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  • 2601. Witt, A
    et al.
    Bergman, Jan
    Södertörn University, Avdelning Naturvetenskap. Karolinska Institute.
    Recent developments in the field of quinazoline chemistry2003In: Current organic chemistry, ISSN 1385-2728, E-ISSN 1875-5348, Vol. 7, no 7, p. 659-677Article in journal (Refereed)
    Abstract [en]

    Recent developments in the chemistry of quinazolines and quinazolinones are discussed. The chemistry of quinazoline alkaloids is reviewed featuring chrysogine, luotonin A, tryptanthrin, febrifugine. and rutaecarpine.

  • 2602. Witt, A
    et al.
    Bergman, Jan
    Södertörn University, Avdelning Naturvetenskap.
    Synthesis and reactions of some 2-vinyl-3H-quinazolin-4-ones2000In: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 56, no 37, p. 7245-7253Article in journal (Refereed)
    Abstract [en]

    A simple, high-yielding synthesis of 2-vinyl-3H-quinazolin-4-one, 2-(1-chlorovinyl)-3H-quinazolin-4-one and 2-(1-bromovinyl)-3H-quinazolin-4-one. The 2-vinylquinazolinones 11a and 14 participate readily in nucleophilic addition reactions. Treatment with both carbon and nitrogen nucleophiles results in a clean conversion into a variety of 2-substituted 3H-quinazolin-4-one derivatives. The 2-(1-halovinyl)-3H-quinazolin-4-ones 11b and Ile reacted with carbon nucleophiles to give several derivatives of 2-substituted 3H-quinazolin-4-one, such as dihydrofurancarboxylic ethyl ester 23.

  • 2603. Witt, A
    et al.
    Bergman, Jan
    Södertörn University, Avdelning Naturvetenskap. Karolinska Institute.
    Total syntheses of the benzodiazepine alkaloids circumdatin F and circumdatin C2001In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 66, no 8, p. 2784-2788Article in journal (Refereed)
    Abstract [en]

    Total syntheses of circumdatin F and circumdatin C, which both possess a 3H-quinazolin-4-one as well as a 1,4-benzodiazepin-5-one moiety, are described. A tripeptide derivative was synthesized as a key intermediate and dehydrated to a benzoxazine by reaction with triphenylphosphine, iodine, and a tertiary amine. The natural products were attained via rearrangements to an amidine intermediate, deprotection with 45% HBr in acetic acid, and cyclization on silica gel.

  • 2604. Witt, A
    et al.
    Gustavsson, A
    Bergman, Jan
    Södertörn University, Avdelning Naturvetenskap. Karolinska Institute.
    Studies towards the synthesis of the benzodiazepine alkaloid auranthine. Synthesis of an acetylated derivative2003In: Journal of Heterocyclic Chemistry, ISSN 0022-152X, E-ISSN 1943-5193, Vol. 40, no 1, p. 29-35Article in journal (Refereed)
  • 2605. Witzgall, P
    et al.
    Trematerra, P
    Liblikas, Ilme
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Bengtsson, M
    Unelius, C. Rikard
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Pheromone communication channels in tortricid moths: lower specificity of alcohol vs. acetate geometric isomer blends2010In: Bulletin of entomological research, ISSN 0007-4853, E-ISSN 1475-2670, Vol. 100, no 2, p. 225-230Article in journal (Refereed)
    Abstract [en]

    Discrimination of conspecific and heterospecific signals is a key element in the evolution of specific mate recognition systems. Lepidopteran pheromone signals are typically composed of several compounds that synergize attraction of conspecific and inhibit attraction of heterospecific males. Blends convey specificity, but not their single components, that are typically shared by several species. Many sex pheromones are blends of geometric or positional isomers of straight-chain acetates, while species-specific blends of analogous alcohols have not been described. We have, therefore, studied the attraction of tortricid moths to the geometric isomers (E,E)-, (E,Z)-, (Z,E)- and (Z,Z)-8,10-dodecadien-1-ol. Only one species responding to these alcohols seemed to be attracted to a blend of two isomers, while most species are attracted to only one alcohol isomer. Lack of a pronounced synergist or antagonist effect of the other geometric isomers explains the lack of specific attraction to isomer blends and reduces accordingly the number of specific communication signals composed of these alcohols. In comparison, many more species respond to the analogous (E,E)-, (E,Z)-, (Z,E)- and (Z,Z)-8,10-dodecadienyl acetates and their binary blends. The acetate isomers all play a behavioural role, either as attractants, attraction synergists or antagonists, and thus promote specific communication with acetate blends. Male moths seem to discriminate the acetate isomers with greater precision than the analogous alcohols. It is proposed that discrimination is facilitated by steric differences between the four acetate isomers, as compared to the more uniform steric properties of the alcohols.

  • 2606.
    Wixe, Torbjörn
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Almqvist, Fredrik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    An improved synthesis of 3-[1-(trifluoromethy1)-3H-1,2-diazirin-3-yl] aniline: a key intermediate in the synthesis of photoaffinity probes2017In: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 58, no 34, p. 3350-3352Article in journal (Refereed)
    Abstract [en]

    An improved synthesis of 3-[3-(trifluoromethyl)-3H-1,2-diazirin-3-yflaniline, achieving an overall yield of 38% over seven steps is reported. Only three chromatographic separations were needed and the preparation of similar to 0.7 g of the target compound was demonstrated. The stability of the diazirine in solution at room temperature while exposed to ambient light was studied. No significant degradation of the compound was observed over the course of five weeks in a 130 mM sample and only minor degradation was observed in weaker samples (10, 5, and 2.5 mM), as demonstrated by H-1 and F-19 NMR.

  • 2607.
    Wolpher, Henriette
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ruthenium(II) Polypyridyl Complexes in Supramolecular Systems relevant to Artificial Photosynthesis2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

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

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

  • 2608.
    Wong, Fiona
    et al.
    Environm Canada, Ctr Atmospher Res Expt, Sci & Technol Branch, Egbert, ON L0L 1N0, Canada.
    Bidleman, Terry F.
    Environm Canada, Ctr Atmospher Res Expt, Sci & Technol Branch, Egbert, ON L0L 1N0, Canada.
    Aging of Organochlorine Pesticides and Polychlorinated Biphenyls in Muck Soil: Volatilization, Bioaccessibility, and Degradation2011In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 45, no 3, p. 958-963Article in journal (Refereed)
    Abstract [en]

    An organic rich muck soil which is highly contaminated with native organochlorine pesticide (OCs) was spiked with known amounts of (13)C-labeled OCs and nonlabeled polychlorinated biphenyls (PCBs). Spiked soils were aged under indoor, outdoor, and sterile conditions and the change in volatility, surrogate bioaccessibility, and degradation of chemicals was monitored periodically over 730 d. Volatility was measured using a fugacity meter to characterize the soil-air partition coefficient (K(SA) = C(SOII)/C(AIR))). The fraction of bioaccessible residues was estimated by comparing recoveries of chemical with a mild extractant, hydroxylpropyl-beta-cyclodextrin (HPCD) vs a harsh extractant, DCM. K(SA) of the spiked OCs in the nonsterile (Indoor, Outdoor) soils were initially lower and approached the K(SA) of native OCs over time, showing reduction of volatility upon aging. HPCD extractability of spiked OCs and PCBs were negatively correlated with K(SA), which suggests that volatility can be used as a surrogate for bioaccessibility. Degradation of endosulfans, PCB 8 and 28 was observed in the nonsterile soils, and (13)C(6)-alpha-HCH showed selective degradation of the (+) enantiomer. Enantiomer fractions (EF) in air and HPCD extracts were lower than in nonsterile soils, suggesting greater sequestering of the (+) enantiomer in the soil during microbial degradation.

  • 2609. Wong, Fiona
    et al.
    Jantunen, Liisa M.
    Pucko, Monika
    Papakyriakou, Tim
    Staebler, Ralf M.
    Stern, Gary A.
    Bidleman, Terry F.
    Air-Water Exchange of Anthropogenic and Natural Organohalogens on International Polar Year (IPY) Expeditions in the Canadian Arctic2011In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 45, no 3, p. 876-881Article in journal (Refereed)
    Abstract [en]

    Shipboard measurements of organohalogen compounds in air and surface seawater were conducted in the Canadian Arctic in 2007-2008. Study areas included the Labrador Sea, Hudson Bay, and the southern Beaufort Sea. High volume air samples were collected at deck level (6 m), while low volume samples were taken at 1 and 15 m above the water or ice surface. Water samples were taken within 7 m. Water concentration ranges (pg L-1) were as follows: alpha-hexachlorocyclohexane (alpha-HCH) 465-1013, gamma-HCH 150-254, hexachlorobenzene (HCB) 4.0-6.4, 2,4-dibromoanisole (DBA) 8.5-38, and 2,4,6-tribromoanisole (TBA) 4.7-163. Air concentration ranges (pg m(-3)) were as follows: alpha-HCH 7.5-48, gamma-HCH 2.1-7.7, HCB 48-71, DBA 4.8-25, and TBA 6.4 - 39. Fugacity gradients predicted net deposition of HCB in all areas, while exchange directions varied for the other chemicals by season and locations. Net evasion of alpha-HCH from Hudson Bay and the Beaufort Sea during open water conditions was shown by air concentrations that averaged 14% higher at 1 m than 15 m. No significant difference between the two heights was found over ice cover. The alpha-HCH in air over the Beaufort Sea was racemic in winter (mean enantiomer fraction, EF = 0.504 +/- 0.008) and nonracemic in late spring-early summer (mean EF = 0.476 +/- 0.010). This decrease in EF was accompanied by a rise in air concentrations due to volatilization of nonracemic alpha-HCH from surface water (EF = 0.457 +/- 0.019). Fluxes of chemicals during the southern Beaufort Sea open water season (i.e., Leg 9) were estimated using the Whitman two-film model, where volatilization fluxes are positive and deposition fluxes are negative. The means +/- SD (and ranges) of net fluxes (ng m(-2) d(-1)) were as follows: alpha-HCH 6.8 +/- 3.2 (2.7-13), gamma-HCH 0.76 +/- 0.40 (0.26-1.4), HCB -9.6 +/- 2.7 (-6.1 to -15), DBA 1.2 +/- 0.69 (0.04-2.0), and TBA 0.46 +/- 1.1 ng m(-2) d(-1) (-1.6 to 2.0).

  • 2610. Wu, Emilia L.
    et al.
    Fleming, Patrick J.
    Yeom, Min Sun
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Klauda, Jeffery B.
    Fleming, Karen G.
    Im, Wonpil
    E. coil Outer Membrane and Interactions with OmpLA2014In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 106, no 11, p. 2493-2502Article in journal (Refereed)
    Abstract [en]

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

  • 2611.
    Wu, Xiongyu
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Eriksson, Caroline
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Wohlfarth, Ariane
    Linköping University, Department of Medical and Health Sciences, Division of Drug Research. Linköping University, Faculty of Medicine and Health Sciences. National Board Forens Med, Department Forens Genet and Forens Toxicol, Linkoping, Sweden.
    Wallgren, Jakob
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Kronstrand, Robert
    Linköping University, Department of Medical and Health Sciences, Division of Drug Research. Linköping University, Faculty of Medicine and Health Sciences. National Board Forens Med, Department Forens Genet and Forens Toxicol, Linkoping, Sweden.
    Josefsson, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering. National Board Forens Med, Department Forens Genet and Forens Toxicol, Linkoping, Sweden.
    Dahlén, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Konradsson, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Synthesis and identification of metabolite biomarkers of 25C-NBOMe and 25I-NBOMe2017In: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 73, no 45, p. 6393-6400Article in journal (Refereed)
    Abstract [en]

    Synthetic routes have been developed for synthesis of potential metabolites of 25C-NBOMe and 25I-NBOMe. Nine potential metabolites have been synthesized, among which compounds 8 and 20a could be used as metabolite biomarkers of 25C-NBOMe and 20b of 25I-NBOMe in urinary detection at forensic laboratories to prove intake. (C) 2017 Elsevier Ltd. All rights reserved.

    The full text will be freely available from 2019-09-18 15:32
  • 2612.
    Wu, Xiongyu
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Silverå Ejneby, Malin
    Linköping University, Department of Clinical and Experimental Medicine, Divison of Neurobiology. Linköping University, Faculty of Medicine and Health Sciences.
    Ottosson, Nina
    Linköping University, Department of Clinical and Experimental Medicine, Divison of Neurobiology. Linköping University, Faculty of Medicine and Health Sciences.
    Elinder, Fredrik
    Linköping University, Department of Clinical and Experimental Medicine, Divison of Neurobiology. Linköping University, Faculty of Medicine and Health Sciences.
    Konradsson, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    A Suzuki-Miyaura Coupling of ortho-Hydroxyaryl Bromide with Isopropenylboronic Pinacol Ester: Synthesis of the Potassium-Channel Opener (+)-Callitrisic Acid2018In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 14, p. 1730-1734Article in journal (Refereed)
    Abstract [en]

    A Suzuki-Miyaura coupling reaction of ortho-hydroxy-aromatic bromide 8 with isopropenylboronic acid pinacol ester has been investigated. It was found that the catalyst of Pd-2(dba)(3)/PCy3 in dioxan-water gave good yield by suppressing the formation of isomeric side product 14. (+)-Callitrisic acid was synthesized from (+)-podocarpic acid using this condition with an overall yield of 54 % in about five steps. (+)-Callitrisic acid was found to be almost three times more potent than dehydroabietic acid to open a voltage-gated potassium channel.

  • 2613.
    Wärme, Rikard
    Umeå University, Faculty of Science and Technology, Chemistry.
    New methods and reagents for small scale synthesis of phosphor organic compounds with focus on the phosphonic acids and their analogues2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The development of a synthetic method of radiolabelled methylphosphono-fluoridates on a milligram scale is presented. The aim of this method is, besides affording high yield, to choose reaction pathways and reagents so that handling and transfer of labelled toxic substances is minimised, thereby reducing the risk of exposure as much as possible. The only substituent that is stable enough to be labelled is the methyl group, directly bonded to phosphorus. A drawback when labelling the methyl group is that it requires the label to be introduced early in the synthesis since the carbon-phosphorus bond of the methyl substituent usually has to be synthesized a few steps ahead of the final product.

    Two new classes of reagents for halogenation of phosphorus oxyacids have been developed. Firstly, four different analogues of α-chloroenamines and α-fluoroenamines were evaluated. Secondly, cyanuric fluoride was assessed in solution, but more importantly, as a resin-bound reagent. The reagents are evaluated for halogenation of phosphinic, phosphonic and phosphoric acids. Cyanuric fluoride is also successfully loaded on a polystyrene resin and used as a solid-phase reagent. The reagents produce high yields and low levels of impurities on a milligram scale.

    Furthermore, a new method for the preparation of mono-alkylated phosphonic acids on a small scale has been developed. The new method utilises the crystal water bound to certain salts to liberate limited amounts of water in a controlled manner. Phosphonic dichlorides are in this way reacted with water to form anhydrides. The anhydride is then cleaved with an appropriate alcohol to produce mono-alkylated phosphonic acids.

