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  • 301.
    Deng, Youqian
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Teresa, Bartholomeyzik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Control of Selectivity in Palladium-Catalyzed Oxidative Carbocyclization/Borylation of Allenynes2013Inngår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 52, nr 24, s. 6283-6287Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In control: A highly selective carbocyclization/borylation of allenynes with bis(pinacolato)diboron (B2pin2) under palladium catalysis and with p-benzoquinone (BQ) as the oxidant was developed. The use of either LiOAc⋅2 H2O with 1,2-dichloroethane (DCE) as the solvent or BF3⋅Et2O together with THF is crucial for the selective formation of borylated trienes and vinylallenes, respectively.

  • 302.
    Deska, Jan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Enzymatic kinetic resolution of primary allenic alcohols. Application to the total synthesis and stereochemical assignment of striatisporolide A2009Inngår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 7, nr 17, s. 3379-3381Artikkel i tidsskrift (Fagfellevurdert)
  • 303.
    Deska, Jan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    del Pozo Ochoa, Carolina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Chemoenzymatic dynamic kinetic resolution of axially chiral allenes2010Inngår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, nr 15, s. 4447-4451Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dimeric palladium bromide complexes bearing monodentate N-heterocyclic carbene ligands have been identified as efficient catalysts for the chemoselective racemization of axially chiral allenyl alcohols. In combination with porcine pancreatic lipase as biocatalyst, a dynamic kinetic resolution has been developed, giving access to optically active allenes in good yield and high enantiomeric purity (

  • 304.
    Dey, Chandan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lindstedt, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Olofsson, Berit
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. Wallenberg Research Centre at Stellenbosch University, South Africa.
    Metal-Free C-Arylation of Nitro Compounds with Diaryliodonium Salts2015Inngår i: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 17, nr 18, s. 4554-4557Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An efficient, mild, and metal-free arylation of nitro-alkanes with diaryliodonium salts has been developed, giving easy access to tertiary nitro compounds. The reaction proceeds in high yields without the need for excess reagents and can be extended to alpha-arylation of nitroesters. Nitroalkanes were selectively C-arylated in the presence of other easily arylated functional groups, such as phenols and aliphatic alcohols.

  • 305.
    Diner, Colin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Recent Advances in the Preparation and Application of Allylboron Species in Organic Synthesis2017Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, nr 1, s. 2-14Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    In this Perspective we will highlight the most important recent breakthroughs in selective allylboron chemistry (both the synthesis and application of these species). In addition we will provide an outlook toward the future of this promising subfield of organic synthesis.

  • 306. Dorange, Ismet
    et al.
    Löfstedt, Joakim
    Franzén, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Närhi, Katja
    Bäckvall, Jan E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Allenes as Carbon Nucleophiles in Intramolecular Attack on (π-1,3-diene)Palladium Complexes: Evidence for trans-Carbopalladation of the 1,3-Diene2003Inngår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 9, nr 14, s. 3445-3449Artikkel i tidsskrift (Fagfellevurdert)
  • 307. Duan, Lele
    et al.
    Bozoglian, Fernando
    Mandal, Sukanta
    Stewart, Beverly
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Privalov, Timofei
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Llobet, Antoni
    Sun, Licheng
    A molecular ruthenium catalyst with water-oxidation activity comparable to that of photosystem II2012Inngår i: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 4, nr 5, s. 418-423Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Across chemical disciplines, an interest in developing artificial water splitting to O-2 and H-2, driven by sunlight, has been motivated by the need for practical and environmentally friendly power generation without the consumption of fossil fuels. The central issue in light-driven water splitting is the efficiency of the water oxidation, which in the best-known catalysts falls short of the desired level by approximately two orders of magnitude. Here, we show that it is possible to close that 'two orders of magnitude' gap with a rationally designed molecular catalyst [Ru(bda)(isoq)(2)] (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; isoq = isoquinoline). This speeds up the water oxidation to an unprecedentedly high reaction rate with a turnover frequency of >300 s(-1). This value is, for the first time, moderately comparable with the reaction rate of 100-400 s(-1) of the oxygen-evolving complex of photosystem II in vivo.

