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  • 1501. Wei, Wen-Jie
    et al.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Liao, Rong-Zhen
    Theoretical Study of the Mechanism of the Nonheme Iron Enzyme EgtB2017Ingår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, nr 6, s. 3589-3599Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    EgtB is a nonheme iron enzyme catalyzing the C - S bond formation between gamma-glutamyl cysteine (gamma GC) and N-alpha-trimethyl histidine (TMH) in the ergothioneine biosynthesis. Density functional calculations were performed to elucidate and delineate the reaction mechanism of this enzyme. Two different mechanisms were considered, depending on whether the sulfoxidation or the S C bond formation takes place first. The calculations suggest that the S - O bond formation occurs first between the thiolate and the ferric superoxide, followed by homolytic O-O bond cleavage, very similar to the case of cysteine dioxygenase. Subsequently, proton transfer from a second-shell residue Tyr377 to the newly generated iron - oxo moiety takes place, which is followed by proton transfer from the TMH imidazole to Tyr377, facilitated by two crystallographically observed water molecules. Next, the S C bond is formed between gamma GC and TMH, followed by proton transfer from the imidazole CH moiety to Tyr377, which was calculated to be the rate-limiting step for the whole reaction, with a barrier of 17.9 kcal/mol in the quintet state. The calculated barrier for the rate-limiting step agrees quite well with experimental kinetic data. Finally, this proton is transferred back to the imidazole nitrogen to form the product. The alternative thiyl radical attack mechanism has a very high barrier, being 25.8 kcal/mol, ruling out this possibility.

  • 1502. Wellens, Adinda
    et al.
    Garofalo, Corinne
    Nguyen, Hien
    Van Gerven, Nani
    Slättegård, Rikard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Hernalsteens, Jean-Pierre
    Wyns, Lode
    Oscarson, Stefan
    De Greve, Henri
    Hultgren, Scott
    Bouckaert, Julie
    Intervening with urinary tract infections using anti-adhesives based on the crystal structure of the FimH-oligomannose-3 complex2008Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 3, nr 4, s. e2040; 1-13Artikel i tidskrift (Refereegranskat)
  • 1503.
    Wettergren, Jenny
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Selective transfer hydrogenations: Catalyst development and mechanistic investigations2008Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    By generating a library of amino acid-based ligands, pseudo-dipeptides, and combining them with transition metals, we have created selective and efficient ruthenium and rhodium catalysts for the asymmetric transfer hydrogenation of ketones. The ruthenium-catalyzed reaction was studied in detail, and we found that alkali metals play a crucial role for the reactivity and selectivity of the reaction. Furthermore, we have performed kinetic studies on the catalytic system, and the experimental data does neither support the established inner-sphere nor the classical outer-sphere mechanism. Hence, a novel mechanism for the ruthenium-pseudo-dipeptide-catalyzed transfer hydrogenation is proposed. In this unprecedented outer-sphere mechanism, a hydride and an alkali metal ion are transferred from the donor to the ruthenium complex in the rate determining step.

    In addition, the pseudo-dipeptide ligands were employed in the rhodium-catalyzed transfer hydrogenation of aryl alkyl ketones to yield the corresponding alcohols in high yields and excellent enantioselectivities (up to 98% ee). The study revealed that the alkali metals, so important in the ruthenium analogue of the reaction, do not improve the enantioselectivity of the reaction. Deuterium labeling experiments showed that the reaction follows the mono hydridic route.

    Furthermore, a novel method for efficient catalyst screening has been developed. We have demonstrated that ligand synthesis, catalyst formation, and enantioselective catalysis can be performed using an in situ one-pot procedure. The efficacy of the concept was demonstrated in the enantioselective reduction of ketones. In addition to the simplification of the catalyst formation, this approach resulted in improvement of the product ee.

    Finally, the development of a reduction protocol for the transfer hydrogenation of ketones to alcohols without the involvement of transition metal catalysts is described. Using microwave irradiation, a range of ketones was efficiently reduced in high yields using catalytic amounts of lithium 2-propoxide in 2-propanol.

  • 1504.
    Wettergren, Jenny
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    In Situ Formation of Ligand and Catalyst: Application in Ruthenium-Catalyzed Enantioselective Reduction of Ketones2007Ingår i: Regio- and Stereo-Controlled Oxidations and Reductions, Wiley, England , 2007, s. 121-124Kapitel i bok, del av antologi (Refereegranskat)
  • 1505.
    Wettergren, Jenny
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Buitrago, Elina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ryberg, Per
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mechanistic Investigation on the Asymmetric Transfer Hydrogenation of Ketones Catalyzed by Pseudo-Dipeptides Ruthenium complexes2009Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, nr 23, s. 5709-5718Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lithium-powered: A kinetic investigation into the asymmetric transfer hydrogenation of non-activated aryl alkyl ketones, catalyzed by N-Boc-protected -amino acid hydroxyamide ruthenium–arene complexes, has revealed that the reactions proceed through an unprecedented bimetallic outer-sphere mechanism. Under optimized conditions, these catalysts provide access to secondary alcohols in high yields and with excellent enantioselectivities (>99 % ee).

    The combination of N-Boc-protected -amino acid hydroxyamides (pseudo-dipeptides) and [{Ru(p-cymene)Cl2}2] resulted in the formation of superior catalysts for the asymmetric transfer hydrogenation (ATH) of non-activated aryl alkyl ketones in propan-2-ol. The overall kinetics of the ATH of acetophenone to form 1-phenylethanol in the presence of ruthenium pseudo-dipeptide catalysts were studied, and the individual rate constants for the processes were determined. Addition of lithium chloride to the reaction mixtures had a strong influence on the rates and selectivities of the processes. Kinetic isotope effects (KIEs) for the reduction were determined and the results clearly show that the hydride transfer is rate-determining, whereas no KIEs were detected for the proton transfer. From these observations a novel bimetallic outer-sphere-type mechanism for these ATH process is proposed, in which the bifunctional catalysts mediate the transfer of a hydride and an alkali metal ion between the hydrogen donor and the substrate. Furthermore, the use of a mixture of propan-2-ol and THF (1:1) proved to enhance the rates of the ATH reactions. A series of aryl alkyl ketones were reduced under these conditions in the presence of 0.5 mol % of catalyst, and the corresponding secondary alcohols were formed in high yields and with excellent enantioselectivities (>99 % ee) in short reaction times.

