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  • 1. Abrahamsson, Maria
    et al.
    Wolpher, Henriette
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johansson, Olof
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Larsson, Jan
    Kritikos, Mikael
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Structural Chemistry.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Structural Chemistry.
    Norrby, Per-Ola
    Bergquist, Jonas
    Sun, Licheng
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hammarström, Leif
    A New Strategy for Improvement of Photophysical Properties in Ruthenium(II) Polypyridyl Complexes. Synthesis, Photophysical and Electrochemical characterisation of Six Mononuclear Ruthenium(II) Bisterpyridine Type Complexes2005In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 44, no 9, p. 3215-3225Article in journal (Refereed)
    Abstract [en]

    The synthesis and characterization of six ruthenium(II) bistridentate polypyridyl complexes is described. These were designed on the basis of a new approach to increase the excited-state lifetime of ruthenium(II) bisterpyridine-type complexes. By the use of a bipyridylpyridyl methane ligand in place of terpyridine, the coordination environment of the metal ion becomes nearly octahedral and the rate of deactivation via ligand-field (i.e., metal-centered) states was reduced as shown by temperature-dependent emission lifetime studies. Still, the possibility to make quasi-linear donor−ruthenium−acceptor triads is maintained in the complexes. The most promising complex shows an excited-state lifetime of τ = 15 ns in alcohol solutions at room temperature, which should be compared to a lifetime of τ = 0.25 ns for [Ru(tpy)2]2+. The X-ray structure of the new complex indeed shows a more octahedral geometry than that of [Ru(tpy)2]2+. Most importantly, the high excited-state energy was retained, and thus, so was the potential high reactivity of the excited complex, which has not been the case with previously published strategies based on bistridentate complexes.

  • 2.
    Aggarwal, Varinder K.
    et al.
    Bristol University.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry. University of Bristol, Bristol, UK.
    Enantioselective α-arylation of cyclohexanones with diaryl iodonium salts: Application to the synthesis of (-)-epibatidine.2005In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 44, no 34, p. 5516-5519Article in journal (Refereed)
    Abstract [en]

    The direct asym. α-arylation of prochiral ketones has been effected using chiral lithium amide bases and diaryl iodonium salts. The methodol. has been employed in a short total synthesis of the alkaloid (-)-epibatidine. [on SciFinder(R)]

  • 3. Casas, J
    et al.
    Engqvist, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ibrahem, I
    Kaynak, B
    Córdova, A
    Direct Amino Acid-Catalyzed Asymmetric Synthesis of Polyketide Sugars2005In: Angewandte Chemie International ed., ISSN 1433-7851, Vol. 44, no 9, p. 1343-1345Article in journal (Refereed)
  • 4.
    Córdova, Armando
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Engqvist, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ibrahem, Ismail
    Casas, Jésus
    Sundén, Henrik
    Plausible origins of homochirality in the amino acid catalyzed neogenesis of carbohydrates2005In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 2005, p. 2047-2049Article in journal (Refereed)
    Abstract [en]

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

  • 5.
    Córdova, Armando
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ibrahem, Ismail
    Casas, Jesús
    Sundén, Henrik
    Engqvist, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Reyes, Efraim
    Amino Acid-Catalyzed Neogenesis of Carbohydrates: A Plausible Ancient Transformation2005In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 11, no 16, p. 4772-4784Article in journal (Refereed)
    Abstract [en]

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

  • 6.
    Fransson, Ann-Britt L.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Borén, Linnéa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pàmies, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kinetic Resolution and Chemoenzymatic Dynamic Kinetic Resolution of Functionalized γ-Hydroxy Amides2005In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 70, no 7, p. 2582-2587Article in journal (Refereed)
    Abstract [en]

