Change search
Refine search result
12 1 - 50 of 58
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 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.
    Anderlund, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dinuclear Manganese Complexes for Artificial Photosynthesis: Synthesis and Properties2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the synthesis and characterisation of a series of dinuclear manganese complexes. Their ability to donate electrons to photo-generated ruthenium(III) has been investigated in flash photolysis experiments followed by EPR-spectroscopy. These experiment shows several consecutive one-electron transfer steps from the manganese moiety to ruthenium(III), that mimics the electron transfer from the oxygen evolving centre in photosystem II.

    The redox properties of these complexes have been investigated with electro chemical methods and the structure of the complexes has been investigated with different X-ray techniques. Structural aspects and the effect of water on the redox properties have been shown.

    One of the manganese complexes has been covalently linked in a triad donor-photosensitizer-acceptor (D–P–A) system. The kinetics of this triad has been investigated in detail after photo excitation with both optical and EPR spectroscopy. The formed charge separated state (D–P–A+) showed an unusual long lifetime for triad based on ruthenium photosensitizers.

    The thesis also includes a study of manganese-salen epoxidation reactions that we believe can give an insight in the oxygen transfer mechanism in the water oxidising complex in photosystem II.

  • 4. 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)
  • 5.
    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.

  • 6.
    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.

  • 7.
    Edin, Michaela
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ruthenium-catalyzed redox reactions and lipase-catalyzed asymmetric transformations of alcohols2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

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

  • 8.
    Eklund, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Computational Analysis of Carbohydrates: Dynamical Properties and Interactions2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

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

  • 9.
    Engqvist, Magnus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Direct Amino Acid-Catalyzed Enantioselective α-Oxidation Reactions and Asymmetric de novo Synthesis of Carbohydrates2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

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

  • 10.
    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.

  • 11.
    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)
  • 12.
    Gemma, Emiliano
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of Oligosaccharides for Interaction Studies with Various Lectins2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, the syntheses of oligosaccharides for interaction studies with various lectins are described. The first section reports the syntheses of tetra, tri- and disaccharides corresponding to truncated versions of the glucosylated arm of Glc1Man9(GlcNAc)2, found in the biosynthesis of N-glycans. The thermodynamic parameters of their interaction with calreticulin, a lectin assisting and promoting the correct folding of newly synthesised glycoproteins, were established by isothermal titration calorimetry. In the second section, a new synthetic pathway leading to the same tetra- and trisaccharides is discussed. Adoption of a convergent strategy and of a different protecting group pattern resulted in significantly increased yields of the target structures. The third section describes the syntheses of a number of monodeoxy-trisaccharides related to the above trisaccharide Glc-α-(1→3)-Man-α-(1→2)-Man-α-OMe. Differentsynthetic approaches were explored and the choice of early introduction of the deoxy functionality proved the most beneficial. In the last section, the synthesis of spacer-linked LacNAc dimers as substrates for the lectins galectin-1 and -3 is presented. This synthesis was realized by glycosidation of a number diols with peracetylated LacNAc-oxazoline. Pyridinium triflate was tested as a new promoter, affording the target dimers in high yields. This promoter in combination with microwave irradiation gave even higher yields and also shortened the reaction times.

  • 13.
    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.

  • 14. 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.

  • 15.
    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)
  • 16. 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)
  • 17.
    Kjellgren, Johan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Employment of Palladium Pincer Complex Catalysts and Lewis Acids for Synthesis and Transformation of Organometallic Compounds2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is mainly focused on the development of new palladium catalyzed transformations using so-called “pincer” complexes. These complexes were applied as catalysts in two important areas of organometallic chemistry: substitution of propargylic substrates by dimetallic reagents; and allylation of aldehydes and imines by allylstannanes. In addition, this thesis includes studies on Lewis acid mediated cyclization reactions of allylsilanes with aldehydes.

    Pincer complex catalyzed substitution of various propargylic substrates could be achieved under mild conditions using tin and silicon based dimetallic reagents to obtain propargyl- and allenylstannanes and silanes. The regioselectivity of the substitution reaction strongly depends on the steric and electronic effects of the propargylic substrate. According to our mechanistic studies the key intermediate of the reaction is an organostannane (or silane) coordinated pincer complex. DFT modeling studies on the transfer of the trimethylstannyl functionality to the propargylic substrate revealed a novel mechanism, which is based on the unique topology of the pincer-complex catalysts.

    Our further studies showed that palladium pincer complexes can be employed as efficient catalysts for electrophilic allylic substitution of allylstannanes with aldehyde and imine substrates. In contrast to previous applications for electrophilic allylic substitutions via bis-allylpalladium complexes, this reaction involves mono-allylpalladium intermediates which were observed by 1H-NMR spectroscopy.

    The last chapter of this thesis is focused on Lewis-acid mediated cyclization of hydroxy functionalized allylsilanes, which afford tetrahydropyran derivatives with a high stereoselectivity.

  • 18. 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)
  • 19. 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)
  • 20.
    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)
  • 21.
    Kullberg, Martin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Studies on nucleoside H-phosphonoselenoate chemistry and chalcogen exchange reaction between P(V) and P(III) compounds2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, the chemistry of compounds containing P-Se bonds has been studied. As a new addition to this class of compounds, H-phosphonoselenoate monoesters, have been introduced and two synthetic pathways for their preparation have been developed.

    The reactivity of H-phosphonoselenoate monoesters towards a variety of condensing agents has been studied. From these, efficient conditions for the synthesis of H-phosphonoselenoate diesters have been developed. The produced diesters have subsequently been used in oxidative transformations, which gave access to the corresponding P(V) compounds, e.g. dinucleoside phosphoroselenoates or dinucleoside phosphoroselenothioates.

