees up to 99%) were therefore obtained in both enantiomers of the alcohol products using a wide range of substrates.

  • 165. Coll, Mercedes
    et al.
    Pamies, Oscar
    Adolfsson, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dieguez, Montserrat
    Second-Generation Amino Acid Furanoside Based Ligands from D-Glucose for the Asymmetric Transfer Hydrogenation of Ketones2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 12, p. 3821-3828Article in journal (Refereed)
    Abstract [en]

    A novel series of modular amino acid thioamide ligands functionalized with carbohydrates were introduced and employed in the rhodium-catalyzed asymmetric transfer hydrogenation (ATH) of aryl alkyl ketones, including the less-studied heteroaromatic ketones. The ligands are based on amino acid hydroxyamides (pseudodipeptides), which are the most successful ligands previously used in asymmetric hydrogen transfer reactions. High enantioselectivities [up to 99% enantiomeric excess (ee)] were achieved in the ATH of a wide range of aryl alkyl ketones by using catalysts generated insitu from [RhCl2Cp*](2) (Cp*=C5Me5) and thioamide ligands comprising a 3-benzyl glucofuranoside backbone and a bulky isopropyl group in the -amino acid moiety. Interestingly, both enantiomers of the alcohol products can readily be obtained with high enantioselectivity by simply changing the absolute configuration of the -amino acid. The good performance can be extended to a very challenging class of industrially interesting heteroaromatic ketones (up to 99%ee).

  • 166. Coll, Mercedes
    et al.
    Pàmies, Oscar
    Adolfsson, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Diéguez, Montserrat
    Carbohydrate-based pseudo-dipeptides: new ligands for the highly enantioselective Ru-catalyzed transfer hydrogenation reaction2011In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 47, no 44, p. 12188-12190Article in journal (Refereed)
    Abstract [en]

    Ruthenium-complexes of novel carbohydrate based pseudo-dipeptide ligands effectively and selectively catalyze the reduction of a broad range of aryl–alkyl ketones under ATH conditions. Excellent enantioselectivities (>99% ee) are obtained using aminosugars as the sole source of chirality.

  • 167.
    Cordova, Armando
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lin, Shuangzheng
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tseggai, Abrehet
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Concise catalytic asymmetric total synthesis of biologically active tropane alkaloids2012In: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 354, no 7, p. 1363-1372Article in journal (Refereed)
    Abstract [en]

    A general strategy for the total asymmetric synthesis of valuable tropane alkaloids by catalytic stereoselective transformations is disclosed. The power of this approach is exemplified by the concise catalytic enantioselective total syntheses of (+)-methylecgonine, (-)-cocaine and (+)-cocaine as well as the first catalytic asymmetric total syntheses of a cocaine C-1 derivative and (+)-ferruginine starting from 5-oxo-protected-a,beta-unsaturated enals using only two and three column chromatographic purification steps, respectively.

  • 168.
    Cortés González, Miguel A.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nordeman, Patrik
    Bermejo Gómez, Antonio
    Stockholm University, Faculty of Science, Department of Organic Chemistry. AstraZeneca PET Centre at Karolinska Institutet, Sweden.
    Meyer, Denise N.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Antoni, Gunnar
    Schou, Magnus
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    [F-18]fluoro-benziodoxole: a no-carrier-added electrophilic fluorinating reagent. Rapid, simple radiosynthesis, purification and application for fluorine-18 labelling2018In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, no 34, p. 4286-4289Article in journal (Refereed)
    Abstract [en]

    Operationally simple radiosynthesis and purification of [F-18]fluoro-benziodoxole was developed starting from a cyclotron produced [F-18]F- precursor, [F-18]TBAF, and tosyl-benziodoxole. The synthetic utility of [F-18]fluoro-benziodoxole was demonstrated by electrophilic fluorocyclization of o-styrilamides proceeding with high RCC (typically 50-90%) and high molar activity (up to 396 GBq mol(-1)).