  • 1506.
    Wettergren, Jenny
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Buitrago, Elina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ryberg, Per
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mechanistic investigations into the asymmetric transfer hydrogenation of ketones catalyzed by pseudo-dipeptide ruthenium complexes2009Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, nr 23, s. 5709-5718Artikel i tidskrift (Refereegranskat)
  • 1507.
    Wettergren, Jenny
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bøgevig, Anders
    Portier, Maude
    Adolfsson, Hans
    Ruthenium-Catalyzed Enantioselective Reduction of Electron-Rich Aryl Alkyl Ketones2006Ingår i: Advanced Synthesis and Catalysis, ISSN 1615-4150, Vol. 348, nr 10-11, s. 1277-1282Artikel i tidskrift (Refereegranskat)
  • 1508.
    Wettergren, Jenny
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Zaitsev, Alexey
    Adolfsson, Hans
    Rhodium-Catalyzed Asymmetric Transfer Hydrogenation of Aryl Alkyl Ketones Employing Ligands Derived from Amino Acids2007Ingår i: Advanced Synthesis and Catalysis, ISSN 1615-4150, Vol. 349, nr 17-18, s. 2556-2562Artikel i tidskrift (Refereegranskat)
  • 1509.
    Wettergren, Jenny
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Zaitsev, Alexey B.
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Asymmetric transfer hydrogenation of ketones: development of amino acid derived transition metal catalysts2008Ingår i: Abstracts of Papers, 235th ACS National Meeting, New Orleans, LA, United States, April 6-10, 2008, 2008Konferensbidrag (Övrigt vetenskapligt)
  • 1510.
    Wettergren, Jenny
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Zaitsev, Alexey B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Rhodium-catalyzed asymmetric transfer hydrogenation of aryl alkyl ketones employing ligands derived from amino acids2007Ingår i: Advanced Synthesis & Catalysis, ISSN 1615-4150, Vol. 349, s. 2556-2562Artikel i tidskrift (Refereegranskat)
  • 1511.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    A perspective on the primary and three-dimensional structures of carbohydrates2013Ingår i: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 378, s. 123-132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbohydrates, in more biologically oriented areas referred to as glycans, constitute one of the four groups of biomolecules. The glycans, often present as glycoproteins or glycolipids, form highly complex structures. In mammals ten monosaccharides are utilized in building glycoconjugates in the form of oligo-(up to about a dozen monomers) and polysaccharides. Subsequent modifications and additions create a large number of different compounds. In bacteria, more than a hundred monosaccharides have been reported to be constituents of lipopolysaccharides, capsular polysaccharides, and exopolysaccharides. Thus, the number of polysaccharide structures possible to create is huge. NMR spectroscopy plays an essential part in elucidating the primary structure, that is, monosaccharide identity and ring size, anomeric configuration, linkage position, and sequence, of the sugar residues. The structural studies may also employ computational approaches for NMR chemical shift predictions (CASPER program). Once the components and sequence of sugar residues have been unraveled, the three-dimensional arrangement of the sugar residues relative to each other (conformation), their flexibility (transitions between and populations of conformational states), together with the dynamics (timescales) should be addressed. To shed light on these aspects we have utilized a combination of experimental liquid state NMR techniques together with molecular dynamics simulations. For the latter a molecular mechanics force field such as our CHARMM-based PARM22/SU01 has been used. The experimental NMR parameters acquired are typically H-1, H-1 cross-relaxation rates (related to NOEs), (3)JCH and (3)JCC trans-glycosidic coupling constants and H-1, C-13-and H-1, H-1-residual dipolar couplings. At a glycosidic linkage two torsion angles phi and psi are defined and for 6-substituted residues also the omega torsion angle is required. Major conformers can be identified for which highly populated states are present. Thus, in many cases a well-defined albeit not rigid structure can be identified. However, on longer timescales, oligosaccharides must be considered as highly flexible molecules since also anti-conformations have been shown to exist with H-C-O-C torsion angles of similar to 180 degrees, compared to syn-conformations in which the protons at the carbon atoms forming the glycosidic linkage are in close proximity. The accessible conformational space governs possible interactions with proteins and both minor changes and significant alterations occur for the oligosaccharides in these interaction processes. Transferred NOE NMR experiments give information on the conformation of the glycan ligand when bound to the proteins whereas saturation transfer difference NMR experiments report on the carbohydrate part in contact with the protein. It is anticipated that the subtle differences in conformational preferences for glycan structures facilitate a means to regulate biochemical processes in different environments. Further developments in the analysis of glycan structure and in particular its role in interactions with other molecules, will lead to clarifications of the importance of structure in biochemical regulation processes essential to health and disease.

  • 1512.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Computational and experimental analysis of oligosaccharide conformation and dynamics2011Ingår i: Abstracts of Papers, 241st ACS National Meeting & Exposition, Anaheim, CA, United States, March 27-31, 2011, American Chemical Society (ACS), 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    Carbohydrate structures in the form of glycoconjugates are found in Nature, e.g., as N- and O-linked glycoproteins, glycolipids, short-chain lipopolysaccharides also referred to as lipooligosaccharides and saponins.  The carbohydrate constituent may be studied as part of the glycoconjugate or as oligosaccharides. A number of experimental biophysical techniques are available in order to investigate their conformation and dynamics, in particular, NMR spectroscopy, both in solution and in the solid state, X-ray diffraction on crystals, neutron diffraction with isotopic substitution carried out in the solution state, optical rotation, ultrasonic relaxation and more recently Raman optical activity. Computational approaches including molecular mechanics,1 molecular dynamics simulations,2 ab initio and DFT methods3 may subsequently be employed to study and interpret conformational equilibria based on experimental data. The use of carbon-13 site-specifically synthesized oligosaccharides for obtaining, in particular, conformationally dependent trans-glycosidic homo- and heteronuclear coupling constants and interpretation of conformational equilibria from these based on recently developed Karplus-type relationships for spin-spin coupling constants over three bonds4 will be presented for different oligosaccharides in quest for a description of the population distribution of the torsion angles at the glycosidic linkage.