    An efficient kinetic resolution of racemic gamma-hydroxy amides 1 was performed via Pseudomas cepacia lipase (PS-C)-catalyzed transesterification. The enzyme PS-C tolerates both variation in the chain length and different functionalities giving good to high enantioselectivity (E values of up to > 250). The combination of enzymatic kinetic resolution with a ruthenium-catalyzed racemization led to a dynamic kinetic resolution. The use of 2,4-dimethyl-3-pentanol as a hydrogen source to suppress ketone formation in the dynamic kinetic resolution yields the corresponding acetates in good yield and good to high enantioselectivity (ee's up to 98%). The synthetic utility of this procedure was illustrated by the practical synthesis of the versatile intermediate gamma-lactone (R)-5-methyltetrahydrofuran-2-one.

  • 7.
    Fryxelius, Jacob
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eilers, Gerriet
    Feyziyev, Yashar
    Magnuson, Ann
    Sun, Licheng
    Lomoth, Reiner
    Synthesis and redox properties of a [meso-tris(4-nitrophenyl)corrolato]Mn(III) complex2005In: Journal of Porphyrins and Phtalocyanines, Vol. 9, p. 379-386Article in journal (Refereed)
  • 8.
    Gemma, Emiliano
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lahmann, Martina
    Oscarson, Stefan
    Synthesis of the tetrasaccharide α-D-Glcp-(1→3)-α-D-Manp-(1→2)-α-D-Manp-(1→2)-α-D-Manp recognised by Calreticulin/Calnexin2005In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 340, no 16, p. 2558-2562Article in journal (Refereed)
    Abstract [en]

    The title compound as its methyl glycoside was efficiently synthesized using a block synthesis approach. Halide-assisted glycosidations between 6-O-acetyl-2,3,4-tri-O-benzyl-α-d-glucopyranosyl iodide and ethyl 2-O-acetyl-4,6-di-O-benzyl-1-thio-α-d-mannopyranoside using triphenylphosphine oxide as promoter yielded, with complete α-selectivity, a disaccharide building block in high yield. The perbenzylated derivative of this proved to be an excellent donor affording 88% of the protected target tetrasaccharide in an NIS/AgOTf-promoted coupling to a known methyl dimannoside acceptor. Deprotection through catalytic hydrogenolysis then gave the target compound in 47% overall yield.

  • 9. ibrahem, Ismail
    et al.
    Samec, Joseph S M
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Córdiva, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Enantioselective addition of aldehydes to amines via combined catalytic biomimetic oxidation and organocatalytic C-C- bond formation2005In: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 46, no 23, p. 3965-3968Article in journal (Refereed)
    Abstract [en]

    The biomimetic catalytic enantioselective addition of aldehydes to amines is reported. This was accomplished by combining biomimetic coupled catalytic aerobic oxidation of amines involving ruthenium-induced dehydrogenation and organocatalytic asymmetric Mannich reactions. The novel one-pot reactions furnished β-amino aldehyde and α-amino acid derivatives in high yields with excellent chemoselectivity and up to >99% ee.

  • 10.
    Johansson, Mikael
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lindén, Auri A.
    Bäckvall, Jan-E.
    Osmium-catalyzed dihydroxylation of alkenes by H2O2 in room temperature ionic liquid co-catalyzed by VO(acac)2 or MeReO32005In: Journal of organometallic chemistry, ISSN 0022-328X, Vol. 690, no 15, p. 3614-3619Article in journal (Refereed)
  • 11. Johansson, Mikael
    et al.
    Lindén, Auri
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Osmium-Catalyzed Dihydroxylaition of Alkenes by H2O2 in Room Temperature Ionic Liquid co-Catalyzed by VO(acac)2 or MeReO32005In: Journal of Organometallic Chemistry, ISSN 0022-328X, Vol. 690, no 15, p. 3614-3619Article in journal (Refereed)
  • 12. Kjellgren, Johan
    et al.
    Aydin, Johanes
    Wallner, Olov
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Saltanova, Irina V.
    Szabó, Kálmán J
    Palladium Pincer Complex Catalyzed Cross-Coupling of Vinyl Epoxides and Aziridines with Organoboronic Acids2005In: Chemistry : a European journal, ISSN 0947-6539, Vol. 11, no 18, p. 5260-5268Article in journal (Refereed)
  • 13. Kjellgren, Johan
    et al.
    Aydin, Juhanes
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Wallner, Olov A.
    Saltanova, Irina
    Szabó, Kálmán J.
    Palladium Pincer Complex Catalyzed Cross-Coupling of Vinyl Epoxides and Aziridines with Organoboronic Acids2005In: Chemistry - A European Journal, ISSN 0947-6539, Vol. 11, no 18, p. 5260-5268Article in journal (Refereed)
  • 14.
    Kjellgren, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sundén, Henrik
    Szabó, Kálmán J.
    Palladium pincer complex-catalyzed stannyl and silyl transfer to propargylic substrates: Synthetic scope and mechanism2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 6, p. 1787-1796Article in journal (Refereed)
  • 15.
    Kullberg, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stawinski, Jacek
    Nucleoside H-phosphonates XX: Efficient method for the preparation of nucleoside H-phosphonoselenoate monoesters2005In: Synthesis (Stuttgart), ISSN 0039-7881, E-ISSN 1437-210X, no 10, p. 1668-1674Article in journal (Refereed)
  • 16.
    Kullberg, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stawinski, Jacek
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Preparation of nucleoside H-phosphonoselenoate monoesters via the phosphinate approach2005In: Nucleosides, Nucleotides & Nucleic Acids, ISSN 1525-7770, E-ISSN 1532-2335, Vol. 24, no 10-12, p. 1627-1633Article in journal (Refereed)
    Abstract [en]

    An efficient entry to nucleoside 3'-H-phosphonoselenoate monoesters via phosphinate intermediates was developed. It involves a reaction of suitably protected nucleosides with triethylammonium phosphinate in the presence of pivaloyl chloride, followed by selenization of the intermediate nucleoside phosphinates with triphenylphosphine selenide, to produce the corresponding nucleoside H-phosphonoselenoates in 86-92% yields.

  • 17.
    Kullberg, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stawinski, Jacek
    Theoretical investigation on the mechanism of chalcogen exchange reaction between P(V) and P(III) compounds2005In: Journal of Organometallic chemistry, ISSN 0022-328X, Vol. 690, p. 2571-2576Article in journal (Refereed)
  • 18.
    Landersjö, Clas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jansson, Jennie L. M.
    Maliniak, Arnold
    Widmalm, Göran
    Conformational analysis of the tetrasaccharide Lacto-N-neotetraose based on solution state NMR spectroscopy and molecular dynamics simulations2005In: Journal of Physical Chemistry B, ISSN 1089-5647, Vol. 109, no 36, p. 17320-17326Article in journal (Refereed)
  • 19.
    Larsson Birgander, Pernilla
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Bug, Stefanie
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Gordon, Euan
    Dahlroth, Sue-Li
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Kasrayan, Alex
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Westman, MariAnn
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Euan, Gordon
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Nucleotide-dependent formation of catalytically competent dimers from engineered monomeric ribonucleotide reductase protein R12005In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 280, no 15, p. 14997-15003Article in journal (Refereed)
    Abstract [en]

    Each catalytic turnover by aerobic ribonucleotide reductase requires the assembly of the two proteins, R1 (α2) and R2 (β2), to produce deoxyribonucleotides for DNA synthesis. The R2 protein forms a tight dimer, whereas the strength of the R1 dimer differs between organisms, being monomeric in mouse R1 and dimeric in Escherichia coli. We have used the known E. coli R1 structure as a framework for design of eight different mutations that affect the helices and proximal loops that comprise the dimer interaction area. Mutations in loop residues did not affect dimerization, whereas mutations in the helices had very drastic effects on the interaction resulting in monomeric proteins with very low or no activity. The monomeric N238A protein formed an interesting exception, because it unexpectedly was able to reduce ribonucleotides with a comparatively high capacity. Gel filtration studies revealed that N238A was able to dimerize when bound by both substrate and effector, a result in accordance with the monomeric R1 protein from mouse. The effects of the N238A mutation, fit well with the notion that E. coli protein R1 has a comparatively small dimer interaction surface in relation to its size, and the results illustrate the stabilization effects of substrates and effectors in the dimerization process. The identification of key residues in the dimerization process and the fact that there is little sequence identity between the interaction areas of the mammalian and the prokaryotic enzymes may be of importance in drug design, similar to the strategy used in treatment of HSV infection.

  • 20. Linde, Christian
    et al.
    Anderlund, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Björn
    The Effect of Phenolates in the Mn(salen)-Catalyzed Epoxidation Reaction2005In: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 46, no 33, p. 5597-5600Article in journal (Refereed)
    Abstract [en]

    By addition of 2,4,6-tri-tert-butylphenolate in the Mn(salen) catalyzed epoxidation of cis-alkenes with iodosobenzene, essentially pure trans-epoxides can be obtained.

  • 21.
    Lindén, Auri
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hermanns, Nina
    Ott, Sascha
    Krüger, Lars
    Bäckvall, Jan-Erling
    Preparation and Properties of N,N,N-1,3,5-Trialkylated Flavin Derivatives and Their Activity as Redox Catalysts2005In: Chemistry - A European Journal, ISSN 0947-6539, Vol. 11, no 1, p. 112-119Article in journal (Refereed)
  • 22. Martín-Matute, B.
    et al.
    Bogár, Krisztián
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Edin, M.
    Kaynak, F.
    Bäckvall, Jan-E.
    Highly Efficient Redox Isomerization of Allylic Alcohols at Ambient Temperature Catalyzed by Novel Ruthenium-Cyclopentadienyl Complexes–Insight into the Racemization Mechanism2005In: Chemistry : a European journal, ISSN 0947-6539, Vol. 11, no 20, p. 5832-5842Article in journal (Refereed)
  • 23. Martín-Matute, B.
    et al.
    Edin, M.
    Bogár, Krisztián
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kaynak, F.
    Bäckvall, Jan-E.
    Combined Ruthenium(II) and Lipase Catalysis for Efficient Dynamic Kinetic Resolution of Secondary Alcohols. Insight into the Racemization Mechanism2005In: Journal of the American Chemical Society, ISSN 0002-7863, Vol. 127, no 24, p. 8817-8825Article in journal (Refereed)
  • 24.
    Martín-Matute, Belén
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bogár, Krisztián
    Edin, Michaela
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kaynak, F. Betül
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Highly efficient redox isomerization of allylic alcohols at ambient temperature catalyzed by novel ruthenium cyclopentadienyl complexes: New insight into the mechanism2005In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 11, no 20, p. 5832-5842Article in journal (Refereed)
    Abstract [en]

    A range of ruthenium cyclopentadienyl (Cp) complexes have been prepared and used for isomerization of allylic alcohols to the corresponding saturated carbonyl compounds. Complexes bearing CO ligands show higher activity than those with PPh3 ligands. The isomerization rate is highly affected by the substituents on the Cp ring. Tetra(phenyl)methyl-substituted catalysts rapidly isomerize allylic alcohols under very mild reaction conditions (ambient temperature) with short reaction times. Substituted allylic alcohols have been isomerized by employing Ru–Cp complexes. A study of the isomerization catalyzed by [Ru(Ph5Cp)(CO)2H] (14) indicates that the isomerization catalyzed by ruthenium hydrides partly follows a different mechanism than that of ruthenium halides activated by KOtBu. Furthermore, the lack of ketone exchange when the isomerization was performed in the presence of an unsaturated ketone (1 equiv), different from that obtained by dehydrogenation of the starting allylic alcohol, supports a mechanism in which the isomerization takes place within the coordination sphere of the ruthenium catalyst.