  • 169. Cosner, Casey C.
    et al.
    Iska, Vijaya Bhaskara Reddy
    Chatterjee, Anamitra
    Markiewicz, John T.
    Corden, Steven J.
    Löfstedt, Joakim
    Ankner, Tobias
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Richer, Joshua
    Hulett, Tyler
    Schauer, Douglas J.
    Wiest, Olaf
    Helquist, Paul
    Evolution of Concise and Flexible Synthetic Strategies for Trichostatic Acid and the Potent Histone Deacetylase Inhibitor Trichostatin A2013In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 1, p. 162-172Article in journal (Refereed)
    Abstract [en]

    (R)-(+)-Trichostatic acid and (R)-(+)-trichostatin A (TSA) are natural products that have attracted considerable attention in the field of epigenetic therapies. TSA in particular is a naturally occurring hydroxamic acid having potent activity as a histone deacetylase inhibitor (HDACi) and having significant potential for treatment of a myriad of genetically based diseases. Development of TSA and other trichostatic acid derivatives into useful small-molecule therapies has been hindered by the low natural abundance and high cost associated with these compounds. We report herein our collective efforts towards the development of concise and scalable routes for the synthesis of trichostatic acid and TSA in both racemic and enantioenriched forms. Three independent synthetic pathways were developed with varying degrees of efficiency and convergency. In the first synthesis, the key step was a vinylogous Horner-Wadsworth-Emmons condensation. A Marshall propargylation reaction was used as the key step in the second synthesis, and Pd-catalyzed a-alkenylation of a ketone zinc enolate by using various functionalized alkenyl or dienyl halides was developed for the third synthesis. The second pathway proved to be readily amenable to an enantioselective modification, and both the second and third pathways were straightforwardly adapted for the facile preparation of new analogues of trichostatic acid and TSA.

  • 170. Cotton, Hanna K.
    et al.
    Norinder, Jakob
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Screening of Ligands in the Asymmetric Metallocenethiolatocopper(I)-Catalyzed Allylic Substitution with Grignard Reagents2006In: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 62, no 24, p. 5632-5640Article in journal (Refereed)
    Abstract [en]

    Screening of metallocenethiolate ligands for copper(I)-catalyzed substitution of allylic acetates with Grignard reagents has been carried out. The previously used ligand, lithium (R,Sp)-2-(1-dimethylaminoethyl)ferrocenylthiolate (4a), possessing both central and planar chirality, was the starting point for the screening. It was found that the diastereomeric ligand lithium (R,Rp)-2-(1-dimethylaminoethyl)ferrocenylthiolate (4b) exhibiting reversed planar chirality gave increased enantioselectivity in the allylic substitution, at least when cinnamyl acetate was used as a substrate. The ruthenocene-based ligand lithium (R,Sp)-2-(1-dimethylaminoethyl)ruthenocenylthiolate (4c) gave an enhanced reaction rate, but lower chiral induction. The use of disulfide bis[(R,Sp)-2-(1-dimethylaminoethyl)ferrocenyl]disulfide (7a) as a ligand precursor worked well but resulted in lower enantioselectivity.

  • 171.
    Covarrubias, Adrian Suarez
    et al.
    Department of Cell and Molecular Biology, Uppsala University, Sweden.
    Högbom, Martin
    Department of Cell and Molecular Biology, Uppsala University, Sweden.
    Bergfors, Terese
    Department of Cell and Molecular Biology, Uppsala University, Sweden.
    Carroll, Paul
    Institute for Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, London.
    Mannerstedt, Karin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Oscarson, Stefan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Parish, Tanya
    Institute for Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, London.
    Jones, T Alwyn
    Department of Cell and Molecular Biology, Uppsala University, Sweden.
    Mowbray, Sherry L
    Department of Molecular Biology, Swedish University of Agricultural Sciences, Biomedical Center, Uppsala, Sweden.
    Structural, biochemical, and in vivo investigations of the threonine synthase from Mycobacterium tuberculosis.2008In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 381, no 3, p. 622-33Article in journal (Refereed)
    Abstract [en]