  • 1513.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    General NMR Spectroscopy of Carbohydrates and Conformational Analysis in Solution2007Ingår i: Molecular Interactions Biochemistry of Glycans, Elsevier Ltd , 2007, s. 101-132Kapitel i bok, del av antologi (Refereegranskat)
  • 1514. Wieczorek, Birgit
    et al.
    Träff, Annika
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Krumlinde, Patrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Dijkstra, Harm P.
    Egmond, Maarten R.
    van Koten, Gerard
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Klein Gebbink, Robertus J. M.
    Covalent anchoring of a racemization catalyst to CALB-beads: towards dual immobilization of DKR catalysts2011Ingår i: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 52, nr 14, s. 1601-1604Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The preparation of a heterogeneous bifunctional catalytic system, combining the catalytic properties of an organometallic catalyst (racemization) with those of an enzyme (enantioselective acylation) is described. A novel ruthenium phosphonate inhibitor was synthesized and covalently anchored to a lipase immobilized on a solid support (CALB, Novozym® 435). The immobilized bifunctional catalytic system showed activity in both racemization of (S)-1-phenylethanol and selective acylation of 1-phenylethanol.

  • 1515. Wieczorek, Birgit
    et al.
    Träff, Annika
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Krumlinde, Patrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Dijkstra, Harm P.
    Egmond, Maarten R.
    van Koten, Gerard
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Klein Gebbink, Robertus J.M.
    Site-Specific Covalent Immobilization of a Racemization Catalyst onto Lipase-containing BeadsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The synthesis and application of the novel heterogeneous bifunctional catalyst CALB-5 as a racemization and resolution catalyst for the dynamic kinetic resolution is described. The semisynthetic ruthenium lipase hybrid CALB-5 was obtained by inhibiting CALB beads with the novel ruthenium phosphonate complex 5 possessing a lipase active site-directed phosphonate group. By partially inhibiting the lipase beads with 5, a bifunctional catalytic system was obtained. Racemization, by the Ru-catalytic site, gave 0% ee after 24 h, and the kinetic resolution, enzymatic acylation by the uninhibited CALB sites, gave 28% conversion of 1-phenylethanol after 3 h with >99% ee of the acetylated product. A dynamic kinetic resolution experiment of (S)-1-phenylethanol with CALB-5 gave the acylated (R)-product in 18% yield and with >99% ee.

  • 1516.
    Wikmark, Ylva
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Engineering Candida antarctica Lipase A for Enantioselective Transformations in Organic Synthesis: Design, Immobilization and Organic Solvent Screening of Smart Enzyme Libraries2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The use of enzymes as catalysts in organic synthesis constitutes an attractive alternative to conventional chemical catalysis. Enzymes are non-toxic and biodegradable and they can operate under mild reaction conditions. Furthermore, they often display high chemo-, regio- and stereoselectivity, enabling specific reactions with single product outcome.

    By the use of protein engineering, enzymes can be altered for the specific needs of the researcher. The major part of this thesis describes engineering of lipase A from Candida antarctica (CalA), for improved enantioselectivity in organic synthetic transformations.

    The first part of the thesis describes a highly combinatorial method for the introduction of mutation sites in an enzyme library. By the simultaneous introduction of nine mutations, we found an enzyme variant with five out of the nine possible mutations. This quintuple variant had an enlarged active site pocket and was enantioselective and active for our model substrate, an ibuprofen ester. This is a bulky substrate for which the wild-type enzyme shows no enantioselectivity and very poor activity.

    In the second part of the thesis, we continued our approach of combinatorial, focused enzyme libraries. This time we aimed at decreasing the alcohol pocket of CalA, in order to increase the enantioselectivity for small and medium-sized secondary alcohols. The enzyme library was bound on microtiter plates and screened by a transacylation reaction in organic solvent. This library yielded an enzyme variant with high enantioselectivity for the model substrate 1-phenyl ethanol, and high to excellent selectivity for other alcohols tested. Screening in organic solvent is advantageous since a potential hit is more synthetically useful.

    In the third part of the thesis, we used manipulated beads of controlled porosity glass (EziG™) for enzyme immobilization, and demonstrated the generality of this carrier for several enzyme classes. EziG™ allowed fast enzyme immobilization with simultaneous purification and yielded active biocatalysts in all cases.

    The last project describes the function of the proposed active site flap in CalA. In our study, we removed this motif. The engineered variant was compared to the wild-type enzyme by testing the amount of interfacial activation and the selectivity for certain alcohols. We showed that the motif is indeed controlling the entrance to the active site and that the flap is not part of the enantioselectivity determining machinery. 

  • 1517.
    Wikmark, Ylva
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Engelmark Cassimjee, Karim
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lihammar, Richard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Removing the Active-Site Flap in Lipase A from Candida antarctica Produces a Functional Enzyme without Interfacial Activation2016Ingår i: ChemBioChem (Print), ISSN 1439-4227, E-ISSN 1439-7633, Vol. 17, nr 2, s. 141-145Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A mobile region is proposed to be a flap that covers the active site of Candida antarctica lipase A. Removal of the mobile region retains the functional properties of the enzyme. Interestingly interfacial activation, required for the wild-type enzyme, was not observed for the truncated variant, although stability, activity, and stereoselectivity were very similar for the wild-type and variant enzymes. The variant followed classical Michaelis-Menten kinetics, unlike the wild type. Both gave the same relative specificity in the transacylation of a primary and a secondary alcohol in organic solvent. Furthermore, both showed the same enantioselectivity in transacylation of alcohols and the hydrolysis of alcohol esters, as well as in the hydrolysis of esters chiral at the acid part.

  • 1518.
    Wikmark, Ylva
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Humble, Maria Svedendahl
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Combinatorial Library Based Engineering of Candida antarctica Lipase A for Enantioselective Transacylation of sec-Alcohols in Organic Solvent2015Ingår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 54, nr 14, s. 4284-4288Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method for determining lipase enantioselectivity in the transacylation of sec-alcohols in organic solvent was developed. The method was applied to a model library of Candida antarctica lipase A (CalA) variants for improved enantioselectivity (E values) in the kinetic resolution of 1-phenylethanol in isooctane. A focused combinatorial gene library simultaneously targeting seven positions in the enzyme active site was designed. Enzyme variants were immobilized on nickel-coated 96-well microtiter plates through a histidine tag (His6 -tag), screened for transacylation of 1-phenylethanol in isooctane, and analyzed by GC. The highest enantioselectivity was shown by the double mutant Y93L/L367I. This enzyme variant gave an E value of 100 (R), which is a dramatic improvement on the wild-type CalA (E=3). This variant also showed high to excellent enantioselectivity for other secondary alcohols tested.