    Furthermore, a new selenizing agent, triphenyl phosphoroselenoate, has been developed for selenization of P(III) compounds. This reagent has high solubility in organic solvents and was found to convert phosphite triesters and H-phosphonate diesters efficiently into the corresponding phosphoroselenoate derivatives.

    The selenization of P(III) compounds with triphenyl phosphoroselenoate proceeds through a selenium transfer reaction. A computational study was performed to gain insight into a mechanism for this reaction. The results indicate that the transfer of selenium or sulfur from P(V) to P(III) compounds proceeds most likely via an X-philic attack of the P(III) nucleophile on the chalcogen of the P(V) species. For the transfer of oxygen, the reaction may also proceed via an edge attack on the P=O bond.

  • 22.
    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)
  • 23.
    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.

  • 24.
    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)
  • 25.
    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)
  • 26.
    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.

  • 27.
    Lavén, Gaston
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stawinski, Jacek
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthetic Studies on the Preparation of Dinucleoside Phenyl-Phosphonates and Phenyl-Phosphonothioates via Palladium(0) Catalyzed Cross-Coupling2005In: / [ed] Michal Hocek, 2005, p. 195-199Conference paper (Refereed)
    Abstract [en]

    Separate diastereomers of protected dithymidine (3'-5')-phenylphosphonates and dithymidine (3'-5')phenylphosphonothioate were obtained via a palladium(0) catalysed stereo-specific cross-coupling reaction of separate diastereomers of corresponding dinucleoside H-phosphonate and dinucleoside H-phosphonothioate with halobenzenes.

  • 28. 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.

  • 29.
    Lindén, Auri
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Flavins as Biomimetic Catalysts for Sulfoxidation by H2O2: Catalyst Immobilization in Ionic Liquid for H2O2 Oxidations2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the development of catalytic oxidation reactions utilizing hydrogen peroxide as terminal oxidant. The main focus has been to find flavin catalysts that are easy to handle and stable to store but still able to perform the desired reaction. A variety of dihydroflavins were prepared and the electrochemical oxidation potentials were measured and compared with their catalytic activity.

    A flavin catalyst was applied in the sulfoxidation of allylic and vinylic sulfides by H2O2. This transformation was highly chemoselective and the sulfoxides were obtained without formation of other oxidation products. The scope of the reaction was demonstrated by applying the method on substrates with a wide range of functional groups such as a tertiary amine. Another flavin catalyst was immobilized in the ionic liquid [BMIm]PF6 and used for sulfoxidations by H2O2. The chemoselectivity was maintained in this system and the catalyst-ionic liquid system could be recycled several times.

    Finally two bimetallic catalyst systems for the dihydroxylation of alkenes by H2O2 were immobilized in the ionic liquid. These systems employed either vanadium acetylacetonate VO(acac)2 or methyl trioxorhenium (MTO) as co-catalysts together with the substrate-selective osmium catalyst. Good to excellent yields of the diols were obtained.

  • 30.
    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)
  • 31. 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)
  • 32. 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)
  • 33.
    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.

  • 34.
    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.

  • 35.
    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

  • 36.
    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.

  • 37.
    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)
  • 38.
    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)
  • 39.
    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)
  • 40.
    Samec, Joseph S M
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ruthenium-catalyzed hydrogen transfer involving amines and imines: Mechanistic studies and synthetic applications2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with ruthenium-catalyzed hydrogen transfer involving amines and imines and is divided into two parts.

    In Part 1 a mechanistic study has been performed. The complexation of the imine to the catalyst and the decomplexation patterns of the formed ruthenium-amine complexes, isotope studies, and exchange studies show that the mechanism of the hydrogen transfer involving amines and imines is different from the hydrogen transfer involving alcohols and carbonyls.

    In Part 2 synthetic applications of the hydrogen transfer is presented. First the rutheniumcatalyzed transfer hydrogenation of imines by 2-propanol in an unpolar solvent was investigated. The corresponding amines were isolated in good to excellent yields. Even imines bearing labile functional groups were smoothly transferred to amines with very low catalyst loadings and short reaction times employing microwave heating. Then the reverse reaction, transfer dehydrogenation of amines to imines, was investigated using either MnO2 or oxygen as terminal oxidant. Important products such as aldimines, ketimines, and non benzylic anilines were prepared in the aerobic oxidation. We also demonstrated that the aerobic oxidation is compatible with proline-mediated organocatalysis, yielding amines in high yields and ee:s. Finally the racemization of chiral amines was investigated. A cumbersome side product formation was investigated and hampered by the use of a mild hydrogen donor, giving a mild and efficient racemization process for both primary and secondary amines.

  • 41.
    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.

  • 42.
    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)
  • 43.
    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.

  • 44.
    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.

  • 45. 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.

  • 46.
    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)
  • 47.
    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.

  • 48. 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)
  • 49.
    Teodorovic, Peter
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of oligosaccharides related to the capsular polysaccharide of Neisseria meningitidis serotype A2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In order to find suitable stable vaccine candidates against Neisseria meningitidis group A, several structures related to the capsular polysaccharide have been synthesised. The first part of the thesis describes the synthesis of C-phosphonate analogues starting from glucose. The key step is a Mitsunobu coupling of a methyl C-phosphonate monomer to the 6-hydroxyl group of a 2-acetamido mannose derivative. Contained within this work is a description of an improved synthesis of 2-azido-2-deoxy-D-mannopyranose. The second part outlines the synthesis of structural elements present in the native capsular polysaccharide of Neisseria meningitidis serotype A including different acetylation and phosphorylation patterns. The final chapter describes an improved synthesis of the Lewis b hexasaccharide needed for purification of and interaction studies with the Helicobacter pylori adhesin BabA.

  • 50. 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)
12 1 - 50 of 58
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf