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  • 951.
    Volkov, Alexey
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic Amide Reductions under Hydrosilylation Conditions2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis covers the development of catalytic methodologies for the mild and chemoselective reductions of amides. The first part of the thesis describes the use of a Fe(II)/NHC catalyst for the deoxygenation of aromatic tertiary amides to corresponding amines. The protocol is characterized by low catalyst loading, mild reaction conditions and the use of air and moisture stable polymethylhydrosilaxane (PMHS) as the hydride source.

    The second part concerns the development of a protocol for the room temperature deoxygenation of a wide range of tertiary amides to amines using catalytic amounts of Et2Zn and LiCl together with PMHS. The system displayed high levels of chemoselectivity tolerating various reducible groups such as nitro, nitrile, and olefin functionalities, and was shown to be applicable for the reduction of aromatic, heteroaromatic and aliphatic tertiary amides.

    The attempts to expand the scope of the Fe-based protocol to accommodate benzylic tertiary amides led to the development of a transition metal-free catalytic system based on KOtBu for the formation of enamines. The final products constitute an important class of precursors for a wide range of valuable compounds in organic chemistry. Moreover, avoiding the use of transition metals in the protocol allowed the desired products to be obtained without the hazardous metal contaminants.

    The last chapter of the thesis describes the Mo(CO)6-catalyzed hydrosilylation of amides. The Mo-based catalyst was proven to mediate the deoxygenation of α,β-unsaturated tertiary and secondary amides to the corresponding allylamines without reduction of the olefinic bonds. Further development of the catalytic system revealed an unprecedented chemoselectivity in the hydrosilylation of aromatic and certain aliphatic tertiary amides in the presence of a variety of reducible groups along with aldehydes and imines that were tolerated for the first time. Moreover, it was possible to control the reaction outcome by variation of the reaction temperature to obtain either amines or aldehydes as the major products. The synthetic utility of the developed Mo(CO)6-catalyzed protocols was further demonstrated in the synthesis of the pharmaceuticals Naftifine and Donepezil.

  • 952.
    Volkov, Alexey
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic Hydrosilylation of Amides2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, different protocols and approaches are described for thehydrosilylation of tertiary amides to amines or enamines. The development of simple andeffective methods for the production of amines from amides is of great importance to bothacademic and industrial users, since the final product represents a valuable building blockfor fine and bulk chemicals. Furthermore, enamines constitute important starting materialsto a variety of functionalized and complex organic compounds.

    The first part of the thesis focuses on the development and investigation of acatalytic protocol for the reduction of amides to amines using an inexpensive and efficientiron catalyst together with cost-effective, stable, and non-toxic PMHS(poly(methylhydrosiloxane)) as the hydride source. The active catalytic species was formedin situ by combining Fe(OAc)2 as the iron source and easily synthesized imidazolium salts.

    The second part deals with a novel transition metal–free catalytic hydrosilylationmethodology for the transformation of amides to the corresponding amines or enamines. Itwas found that nucleophilic activation of the trialkoxysilanes by potassium tert-butoxidefacilitates the reduction of benzylic amides to enamines; aliphatic and benzamides toamines. Furthermore, a simple way to tune the selectivity of the reduction of aliphaticamides was found.

  • 953.
    Volkov, Alexey
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Buitrago, Elina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Adolfsson, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Direct Hydrosilylation of Tertiary Amides to Amines by an In Situ Formed Iron/N-Heterocyclic Carbene Catalyst2013In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 11, p. 2066-2070Article in journal (Refereed)
    Abstract [en]

    Tertiary amides were efficiently reduced to their corresponding tertiary amines in high isolated yields by using the commercially available and inexpensive polymeric silane polymethylhydrosiloxane (PMHS) as the reducing agent. The reaction is efficiently catalyzed by an in situ generated iron/N-heterocyclic carbene complex (1 mol-%) obtained from iron(II) acetate and 1-(2-hydroxy-2-phenylethyl)-3-methylimidazolium triflate ([PhHEMIM][OTF]). A catalytic amount of lithium chloride (1 mol-%) present in the reaction mixture significantly reduced the reaction time and increased the chemoselectivity of the reduction process.

  • 954.
    Volkov, Alexey
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tinnis, Fredrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Adolfsson, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic Reductive Dehydration of Tertiary Amides to Enamines under Hydrosilylation Conditions2014In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 16, no 3, p. 680-683Article in journal (Refereed)
    Abstract [en]

    Tertiary amides are efficiently reduced to their corresponding enamines under hydrosilylation conditions, using a transition-metal-free catalytic protocol based on t-BuOK (5 mol %) and (MeO)(3)SiH or (EtO)(3)SiH as the reducing agent. The enamines were formed with high selectivity in good-to-excellent yields.

  • 955.
    Volkov, Alexey
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tinnis, Fredrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Slagbrand, Tove
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pershagen, Ida
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Adolfsson, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mo(CO)6 catalysed chemoselective hydrosilylation of alpha,beta-unsaturated amides for the formation of allylamines2014In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 50, no 93, p. 14508-14511Article in journal (Refereed)
    Abstract [en]

    Molybdenum hexacarbonyl (Mo(CO)(6)) was used as an efficient catalyst for the chemoselective reduction of the amide functionality in alpha,beta-unsaturated compounds, under hydrosilylation conditions using 1,1,3,3-tetramethyldisiloxane (TMDS) as the hydride source.

  • 956.
    Volkov, Alexey
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tinnis, Fredrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stagbrand, Tove
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Trillo, Paz
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Adolfsson, Hans
    Chemoselective reduction of carboxamides2016In: Chemical Society Reviews, ISSN 0306-0012, E-ISSN 1460-4744, Vol. 45, no 24, p. 6685-6697Article, review/survey (Refereed)
    Abstract [en]

    The reduction of amides gives access to a wide variety of important compounds such as amines, imines, enamines, nitrites, aldehydes and alcohols. The chemoselective transformation into these functional groups is challenging due to the intrinsic stability of the amide bond; nevertheless, the ability to reduce highly stable carboxamides selectively in the presence of sensitive functional groups is of high synthetic value for academic and industrial chemists. Hydride-based reagents such as LiAlH4 or diboranes are today the most commonly used compounds for amide reductions, and apart from the substantial amount of waste generated using these methods, they lack tolerance to most other functional groups. This tutorial review provides an overview of the recent progress made in the development of chemoselective protocols for amide reduction and gives an insight to their advantages and drawbacks.

  • 957.
    Volla, Chandra M. R.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Aerobic Domino Oxidative Carbocyclization-Alkynylation of Allenynes2013In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 52, no 52, p. 14209-14213Article in journal (Refereed)
  • 958.
    Volla, Chandra M. R.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Oxidative Domino Carbocyclization-Arylation of Bisallenes2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 10, p. 6398-6402Article in journal (Refereed)
    Abstract [en]

    Herein we report a highly efficient and site selective palladium-catalyzed oxidative carbocyclization arylation reaction of bisallenes and arylboronic acids under operationally simple conditions for the selective synthesis of cyclohexadiene derivatives. The palladium source and the solvent proved to be crucial for the selectivity and the reactivity displayed. Interestingly, in the absence of the nucleophile, an oxidative carbocyclization-beta-elimination pathway predominates. The reaction conditions are compatible with a wide range of functional groups, and the reaction exhibits broad substrate scope. Furthermore, key information regarding the mechanism was obtained using control experiments and kinetic studies.

  • 959.
    Volla, Chandra M. R.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Oxidative Domino Carbocyclization- Carbonylation-Alkynylation of Enallenes2014In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 16, no 16, p. 4174-4177Article in journal (Refereed)
    Abstract [en]

    An oxidative carbocyclization-carbonylation-alkynylation reaction cascade has been developed using catalytic amounts of palladium(II) salts. The domino reaction proceeds efficiently, giving the corresponding ynones in good to excellent yields under operationally simple conditions. A wide range of aromatic and aliphatic terminal alkynes with various functional groups are tolerated under the reaction conditions.

  • 960.
    Volla, Chandra M. R.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mazuela, Javier
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Oxidative Carbocyclization-Carbonylation of Allenynes and Enallenes2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 25, p. 7608-7612Article in journal (Refereed)
    Abstract [en]

    A highly efficient oxidative carbocyclization-carbonylation reaction cascade of allenynes and enallenes has been developed using a Pd-II salt in low catalytic amounts under ambient temperature and pressure (1 atm of carbon monoxide). The use of DMSO as an additive was found to be important for an efficient reaction. A wide range of alcohols as trapping reagents were used to give the corresponding esters in good yields.

  • 961. von Langermann, Jan
    et al.
    Kaspereit, Malte
    Shakeri, Mozaffar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lorenz, Heike
    Hedberg, Martin
    Jones, Matthew J.
    Larson, Kerstin
    Herschend, Bjorn
    Arnell, Robert
    Temmel, Erik
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kienle, Achim
    Seidel-Morgenstern, Andreas
    Design of an Integrated Process of Chromatography, Crystallization and Racemization for the Resolution of 2 ',6 '-Pipecoloxylidide (PPX)2012In: Organic Process Research & Development, ISSN 1083-6160, E-ISSN 1520-586X, Vol. 16, no 2, p. 343-352Article in journal (Refereed)
    Abstract [en]

    An integrated process for the chiral separation of the industrially relevant substance 2',6'-pipecoloxylidide (PPX), an intermediate in the manufacture of a number of anesthetics, was developed. By combining three different techniques, chromatography, crystallization, and racemization, high productivity was achieved. All unit operations were executed using a common solvent system, full recycling, and a minimum of solvent exchanges or removals. The target molecule was obtained with an enantiopurity of >99.5 wt %.

  • 962.
    Västilä, Patrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Development of highly modular ligands for use in asymmetric transition-metal catalyzed reactions2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The synthesis and evaluation of ligands for use in asymmetric transition metal catalyzed reactions is a widely used concept to achieve improved enantioselectivity in a variety of different transformations. The present thesis decribes the synthesis of a number of different oxazoline-based ligands and their use in titanum-catalyzed addition of diethyl zinc to aliphatic and aromatic aldehydes. Interestingly, the presence of catalytic amounts of titanium in our system was sufficient to achieve effective catalysis in contrast to what has been previously reported concerning titanium-catalyzed addition of diethyl zinc to aldehydes.

    The synthesis and evaluation of a library of novel dipeptide-like ligands are described and these ligands were employed in connection with ruthenium-catalyzed transfer hydrogenation of aromatic ketones. Excellent enantioselectivities and yields were obtained.

    Furthermore, the novel concept of forming the ligand and catalyst in situ in a one-pot system was explored. In addition to significant simplification, this approach resulted in improvements in both enantioselectivity (minor) and reaction rate (2-3 fold) compared to previously studied procedures.

    The surprizing influence of alkali salts on ruthenium-catalyzed transfer hydrogenation involving these dipeptide-like ligands are described and discussed. In the presence of these additives the ruthenium-catalyzed transfer hydrogenation performed with higher enantioselecitvity and reactivity.

    Finally, mechanistic studies concerning ruthenium-catalyzed transfer hydrogenation involving the dipeptide-like ligands are also described and discussed.

  • 963.
    Wachtmeister, Johanna
    Stockholm University.
    Synthesis of Potential Inhibitors Against HIV1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the syntheses of various potential inhibitors of HIV, e.g. some 3´-hydroxymethyl-substituted carbocyclic nucleoside analogues as reverse transcriptase inhibitors and some symmetry-based peptidomimetics as protease inhibitors.

    Enantiomerically pure (3S,4S)-bis-(hydroxymethyl)cyclopentanone ethylene glycol ketal was used in the syntheses of eight functionalized cyclopentanol intermediates. These were either condensed with 6-chloropurine bases using the Mitsunobu reaction or converted into the corresponding cyclopentylamines, on which the purine bases were built up.

    The influence of the central hydroxyl groups on the anti-viral activity of L-mannaric acid based HIV-1 protease inhibitors was investigated. L-Iditol was used as the chiral precursor in the synthesis of the inhibitors with inverted configuration at C-3 and C-4.

    All target compounds described in this thesis were evaluated for anti-viral activity against the human immunodeficiency virus.

  • 964.
    Wagner, Samuel
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Klepsch, Mirjam M.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Schlegel, Susan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Appel, Ansgar
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Draheim, Roger
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Tarry, Michael
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Högbom, Martin
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    van Wijk, Klaas J.
    Slotboom, Dirk J.
    Persson, Jan O.
    Stockholm University, Faculty of Science, Department of Mathematics.
    de Gier, Jan-Willem
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Tuning Escherichia coli for membrane protein overexpression2008In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, no 38, p. 14371-17376Article in journal (Refereed)
    Abstract [en]

    A simple generic method for optimizing membrane protein overexpression in Escherichia coli is still lacking. We have studied the physiological response of the widely used “Walker strains” C41(DE3) and C43(DE3), which are derived from BL21(DE3), to membrane protein overexpression. For unknown reasons, overexpression of many membrane proteins in these strains is hardly toxic, often resulting in high overexpression yields. By using a combination of physiological, proteomic, and genetic techniques we have shown that mutations in the lacUV5 promoter governing expression of T7 RNA polymerase are key to the improved membrane protein overexpression characteristics of the Walker strains. Based on this observation, we have engineered a derivative strain of E. coli BL21(DE3), termed Lemo21(DE3), in which the activity of the T7 RNA polymerase can be precisely controlled by its natural inhibitor T7 lysozyme (T7Lys). Lemo21(DE3) is tunable for membrane protein overexpression and conveniently allows optimizing overexpression of any given membrane protein by using only a single strain rather than a multitude of different strains. The generality and simplicity of our approach make it ideal for high-throughput applications.

  • 965.
    Wahlström, Karolina
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Development and characterisation of protecting groups that enhance the solubility of synthetic peptides: Methods to improve the aqueous solubility of hydrophobic peptides2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Chemical synthesis of peptides is generally performed by solid phase peptide synthesis (SPPS). Although SPPS is a rapid and convenient method to prepare peptides, the major methodological problem in SPPS is related to solvation/solubility. Poor solvation of the peptide during the synthesis on solid phase will frequently lead to deletion peptides and if the peptide is poorly soluble after it has been cleaved from the resin, it can be difficult to purify by liquid chromatography. In order to increase the solubility of peptides, two new amino acid derivatives and a modification of the 2-hydroxy-4-methoxy-benzyl (Hmb) group, a protecting group for the peptide bond, have been developed. The Boc-N-methyl-N-[(2-methylamino)ethyl]carbamoyl (Boc-Nmec) group was used for protection of aromatic hydroxyl groups of tyrosine and the Hmb group. The Boc-4-(N-methyl-amino)butanoyl (Boc-Nmbu) group was used for protection of the indole nitrogen on tryptophan. The new derivatives were introduced into model peptides by standard protocol for Fmoc chemistry. The Boc protection of the Nmec/Nmbu group is removed during the cleavage of the peptide from the resin but the Nmec/Nmbu group is still attached to the peptide. The Nmec/Nmbu group contains a secondary amino group that is protonated at low pH and thereby increases the solubility during purification and handling of the peptide in aqueous solutions. By raising the pH the Nmec (pH 8)/Nmbu (pH 9) group is cleaved by an intramolecular cyclization reaction to give the fully deprotected peptide. Amyloid b (1-42) is a large peptide that is very difficult both to assemble on solid phase and to purify by HPLC.  It is shown that by using the Boc-Nmec protected dipeptides, amyloid b (1-42) could be synthesized by SPPS with only traces of by-products and that the peptide was easy to purify by HPLC. It is likely that the new protecting groups would be very useful in synthesis and handling of hydrophobic peptides.

     

     

  • 966.
    Wahlström, Karolina
    et al.
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Planstedt, Ove
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Undén, Anders
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    A carbamoyl-protective group for tyrosine that facilitatespurification of hydrophobic synthetic peptides2008In: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 49, no 23, p. 3779-3781Article in journal (Refereed)
  • 967.
    Wallin, Richard
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kalek, Marcin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bartoszewicz, Agnieszka
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Thelin, Mats
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stawinski, Jacek
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    On the sulfurization of H-phosphonate diesters and phosphite triesters using elemental sulfur2009In: Phosphorus Sulfur and Silicon and the Related Elements, ISSN 1042-6507, E-ISSN 1563-5325, Vol. 184, no 4, p. 908-916Article in journal (Refereed)
  • 968.
    Wallner, Olov
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Synthesis and Transformations of Organometallic Compounds2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is focused on two important fields of palladium catalysis: the development of electrophilic allylic substitution reactions via bis-allylpalladium intermediates; and application of palladium pincer-complexes in the synthesis and transformations of organometallic compounds.

    Palladium-catalyzed electrophilic allylation of aldehyde and imine substrates could be achieved using readily available allyl chlorides and acetates by employing hexamethylditin or bis(pinacolato)diboron reagents. The reaction proceeds under mild and neutral reaction conditions with high regioselectivity, providing the branched homoallylic products. The stereoselectivity of the reaction depends on the steric and electronic effects of the allylic substituents of the substrates. DFT modeling of the electrophilic attack on the bis-allylpalladium intermediate of the reaction revealed the origin of the regio- and stereoselectivity of the reaction.

    Palladium pincer-complexes were employed as catalysts in a variety of reactions such as stannylation, selenylation, allylation, and cross coupling reactions with various electrophiles. Allylic stannylation in the presence of hexamethylditin was achieved by use of an NCN palladium pincer-complex catalyst. In contrast to the reactions catalyzed by traditional palladium catalysts, isolation of functionalized allyl stannanes was possible due to the special features of the pincer-complex catalyst. Extension of the scope of the palladium pincer-complex catalyzed electrophilic allylation reactions was achieved by using potassium trifluoro(allyl)borate instead of allyl stannanes. In addition, asymmetric electrophilic allylation of sulfonimines was achieved by employment of novel BINOL-based palladium pincer-complexes. The enantioselectivity of the pincer-complex catalyst was fine-tuned by employment of substituted analogs of BINOL.

  • 969.
    Wang, Dong
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    New Reactions with Allyl- and Allenylboron Reagents: Transition-Metal-Catalyzed and Transition-Metal-Free Carbon-Carbon Bond Formation Processes2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Organoboron compounds have been widely used in carbon-carbon bond formation reactions in organic synthesis and catalysis. This thesis is focused on cross-coupling reactions of allyl-, allenylboronic acids and their ester derivatives via transition metal catalysis or transition-metal-free processes.

    The first part of the thesis describes Cu-catalyzed C(sp3)-C(sp3) formation reactions involving allylboronic acids and α-diazoketones. This coupling process shows high γ-regioselectivity, resulting in branched allylic products. When stereodefined cyclic allylboronic acids were employed as the substrate, the relative facial configuration was retained in the reaction product.

    The second part involves Pd-catalyzed cross-coupling of allylboronic acid and α-diazoketones. The reaction proceeds with high α-regioselectivity, affording linear allylic products. Accordingly, the palladium- and copper-catalyzed cross-coupling of allylboronic acid and α-diazoketones occurs with opposite regioselectivity.

    The third part concerns a new transition-metal-free carbon-carbon bond formation between allenylboronic acids and in situ generated diazo compounds. The diazo compounds are generated from tosylhydrazones in the presence of base. The reaction is suitable for synthesis of densely substituted conjugated dienes with high Z-selectivity.

    In the final part, the allylation of quinones with allylboronates is presented. The reaction was performed without any catalyst or additive. Various quinones can be employed as substrates, including unsubstituted, monosubstituted benzoquinones and naphthoquinones.

  • 970.
    Wang, Dong
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    de Wit, Martin J. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of Densely Substituted Conjugated Dienes by Transition-Metal-Free Reductive Coupling of Allenylboronic Acids and Tosylhydrazones2018In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 83, no 15, p. 8786-8792Article in journal (Refereed)
    Abstract [en]

    Tosylhydrazones and allenylboronic acids underwent a transition-metal-free reductive coupling reaction. This process is suitable for synthesis of tetra- and pentasubstituted conjugated dienes. The corresponding allenyl-Bpin substrate showed a very poor reactivity. The reaction is suggested to involve coupling of the in situ formed diazo compound and allenylboronic acid. The intermediate formed in this coupling undergoes allenyl migration followed by protodeboronation to furnish a conjugated diene as major product.

  • 971.
    Wang, Dong
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Copper-Catalyzed, Stereoselective Cross-Coupling of Cyclic Allyl Boronic Acids with alpha-Diazoketones2017In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 19, no 7, p. 1622-1625Article in journal (Refereed)
    Abstract [en]

    In this study; we present the synthesis of new, Stereodefined allylboronic adds employed to investigate the stereochemistry of the Cu-catalyzed cross-coupling of allylboronic acids with alpha-diazoketones. According to our results, this reaction proceeds with retention of the relative configurtion of the allylberonic acid substrate. We suggest that the stereoinduction step involves a syn S(E)2'-type transrnetalation of the allylboronic acid substrate with a Cu-carbene species.

  • 972. Wang, Lei
    et al.
    Duan, Lele
    Stewart, Beverly
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pu, Maoping
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Liu, Jianhui
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    Toward Controlling Water Oxidation Catalysis: Tunable Activity of Ruthenium Complexes with Axial Imidazole/DMSO Ligands2012In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 45, p. 18868-18880Article in journal (Refereed)
    Abstract [en]

    Using the combinations of imidazole and dimethyl :sulfoxide (DMSO) as axial ligands and 2,2'-bipyridine-6,6'-dicarboxylate (bda) as the equatorial ligand, we have synthesized six novel ruthenium complexes with noticeably different activity as water oxidation catalysts (WOCs). In four C-s symmetric Ru-II(kappa(3)-bda)(DMSO)L-2 complexes L = imidazole (1), N-methylimidazole (2), 5-methylimidazole (3), and 5-bromo-N-methylimidazole (4). Additionally, in two C-2v symmetric Ru-II(kappa(4)-bda)L-2 complexes L = 5-nitroimidazole (5) and 5-bromo-N-methylimidazole (6), that is, fully equivalent axial imidazoles. A detailed characterization of all complexes and the mechanistic investigation of the catalytic water oxidation have been carried out with a number of experimental techniques, that is, kinetics, electrochemistry and high resolution mass spectrometry (HR-MS), and density functional theory (DFT) calculations. We have observed the in situ formation: of a Ru-II-complex with the accessible seventh coordination position. The measured catalytic activities and kinetics of complex 1-6 revealed details about an important structure activity relation: the connection between the nature of axial ligands in the combination and either the increase or decrease of the catalytic activity. In particular, an axial DMSO group substantially increases the turnover frequency of WOCs reported in article, with the ruthenium-complex having one axial 5-bromo-N-methylimidazole and one axial DMSO: (4), we have obtained a high initial turnover frequency of similar to 180 s(-1). DFT modeling Of the binuclear reaction pathway of the O-O bond formation in catalytic Water oxidation further corroborated the concept of the mechanistic significance of the axial ligands and rationalized the experimentally observed difference in the activity of complexes with imidazole/DMSO and imidazole/imidazole combinations of axial ligands.

  • 973. Wang, Zhen
    et al.
    Liu, Jian-Hui
    He, Cheng-Jiang
    Jiang, Shi
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Li-Cheng
    Azadithiolates cofactor of the iron-only hydrogenase and its PR3-monosubstituted derivatives: Synthesis, structure, electrochemistry and protonation2007In: Journal of Organometallic Chemistry, ISSN 0022-328X, E-ISSN 1872-8561, Vol. 692, no 24, p. 5501-5507Article in journal (Refereed)
    Abstract [en]

    The core structure (mu-SCH2)(2)NH[Fe-2(CO)(6)](5) of Fe-only hydrogenases active site model has been synthesized by the condensation of iron carbonyl sulfides, formaldehyde and silyl protected amine. Its monosubstituted complexes (mu-SCH2)(2)NH[Fe-2(CO)(5)PR3] (R = Ph (6), Me (7)) were accordingly prepared. The coordination configurations of 5 and 6 were characterized by X-ray crystallography. Protonation of complex 7 to form the N-protonated product occurs in an acetonitrile solution upon addition of triflic acid. The redox properties of these model complexes were studied by cyclic voltammetry.

  • 974. Wang, Zhen
    et al.
    Liu, Jianhui
    He, Chengjiang
    Jiang, Shi
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    Diiron azadithiolates with hydrophilic phosphatriazaadamantane ligand as iron-only hydrogenase active site models: Synthesis, structure, and electrochemical study2007In: Inorganica Chimica Acta, ISSN 0020-1693, E-ISSN 1873-3255, Vol. 360, no 7, p. 2411-2419Article in journal (Refereed)
    Abstract [en]

    Three novel complexes (mu-adt)[Fe-2(CO)(5)PTA] (2-PTA), (mu-adt)[Fe-2(CO)(4)PTA(2)](2-PTA(2)) and (mu-adt)[Fe-2(CO)(5)DAPTA] (2-DAPTA), where adt is SCH2N(CH2CH2CH3)CH2S, PTA stands for 1,3,5-triaza-7-phosphaadamantane and DAPTA is 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane, were prepared as the models of the iron hydrogenase active site through controlled CO displacement of (mu-adt)[Fe-2(CO)(6)] with PTA and DAPTA. The coordination configurations of 2-PTA and 2-PTA(2) were characterized by X-ray crystallography. The disubstituted diiron complex 2-PTA(2) features a basal/apical coordination mode, instead of the typical transoid basal/basal configuration. Protonation of three complexes only occurred at the bridging-N atom, rather than at the tertiary nitrogen atom on the PTA or DAPTA ligands. Electrochemical properties of the complexes were studied in acetonitrile or a mixture of acetonitrile and water in the presence of acetic acid, by cyclic voltammetry. The current sensitivity of the reduced species to acid concentration in the presence of H2O is greater than in the pure CH3CN solution.

  • 975. Wangsell, Fredrik
    et al.
    Nordeman, Patrik
    Savmarker, Jonas
    Emanuelsson, Rikard
    Jansson, Katarina
    Lindberg, Jimmy
    Rosenquist, Asa
    Samuelsson, Bertil
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Larhed, Mats
    Investigation of alpha-phenylnorstatine and alpha-benzylnorstatine as transition state isostere motifs in the search for new BACE-1 inhibitors2011In: Bioorganic & Medicinal Chemistry, ISSN 0968-0896, E-ISSN 1464-3391, Vol. 19, no 1, p. 145-155Article in journal (Refereed)
    Abstract [en]

    Inhibition of the BACE-1 protease enzyme has over the recent decade developed into a promising drug strategy for Alzheimer therapy. In this report, more than 20 new BACE-1 protease inhibitors based on alpha-phenylnorstatine, alpha-benzylnorstatine, iso-serine, and beta-alanine moieties have been prepared. The inhibitors were synthesized by applying Fmoc solid phase methodology and evaluated for their inhibitory properties. The most potent inhibitor, tert-alcohol containing (R)-12 (IC(50) = 0.19 mu M) was co-crystallized in the active site of the BACE-1 protease, furnishing a novel binding mode in which the N-terminal amine makes a hydrogen bond to one of the catalytic aspartic acids.

  • 976.
    Warner, Madeleine
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hydrogen transfer reactions catalyzed by a cyclopentadienyl ruthenium complex: Mechanistic studies and dynamic kinetic resolution.2010Licentiate thesis, comprehensive summary (Other academic)
  • 977.
    Warner, Madeleine C.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Casey, Charles P.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Shvo's Catalyst in Hydrogen Transfer Reactions2011In: BIFUNCTIONAL MOLECULAR CATALYSIS, 2011, p. 85-125Conference paper (Refereed)
    Abstract [en]

    This chapter reviews the use of Shvo's catalyst in various hydrogen transfer reactions and also discusses the mechanism of the hydrogen transfer. The Shvo catalyst is very mild to use since no activation by base is required in the transfer hydrogenation of ketones or imines or in the transfer dehydrogenation of alcohols and amines. The Shvo catalyst has also been used as an efficient racemization catalyst for alcohols and amines. Many applications of the racemization reaction are found in the combination with enzymatic resolution leading to a dynamic kinetic resolution (DKR). In these dynamic resolutions, the yield based on the starting material can theoretically reach 100%. The mechanism of the hydrogen transfer from the Shvo catalyst to ketones (aldehydes) and imines as well as the dehydrogenation of alcohols and amines has been studied in detail over the past decade. It has been found that for ketones (aldehydes) and alcohols, there is a concerted transfer of the two hydrogens involved, whereas for typical amines and imines, there is a stepwise transfer of the two hydrogens. One important question is whether the substrate is coordinated to the metal or not in the hydrogen transfer step(s). The pathway involving coordination to activate the substrate is called the inner-sphere mechanism, whereas transfer of hydrogen without coordination is called the outer-sphere mechanism. These mechanistic proposals together with experimental and theoretical studies are discussed.

  • 978.
    Warner, Madeleine C.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nagendiran, Anuja
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bogár, Krisztián
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Enantioselective Route to Ketones and Lactones from Exocyclic Allylic Alcohols via Metal and Enzyme Catalysis2012In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 14, no 19, p. 5094-5097Article in journal (Refereed)
    Abstract [en]

    A general and efficient route for the synthesis of enantiomerically pure a-substituted ketones and the corresponding lactones has been developed. Ruthenium- and enzyme-catalyzed dynamic kinetic resolution (DKR) with a subsequent Cu-catalyzed alpha-allylic substitution are the key steps of the route. The a-substituted ketones were obtained in high yields and with excellent enantiomeric excess. The methodology was applied to the synthesis of a naturally occurring caprolactone, (R)-10-methyl-6-undecanolide, via a subsequent Baeyer-Villiger oxidation.

  • 979.
    Warner, Madeleine C.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Shevchenko, Grigory A.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jouda, Suzan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bogar, Krisztian
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dynamic Kinetic Resolution of Homoallylic Alcohols: Application to the Synthesis of Enantiomerically Pure 5,6-Dihydropyran-2-ones and delta-Lactones2013In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 19, no 41, p. 13859-13864Article in journal (Refereed)
    Abstract [en]

    Dynamic kinetic resolution of various homoallylic alcohols with the use of Candida antarctica lipaseB and ruthenium catalyst 2 afforded homoallylic acetates in high yields and with high enantioselectivity. These enantiopure acetates were further transformed into homoallylic acrylates after hydrolysis of the ester function and subsequent DMAP-catalyzed esterification with acryloyl chloride. After ring-closing metathesis 5,6-dihydropyran-2-ones were obtained in good yields. Selective hydrogenation of the carboncarbon double bond afforded the corresponding -lactones without loss of chiral information.

  • 980.
    Warner, Madeleine C
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    CO dissociation mechanism in racemization of alcohols by a cyclopentadienyl ruthenium dicarbonyl catalyst2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 9, p. 2820-2823Article in journal (Refereed)
    Abstract [en]

    13CO exchange studies of racemization catalyst (η5-Ph5C5)Ru(CO)2Cl and (η5-Ph5C5)Ru(CO)2(Ot-Bu) by 13C NMR spectroscopy are reported. CO exchange for the active catalyst form, (η5-Ph5C5)Ru(CO)2(Ot-Bu) is approximately 20 times faster than that for the precatalyst (η5-Ph5C5)Ru(CO)2Cl. An inhibition on the rate of racemization of (S)-1-phenylethanol was observed on addition of CO. These results support the hypothesis that CO dissociation is a key step in the racemization of sec-alcohols by (η5-Ph5C5)Ru(CO)2Cl, as also predicted by DFT calculations.

  • 981. Watcharinyanon, Somsakul
    et al.
    Puglia, Carla
    Göthelid, Emmanuelle
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Moons, Ellen
    Johansson, Lars S.O.
    Molecular orientation of thiol-derivatized tetraphenylporphyrin on gold studied by XPS and NEXAFS2009In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, no 7, p. 1026-1033Article in journal (Refereed)
  • 982.
    Weber, Jens
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Impact of cross-linking density and glassy chain dynamics on pore stability in mesoporous poly(styrene)2009In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 42, no 21, p. 8234-8240Article in journal (Refereed)
    Abstract [en]

    Mesoporous poly(styrene) (PS) containing various amounts of the cross-linker divinylbenzene was synthesized by a hard-templating routine using pressed pellets of fumed silica as templates. Porous polymers with a surface area of 215 m2g-1 and porosities up to ~35 vol.-% could be obtained. The impact of the cross-linker content and the processing on the porosity of the materials was investigated by nitrogen sorption and small angle X-ray scattering. The surface area of the nascent porous PS increases and the pore size decrease with increasing amount of cross-linker. Furthermore, it was found that the porous polymers loose surface area at temperatures that are substantially below the glass transition temperature, Tg, of bulk polystyrene. The loss in surface area at temperatures below 65°C suggests that partial pore collapse also may be induced in the glassy state. Finally, the stability of the mesopores against solvent swelling was investigated. A critical pore collapse was found at a cross-linker content of ~ 20 wt.-%. In this context, also the existence of traced porosity, i.e. a non accessible mesostructure or porosity, could be confirmed.

  • 983. Wei, Wen-Jie
    et al.
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Liao, Rong-Zhen
    Theoretical Study of the Mechanism of the Nonheme Iron Enzyme EgtB2017In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, no 6, p. 3589-3599Article in journal (Refereed)
    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.

  • 984. Wellens, Adinda
    et al.
    Garofalo, Corinne
    Nguyen, Hien
    Van Gerven, Nani
    Slättegård, Rikard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    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 complex2008In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 3, no 4, p. e2040; 1-13Article in journal (Refereed)
  • 985.
    Wettergren, Jenny
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selective transfer hydrogenations: Catalyst development and mechanistic investigations2008Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 986.
    Wettergren, Jenny
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Buitrago, Elina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ryberg, Per
    Adolfsson, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanistic Investigation on the Asymmetric Transfer Hydrogenation of Ketones Catalyzed by Pseudo-Dipeptides Ruthenium complexes2009In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, no 23, p. 5709-5718Article in journal (Refereed)
    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.

  • 987.
    Wettergren, Jenny
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Buitrago, Elina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ryberg, Per
    Adolfsson, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanistic investigations into the asymmetric transfer hydrogenation of ketones catalyzed by pseudo-dipeptide ruthenium complexes2009In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, no 23, p. 5709-5718Article in journal (Refereed)
  • 988.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    A perspective on the primary and three-dimensional structures of carbohydrates2013In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 378, p. 123-132Article in journal (Refereed)
    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.

  • 989.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Computational and experimental analysis of oligosaccharide conformation and dynamics2011In: Abstracts of Papers, 241st ACS National Meeting & Exposition, Anaheim, CA, United States, March 27-31, 2011, American Chemical Society (ACS), 2011Conference paper (Refereed)
    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.

  • 990. Wieczorek, Birgit
    et al.
    Träff, Annika
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Krumlinde, Patrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dijkstra, Harm P.
    Egmond, Maarten R.
    van Koten, Gerard
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Klein Gebbink, Robertus J. M.
    Covalent anchoring of a racemization catalyst to CALB-beads: towards dual immobilization of DKR catalysts2011In: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 52, no 14, p. 1601-1604Article in journal (Refereed)
    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.

  • 991. Wieczorek, Birgit
    et al.
    Träff, Annika
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Krumlinde, Patrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dijkstra, Harm P.
    Egmond, Maarten R.
    van Koten, Gerard
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Klein Gebbink, Robertus J.M.
    Site-Specific Covalent Immobilization of a Racemization Catalyst onto Lipase-containing BeadsManuscript (preprint) (Other academic)
    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.

  • 992.
    Wikmark, Ylva
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Engineering Candida antarctica Lipase A for Enantioselective Transformations in Organic Synthesis: Design, Immobilization and Organic Solvent Screening of Smart Enzyme Libraries2015Doctoral thesis, comprehensive summary (Other academic)
    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. 

  • 993.
    Wikmark, Ylva
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Engelmark Cassimjee, Karim
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lihammar, Richard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Removing the Active-Site Flap in Lipase A from Candida antarctica Produces a Functional Enzyme without Interfacial Activation2016In: ChemBioChem (Print), ISSN 1439-4227, E-ISSN 1439-7633, Vol. 17, no 2, p. 141-145Article in journal (Refereed)
    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.

  • 994.
    Wikmark, Ylva
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Humble, Maria Svedendahl
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Combinatorial Library Based Engineering of Candida antarctica Lipase A for Enantioselective Transacylation of sec-Alcohols in Organic Solvent2015In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 54, no 14, p. 4284-4288Article in journal (Refereed)
    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.

  • 995.
    Willy, Benjamin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Development of pincer complex-catalyzed oxidative C-H activation borylation reactions: Synthetic applications and mechanistic studies2010In: Abstracts of Papers, 239th ACS National Meeting, San Francisco, CA, United States, March 21-25, 2010, Washington D C: American Chemical Society , 2010Conference paper (Other academic)
  • 996.
    Winnberg, Ulrika
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Environmental Chemistry.
    Rydén, Andreas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Environmental Chemistry.
    Löfstrand, Karin
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Asplund, Lillemor
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Environmental Chemistry.
    Bignert, Anders
    Marsh, Göran
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Environmental Chemistry.
    Novel Octabrominated Phenolic Diphenyl Ether Identified in Blue Mussels from the Swedish West Coast2014In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 48, no 6, p. 3319-3326Article in journal (Refereed)
    Abstract [en]

    Hydroxylated (OH−) and methoxylated (MeO−) polybrominated diphenyl ethers (PBDEs) are compounds present in the marine environment and OH–PBDEs are of toxicological concern and are therefore of interest to monitor in the environment. A phenolic octaBDE was tentatively identified in the phenolic fraction of previously analyzed mussel samples after methylation of the halogenated phenolic compounds (HPCs). The aim of the present study was to confirm the identity of this compound in blue mussels and investigate whether the analyte is diOH– and/or OH–MeO–octaBDE. Two reference standards, 6,6′-dimethoxy-2,2′,3,3′,4,4′,5,5′-octabromodiphenyl ether (6,6′-diMeO–BDE194) and 6-ethoxy-6′-methoxy-2,2′,3,3′,4,4′,5,5′-octabromodiphenyl ether (6-EtO-6′-MeO–BDE194) were prepared via O-arylation of 2,3,4,5-tetrabromo-6-methoxyphenol and 2,3,4,5-tetrabromo-6-ethoxyphenol, respectively, with a novel unsymmetrical diaryliodonium salt, 2,3,4,5-tetrabromo-6-methoxydiphenyliodonium triflate. The GC retention time and GC/MS spectrum of the synthesized 6,6′-diMeO–BDE194 correspond well with the analyte in the methylated phenolic fraction of a mussel extract from a previous study. Structural analysis performed in this study indicate that the synthesized 6,6′-diMeO–BDE194 and 6-EtO-6′-MeO–BDE194 correspond well with 6-hydroxy-6′-methoxy-2,2′,3,3′,4,4′,5,5′-octabromodiphenyl ether (6-OH–6′-MeO–BDE194) after methylation and ethylation, respectively, of the HPCs in the mussel extracts. The compound 6-OH–6′-MeO–BDE194 was identified and quantified in new mussels, sampled in 2012 from two locations on the Swedish west coast, with geometric mean concentrations of 3700 and 410 ng/g fat, respectively.

  • 997.
    Winqvist, Anna
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Studies towards a method for incorporation of 3'-deoxy-3'-C-methylenephosphonate linkages into oligonucleotides2002Doctoral thesis, comprehensive summary (Other academic)
    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).

  • 998.
    Wolpher, Henriette
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ruthenium(II) Polypyridyl Complexes in Supramolecular Systems relevant to Artificial Photosynthesis2005Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 999. Wu, Emilia L.
    et al.
    Fleming, Patrick J.
    Yeom, Min Sun
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Klauda, Jeffery B.
    Fleming, Karen G.
    Im, Wonpil
    E. coil Outer Membrane and Interactions with OmpLA2014In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 106, no 11, p. 2493-2502Article in journal (Refereed)
    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.

  • 1000.
    Wu, Haibo
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Margarita, Cristiana
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jongcharoenkamol, Jira
    Singh, Thishana
    Nolan, Mark
    Andersson, Pher
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Highly Efficient Kinetic Resolution of Allylic Alcohols via Iridium-Catalyzed Asymmetric HydrogenationManuscript (preprint) (Other academic)
171819202122 951 - 1000 of 1054
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