    Threonine biosynthesis is a general feature of prokaryotes, eukaryotic microorganisms, and higher plants. Since mammals lack the appropriate synthetic machinery, instead obtaining the amino acid through their diet, the pathway is a potential focus for the development of novel antibiotics, antifungal agents, and herbicides. Threonine synthase (TS), a pyridoxal-5-phosphate-dependent enzyme, catalyzes the final step in the pathway, in which L-homoserine phosphate and water are converted into threonine and inorganic phosphate. In the present publication, we report structural and functional studies of Mycobacterium tuberculosis TS, the product of the rv1295 (thrC) gene. The structure gives new insights into the catalytic mechanism of TSs in general, specifically by suggesting the direct involvement of the phosphate moiety of the cofactor, rather than the inorganic phosphate product, in transferring a proton from C4' to C(gamma) in the formation of the alphabeta-unsaturated aldimine. It further provides a basis for understanding why this enzyme has a higher pH optimum than has been reported elsewhere for TSs and gives rise to the prediction that the equivalent enzyme from Thermus thermophilus will exhibit similar behavior. A deletion of the relevant gene generated a strain of M. tuberculosis that requires threonine for growth; such auxotrophic strains are frequently attenuated in vivo, indicating that TS is a potential drug target in this organism.

  • 172. Cribiù, Riccardo
    et al.
    Borbas, K. Eszter
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Cumpstey, Ian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    On the synthesis of vinyl and phenyl C-furanosides by stereospecific debenzylative cycloetherification2009In: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 65, no 10, p. 2022-2031Article in journal (Refereed)
  • 173.
    Cribiù, Riccardo
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Cumpstey, Ian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stereospecific debenzylative cycloetherification of carbohydrate-derived allylic alcohols, ethers and esters to form vinyl C-furanosides2008In: Chemical Communications, ISSN 1359-7345, no 10, p. 1246-1248Article in journal (Refereed)
  • 174. Crovetto, Luis
    et al.
    Paredes, Jose M.
    Rios, Ramon
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Talavera, Eva M.
    Avarez-Pez, Jose M.
    Photophysics of a xanthenic derivative dye useful as an ""On/Off"" fluorescence probe2007In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 111, no 51, p. 13311-13320Article in journal (Refereed)
    Abstract [en]

    The photophysical behavior of a new fluorescein derivative has been explored by using absorption and steady-state and time-resolved fluorescence measurements. The influence of ionic strength, as well as total buffer concentration, on both the absorbance and fluorescence has been investigated. The apparent acidity constant of the dye determined by absorbance is almost independent of the added buffer and salt concentrations. A semiempirical model is proposed to rationalize the variations in the apparent pK(a) values. The excited-state proton-exchange reaction around the physiological pH becomes reversible upon addition of phosphate buffer, inducing a pH-dependent change of the steady-state fluorescence and decay times. Fluorescence decay traces, collected as a function of total buffer concentration and pH, were analyzed by global compartmental analysis, yielding the following values of the rate constants describing excited-state dynamics: k(01) = 1.29 x 10(10) s(-1), k(02) = 4.21 x 10(8) s(-1), k(21)approximate to 3 x 10(6) M-1 s(-1), k(12)(B) = 6.40 x 10(8) M-1 s(-1), and k(21)(B) = 2.61 x 10(7) M-1 s(- 1). The decay rate constant values of k(01), k(21), and k(21)(B), along with the low molar absorption coefficient of the neutral form, mean that coupled decays are practically monoexponential at buffer concentrations higher than 0.02 M and any pH. Thus, the pH and buffer concentration can modulate the main lifetime of the dye.

  • 175.
    Csjernyik, Gábor
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bogár, Krisztián
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    New Efficient Ruthenium Catalysts for Racemization of Alcohols at Room Temperature2004In: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 45, no 36, p. 6799-6802Article in journal (Refereed)
    Abstract [en]

    5-Pentaphenylcyclopentadienyl)RuCl(CO)2 was found to catalyze efficiently the racemization of chiral alcohols such as (S)-1-phenylethanol, (S)-1-phenylpropan-2-ol, (S)-4-phenylbutan-2-ol and (S)-4-methoxy-1-phenylethanol at room temperature in the presence of a base. The catalytic activity of three other Ru(II) complexes was also investigated. The effects of halide and solvent were studied as well.

  • 176.
    Csjernyik, Gábor
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Notheisz, Ferenc
    Zsigmond, Ágnes
    Ruthenium-Catalyzed Aerobic Oxidation of Alcohols on Zeolite-Encapsulated Cobalt Salophen Catalyst2002In: Topics in catalysis, ISSN 1022-5528, Vol. 19, no 1, p. 119-124Article in journal (Refereed)
  • 177.
    Csjernyik, Gábor
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Éll, Alida H
    Fadini, Luca
    Pugin, Benoit
    Efficient Ruthenium-Catalyzed Aerobic Oxidation of Alcohols Using a Biomimetic Coupled Catalytic System2002In: Journal of Organic Chemistry, ISSN 0022-3263, Vol. 67, no 5, p. 1657-1662Article in journal (Refereed)
  • 178.
    Cumpstey, Ian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Neodisaccharide diglycosyl compounds: Ethers, thioethers and selenoethers. A survey of their synthesis and biological activity2011In: Comptes rendus. Chimie, ISSN 1631-0748, E-ISSN 1878-1543, Vol. 14, no 2-3, p. 274-285Article in journal (Refereed)
    Abstract [en]

    This article gives an account of the area of nonglycosidically linked neodisaccharide compounds consisting of two monosaccharides linked by formal condensation without using the anomeric centre, i.e. by ether bonds, and also their thioether and selenoether counterparts. Synthetic methods and biological relevance are covered.

  • 179.
    Cumpstey, Ian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    New oligosaccharide analogues: non-glycosidically linked thioether-bridged pseudodisaccharides2006In: Synlett, ISSN 0936-5214, no 11, p. 1711-1714Article in journal (Refereed)
  • 180.
    Cumpstey, Ian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Short synthesis of a benzyl ether protected building block for the synthesis of carbocyclic galactopyranose mimics2010In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 345, no 8, p. 1056-1060Article in journal (Refereed)
  • 181.
    Cumpstey, Ian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Agrawal, Santosh
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Borbas, K. Eszter
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Iridium-catalysed condensation of alcohols and amines as a method for aminosugar synthesis2011In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 47, no 27, p. 7827-7829Article in journal (Refereed)
    Abstract [en]

    Primary carbohydrate amines at primary and secondary carbons are alkylated by alcohols in the presence of [Cp*IrCl2]2. When primary carbohydrate alcohols are used as the coupling partners and in the presence of Cs2CO3, amine-linked pseudodisaccharides are obtained. Secondary carbohydrate alcohols are unaffected under these conditions, which allows regioselective reactions.

  • 182.
    Cumpstey, Ian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Alonzi, Dominic S.
    Butters, Terry D.
    Carbasugar-thioether pseudodisaccharides related to N-glycan biosynthesis2009In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 344, no 4, p. 454-459Article in journal (Refereed)
  • 183.
    Cumpstey, Ian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eriksson, Lars
    Department of Physical, Inorganic and Structural Chemistry.
    Bis(methyl 2,4,6-tri-O-acetyl-beta-D-allofuranosid-3-yl)sulfane2007In: Acta Crystallographica Section E, ISSN 1600-5368, Vol. E63, p. o4197-Article in journal (Refereed)
  • 184.
    Cumpstey, Ian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Frigell, Jens
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pershagen, Elias
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Akhtar, Tashfeen
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Moreno-Clavijo, Elena
    Robina, Inmaculada
    Alonzi, Dominic S.
    Butters, Terry D.
    Amine-linked diglycosides: Synthesis facilitated by the enhanced reactivity of allylic electrophiles, and glycosidase inhibition assays2011In: Beilstein Journal of Organic Chemistry, ISSN 2195-951X, E-ISSN 1860-5397, Vol. 7, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Diglycose derivatives, consisting of two monosaccharides linked at non-anomeric positions by a bridging nitrogen atom, have been synthesised. Conversion of one of the precursor monosaccharide coupling components into an unsaturated derivative enhances its electrophilicity at the allylic position, facilitating coupling reactions. Mitsunobu coupling between nosylamides and 2,3-unsaturated-4-alcohols gave the 4-amino-pseudodisaccharides with inversion of configuration as single regio- and diastereoisomers. A palladium-catalysed coupling between an amine and a 2,3-unsaturated 4-trichloroacetimidate gave a 2-amino-pseudodisaccharide as the major product, along with other minor products. Derivatisation of the C=C double bond in pseudodisaccharides allowed the formation of Man(N4-6)Glc and Man(N4-6)Man diglycosides. The amine-linked diglycosides were found to show weak glycosidase inhibitory activity.

  • 185.
    Cumpstey, Ian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gehrke, Sebastian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Erfan, Sayeh
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Cribiù, Riccardo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Studies on the synthesis of valienamine and 1-epi-valienamine starting from D-glucose or L-sorbose2008In: Carbohydrate Research, ISSN 0008-6215, Vol. 343, no 10-11, p. 1675-1692Article in journal (Refereed)
  • 186.
    Cumpstey, Ian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ramstadius, Clinton
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Akhtar, Tashfeen
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Goldstein, Irwin J
    Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI .
    Winter, Harry C
    Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI .
    Non-glycosidically linked pseudodisaccharides: thioethers, sulfoxides, sulfones, ethers, selenoethers, and their binding to lectins2010In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 10, p. 1951-1970Article in journal (Refereed)
    Abstract [en]

    Hydrolytically stable non-glycosidically linked tail-to-tail pseudodisaccharides are linked by a single bridging atom remote from the anomeric centre of the constituent monosaccharides. Some such pseudodisaccharides with sulfur or oxygen bridges were found to act as disaccharide mimetics in their binding to the Banana Lectin and to Concanavalin A. A versatile synthetic route to a small library of such compounds is described

  • 187.
    Cumpstey, Ian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ramstadius, Clinton
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Borbas, K. Eszter
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Investigation of Coupling Reactions for the Synthesis of Valienamine Pseudodisaccharides2011In: Synlett: Accounts and Rapid Communications in Synthetic Organic Chemistry, ISSN 0936-5214, E-ISSN 1437-2096, no 12, p. 1701-1704Article in journal (Refereed)
    Abstract [en]

    Amine-linked pseudodisaccharides based on valienamine were synthesised by C-N bond-forming reactions between valienol-derived C-1 electrophiles and carbohydrate nitrogen nucleophiles. Palladium-catalysed coupling with trichloroacetimidate leaving groups, Mitsunobu reactions with a nosylamide nucleophile, and alkylation of amines by C-1 bromides were investigated.

  • 188.
    Cumpstey, Ian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ramstadius, Clinton
    Borbas, K. Eszter
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Alonzi, Dominic S.
    Butters, Terry D.
    Synthesis and alpha-Glucosidase II inhibitory activity of valienamine pseudodisaccharides relevant to N-glycan biosynthesis2011In: Bioorganic & Medicinal Chemistry Letters, ISSN 0960-894X, E-ISSN 1090-2120, Vol. 21, no 18, p. 5219-5223Article in journal (Refereed)
    Abstract [en]

    Valienol-derived allylic C-1 bromides have been used as carbaglycosyl donors for alpha-xylo configured valienamine pseudodisaccharide synthesis. We synthesised valienamine analogues of the Glc(alpha 1 -> 3)Glc and Glc(alpha 1 -> 3) Man disaccharides representing the linkages cleaved by alpha-Glucosidase II in N-glycan biosynthesis. These (N1 -> 3)-linked pseudodisaccharides were found to have some alpha-Glucosidase II inhibitory activity, while two other (N1 -> 6)-linked valienamine pseudodisaccharides failed to inhibit the enzyme. (C)

  • 189. Córdova, A
    et al.
    Sundén, H
    Engqvist, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    The Direct Amino Acid-Catalyzed Asymmetric Incorporation of Molecular Oxygen to Organic Compounds2004In: Journal of the American Chemical Society, ISSN 0002-7863, Vol. 126, no 29, p. 8914-8915Article in journal (Refereed)
  • 190.
    Córdova, Armando
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Engqvist, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ibrahem, Ismail
    Casas, Jésus
    Sundén, Henrik
    Plausible origins of homochirality in the amino acid catalyzed neogenesis of carbohydrates2005In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 2005, p. 2047-2049Article in journal (Refereed)
    Abstract [en]

    The intrinsic ability of amino acids to catalyze the asymmetric formation of carbohydrates, which enzymes have mediated for millions of years, with significant amplification of enantiomeric excess suggests a plausible ancient catalytic process for the evolution of homochirality.

  • 191.
    Córdova, Armando
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ibrahem, Ismail
    Casas, Jesús
    Sundén, Henrik
    Engqvist, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Reyes, Efraim
    Amino Acid-Catalyzed Neogenesis of Carbohydrates: A Plausible Ancient Transformation2005In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 11, no 16, p. 4772-4784Article in journal (Refereed)
    Abstract [en]

    Hexose sugars play a fundamental role in vital biochemical processes and their biosynthesis is achieved through enzyme-catalyzed pathways. Herein we disclose the ability of amino acids to catalyze the asymmetric neogenesis of carbohydrates by sequential cross-aldol reactions. The amino acids mediate the asymmetric de novo synthesis of natural L- and D-hexoses and their analogues with excellent stereoselectivity in organic solvents. In some cases, the four new stereocenters are assembled with almost absolute stereocontrol. The unique feature of these results is that, when an amino acid is employed as the catalyst, a single reaction sequence can convert a protected glycol aldehyde into a hexose in one step. For example, proline and its derivatives catalyze the asymmetric neogenesis of allose with >99 % ee in one chemical manipulation. Furthermore, all amino acids tested catalyzed the asymmetric formation of natural sugars under prebiotic conditions, with alanine being the smallest catalyst. The inherent simplicity of this catalytic process suggests that a catalytic prebiotic “gluconeogenesis” may occur, in which amino acids transfer their stereochemical information to sugars. In addition, the amino acid catalyzed stereoselective sequential cross-aldol reactions were performed as a two-step procedure with different aldehydes as acceptors and nucleophiles. The employment of two different amino acids as catalysts for the iterative direct aldol reactions enabled the asymmetric synthesis of deoxysugars with >99 % ee. In addition, the direct amino acid catalyzed C2+C2+C2 methodology is a new entry for the short, highly enantioselective de novo synthesis of carbohydrate derivatives, isotope-labeled sugars, and polyketide natural products. The one-pot asymmetric de novo syntheses of deoxy and polyketide carbohydrates involved a novel dynamic kinetic asymmetric transformation (DYKAT) mediated by an amino acid.

  • 192.
    Córdova, Armando
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Rios, Ramón
    The University of Barcelona, Departament Química Orgànica.
    Highly Z- and enantioselective ring-opening/cross-metathesis reactions and Z-selective ring-opening metathesis polymerization2009In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 48, no 47, p. 8827-8831Article in journal (Refereed)
  • 193. Daikoku, S.
    et al.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kanie, Y.
    Ito, Y.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kanie, O.
    Synthesis and structural investigation of a series of mannose-containing oligosaccharides using mass spectrometry2018In: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 16, no 2, p. 228-238Article in journal (Refereed)
    Abstract [en]

    A series of compounds associated with naturally occurring and biologically relevant glycans consisting of alpha-mannosides were prepared and analyzed using collision-induced dissociation (CID), energy-resolved mass spectrometry (ERMS), and H-1 nuclear magnetic resonance spectroscopy. The CID experiments of sodiated species of disaccharides and ERMS experiments revealed that the order of stability of mannosyl linkages was as follows: 6-linked > 4-linked >= 2-linked > 3-linked mannosyl residues. Analysis of linear trisaccharides revealed that the order observed in disaccharides could be applied to higher glycans. A branched trisaccharide showed a distinct dissociation pattern with two constituting disaccharide ions. The estimation of the content of this ion mixture was possible using the disaccharide spectra. The hydrolysis of mannose linkages at 3- and 6-positions in the branched trisaccharide revealed that the 3-linkage was cleaved twice as fast as the 6-linkage. It was observed that the solution-phase hydrolysis and gas-phase dissociation have similar energetics.

  • 194. Daikoku, Shusaku
    et al.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kanie, Osamu
    Analysis of a series of isomeric oligosaccharides by energy-resolved mass spectrometry: a challenge on homobranched trisaccharides2009In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 23, no 23, p. 3713-3719Article in journal (Refereed)
  • 195.
    Das, Arindam
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Alam, Rauful
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stereocontrol in Synthesis of Homoallylic Amines. Syn Selective Direct Allylation of Hydrazones with Allylboronic Acids2014In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 16, no 14, p. 3808-3811Article in journal (Refereed)
    Abstract [en]

    Allylboronic acids directly react with acyl hydrazones, affording homoallylic amine derivatives. The reaction proceeds with very high syn selectivity, which is the opposite of the stereochemistry observed for allylboration of imines. The reaction can be carried out with both aromatic and aliphatic acyl hydrazones. Based on our studies the excellent syn stereochemistry can be explained by chelation control of the acyl hydrazone and the B(OH)(2) moiety.

  • 196.
    Das, Arindam
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Wang, Dong
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Belhomme, Marie-Charlotte
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Copper-Catalyzed Cross-Coupling of Allylboronic Acids with alpha-Diazoketones2015In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 17, no 19, p. 4754-4757Article in journal (Refereed)
    Abstract [en]

    Copper-catalyzed cross-coupling of substituted allylboronic acids with alpha-diazoketones was studied. This allylation reaction is highly regioselective, providing the branched allylic product. The process involves creation of a new C(sp(3))-C(sp(3)) bond by retaining the keto functional group of the alpha-diazoketone precursor.

  • 197. Das, Biswanath
    et al.
    Daver, Henrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pyrkosz-Bulska, Monika
    Persch, Elke
    Barman, Suman K.
    Mukherjee, Rabindranath
    Gumienna-Kontecka, Elzbieta
    Jarenmark, Martin
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nordlander, Ebbe
    A dinuclear zinc(II) complex of a new unsymmetric ligand with an N(5)0(2) donor set; A structural and functional model for the active site of zinc phosphoesterases2014In: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 132, p. 6-17Article in journal (Refereed)
    Abstract [en]

    The dinuclear complex [Zn-2(DPCPMP)(pivalate)](C10(4)), where DPCPMP is the new unsymmetrical ligand [2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin2-y1)methyl)amino)acetic acid], has been synthesized and characterized. The complex is a functional model for zinc phosphoesterases with dinuclear active sites. The hydrolytic efficacy of the complex has been investigated using bis-(2,4-dinitrophenyl)phosphate(BDNPP), a DNA analog, as substrate. Speciation studies using potentiometric titrations have been performed for both the ligand and the corresponding dizinc complex to elucidate the formation of the active hydrolysis catalyst; they reveals that the dinuclear zinc(II) complexes, [Zn-2(DPCPMP)](2) and [Zn-2(DPCPMP)(OH)1 predominate the solution above pH 4. The relatively high pKa of 8.38 for water deprotonation suggests that a terminal hydroxide complex is formed. Kinetic investigations of BDNPP hydrolysis over the pH range 5.5-11.0 and with varying metal to ligand ratio (metal salt:ligand = 0.5:1 to 3:1) have been performed. Variable temperature studies gave the activation parameters triangle H double dagger = 95.6 kJ mol(-1), triangle S double dagger = 44.8 J mo1(-1) K-1, and 6,triangle G double dagger = 108.0 kJ mo1-1. The cumulative results indicate the hydroxido-bridged dinuclear Zn(II) complex [Zn-2(DPCPMP)(mu-OH)] (+) as the effective catalyst. The mechanism of hydrolysis has been probed by computational modeling using density functional theory (DFF). Calculations show that the reaction goes through one concerted step (S(N)2 type) in which the bridging hydroxide in the transition state becomes terminal and performs a nucleophilic attack on the BDNPP phosphorus; the leaving group dissociates simultaneously in an overall inner sphere type activation. The calculated free energy barrier is in good agreement with the experimentally determined activation parameters.

  • 198. Das, Biswanath
    et al.
    Daver, Henrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Singh, Amrendra
    Singh, Reena
    Haukka, Matti
    Demeshko, Serhiy
    Meyer, Franc
    Lisensky, George
    Jarenmark, Martin
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nordlander, Ebbe
    A Heterobimetallic FeIIIMnII Complex of an Unsymmetrical Dinucleating Ligand: A Structural and Functional Model Complex for the Active Site of Purple Acid Phosphatase of Sweet Potato2014In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, Vol. 2014, no 13, p. 2204-2212Article in journal (Refereed)
    Abstract [en]