  • 308.
    Duan, Lele
    et al.
    Department of Chemistry, Royal Institute of Technology .
    Nyhlén, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Fischer, Andreas
    Department of Chemistry, Royal Institute of Technology .
    Xu, Yunhua
    Department of Chemistry, Royal Institute of Technology .
    Privalov, Timofei
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sun, Licheng
    Department of Chemistry, Royal Institute of Technology .
    Highly Active Mononuclear Ru Catalysts for Water Oxidation: O-O Bond Formation via Direct Radical CouplingInngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Artikkel i tidsskrift (Fagfellevurdert)
  • 309. Dutheuil, Guillaume
    et al.
    Selander, Nicklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Aggarwal, Varinder K.
    Direct synthesis of functionalized allylic boronic esters from allylic alcohols and inexpensive reagents and catalysts2008Inngår i: Synthesis (Stuttgart), ISSN 0039-7881, E-ISSN 1437-210X, nr 14, s. 2293-2297Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A remarkably simple and effective system for the direct conversion of allylic alcohols into high value allylic boronic esters using commercially available reagents and catalysts is described.

  • 310.
    Dziedzic, Pawel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Amino acid-catalyzed synthesis of amino acid derivatives: Application and semi-synthesis of Paclitaxel, Docetaxel and their derivatives2010Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis deals with different applications of organocatalysis, where amino acid derivatives and small peptides are applied as catalysts. First, the development of environmentally friendly aldol reactions, carried out in aqueous media is illustrated. The corresponding β-hydroxy ketones are formed with ee´s up to 99%. Chapter 3 describes the ability of β3-amino acids to selectively catalyze Mannich-type reactions and govern the formation of products with high anti-selectivity (up to >19:1) and ee´s up to 99%. In the following chapter, an amino acid-catalyzed one-pot three component Mannich reaction between dihydroxyacetone and PMP-protected imines, is presented. The corresponding a,a’-dihydroxy-b-aminoketones are obtained in high yields and with 82-95% ee. Next, an aza-Morita-Baylis-Hillman reaction was investigated where L-proline is the catalyst. The reaction proceeds with excellent chemo- and enantioselectivity to give the corresponding compounds in good yields and with 97-99% ee. Finally, the last part describes development of a proline-catalyzed Mannich reation between N-acyl imines and protected α-hydroxyaldehyes, providing access to different α-hydroxy-β-amino acids in good yields and high enantioselctivity (92-99% ee). The obtained amino acids were further applied in the semisynthesis of paclitaxel and docetaxel derivatives.

  • 311.
    Dziedzic, Pawel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Asymmetric Organocatalytic Aldol and Mannich Reactions Catalyzed by Amino Acid-Derivatives and Small Peptides with a Primary Amine Functionality2008Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 312.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bartoszewicz, Agnieszka
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Inorganic ammonium salts as catalysts for direct aldol reactions in the presence of water2009Inngår i: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 50, nr 52, s. 7242-7245Artikkel i tidsskrift (Fagfellevurdert)
  • 313.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Acyclic beta-amino acid catalyzed asymmetric anti-selective Mannich-type reactions2007Inngår i: Tetrahedron: asymmetry, ISSN 0957-4166, E-ISSN 1362-511X, Vol. 18, nr 9, s. 1033-1037Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     The ability of a primary amine containing acyclic beta(3)-amino acids to catalyze direct asymmetric anti-selective Mannich-type reactions is presented. The reactions are generally highly diastereo- and enantioselective to give the corresponding Mannich products with up to >19:1 dr (anti/syn) and 88-99% ee.

  • 314.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ibrahem, Ismail
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Direct catalytic asymmetric three-component Mannich reactions with dihydroxyacetone: enantioselective synthesis of amino sugar derivatives2008Inngår i: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 49, nr 5, s. 803-807Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Highly enantioselective, amino acid-catalyzed, one-pot three-component asymmetric Mannich reactions between dihydroxyacetone, p-anisidine, and aldehydes are presented. The reactions proceeded with high chemo- and stereoselectivity and furnished the corresponding α,α′-dihydroxy-β-aminoketones in high yields with 82–95% ee.

  • 315.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Schyman, Patric
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kullberg, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Highly enantioselective organocatalytic addition of aldehydes to acylimines: Asymmetric syntheses of the paclitaxel and docetaxel side-chains and their analogs2010Inngår i: Abstracts of Papers, 239th ACS National Meeting, San Francisco, CA, United States, March 21-25, 2010, Washington, D C: American Chemical Society , 2010Konferansepaper (Annet vitenskapelig)
  • 316.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Schyman, Patric
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Avdelningen för fysikalisk kemi.
    Kullberg, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Highly enantioselective organocatalytic addition of aldehydes to N-(phenylmethylene)benzamides: Asymmetric synthesis of the paclitaxel side chain and its analogues2009Inngår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, nr 16, s. 4044-4048Artikkel i tidsskrift (Fagfellevurdert)
  • 317.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Vesely, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Catalytic asymmetric synthesis of the docetaxel (Taxotere) side chain: organocatalytic highly enantioselective synthesis of esterification-ready alpha-hydroxy-beta-amino acids2008Inngår i: Tetrahedron Letters, ISSN 0040-4039, Vol. 49, nr 47, s. 6631-6634Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A highly enantioselective catalytic route to protected β-amino-α-hydroxy acids, such as the side chain of Taxotere, is presented. The organocatalytic asymmetric reactions between unmodified protected α-oxyaldehydes and N-Boc-protected aryl imines give the corresponding compound with up to >19:1 dr and 99–99% ee.