  • 2614.
    Wärme, Rikard
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Juhlin, Lars
    Swedish Defence Research Agency, Division of NBC-Defence, Department of Threat Assessment, Umeå.
    A new microscale method for the conversion of phosphorus oxyacids to their fluorinated analogues, using cyanuric fluoride in solution and on solid support2010In: Phosphorus Sulfur and Silicon and the Related Elements, ISSN 1042-6507, E-ISSN 1563-5325, Vol. 185, no 12, p. 2402-2408Article in journal (Refereed)
    Abstract [en]

    Cyanuric fluoride, in solution or loaded onto a Wang resin, is successfully used as a fluorinating agent for phosphorus oxy acids. The reaction is very efficient with high yields and easy workup procedures, thereby in general generating products in quantitative yields. The cyanuric fluoride is proven suitable for micromolar scale synthesis of analytical standards, particularly in its resin-bound form.

  • 2615.
    Wärme, Rikard
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Juhlin, Lars
    Swedish Defence Research Agency, Division of NBC-Defence, Department of Threat Assessment, Umeå.
    A new one-pot microscale synthesis of alkyl alkylphosphonic acids utilizing water release of inorganic saltsManuscript (preprint) (Other academic)
  • 2616.
    Wångsell, Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Organic Chemistry. Linköping University, The Institute of Technology.
    Design and Synthesis of Serine and Aspartic Protease Inhibitors2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the design and synthesis of compounds that are

    intended to inhibit serine and aspartic proteases. The first part of the text deals with preparation of inhibitors of the hepatitis C virus (HCV) NS3 serine protease. Hepatitis C is predominantly a chronic disease that afflicts about 170 million people worldwide. The NS3 protease, encoded by HCV, is essential for replication of the virus and has become one of the main targets when developing drugs to fight HCV. The inhibitors discussed here constitute surrogates for the widely used N-acyl-hydroxyproline isostere designated 4-hydroxy-cyclopentene. The stereochemistry of the 4-hydroxy-cyclopentene scaffold was determined by nuclear overhauser effect spectroscopy (NOESY) and the regiochemistry by heteronuclear multiple bond correlation (HMBC). The scaffold was decorated with different substituents to obtain both linear and macrocyclic HCV NS3 protease inhibitors that display low nanomolar activity. The second part of the thesis describes the design and synthesis of potential aspartic protease inhibitors. The hydroxyethylene motif was used as a noncleavable transition state isostere. The synthetic route yielded a pivotal intermediate with excellent stereochemical control, which was corroborated by NOESY experiments. This intermediate can be diversified with different substituents to furnish novel aspartic protease inhibitors.

  • 2617. Wångsell, Fredrik
    et al.
    Russo, Francesco
    Sävmarker, Jonas
    Åsa, Rosenquist
    Samuelsson, Bertil
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Larhed, Mats
    Design and synthesis of BACE-1 inhibitors utilizing a tertiary hydroxyl motif as the transition state mimic2009In: Bioorganic & Medicinal Chemistry Letters, ISSN 0960-894X, Vol. 19, no 16, p. 4711-4714Article in journal (Refereed)
  • 2618.
    Xiao, You-Cai
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Moberg, Christina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Silaborative Carbocyclizations of 1,7-Enynes. Diastereoselective Preparation of Chromane Derivatives2016In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 18, no 2, p. 308-311Article in journal (Refereed)
    Abstract [en]

    Palladium(0)-catalyzed carbocyclization of 1,7-enynes mediated by (chlorodimethylsilyl)pinacolborane proceeds with 1,8-addition of the silicon and boron functions to give functionalized cyclohexane derivatives with boron attached to the exocyclic olefin. A variety of chromane dervatives are accessible by this method. In contrast to the analogous reactions with 1,6-enynes, the configuration of the newly formed stereogenic center is controlled by a stereogenic center present in the substrate.