    The heterodinuclear mixed-valence complex [FeMn(ICIMP)(OAc)(2)Cl] (1) {H2ICIMP = 2-(N-carboxylmethyl)-[N-(N-methylimidazolyl-2-methyl)aminomethyl]-[6-(N-isopropylmethyl)-[N-(N-methylimidazolyl-2-methyl)]aminomethyl-4-methylphenol], an unsymmetrical N4O2 donor ligand} has been synthesized and fully characterized by several spectroscopic techniques as well as by X-ray crystallography. The crystal structure of the complex reveals that both metal centers in 1 are six-coordinate with the chloride ion occupying the sixth coordination site of the Mn-II ion. The phenoxide moiety of the ICIMP ligand and both acetate ligands bridge the two metal ions of the complex. Mossbauer spectroscopy shows that the iron ion in 1 is high-spin Fe-III. Two quasi-reversible redox reactions for the complex, attributed to the (FeMnII)-Mn-III/(FeMnII)-Mn-II (at -0.67 V versus Fc/Fc(+)) and (FeMnII)-Mn-III/(FeMnIII)-Mn-III (at 0.84 V), were observed by means of cyclic voltammetry. Complex 1, with an Fe-III-Mn-II distance of 3.58 angstrom, may serve as a model for the mixed-valence oxidation state of purple acid phosphatase from sweet potato. The capability of the complex to effect organophosphate hydrolysis (phosphatase activity) has been investigated at different pH levels (5.5-11) by using bis(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. Density functional theory calculations indicate that the substrate coordinates to the Mn-II ion. In the transition state, a hydroxide ion that bridges the two metal ions becomes terminally coordinated to the Fe-III ion and acts as a nucleophile, attacking the phosphorus center of BDNPP with the concomitant dissociation of the leaving group.

  • 199. Das, Biswanath
    et al.
    Lee, Bao-Lin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Karlsson, Erik A.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Torbjörn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Shatskiy, Andrey
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Demeshko, Serhiy
    Liao, Rong-Zhen
    Laine, Tanja M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Haukka, Matti
    Zeglio, Erica
    Abdel-Magied, Ahmed F.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Meyer, Franc
    Kärkäs, Markus D.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johnston, Eric V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nordlander, Ebbe
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Water oxidation catalyzed by molecular di- and nonanuclear Fe complexes: importance of a proper ligand framework2016In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 45, no 34, p. 13289-13293Article in journal (Refereed)
    Abstract [en]

    The synthesis of two molecular iron complexes, a dinuclear iron(III,III) complex and a nonanuclear iron complex, based on the di-nucleating ligand 2,2'-(2-hydroxy-5-methyl-1,3-phenylene)bis(1H-benzo[d]imidazole-4-carboxylic acid) is described. The two iron complexes were found to drive the oxidation of water by the one-electron oxidant [Ru(bpy)(3)](3+).

  • 200.
    Daver, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Das, Biswanath
    Nordlander, Ebbe
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Theoretical Study of Phosphodiester Hydrolysis and Transesterification Catalyzed by an Unsymmetric Biomimetic Dizinc Complex2016In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 55, no 4, p. 1872-1882Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations have been used to investigate the reaction mechanisms of phosphodiester hydrolysis and transesterification catalyzed by a dinuclear zinc complex of the 2-(N-isopropyl-N-((2-pyridyl)methyl)-aminomethyl)-6-(N-(carboxylmethyl)-N-((2-pyridyl)methyl)amino-methyl)-4-methylphenol (IPCPMP) ligand, mimicking the active site of zinc phosphotriesterase. The substrates bis(2,4)-dinitrophenyl phosphate (BDNPP) and 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) were employed as analogues of DNA and RNA, respectively. A number of different mechanistic proposals were considered, with the active catalyst harboring either one or two hydroxide ions. It is concluded that for both reactions the catalyst has only one hydroxide bound, as this option yields lower overall energy barriers. For BDNPP hydrolysis, it is suggested that the hydroxide acts as the nucleophile in the reaction, attacking the phosphorus center of the substrate. For HPNP transesterification, on the other hand, the hydroxide is proposed to act as a Bronsted base, deprotonating the alcohol moiety of the substrate, which in turn performs the nucleophilic attack. The calculated overall barriers are in good agreement with measured rates. Both reactions are found to proceed by essentially concerted associative mechanisms, and it is demonstrated that two consecutive catalytic cycles need to be considered in order to determine the rate-determining free energy barrier.

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