  • 318.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Weibiao, Zou
    Hafrén, Jonas
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    The small peptide-catalyzed direct asymmetric aldol reaction in water2006Inngår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 4, s. 38-40Artikkel i tidsskrift (Fagfellevurdert)
  • 319.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Zhao, Gui-ling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Practical amino acid-catalyzed asymmetric synthesis pf protected α-hydroxy-amino aldehydes and acidsManuskript (preprint) (Annet vitenskapelig)
  • 320.
    Edin, Michaela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ruthenium-catalyzed redox reactions and lipase-catalyzed asymmetric transformations of alcohols2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The major part of this thesis describes the synthesis of enantiopure alcohols and diols by combining ruthenium-catalyzed redox reactions that lead to racemization or epimerization and lipase-catalyzed asymmetric trans-formations in one-pot.

    A mechanistic study of the unexpected facile formation of meso-diacetate products found in enzyme-catalyzed acetylations of alkanediols with Candida antarctica lipase B (CALB) was first performed. By deuterium labeling it was found that the formation of meso-diacetates proceeds via different mechanisms for 2,4-pentanediol and 2,5-hexanediol. Whereas the first reacts via an intramolecular acyl migration, the latter proceeds via a direct, anomalous S-acylation of the alcohol. The acyl migration occurring in the 2,4-pentanediol monoacetate was taken advantage of in asymmetric transformations of substituted 1,3-diols by combining it with a ruthenium-catalyzed epimerization and an enzymatic transesterification using CALB. The in situ coupling of these three processes results in de-epimerization and deracemization of acyclic, unsymmetrical 1,3-diols and constitutes a novel dynamic kinetic asymmetric transformation (DYKAT) concept.

    Racemization of secondary alcohols effected by a new ruthenium complex was combined in one-pot with an enzyme-catalyzed transesterification, leading to a chemoenzymatic dynamic kinetic resolution (DKR) operating at room temperature. Aromatic, aliphatic, heterocyclic and functionalized alcohols were subjected to the procedure. A mechanism for racemization by this ruthenium complex has been proposed and experimental indications for hydrogen transfer within the coordination sphere of ruthenium were found. The same ruthenium catalyst was used for epimerization in DYKAT of 1,2-diols, and a very similar complex was employed in isomerization of allylic alcohols to saturated ketones. The former method is a substrate extension of the above principle applied for DYKAT of 1,3-diols. The combination of a lipase and an organocatalyst was demonstrated by linking a lipase-catalyzed transesterification to a proline-mediated aldol reaction for the production of enantiopure (S)-β-hydroxy ketones and acetylated (R)-aldols.

  • 321.
    Edin, Michaela
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    On the mechanism of the unexpected facile formation of meso-diacetate products in enzymatic acetylation of alkanediols2003Inngår i: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 68, s. 2216-2222Artikkel i tidsskrift (Fagfellevurdert)
  • 322.
    Edin, Michaela
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Córdova, Armando
    Tandem enantioselective organo- and biocatalysis: a direct entry for the synthesis of enantiomerically pure aldols2004Inngår i: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 45, s. 7697-7701Artikkel i tidsskrift (Fagfellevurdert)
  • 323.
    Edin, Michaela
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Martín-Matute, Belén
    Bäckvall, Jan-E.
    Dynamic kinetic asymmetric transformation of 1,2-diols: an enantioselective synthesis of syn-1,2-diacetatesManuskript (Annet vitenskapelig)
  • 324.
    Edin, Michaela
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Steinreiber, Johannes
    Bäckvall, Jan-E.
    One-pot synthesis of enantiopure syn-1,3-diacetates from racemic diastereomeric mixtures of 1,3-diols by dynamic kinetic asymmetric transformation2004Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 101, s. 5761-5766Artikkel i tidsskrift (Fagfellevurdert)
  • 325.
    Eklund, Robert
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Computational Analysis of Carbohydrates: Dynamical Properties and Interactions2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis a computational complement to experimental observables will be presented. Computational tools such as molecular dynamics and quantum chemical tools will be used to aid in the interpretation of experimentally (NMR) obtained structural data. The techniques are applied to study the dynamical features of biologically important carbohydrates and their interaction with proteins. When evaluating conformations, molecular mechanical methods are commonly used. Paper I, highlights some important considerations and focuses on the force field parameters pertaining to carbohydrate moieties. Testing of the new parameters on a trisaccharide showed promising results. In Paper II, a conformational analysis of a part of the repeating unit of a Shigella flexneri bacterium lipopolysaccharide using the modified force field revealed two major conformational states. The results showed good agreement with experimental data. In Paper III, a trisaccharide using Langevin dynamics was investigated. The approach used in the population analysis included a least-square fit technique to match T1 elaxation parameters. The results showed good agreement with experimental T-ROE build-up curves, and three states were concluded to be involved. In Paper IV, carbohydrate moieties were used in the development of prodrug candidates, to “hide” peptide opioid receptor agonists. Langevin dynamics and quantum chemical methods were employed to elucidate the structural preference of the compound. The results showed a chemical shift difference between hydrogens across the ring for the two isomers as well as a difference in the coupling constant, when taking the dynamics into account. In Paper V, the interaction of the Salmonella enteritidis bacteriophage P22 with its host bacterium, involves an initial hydrolysis of the O-antigenic polysaccharide (O-PS). Docking calculations were used to examine the binding between the Phage P22 tail-spike protein and the O-PS repeating unit. Results indicated a possible active site in conjunction with NMR measurements.

  • 326.
    Eklund, Robert
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lycknert, Kristina
    Söderman, Peter
    Widmalm, Göran
    Söderman,
    A conformational dynamics study of a-L-Rhap-(1-->2)[a-L-Rhap-(1-->3)]-a-L-Rhap-OMe in solution by NMR experiments and molecular simulationsManuskript (Annet vitenskapelig)
  • 327.
    Eklund, Robert
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Roscic, Maja
    Nordmark, Eva-Lisa
    Widmalm, Göran
    Horvat, Stefica
    Stereochemical assignment of diastereomeric imidazolidinone ring containing bicyclic sugar-peptide addects: NMR Spectroscopy and molecular calculations2004Inngår i: European Journal of Organic Chemistry, ISSN 1434-193X, nr 22, s. 4641-4647Artikkel i tidsskrift (Fagfellevurdert)
  • 328.
    Eklund, Robert
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Molecular dynamics simulations of an oligosaccharide using a force field modified for carbohydrates2003Inngår i: Carbohydrate Research, ISSN 0008-6215, Vol. 338, nr 5, s. 393-398Artikkel i tidsskrift (Fagfellevurdert)
  • 329.
    Ekström, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Transition Metal Hydrides: Biomimetic Studies and Catalytic Applications2007Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis, studies of the nature of different transition metal-hydride complexes are described. The first part deals with the enantioswitchable behaviour of rhodium complexes derived from amino acids, applied in asymmetric transfer hydrogenation of ketones. We found that the use of amino acid thio amide ligands resulted in the formation of the R-configured product, whereas the use of the corresponding hydroxamic acid- or hydrazide ligands selectively gave the S-alcohol.

    Structure/activity investigations revealed that the stereochemical outcome of the catalytic reaction depends on the ligand mode of coordination.

    In the second part, an Fe hydrogenase active site model complex with a labile amine ligand has been synthesized and studied. The aim of this study was to find a complex that efficiently catalyzes the reduction of protons to molecular hydrogen under mild conditions. We found that the amine ligand functions as a mimic of the loosely bound ligand which is part of the active site in the hydrogenase.

    Further, an Fe hydrogenase active site model complex has been coupled to a photosensitizer with the aim of achieving light induced hydrogen production. The redox properties of the produced complex are such that no electron transfer from the photosensitizer part to the Fe moiety occurs.

    In the last part of this thesis, the development of a protocol for the transfer hydrogenation of ketones to secondary alcohols without the involvement of transition metal catalysts is described. A variety of ketones were efficiently reduced in 2-propanol using catalytic amounts of alkali alkoxide under microwave irradiation.

  • 330.
    Ekström, Jesper
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Abrahamsson, Maria
    Olson, Carol
    Bergquist, Jonas
    Kanyak, Feliz B.
    Eriksson, Lars
    Sun, Licheng
    Åkermark, Björn
    Becker, Hans-Christian
    Hammarström, Leif
    Ott, Sascha
    Bio Inspired Side-on Attachment of a Ruthenium Photo-sensitizer to an Iron Hydrogenase Active Site Model2006Inngår i: Dalton Transactions, ISSN 1477-9226, nr 38, s. 4599-4606Artikkel i tidsskrift (Fagfellevurdert)
  • 331.
    Ekström, Jesper
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Wettergren, Jenny
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    A Simple and Efficient Catalytic Method for the Reduction of Ketones2007Inngår i: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 349, nr 10, s. 1609-1613Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A range of ketones was efficiently reduced in the presence of catalytic amounts of lithium isopropoxide in 2-propanol under microwave heating, with alcohol products being formed in yields up to 99 %.

  • 332.
    Endo, Yoshinori
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Aerobic Lactonization of Diols by Biomimetic Oxidation2011Inngår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, nr 45, s. 12596-12601Artikkel i tidsskrift (Fagfellevurdert)
  • 333.
    Endo, Yoshinori
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Biomimetic Oxidative Coupling of Benzylamines and 2-Aminophenols: Synthesis of Benzoxazoles2012Inngår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 18, nr 43, s. 13609-13613Artikkel i tidsskrift (Fagfellevurdert)
  • 334.
    Engelmark Cassimjee, Karim
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kadow, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Wikmark, Ylva
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Svedendahl Humble, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Rothstein, M. L.
    Rothstein, D. M.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    A general protein purification and immobilization method on controlled porosity glass: biocatalytic applications2014Inngår i: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 50, nr 65, s. 9134-9137Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A general combined purification and immobilization method to facilitate biocatalytic process development is presented. The support material, EziG (TM), is based on controlled porosity glass (CPG) or polymer-coated versions thereof (HybCPG) and binds protein affinity tags. Biocatalytic reactions in aqueous and organic media with seven enzymes of biocatalytic interest are shown.

  • 335.
    Engelmark Cassimjee, Karim
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Manta, Bianca
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    A quantum chemical study of the ω-transaminase reaction mechanism2015Inngår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 13, nr 31, s. 8453-8464Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    ω-Transaminases are valuable tools in biocatalysis due to their stereospecificity and their broad substrate range. In the present study, the reaction mechanism of Chromobacterium violaceum ω-transaminase is investigated by means of density functional theory calculations. A large active site model is designed based on the recent X-ray crystal structure. The detailed energy profile for the half-transamination of (S)-1-phenylethylamine to acetophenone is calculated and the involved transition states and intermediates are characterized. The model suggests that the amino substrate forms an external aldimine with the coenzyme pyridoxal-5′-phosphate (PLP), through geminal diamine intermediates. The external aldimine is then deprotonated in the rate-determining step, forming a planar quinonoid intermediate. A ketimine is then formed, after which a hemiaminal is produced by the addition of water. Subsequently, the ketone product is obtained together with pyridoxamine-5′-phosphate (PMP). In the studied half-transamination reaction the ketone product is kinetically favored. The mechanism presented here will be valuable to enhance rational and semi-rational design of engineered enzyme variants in the development of ω-transaminase chemistry.

  • 336.
    Engqvist, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Direct Amino Acid-Catalyzed Enantioselective α-Oxidation Reactions and Asymmetric de novo Synthesis of Carbohydrates2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The ability of amino acids to form nucleophilic enamines with aldehydes and ketones has been used in the development of asymmetric α-oxidation reactions with electrophilic oxidizing agents. Singlet molecular oxygen has for the first time been asymmetrically incorporated into aldehydes and ketones, and the products were isolated as their corresponding diols in good yields and ee’s. Organocatalytic α-oxidations of cyclic ketones with iodosobenzene and N-sulfonyloxaziridine were also possible and furnished after reduction the product diols in generally low yields and in low to good ee’s. Amino acids have also been shown to catalyze the formation of carbohydrates by sequential aldol reactions. For example, proline and hydroxy proline mediate a highly selective trimerisation of α-benzyloxyacetaldehyde into allose, which was obtained in >99 % ee. Non linear effect studies of this reaction revealed the largest permanent nonlinear effect observed in a proline-catalyzed reaction to date. Moreover, polyketides were also assembled in a similar fashion by an amino acid-catalyzed one-pot reaction, and was successful for the trimerisation of propionaldehyde, however the sequential cross aldol reactions suffered from lower selectivities. This problem was overcome by the development of a two-step synthesis that enabled the formation of a range of polyketides with excellent selectivities from a variety of aldehydes. The method furnishes the polyketides via the shortest route reported and in comparable product yields to most multi-step synthesis. All polyketides were isolated as single diastereomers with >99 % ee. Based on the observed amino acid-catalysis, amino acids are thought to have taken part in the prebiotic formation of tetroses and hexoses.

  • 337.
    Engqvist, Magnus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Casas, J
    Sundén, H
    Ibrahem, I
    Córdova, A
    Direct Organoctalytic Asymmetric α-Oxidation of Ketones with Iodosobenzene and N-sulfonyloxaziridine2004Inngår i: Tetrahedron letters, ISSN 0040-4039, Vol. 46, nr 12, s. 2053-2057Artikkel i tidsskrift (Fagfellevurdert)
  • 338.
    Engström, Karin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Enantioselective biotransformations using engineered lipases from Candida antarctica2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Enzymes are attractive catalysts in organic synthesis since they are efficient, selective and environmentally friendly. A large number of enzyme-catalyzed transformations have been described in the literature. If no natural enzyme can carry out a desirable reaction, one possibility is to modify an existing enzyme by protein engineering and thereby obtain a catalyst with the desired properties. In this thesis, the development of enantioselective enzymes and their use in synthetic applications is described. 

    In the first part of this thesis, enantioselective variants of Candida antarctica lipase A (CALA) towards α-substituted p-nitrophenyl esters were developed by directed evolution. A highly selective variant of CALA towards p-nitrophenyl 2-phenylpropanoate was developed by pairwise randomization of amino acid residues close to the active site. The E value of this variant was 276 compared to 3 for the wild type.

    An approach where nine residues were altered simultaneously was used to discover another highly enantioselective CALA variant (E = 100) towards an ibuprofen ester. The sterical demands of this substrate made it necessary to vary several residues at the same time in order to reach a variant with improved properties.

    In the second part of the thesis, a designed variant of Candida antarctica lipase B (CALB) was employed in kinetic resolution (KR) and dynamic kinetic resolution (DKR) of secondary alcohols. The designed CALB variant (W104A) accepts larger substrates compared to the wild type, and by the application of CALB W104A, the scope of these resolutions was extended.

    First, a DKR of phenylalkanols was developed using CALB W104A. An enzymatic resolution was combined with in situ racemization of the substrate, to yield the products in up to 97% ee. Secondly, the KR of diarylmethanols with CALB W104A was developed. By the use of diarylmethanols with two different aryl groups, highly enantioselective transformations were achieved.

  • 339.
    Engström, Karin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Protein engineering of enzymes for improved enantioselectivity and application of engineered enzymes in organic synthesis2010Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 340.
    Engström, Karin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Johnston, Eric V.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Verho, Oscar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Gustafson, Karl P. J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Shakeri, Mozaffar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Co-immobilization of an Enzyme and a Metal into the Compartments of Mesoporous Silica for Cooperative Tandem Catalysis: An Artificial Metalloenzyme2013Inngår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 52, nr 52, s. 14006-14010Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Surpassing nature: A hybrid catalyst in which Candida antarctica lipase B and a nanopalladium species are co-immobilized into the compartments of mesoporous silica is presented. The metal nanoparticles and the enzyme are in close proximity to one another in the cavities of the support. The catalyst mimics a metalloenzyme and was used for dynamic kinetic resolution of a primary amine in high yield and excellent enantioselectivity.

  • 341.
    Engström, Karin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Nyhlén, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sandström, Anders G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Directed evolution of an enantioselective lipase with broad substrate scope for hydrolysis of α-substituted esters2010Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, nr 20, s. 7038-7042Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A variant of Candida antarctica lipase A (CalA) was developed for the hydrolysis of α-substituted p-nitrophenyl esters by directed evolution. The E values of this variant for 7 different esters was 45−276, which is a large improvement compared to 2−20 for the wild type. The broad substrate scope of this enzyme variant is of synthetic use, and hydrolysis of the tested substrates proceeded with an enantiomeric excess between 95−99%. A 30-fold increase in activity was also observed for most substrates. The developed enzyme variant shows (R)-selectivity, which is reversed compared to the wild type that is (S)-selective for most substrates.

  • 342.
    Engström, Karin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Nyhlén, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sandström, Anders G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Enantioselective Kinetic Resolution of p-Nitrophenyl 2-Phenylpropanoate by a Variant of Candida antarctica Lipase A Developed by Directed Evolution2010Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, nr 20, s. 7038-7042Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A variant of Candida antarctica lipase A (CalA) was developed for the hydrolysis of α-substituted p-nitrophenyl esters by directed evolution. The E values of this variant for 7 different esters was 45−276, which is a large improvement compared to 2−20 for the wild type. The broad substrate scope of this enzyme variant is of synthetic use, and hydrolysis of the tested substrates proceeded with an enantiomeric excess between 95−99%. A 30-fold increase in activity was also observed for most substrates. The developed enzyme variant shows (R)-selectivity, which is reversed compared to the wild type that is (S)-selective for most substrates.

  • 343.
    Engström, Karin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Shakeri, Mozaffar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Dynamic Kinetic Resolution of β-Amino Esters by a Heterogeneous System of a Palladium Nanocatalyst and Candida antarctica Lipase A2011Inngår i: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, nr 10, s. 1827-1830Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A dynamic kinetic resolution (DKR) of β-amino esters have been developed by the use of a heterogeneous racemization catalyst and an immobilized enzyme that accepts aromatic, heteroaromatic and aliphatic substrates. The reaction conditions were optimized to yield an efficient catalytic system without by-product formation. The products are obtained in 96–99 % ee and high yields

  • 344.
    Engström, Karin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Vallin, Michaela
    Hult, Karl
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kinetic resolution of diarylmethanols using a mutated variant of lipase CALB2012Inngår i: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 68, nr 37, s. 7613-7618Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An enzymatic kinetic resolution of diarylmethanols via acylation has been developed. This was achieved by the use of a mutated variant of CALB that accepts larger substrates compared to the wild type. By the use of diarylmethanols with two differently sized aryl groups, enantioselective transformations were achieved. A larger size-difference led to a higher enantioselectivity. In addition, substrates with electronically different aryl groups, such as phenyl and pyridyl, also gave an enantioselective reaction. The highest E value was observed with a substrate where steric and electronic effects were combined.

  • 345.
    Engström, Karin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Vallin, Michaela
    Syrén, Per-Olof
    Hult, Karl
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mutated variant of Candida antarctica lipase B in (S)-selective dynamickinetic resolution of secondary alcohols2011Inngår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 9, nr 1, s. 81-82Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An (S)-selective dynamic kinetic resolution of secondaryalcohols, employing a mutated variant of Candida antarcticalipase B (CalB) gave products in 84–88% yield and in 90–97%ee.

  • 346.
    Engström, Olof
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Carbohydrate dynamics and interactions studied by NMR spectroscopy2013Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The combination of NMR spectroscopy and molecular dynamics (MD) simulations are powerful tools in the studying of bioorganic molecules in solution. In this thesis two such studies are presented with focus on the NMR aspect. The caffeine association to sugars (D-glucose and sucrose) was investigated by NMR titrations and NOESY experiments in paper I. The observations from the NMR experiments confirmed MD simulations showing that the binding occurs by a face-to-face interaction between the aromatic surface of the caffeine and axial protons of the sugar ring. Different sugar molecules and residues have different preferences regarding which side of the sugar ring that are involved in the binding. The sucrose residues bind with only one ring face each whereas β-D-glucopyranose has two sides of similar binding probability and the α-D-glucopyranose has something in between. The MD simulations showed that the driving force of the binding is partly driven by hydration effects that favor the enthalpy of the system. A new approach to calculate NMR relaxation parameters (that is dependent on molecular motions) from computational simulations is presented in paper II. Each sugar residue is assumed to be a rigid unit connected by flexible joints in the approach, thus the name diffusive chain model (DCM). The simplified model together with a stochastic simulation approach lowers the computational cost which makes it possible to acquire long enough trajectories to the calculations of spin relaxation parameters. Two case studies with slightly different methodologies are presented. In one of them, spin relaxation parameters are reproduced for the human milk oligosaccharide LNF-1 in a feasible way by the use of Brownian dynamics.

  • 347.
    Engström, Olof
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Exploring the Molecular Behavior of Carbohydrates by NMR Spectroscopy: Shapes, motions and interactions2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Carbohydrates are essential biomolecules that decorate cell membranes and proteins in organisms. They are important both as structural elements and as identification markers. Many biological and pathogenic processes rely on the identification of carbohydrates by proteins, thereby making them attractive as molecular blueprints for drugs. This thesis describes how NMR spectroscopy can be utilized to study carbohydrates in solution at a molecular level. This versatile technique facilitates for investigations of (i) shapes, (ii) motions and (iii) interactions.

    A conformational study of an E. coli O-antigen was performed by calculating atomic distances from NMR NOESY experiments. The acquired data was utilized to validate MD simulations of the LPS embedded in a membrane. The agreement between experimental and calculated data was good and deviations were proven to arise from spin-diffusion. In another study presented herein, both the conformation and the dynamic behavior of amide side-chains linked to derivatives of D-Fucp3N, a sugar found in the O-antigen of bacteria, were investigated. J-couplings facilitated a conformational analysis and 13C saturation transfer NMR experiments were utilized to measure rate constants of amide cis-trans isomerizations.

    13C NMR relaxation and 1H PFG diffusion measurements were carried out to explore and describe the molecular motion of mannofullerenes. The dominating motions of the mannofullerene spectral density were found to be related to pulsating motions of the linkers rather than global rotational diffusion. The promising inhibition of Ebola viruses identified for a larger mannofullerene can thus be explained by an efficient rebinding mechanism that arises from the observed flexibility in the linker.

    Molecular interactions between sugars and caffeine in water were studied by monitoring chemical shift displacements in titrations. The magnitude of the chemical shift displacements indicate that the binding occurs by a face to face stacking of the aromatic plane of caffeine to the ring plane of the sugar, and that the interaction is at least partly driven by solvation effects. Also, the binding of a Shigella flexneri serotype Y octasaccharide to a bacteriophage Sf6 tail spike protein was investigated. This interaction was studied by 1H STD NMR and trNOESY experiments. A quantitative analysis of the STD data was performed employing a newly developed method, CORCEMA-ST-CSD, that is able to simulate STD data more accurately since the line broadening of protein resonances are accounted for in the calculations.

  • 348.
    Engström, Olof
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mobarak, Hani
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ståhle, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Conformational Dynamics and Exchange Kinetics of N-Formyl and N-Acetyl Groups Substituting 3-Amino-3,6-dideoxy-alpha-D-galactopyranose, a Sugar Found in Bacterial O-Antigen Polysaccharides2017Inngår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 121, nr 41, s. 9487-9497Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Three dimensional shape and conformation of. carbohydrates are important factors in molecular recognition events and the N-acetyl group of a monosaccharide residue can function as a conformational gatekeeper whereby it influences the overall shape of the oligosaccharide. NMR spectroscopy and quantum mechanics (QM) calculations are used herein to investigate both the conformational preferences and the dynamic behavior of N-acetyl and N-formyl substituents of 3-amino-3,6-dideoxy-alpha-D-galactopyranose, a sugar and substitution pattern found in bacterial O-antigen polysaccharides. QM calculations suggest that the amide oxygen can be involved in hydrogen bonding with the axial OH4 group primarily but also with the equatorial OH2 group. However, an NMR J coupling analysis indicates that the 01 torsion angle, adjacent to the sugar ring, prefers an ap conformation where conformations <180 degrees also are accessible, but does not allow for intramolecular hydrogen bonding. In the formyl-substituted compound (4)J(HH) coupling constants to the exo-cyclic group were detected and analyzed. A van't Hoff analysis revealed that the trans conformation at the amide bond is favored by Delta G degrees approximate to - 0.8 kcal.mol(-1) in the formyl-containing compound and with Delta G degrees approximate to -2.5 kcal.mol(-1) when the N-acetyl group is the substituent. In both cases the enthalpic term dominates to the free energy, irrespective of water or DMSO as solvent, with only a small contribution from the entropic term. The cis-trans isomerization of the theta(2) torsion angle, centered at the amide bond, was also investigated by employing H-1 NMR line shape analysis and C-13 NMR saturation transfer experiments. The extracted transition rate constants were utilized to calculate transition energy barriers that were found to be about 20 kcal.mol(-1) in both DMSO-d(6) and D2O. Enthalpy had a higher contribution to the energy barriers in DMSO-d(6) compared to in D2O, where entropy compensated for the loss of enthalpy.

  • 349.
    Engström, Olof
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mobarak, Hani
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ståhle, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Conformational dynamics and exchange kinetics of N-formyl and N-acetyl groups substituting 3-amino-3,6-dideoxy-α-D-galactopyranose, a sugar found in bacterial O-antigen polysaccharidesManuskript (preprint) (Annet vitenskapelig)
  • 350.
    Engström, Olof
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Muñoz, Antonio
    Illescas, Beatriz M.
    Martin, Nazario
    Ribeiro-Viana, Renato
    Rojo, Javier
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Investigation of glycofullerene dynamics by NMR spectroscopy2015Inngår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 13, nr 32, s. 8750-8755Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Glycofullerenes, in which carbohydrate molecules are attached via a linker to a [60]fullerene core, facilitate spherical presentation of glyco-based epitopes. We herein investigate the dynamics of two glycofullerenes, having 12 and 36 mannose residues at their periphery, by NMR translational diffusion and quantitative C-13 relaxation studies employing a model-free approach for their interpretation. The sugar residues are shown to be highly flexible entities with S-2 < 0.2 in both compounds. Notably, the larger glycofullerene with longer linkers shows faster internal dynamics and higher flexibility than its smaller counterpart. The dynamics and flexibility as well as the slower translational diffusion of the larger glycofullerene, thereby favoring rebinding to a receptor, may together with its spatial extension explain why it is better than the smaller one at blocking the DC-SIGN receptor and inhibiting the infection by pseudotyped Ebola virus particles.

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