  • 1519.
    Willy, Benjamin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán J
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Development of pincer complex-catalyzed oxidative C-H activation borylation reactions: Synthetic applications and mechanistic studies2010Ingår i: Abstracts of Papers, 239th ACS National Meeting, San Francisco, CA, United States, March 21-25, 2010, Washington D C: American Chemical Society , 2010Konferensbidrag (Övrigt vetenskapligt)
  • 1520.
    Winqvist, Anna
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Studies towards a method for incorporation of 3'-deoxy-3'-C-methylenephosphonate linkages into oligonucleotides2002Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Synthetic strategies towards 3’-deoxy-3’-C-methylenephosphinate building blocks were explored. The key transformations involved stereoselective hydroboration of 1-[2-O-(tert-butyldimethylsilyl-5-O-(4-methoxytrityl)-3-deoxy-3-C-methylene- ß -D-erythro-pentofuranosyl]uracil to give the corresponding 3’-deoxy-3’-C- hydroxymethyl derivative with ribo-configuration, as well as the further conversion into a precursor with a suitable leaving group, e. g., triflate, for subsequent substitution with the phosphinic acid synthon bis(trimethylsilyl)hypophosphite. Improvements of these steps enabled synthesis of 2’-O-(tert-butyldimethylsilyl-5’-O-( 4-methoxytrityl)-3’-deoxy-3’-C-methylenephosphinate uridine in a respectable overall yield of 40% over 6 steps, from the corresponding 2’-O-(tert-butyldimethylsilyl- 5’-O-(4-methoxytrityl)uridine.

    For the introduction of internucleosidic 3’-deoxy-3’-C-methylenephosphonate linkages into oligonucleotides, a preparatory study of the elongation steps, i. e., coupling of the phosphinate building block to the 5’-hydroxyl function of a nucleoside derivative and subsequent oxidation, was performed. Of several coupling reagents studied for the activation of the phosphinate building block prior to coupling, the most promising proved to be N,N-bis(2-oxo-3-oxazolidin-1-yl)phosphinic chloride. The oxidation of the resulting 3’-deoxy-3’-C-methylenephosphinate ester to the corresponding 3’-deoxy-3’-C-methylenephosphonate linkage was achieved using iodine in pyridine-water, in the presence of a catalyst, i. e., either a base (triethylamine) or an acid (pyridinium salt).

  • 1521. Wojcik, Anna
    et al.
    Broclawik, Ewa
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lundberg, Marcus
    Moran, Graham
    Borowski, Tomasz
    Role of Substrate Positioning in the Catalytic Reaction of 4-Hydroxyphenylpyruvate Dioxygenase-A QM/MM Study2014Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 136, nr 41, s. 14472-14485Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ring hydroxylation and coupled rearrangement reactions catalyzed by 4-hydroxyphenylpyruvate dioxygenase were studied with the QM/MM method ONIOM(B3LYP:AMBER). For electrophilic attack of the ferryl species on the aromatic ring, five channels were considered: attacks on the three ring atoms closest to the oxo ligand (C1, C2, C6) and insertion of oxygen across two bonds formed by them (C1-C2, C1-C6). For the subsequent migration of the carboxymethyl substituent, two possible directions were tested (C1-C2, C1-C6), and two different mechanisms were sought (stepwise radical, single-step heterolytic). In addition, formation of an epoxide (side)product and benzylic hydroxylation, as catalyzed by the closely related hydroxymandelate synthase, were investigated. From the computed reaction free energy profiles it follows that the most likely mechanism of 4-hydroxyphenylpyruvate dioxygenase involves electrophilic attack on the C1 carbon of the ring and subsequent single-step heterolytic migration of the substituent. Computed values of the kinetic isotope effect for this step are inverse, consistent with available experimental data. Electronic structure arguments for the preferred mechanism of attack on the ring are also presented.

  • 1522.
    Wolpher, Henriette
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ruthenium(II) Polypyridyl Complexes in Supramolecular Systems relevant to Artificial Photosynthesis2005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis describes the synthesis and properties of ruthenium complexes relevant to artificial photosynthesis. The work includes preparation of RuIIpolypyridine complexes as well as multi component systems where RuII(bpy)3 or RuII(tpy)2 type complexes are used as photosesnsitizers.

    In the first part, the synthesis and characterisation of bipyridyl(pyridyl)methane type ligands and the corresponding ruthenium(II) bistridentate polypyridyl complexes is described. The bipyridyl-pyridyl methane type ligands were designed to increase the excited state lifetime of ruthenium(II) bisterpyridine-type complexes by altering the ligand field as compared to normal terpyridine ligands.

    In the second part photoinduced electron transfer and formation of charge separated states in donor-photosensitizer dyads or donor-photosensitizer-acceptor triads is studied. The first covalently linked donor-photosensitizer-acceptor triad with tyrosine as electron donor was prepared, and long lived light induced charge separation was observed. RuIIterpyridine complexes linked to carotenoid or tyrosine were also prepared, for studies of light induced charge separation on a TiO2 surface. Tryptofan was covalently linked to Ru(bpy)3 and proton coupled electron transfer from tryptophan to photogenerated ruthenium(III) was demonstrated. A pH-dependent study of the electron transfer rate gave insight into the mechanism of proton coupled electron transfer in amino acids.

    Finally, the last part of the thesis presents the preparation and properties of the first complex containing a photosensitizer covalently linked to a Fe-hydrogenase active site model.

  • 1523.
    Wolpher, Henriette
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Abrahamsson, Maria
    Eriksson, Lars
    Norrby, Per-Ola
    Johansson, Olof
    Bergquist, Jonas
    Hammarström, Leif
    Åkermark, Björn
    Ruthenium complexes of a bipyridyl(pyridyl)methane ligand: Effect of substituents at the methylene group on structure and photophysicsManuskript (Övrigt vetenskapligt)
  • 1524.
    Wolpher, Henriette
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Borgström, Magnus
    Hammarström, Leif
    Bergquist, Jonas
    Sundström, Villy
    Styring, Stenbjörn
    Sun, Licheng
    Åkermark, Björn
    Synthesis and Properties of an Iron Hydrogenase Active Site Model Linked to Ruthenium tris-Bipyridine Photosensitizer2003Ingår i: Inorganic Chemical Communications, Vol. 6, s. 989-991Artikel i tidskrift (Refereegranskat)
  • 1525. Wolpher, Henriette
    et al.
    Johansson, Olof
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Abrahamsson, Maria
    Kritikos, Mikael
    Sun, Licheng
    Åkermark, Björn
    A tridentate ligand for preparation of bisterpyridine-like ruthenium(II) complexes with an increased excited state lifetime2004Ingår i: Inorganic Chemistry Communications, ISSN 1387-7003, Vol. 7, nr 3, s. 337-340Artikel i tidskrift (Refereegranskat)
  • 1526.
    Wolpher, Henriette
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Johansson, Olof
    Abrahamsson, Maria
    Kritikos, Mikael
    Sun, Licheng
    Åkermark, Björn
    A tridentate ligand for preparation of bisterpyridine-like ruthenium(II) complexes with an increased excited state lifetime2004Ingår i: Inorganic Chemistry Communications, ISSN 1387-7003, Vol. 7, nr 3, s. 337-340Artikel i tidskrift (Refereegranskat)
  • 1527.
    Wolpher, Henriette
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pan, Jingxi
    Johansson, Anh
    Lundqvist, Maria
    Persson, Petter
    Bergquist, Jonas
    Polivka, Tomas
    Sun, Licheng
    Åkermark, Björn
    Electron transfer studies of terpyridine based ruthenium(II)-donor dyads attached to nanostructured TiO2Manuskript (Övrigt vetenskapligt)
  • 1528.
    Wolpher, Henriette
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sinha, Subrata
    Pan, Jingxi
    Johansson, Anh
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lundqvist, Maria J.
    Persson, Petter
    Lomoth, Reiner
    Bergquist, Jonas
    Sun, Licheng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sundström, Villy
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Polívka, Tomás
    Synthesis and electron transfer studies of ruthenium-terpyridine-based dyads attached to nanostructured TiO22007Ingår i: Inorganic Chemistry, ISSN 0020-1669, Vol. 46, nr 3, s. 638-651Artikel i tidskrift (Refereegranskat)
  • 1529. Wu, Emilia L.
    et al.
    Engström, Olof
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Jo, Sunhwan
    Stuhlsatz, Danielle
    Yeom, Min Sun
    Klauda, Jeffery B.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Im, Wonpil
    Molecular Dynamics and NMR Spectroscopy Studies of E. coli Lipopolysaccharide Structure and Dynamics2013Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 105, nr 6, s. 1444-1455Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lipopolysaccharide (LPS), a component of Gram-negative bacterial outer membranes, comprises three regions: lipid A, core oligosaccharide, and O-antigen polysaccharide. Using the CHARMM36 lipid and carbohydrate force fields, we have constructed a model of an Escherichia coil R1 (core) 06 (antigen) LPS molecule. Several all-atom bilayers are built and simulated with lipid A only (LIPA) and varying lengths of 0 (LPS0), 5 (LPS5), and 10 (LPS10) O6 antigen repeating units; a single unit of 06 antigen contains five sugar residues. From H-1,H-1-NOESY experiments, cross-relaxation rates are obtained from an O-antigen polysaccharide sample. Although some experimental deviations are due to spin-diffusion, the remaining effective proton-proton distances show generally very good agreement between NMR experiments and molecular dynamics simulations. The simulation results show that increasing the LPS molecular length has an impact on LPS structure and dynamics and also on LPS bilayer properties. Terminal residues in a LPS bilayer are more flexible and extended along the membrane normal. As the core and O-antigen are added, per-lipid area increases and lipid bilayer order decreases. In addition, results from mixed LPS0/5 and LPS0/10 bilayer simulation's show that the LPS O-antigen conformations at a higher concentration of LPS5 and LPS10 are more orthogonal to the membrane and less flexible. The O-antigen concentration of mixed LPS bilayers does not have a significant effect on per-lipid area and hydrophobic thickness. Analysis of ion and water penetration shows that water molecules can penetrate inside the inner core region, and hydration is critical to maintain the integrity of the bilayer structure.

  • 1530. Wu, Emilia L.
    et al.
    Fleming, Patrick J.
    Yeom, Min Sun
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Klauda, Jeffery B.
    Fleming, Karen G.
    Im, Wonpil
    E. coil Outer Membrane and Interactions with OmpLA2014Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 106, nr 11, s. 2493-2502Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The outer membrane of Gram-negative bacteria is a unique asymmetric lipid bilayer composed of phospholipids (PLs) in the inner leaflet and lipopolysaccharides (LPSs) in the outer leaflet. Its function as a selective barrier is crucial for the survival of bacteria in many distinct environments, and it also renders Gram-negative bacteria more resistant to antibiotics than their Gram-positive counterparts. Here, we report the structural properties of a model of the Escherichia coli outer membrane and its interaction with outer membrane phospholipase A (OmpLA) utilizing molecular dynamics simulations. Our results reveal that given the lipid composition used here, the hydrophobic thickness of the outer membrane is similar to 3 angstrom thinner than the corresponding PL bilayer, mainly because of the thinner LPS leaflet. Further thinning in the vicinity of OmpLA is observed due to hydrophobic matching. The particular shape of the OmpLA barrel induces various interactions between LPS and PL leaflets, resulting in asymmetric thinning around the protein. The interaction between OmpLA extracellular loops and LPS (headgroups and core oligosaccharides) stabilizes the loop conformation with reduced dynamics, which leads to secondary structure variation and loop displacement compared to that in a DLPC bilayer. In addition, we demonstrate that the LPS/PL ratios in asymmetric bilayers can be reliably estimated by the per-lipid surface area of each lipid type, and there is no statistical difference in the overall membrane structure for the outer membranes with one more or less LPS in the outer leaflet, although individual lipid properties vary slightly.

  • 1531. Wångsell, Fredrik
    et al.
    Russo, Francesco
    Sävmarker, Jonas
    Åsa, Rosenquist
    Samuelsson, Bertil
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Larhed, Mats
    Design and synthesis of BACE-1 inhibitors utilizing a tertiary hydroxyl motif as the transition state mimic2009Ingår i: Bioorganic & Medicinal Chemistry Letters, ISSN 0960-894X, Vol. 19, nr 16, s. 4711-4714Artikel i tidskrift (Refereegranskat)
  • 1532. Xia, Ming
    et al.
    Liu, Jianhui
    Gao, Yan
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sun, Licheng
    Synthesis and photophysical and electrochemical study of tyrosine covalently linked to high-valent copper(III) and manganese(IV) complexes2007Ingår i: Helvetica Chimica Acta, ISSN 0018-019X, Vol. 90, nr 3, s. 553-561Artikel i tidskrift (Refereegranskat)
  • 1533.
    Xu, Chao
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Deiana, Luca
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Afewerki, Samson
    Incerti-Pradillos, Celia
    Córdova, Oscar
    Guo, Peng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. Mid-Sweden University, Sweden.
    Hedin, Niklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    The Use of Porous Palladium(II)-polyimine in Cooperatively-catalyzed Highly Enantioselective Cascade Transformations2015Ingår i: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 357, nr 9, s. 2150-2156Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Porous organic polymers have prospects as functional substrates for catalysis, with quite different molecular properties from inorganic substrates. Here we disclose for the first time that porous palladium(II)-polyimines are excellent catalysts for cooperatively catalyzed and enantioselective cascade reactions. In synergy with a chiral amine co-catalyst, polysubstituted cyclopentenes and spirocyclic oxindoles, including the all-carbon quaternary stereocenter, were synthesized in high yields. High diastereo- and enantioselectivities were achieved for these dynamic kinetic asymmetric transformations (DYKAT) of enals with propargylic nucleophiles.

  • 1534.
    Xu, Quan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kerdphon, Sutthichat
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Andersson, Pher G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    C-C Coupling of Ketones with Methanol Catalyzed by a N-Heterocyclic Carbene-Phosphine Iridium Complex2015Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 21, s. 3576-3579Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An N-heterocyclic carbene–phosphine iridium complex system was found to be a very efficient catalyst for the methylation of ketone via a hydrogen transfer reaction. Mild conditions together with low catalyst loading (1 mol %) were used for a tandem process which involves the dehydrogenation of methanol, CC bond formation with a ketone, and hydrogenation of the new generated double bond by iridium hydride to give the alkylated product. Using this iridium catalyst system, a number of branched ketones were synthesized with good to excellent conversions and yields.

  • 1535.
    Xu, Quan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kerdphon, Sutthichat
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Rujirawanich, Janjira
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Krajangsri, Suppachai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Andersson, Pher
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Highly Active Cationic NHC, Phosphine Iridium Catalysts for Base Free Asymmetric Hydrogenation of KetonesManuskript (preprint) (Övrigt vetenskapligt)
  • 1536.
    Xu, Yunhua
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthesis and Photoinduced Electron Transfer of Donor-Sensitizer-Acceptor Systems2005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Artificial systems involving water oxidation and solar cells are promising ways for the conversion of solar energy into fuels and electricity. These systems usually consist of a photosensitizer, an electron donor and / or an electron acceptor. This thesis deals with the synthesis and photoinduced electron transfer of several donor-sensitizer-acceptor supramolecular systems.

    The first part of this thesis describes the synthesis and properties of two novel dinuclear ruthenium complexes as electron donors to mimic the donor side reaction of Photosystem II. These two Ru2 complexes were then covalently linked to ruthenium trisbipyridine and the properties of the resulting trinuclear complexes were studied by cyclic voltammetry and transient absorption spectroscopy.

    The second part presents the synthesis and photoinduced electron transfer of covalently linked donor-sensitizer supramolecular systems in the presence of TiO2 as electron acceptors. Electron donors are tyrosine, phenol and their derivatives, and dinuclear ruthenium complexes. Intramolecular electron transfer from the donor to the oxidized sensitizer was observed by transient absorption spectroscopy after light excitation of the Ru(bpy)32+ moiety. The potential applications of Ru2-based electron donors in artificial systems for water oxidation and solar cells are discussed.

    In the final part, the photoinduced interfacial electron transfer in the systems based on carotenoids and TiO2 is studied. Carotenoids are shown to act as both sensitizers and electron donors, which could be used in artificial systems to mimic the electron transfer chain in natural photosynthesis.

  • 1537. Xu, Yunhua
    et al.
    Duan, Lele
    Tong, Lianpeng
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sun, Licheng
    Visible light-driven water oxidation catalyzed by a highly efficient dinuclear ruthenium complex2010Ingår i: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 46, nr 35, s. 6506-6508Artikel i tidskrift (Refereegranskat)
  • 1538.
    Xu, Yunhua
    et al.
    Royal Institute of Technology (KTH).
    Duan, Lele
    Royal Institute of Technology (KTH).
    Åkermark, Torbjörn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tong, Lianpeng
    Royal Institute of Technology (KTH).
    Lee, Bao-Lin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Zhang, Rong
    Dalian University of Technology (DUT), (P.R. China).
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sun, Licheng
    Royal Institute of Technology (KTH), Department of Organic Chemistry.
    Synthesis and catalytic water oxidation activities of ruthenium complexes containing neutral ligands2011Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, nr 34, s. 9520-9528Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two dinuclear and one mononuclear ruthenium complexes containing neutral polypyridyl ligands have been synthesised as pre-water oxidation catalysts and characterised by 1H and 13C NMR spectroscopy and ESI-MS. Their catalytic water oxidation properties in the presence of [Ce-(NH4)2(NO3)6] (CeIV) as oxidant at pH 1.0 have been investigated. At low concentrations of CeIV (5 mM), high turnover numbers of up to 4500 have been achieved. An 18O-labelling experiment established that both O atoms in the evolved O2 originate from water. Combined electrochemical study and electrospray ionisation mass spectrometric analysis suggest that ligand exchange between coordinated 4-picoline and free water produces Ru aquo species as the real water oxidation catalysts.

  • 1539.
    Xu, Yunhua
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Eilers, Gerriet
    Borgström, Magnus
    Pan, Jingxi
    Abrahamsson, Maria
    Magnuson, Ann
    Lomoth, Reiner
    Bergquist, Jonas
    Polivka, Tomas
    Sun, Licheng
    Sundström, Villy
    Styring, Stenbjörn
    Hammarström, Leif
    Åkermark, Björn
    Synthesis and Characterization of Novel Dinuclear Ruthenium Complexes Covalently Linked to Ru(II) Trisbipyridine: an Approach to Mimics of the Donor Side of PS IIManuskript (Övrigt vetenskapligt)
  • 1540. Xu, Yunhua
    et al.
    Fischer, Andreas
    Duan, Lele
    Tong, Lianpeng
    Gabrielsson, Erik
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sun, Licheng
    Chemical and light-driven oxidation of water catalyzed by an efficient dinuclear ruthenium complex2010Ingår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 49, nr 47, s. 8934-8937Artikel i tidskrift (Refereegranskat)
  • 1541.
    Xu, Yunhua
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pan, Jie
    Huang, Ping
    Feyziyev, Yashar
    Lomoth, Reiner
    Hammarström, Leif
    Styring, Stenbjörn
    Polivka, Tomas
    Sundström, Villy
    Åkermark, Björn
    Sun, Licheng
    Synthesis and Photoinduced Electron Transfer Study of a Substituted Phenol Covalently Linked to Ruthenium Trisbipyridine with or without Four Ester GroupsManuskript (Övrigt vetenskapligt)
  • 1542.
    Yang, Bin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Catalytic Stereoselective Formation of C–O, C–C and C–B Bonds: A Voyage from Asymmetric Reactions Enabled by Lipases to Stereoselective Palladium-Catalyzed Oxidative Transformations of Enallenes2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis has been focused on enzymatic kinetic resolutions and stereoselective oxidative transformations of enallenes catalyzed by PdII.

    In the first part of the thesis, a detailed discussion on Candida antarctica lipase B (CALB)-catalyzed kinetic resolution (KR) of δ-functionalized alkan-2-acetates is shown. We gained a deeper insight into the mechanism of enzyme-substrate recognition. Changing from an anhydrous solvent to water or a water-containing organic solvent enhanced the enantioselectivity. The effect of –OH was also confirmed by a lipase mutant suggesting that the water molecule mentioned above can be partly mimicked.

    In the second part of the thesis, we developed an efficient KR for allenic alcohols. On this basis, a novel synthesis of optically pure 2-substituted 2,3-dihydrofurans from allenic alcohols via a Ru-catalyzed cycloisomerization was reported. The developed protocol enabled us to assemble an optically pure precursor for total synthesis with three chiral centers from readily available allenol in 2 days.

    In the third part, we reported a class of reactions involving C–H cleavage under mild conditions: PdII-catalyzed oxidative transformations of enallenes. These reactions are particularly attractive since a number of meticulous structures have been achieved from readily accessible starting materials. The directing effect of an unsaturated hydrocarbon was found to be key for these transformations.

    In the final part, we developed the carbonylative insertion reaction discussed in the third part of the thesis into an asymmetric version. By using this methodology, a number of cyclopentenone compounds were obtained in good to excellent enantioselectivity.

  • 1543.
    Yang, Bin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Development and Application ofEnzymatic Asymmetric Synthesis ofFunctionalized Alcohols2015Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The main focus of this thesis lies on enzymatic asymmetric organic reactions. In the first part ofthis work, we looked into the lipase-catalyzed transesterification and hydrolysis at the molecularlevel. It was shown that the low enantioselectivity of CALB-catalyzed transesterification of a δ-functionalized alkan-2-ol to its acetate does not correlate at all with the high enantioselectivity ofthe CALB-catalyzed hydrolysis of the corresponding acetate in water. This lack of correlation isunusual and for unfunctionalized alkan-2-ol derivatives there is a very good correlation betweenthe enantioselectivity of transesterification of the alcohol and hydrolysis of the correspondingacetate with a high enantioseletivity in both cases. The results confirm previous predictions frommolecular modeling. The water effect was mimicked by CALB variant Ala281Ser, whichshowed an enhanced enantioselectivity in transesterification of δ-functionalized alkan-2-olscompared to wild type CALB.

    In the second part of the thesis, enzymatic kinetic resolution to resolve 1-substituted buta-2,3-dien-1-ol was studied. The initial goal was to use Shvo catalyst as racemization catalyst for anenvisioned dynamic kinetic resolution of this substrate. To our surprise, 2,3-dihydrofurans wasformed when α-allenic alcohols was treated with Shvo catalyst and the chiral center that endedup in the product was unchanged. Based on the KR and cycloisomerization, we furthermoredeveloped a one-pot procedure combining kinetic resolution and cyclization to optically pureoxygen-containing heterocycles. The mechanism of the Ru-catalyzed cycloisomerization wasstudied and a Ru-carbenoid was suggested as a crucial intermediate for forming the 2,3-dihydrofurans.

  • 1544.
    Yang, Bin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lihammar, Richard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Investigation of the Impact of Water on the Enantioselectivity Displayed by CALB in the Kinetic Resolution of δ-Functionalized Alkan-2-ol Derivatives2014Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, nr 42, s. 13517-13521Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is shown that the low enantioselectivity of Candida antarctica lipase B (CALB)-catalyzed transesterification of a δ-functionalized alkan-2-ol to its acetate does not correlate at all with the high enantioselectivity of the CALB-catalyzed hydrolysis of the corresponding acetate in water. This lack of correlation is unusual and for unfunctionalized alkan-2-ol derivatives there is a very good correlation between the enantioselectivity of transesterification of the alcohol and hydrolysis of the corresponding acetate (E>200 in both cases). The results confirm previous predictions from molecular modeling. The water effect was mimicked by CALB variant Ala281Ser, which showed an enhanced enantioselectivity in transesterification of δ-functionalized alkan-2-ols compared to wild-type CALB.

  • 1545.
    Yang, Bin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Qiu, Youai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Control of Selectivity in Palladium(II)-Catalyzed Oxidative Transformations of Allenes2018Ingår i: Accounts of Chemical Research, ISSN 0001-4842, E-ISSN 1520-4898, Vol. 51, nr 6, s. 1520-1531Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Oxidation reactions play a central role in organic synthesis, and it is highly desirable that these reactions are mild and occur under catalytic conditions. In Nature, oxidation reactions occur under mild conditions via cascade processes, and furthermore, they often occur in an enantioselective manner with many of them involving molecular oxygen or hydrogen peroxide as the terminal oxidant. Inspired by the reactions in Nature, we have developed a number of Pd(II)-catalyzed cascade reactions under mild oxidative conditions. These reactions have an intrinsic advantage of step economy and rely on selectivity control in each step. In this Account, we will discuss the control of chemo-, regio-, and diastereoselectivity in Pd(II)-catalyzed dehydrogenative cascade coupling reactions. The enantioselective version of this methodology has also been addressed, and new chiral centers have been introduced using a catalytic amount of a chiral phosphoric acid (CPA). Research on this topic has provided access to important compounds attractive for synthetic and pharmaceutical chemists. These compounds include carbocyclic, heterocyclic, and polycyclic systems, as well as polyunsaturated open-chain structures. Reactions leading to these compounds are initiated by coordination of an allene and an unsaturated pi-bond moiety, such as olefin, alkyne, or another allene, to the Pd(II) center, followed by allene attack involving a C(sp(3))-H cleavage under mild reaction conditions. Recent progress within our research group has shown that weakly coordinating groups (e.g., hydroxyl, alkoxide, or ketone) could also initiate the allene attack on Pd(II), which is essential for the oxidative carbocyclization. Furthermore, a highly selective palladium-catalyzed allenic C(sp(3))-H bond oxidation of allenes in the absence of an assisting group was developed, which provides a novel and straightforward synthesis of [3]dendralene derivatives. For the oxidative systems, benzoquinone (BQ) and its derivatives are commonly used as oxidants or catalytic co-oxidants (electron transfer mediators, ETMs) together with molecular oxygen. A variety of transformations including carbocyclization, acetoxylation, arylation, carbonylation, borylation, beta-hydride elimination, alkynylation, alkoxylation, and olefination have been demonstrated to be compatible with this Pd(II)-based catalytic oxidative system. Recently, several challenging synthetic targets, such as cyclobutenes, seven-membered ring carbocycles, spirocyclic derivatives, functional cyclohexenes, and chiral cyclopentenone derivatives were obtained with high selectivity using these methods. The mechanisms of the reactions were mainly studied by kinetic isotope effects (KIEs) or DFT computations, which showed that in most cases the C(sp(3))-H cleavage is the rate-determining step (RDS) or partially RDS. This Account will describe our efforts toward the development of highly selective and atom-economic palladium(II)-catalyzed oxidative transformation of allenes (including enallenes, dienallenes, bisallenes, allenynes, simple allenes, and allenols) with a focus on overcoming the selectivity problem during the reactions.

  • 1546.
    Yang, Bin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Qiu, Youai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Jiang, Tuo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Wulff, William D.
    Yin, Xiaopeng
    Zhu, Can
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Enantioselective Palladium-Catalyzed Carbonylative Carbocyclization of Enallenes via Cross-Dehydrogenative Coupling with Terminal Alkyne: Efficient Construction of a-Chirality of Ketones2017Ingår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 56, nr 16, s. 4535-4539Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An enantioselective PdII/Brønsted acid-catalyzed carbonylative carbocyclization of enallenes ending with a cross-dehydrogenative coupling (CDC) with a terminal alkyne was developed. VAPOL phosphoric acid was found as the best co-catalyst among the examined 28 chiral acids, for inducing the enantioselectivity of α-chiral ketones. As a result, a number of chiral cyclopentenones were easily synthesized in good to excellent enantiomeric ratio with good yields.

  • 1547.
    Yang, Bin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Zhu, Can
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Qiu, Youai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Enzyme- and Ruthenium-Catalyzed Enantioselective Transformation of alpha-Allenic Alcohols into 2,3-Dihydrofurans2016Ingår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 55, nr 18, s. 5568-5572Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An efficient one-pot method for the enzyme- and ruthenium-catalyzed enantioselective transformation of alpha-allenic alcohols into 2,3-dihydrofurans has been developed. The method involves an enzymatic kinetic resolution and a subsequent ruthenium-catalyzed cycloisomerization, which provides 2,3-dihydrofurans with excellent enantioselectivity (up to >99%ee). A ruthenium carbene species was proposed as a key intermediate in the cycloisomerization.

  • 1548.
    Yang, Hai-Bin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pathipati, Stalin R.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Selander, Nicklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Nickel-Catalyzed 1,2-Aminoarylation of Oxime Ester-Tethered Alkenes with Boronic Acids2017Ingår i: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, nr 12, s. 8441-8445Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A nickel-catalyzed 1,2-aminoarylation of oximeester-tethered alkenes with boronic acids was developed. A variety of pyrroline derivatives were synthesized in good yields via the successive formation of C(sp(3))-N and C(sp(3))-C(sp(2)) bonds. For cyclobutanone-derived oxime esters, the reaction provided aliphatic nitriles incorporating an aromatic group in the gamma-position. A mechanism involving iminyl radical and carbon-centered radical intermediates was proposed.

  • 1549.
    Yang, Hai-Bin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Selander, Nicklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    A redox-economical synthesis of trifluoromethylated enamides with the Langlois reagent2017Ingår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 15, nr 8, s. 1771-1775Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A redox-economical strategy for the synthesis of trifluoromethylated enamides using copper catalysis is reported. The reaction employs the inexpensive Langlois reagent (CF3SO2Na) and takes place without the need of an external oxidant. The trifluoromethylated enamide products can easily be converted into the corresponding ketone, saturated amide or oxazole.

  • 1550.
    Yang, Hai-Bin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Selander, Nicklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Divergent Iron-Catalyzed Coupling of O-Acyloximes with Silyl Enol Ethers2017Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, nr 8, s. 1779-1783Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An iron-catalyzed coupling reaction of O-acyloximes and O-benzoyl amidoximes with silyl enol ethers is reported. The protocol provides access to functionalized pyrroles, 1,6-ketonitriles, pyrrolines and imidazolines via carbon-centered radicals generated from an initially formed iminyl radical. The intramolecular cyclization and ring-opening processes of the iminyl radical take place preferentially over reactions that proceed through a 1,3-hydrogen transfer, providing insights into iron-catalyzed reactions with oxime derivatives. The cheap and environmentally friendly iron catalyst, the broad substrate scope and the functional group compatibility make this protocol useful for synthesis of valuable nitrogen-containing products.

282930313233 1501 - 1550 av 1623
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