  • 25.
    Martín-Matute, Belén
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Edin, Michaela
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bogár, Krisztián
    Kaynak, F. Betül
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Combined ruthenium(II)- and lipase catalysis for efficient dynamic kinetic resolution of sec-alcohols. Insight into a new racemization mechanism2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 24, p. 8817-8825Article in journal (Refereed)
    Abstract [en]

     

    Pentaphenylcyclopentadienyl ruthenium complexes (3) are excellent catalysts for the racemization of secondary alcohols at ambient temperature. The combination of this process with enzymatic resolution of the alcohols results in a highly efficient synthesis of enantiomerically pure acetates at room temperature with short reaction times for most substrates. This new reaction was applied to a wide range of functionalized alcohols including heteroaromatic alcohols, and for many of the latter, enantiopure acetates were efficiently prepared for the first time via dynamic kinetic resolution (DKR). Different substituted cyclopentadienyl ruthenium complexes were prepared and studied as catalysts for racemization of alcohols. Pentaaryl-substituted cyclopentadienyl complexes were found to be highly efficient catalysts for the racemization. Substitution of one of the aryl groups by an alkyl group considerably slows down the racemization process. A study of the racemization of (S)-1-phenylethanol catalyzed by ruthenium hydride η5-Ph5CpRu(CO)2H (8) indicates that the racemization takes place within the coordination sphere of the ruthenium catalyst. This conclusion was supported by the lack of ketone exchange in the racemization of (S)-1-phenylethanol performed in the presence of p-tolyl methyl ketone (1 equiv), which gave <1% of 1-(p-tolyl)ethanol. The structures of ruthenium chloride and iodide complexes 3a and 3c and of ruthenium hydride complex 8 were confirmed by X-ray analysis.

  • 26.
    Nilsson, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kraszewski, Adam
    Institute of Bioorganic Chemistry, Polish Academy of Science.
    Stawinski, Jacek
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Chemical and Stereochemical Aspects of Oxidative Coupling of H Phosphonantes and H-Phosphonothioate Diesters: Reactions with N,N-, N,O- and O,O-Binucleophiles2005In: Letters in organic chemistry, ISSN 1570-1786, Vol. 2, no 2, p. 188-197Article in journal (Refereed)
    Abstract [en]

    Efficient protocols for oxidative coupling of dinucleoside H-phosphonate and dinucleoside Hphosphonothioate diesters with 6-aminohexan-1-ol, hexane-1,6-diamine, and hexane-1,6-diol, promoted by iodine were developed. In the instance of coupling with O-nucleophiles, the presence of t-butyldiphenylsilyl chloride and excess of iodine during oxidative coupling were found to have beneficial effect for these reactions in terms of rates and purity of the formed products

  • 27.
    Nordmark, Eva-Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Zhennai
    Huttunen, Eine
    Widmalm, Göran
    Structural studies of an exopolysaccharide produced by Streptococcus thermophilus THS2005In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 1, p. 105-108Article in journal (Refereed)
    Abstract [en]

    The structure of an extracellular polysaccharide (EPS) from Streptococcus thermophilus THS has been determined. A combination of component analysis, methylation analysis and NMR spectroscopy shows that the polysaccharide is composed of pentasaccharide repeating units. Sequential information was obtained by two-dimensional 1H,1H−NOESY and 1H,13C−HMBC NMR experiments. NMR data indicate different mobility within the EPS with a stiffer backbone and a more flexible side-chain.

  • 28.
    Nordmark, Eva-Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Zhennai
    Huttunen, Eine
    Widmalm, Göran
    Structural studies of the exopolysaccharide produced by Propionibacterium freudenreichii ssp. shermanii JS2005In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 1, p. 521-523Article in journal (Refereed)
  • 29.
    Närhi, Katja
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Franzén, Johan
    Bäckvall, Jan-E.
    Palladium(0)-Catalyzed Cyloisomerization of Enallenes2005In: Chemistry A European Journal, ISSN 0947-6539, Vol. 11, no 23, p. 6937-6943Article in journal (Refereed)
  • 30.
    Olsson, Ulrika
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lycknert, Kristina
    Stenutz, Roland
    Weintraub, Andrej
    Widmalm, Göran
    Structural analysis of the O-antigen polysaccharide from Escherichia coli O1522005In: Carbohydrate Research, ISSN 0008-6215, Vol. 340, p. 167-171Article in journal (Refereed)
  • 31.
    Samec, Joseph S M
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mony, Laetitia
    Bäckvall, Jan-E
    Efficient Ruthenium-Catalyzed Transfer Hydrogenation of Functionalized Imines by Isopropanol under Controlled Microwave Heating2005In: Canadian journal of chemistry (Print), ISSN 0008-4042, E-ISSN 1480-3291, Vol. 83, no 6, p. 909-916Article in journal (Refereed)
    Abstract [en]

    Transfer hydrogenation of various functionalized imines by isopropanol catalyzed by [Ru(CO)(2)(Ph4C4CO)](2) (3) has been studied. The use of either an oil bath or controlled microwave heating in toluene led to an efficient procedure with high turnover frequencies and the product amines were obtained in high yields. An advantage with catalyst 3 over the conventional [Ru-2(CO)(4)(mu-H)(Ph4C4COHOCC4Ph4)] (1) is the absence of an initiation period, which results in a faster reaction with 3 as compared to 1.

  • 32.
    Samec, Joseph S M
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Éll, Alida H
    Bäckvall, Jan-E
    Efficient Ruthenium-Catalyzed Aerobic Oxidation of Amines Using a Biomimetic Coupled Catalytic System2005In: Chemistry : a European journal, ISSN 0947-6539, Vol. 11, no 8, p. 2327-2334Article in journal (Refereed)
  • 33.
    Sebelius, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kálmán J., Szabó
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Allylation of aldehyde and imine substrates with in situ generated allylboronates - a simple route to enantioenriched homoallyl alcohols2005In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 12, p. 2539-2547Article in journal (Refereed)
    Abstract [en]

    Allylation of aldehyde and imine substrates was achieved using easily available allylacetates and diboronate reagents in the presence of catalytic amounts of palladium. This operationally simple one-pot reaction has a broad synthetic scope, as many functionalities including, acetate, carbethoxy, amido and nitro groups are tolerated. The allylation reactions proceed with excellent regio- and stereoselectivity affording the branched allylic isomer. By employment of commercially available chiral diboronates enantioenriched homoallyl alcohols (up to 53% ee) could be obtained. The mechanistic studies revealed that the in situ generated allylboronates react directly with the aldehyde substrates, however the allylation of the sulfonylimine substrate requires palladium catalysis.

  • 34.
    Sebelius, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olsson, Vilhelm J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium Pincer Complex Catalyzed Substitution of Vinyl Cyclopropanes, Vinyl Aziridines, and Allyl Acetates with Tetrahydroxydiboron. An Efficient Route to Functionalized Allylboronic Acids and Potassium Trifluoro(allyl)borates2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 30, p. 10478-10479Article in journal (Refereed)
    Abstract [en]

    Palladium-catalyzed boronation of vinyl cyclopropane, vinyl aziridine, and allyl acetate substrates could be accomplished using tetrahydroxydiboron reagent in the presence of SeCSe pincer complex catalyst 1a. These reactions result in allyl boronic acids, which were converted to synthetically useful trifluoro(allyl)borates or allyl boronates. The catalytic transformations proceed under mild and neutral conditions, and therefore many functionalities Br, COOEt, ArSO2(NH), OAc, and SiRMe2 are tolerated. The selectivity of the presented processes is very high, affording the linear products incorporating a trans double bond.

  • 35. Sjödin, Martin
    et al.
    Styring, Stenbjörn
    Wolpher, Henriette
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Xu, Yunhua
    Sun, Licheng
    Hammarström, Leif
    Switching the redox mechanism: Models for proton coupled electron transfer from tyrosine and tryptophan2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 11, p. 3855-3863Article in journal (Refereed)
    Abstract [en]

    The coupling of electron and proton transfer is an important controlling factor in radical proteins, such as photosystem II, ribinucleotide reductase, cytochrome oxidases, and DNA photolyase. This was investigated in model complexes in which a tyrosine or tryptophan residue was oxidized by a laser-flash generated trisbipyridine-Ru-III moiety in an intramolecular, proton-coupled electron transfer (PCET) reaction. The PCET was found to proceed in a competition between a stepwise reaction, in which electron transfer is followed by deprotonation of the amino acid radical (ETPT), and a concerted reaction, in which both the electron and proton are transferred in a single reaction step (CEP). Moreover, we found that we could analyze the kinetic data for PCET by Marcus' theory for electron transfer. By altering the solution pH, the strength of the Ru-III oxidant, or the identity of the amino acid, we could induce a switch between the two mechanisms and obtain quantitative data for the parameters that control which one will dominate. The characteristic pH-dependence of the CEP rate (M. Sjodin et al. J. Am. Chem. Soc. 2000, 122, 3932) reflects the pH-dependence of the driving force caused by proton release to the bulk. For the pH-independent ETPT on the other hand, the driving force of the rate-determining ET step is pH-independent and smaller. On the other hand, temperature-dependent data showed that the reorganization energy was higher for CEP, while the pre-exponential factors showed no significant difference between the mechanisms. Thus, the opposing effect of the differences in driving force and reorganization energy determines which of the mechanisms will dominate. Our results show that a concerted mechanism is in general quite likely and provides a low-barrier reaction pathway for weakly exoergonic reactions. In addition, the kinetic isotope effect was much higher for CEP (k(H)/k(D) &GT; 10) than for ETPT (k(H)/k(D) = 2), consistent with significant changes along the proton reaction coordinate in the rate-determining step of CEP.

  • 36.
    Slättegård, Rikard
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Teodorovic, Peter
    Kinfe, Henok Hadgu
    Ravenscroft, Neil
    Gammon, David W
    Oscarson, Stefan
    Synthesis of structures corresponding to the capsular polysaccharide of Neisseria meningitidis serogroup A2005In: Organic and biomolecular chemistry, Vol. 3, no 3, p. 3782-3787Article in journal (Refereed)
  • 37.
    Slättegård, Rikard
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Teodorović, Peter
    Hadgu Kinfe, Henok
    Ravenscroft, Neil
    Gammon, David W.
    Oscarson, Stefan
    Synthesis of Structures Corresponding to the Capsular Polysaccharide of Neisseria meningitidis Group A2005In: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 3, no 20Article in journal (Refereed)
    Abstract [en]

     

     

     

     

    Four differently substituted trimers of the CPS repeating unit have been synthesised in order to investigate the

    dependence on oligosaccharide size, acetylation and mode of phosphorylation of glycoconjugate vaccines against

    Neisseria meningitidis

     

    group A. A spacer-containing starting monomer, a H-phosphonate elongating monomer and a

    6-

     

    O

    -phosphorylated H-phosphonate cap monomer have been synthesised and coupled together to afford, after

    deprotection, the target trimer structures differing in their acetylation and phosphorylation substitution

    pattern.

  • 38. Solin, Niclas
    et al.
    Wallner, Olov
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J
    Palladium Pincer-Complex Catalyzed Allylation of Tosylimines by Potassium Trifluoro(allyl)borates2005In: Organic letters, ISSN 1523-7060, Vol. 7, no 4, p. 689-691Article in journal (Refereed)
  • 39. Teodorovic, Peter
    et al.
    Slättegård, Rikard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Oscarson, Stefan
    Improved synthesis of 1,3,4,6-tetra-O-acetyl-2-azido-2-deoxy-a-D-mannopyranose2005In: Carbohydrate Research, Vol. 340, no 340, p. 2675–2676-Article in journal (Refereed)
  • 40.
    Teodorović, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Slättegård, Rikard
    Oscarson, Stefan
    Improved Synthesis of 1,3,4,6-tetra-O-acetyl-2-Azido-2-deoxy-α-D-mannopyranose2005In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 340, no 17, p. 2675-2676Article in journal (Refereed)
    Abstract [en]

    By improved (anhydrous) work-up conditions of a triflate displacement reaction, the yield in the preparation of the versatile synthetic intermediate 1,3,4,6-tetra-O-acetyl-2-azido-2-deoxy-α-d-mannopyranose has been significantly enhanced. This important precursor is now available in three efficient steps from d-glucose.

  • 41. Urbina, Felipe
    et al.
    Nordmark, Eva-Lisa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Zhennai
    Weintraub, Andrej
    Scheutz, Flemming
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural elucidation of the O-antigenic polysaccharide from the enteroaggregative Escherichia coli strain 180/C3 and its immunochemical relationship with Escherichia coli O5 and O652005In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 340, no 4, p. 645-650Article in journal (Refereed)
    Abstract [en]

    The structure of the O-antigen polysaccharide (PS) from the enteroaggregative Escherichia coli strain 180/C3 has been determined. Sugar and methylation analysis together with 1H and 13C NMR spectroscopy were the main methods used. The PS is composed of tetrasaccharide repeating units with the following structure:→2)-β-d-Quip3NAc-(1→3)-β-d-Ribf-(1→4)-β-d-Galp-(1→3)-α-d-GalpNAc-(1→Analysis of NMR data indicates that the presented sequence of sugar residues also represents the biological repeating unit of the O-chain. The structure is closely related to that of O-antigen polysaccharide from E. coli O5 and partially to that of E. coli O65. The difference between the O-antigen from the 180/C3 strain and that of E. coli O5 is the linkage to the d-Quip3NAc residue, which in the latter strain is 4-O-substituted. The E. coli O65 O-antigen contains as part of its linear pentasaccharide repeating unit a similar structural element, namely →4)-β-d-GalpA-(1→3)-α-d-GlcpNAc-(1→2)-β-d-Quip3NAc-(1→, thereby indicating that a common epitope could be present for the two polysaccharides. Monospecific anti-E. coli O5 rabbit serum did not distinguish between the two positional isomeric structures neither in slide agglutination nor in an indirect enzyme immunoassay. The anti-O65 serum did react with both the 180/C3 and O5 LPS showing a partial cross-reactivity.

  • 42.
    Västilä, Patrik
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pastor, Isidro
    Adolfsson, Hans
    2-(Aminomethyl)-oxazolines: Highly modular scaffold for the preparation of novel asymmetric ligands2005In: Journal of Organic Chemistry, Vol. 70, no 8, p. 2921-2929Article in journal (Refereed)
  • 43. Västilä, Patrik
    et al.
    Wettergren, Jenny
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Adolfsson, Hans
    In situ formation of ligand and catalyst- application in ruthenium-catalyzed enantioselective reduction of ketones2005In: Chemical communications, ISSN 1359-7345, no 32, p. 4039-4041Article in journal (Refereed)
  • 44.
    Wallner, Olov
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J
    Employment of Palladium Pincer-Complexes in Phenylselenylation of Organohalides2005In: Journal of Organic Chemistry, ISSN 0022-3263, Vol. 70, no 23, p. 9215-9221Article in journal (Refereed)
1 - 44 of 44
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