  • 2619. Xie, H.
    et al.
    Fan, Ting
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Lei, Q.
    Fang, W.
    New progress in theoretical studies on palladium-catalyzed C−C bond-forming reaction mechanisms2016In: Science China Chemistry, ISSN 1674-7291, p. 1-16Article in journal (Refereed)
    Abstract [en]

    This review reports a series of mechanistic studies on Pd-catalyzed C−C cross-coupling reactions via density functional theory (DFT) calculations. A brief introduction of fundamental steps involved in these reactions is given, including oxidative addition, transmetallation and reductive elimination. We aim to provide an important review of recent progress on theoretical studies of palladium-catalyzed carbon–carbon cross-coupling reactions, including the C−C bond formation via C−H bond activation, decarboxylation, Pd(II)/Pd(IV) catalytic cycle and double palladiums catalysis.

  • 2620.
    Xie, Sheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Fukumoto, Ryo
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Yan, Mingdi
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. University of Massachusetts, United States.
    Anilide Formation from Thioacids and Perfluoroaryl Azides2015In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 80, no 9, p. 4392-4397Article in journal (Refereed)
    Abstract [en]

    A metal-free method for fast and clean anilide formation from perfluoroaryl azide and thioacid is presented. The reaction proved highly efficient, displaying fast kinetics, high yield, and good chemoselectivity. The transformation was compatible with various solvents and tolerant to a wide variety of functional groups, and it showed high performance in polar protic/aprotic media, including aqueous buffer systems.

  • 2621.
    Xie, Sheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. Univ Massachusetts Lowell, Dept Chem, Lowell, MA 01854 USA.
    Lopez, Steven A.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Yan, Mingdi
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. Department of Chemistry, University of Massachusetts Lowell, Lowell, MA, United States .
    Houk, K. N.
    1,3-Dipolar Cycloaddition Reactivities of Perfluorinated Aryl Azides with Enamines and Strained Dipolarophiles2015In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, no 8, p. 2958-2966Article in journal (Refereed)
    Abstract [en]

    The reactivities of enamines and predistorted (strained) dipolarophiles toward perfluoroaryl azides (PFAAs) were explored experimentally and computationally. Kinetic analyses indicate that PFAAs undergo (3 + 2) cycloadditions with enamines up to 4 orders of magnitude faster than phenyl azide reacts with these dipolarophiles. DFT calculations were used to identify the origin of this rate acceleration. Orbital interactions between the cycloaddends are larger due to the relatively low-lying LUMO of PFAAs. The triazolines resulting from PFAAenamine cycloadditions rearrange to amidines at room temperature, while (3 + 2) cycloadditions of enamines and phenyl azide yield stable, isolable triazolines. The 1,3-dipolar cycloadditions of norbornene and DIBAC also show increased reactivity toward PFAAs over phenyl azide but are slower than enamineazide cycloadditions.

  • 2622.
    Xie, Sheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Manuguri, Sesha
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hao, Nanjing
    Zhang, Yang
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Zhou, Juan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Yan, Mingdi
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. University of Massachusetts, United States .
    Design and synthesis oftheranostic antibiotic nanodrugs that display size-dependent antibacterial activity and luminescenceManuscript (preprint) (Other academic)
  • 2623.
    Xie, Sheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Manuguri, Sesha
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Proietti, Giampiero
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Romson, Joakim
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cellular Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Inge, A. K.
    Wu, B.
    Zhang, Yang
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Häll, Daniel
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Yan, Mingdi
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Design and synthesis of theranostic antibiotic nanodrugs that display enhanced antibacterial activity and luminescence2017In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 114, no 32, p. 8464-8469Article in journal (Refereed)
    Abstract [en]

    We report the modular formulation of ciprofloxacin-based pure theranostic nanodrugs that display enhanced antibacterial activities, as well as aggregation-induced emission (AIE) enhancement that was successfully used to image bacteria. The drug derivatives, consisting of ciprofloxacin, a perfluoroaryl ring, and a phenyl ring linked by an amidine bond, were efficiently synthesized by a straightforward protocol from a perfluoroaryl azide, ciprofloxacin, and an aldehyde in acetone at room temperature. These compounds are propeller-shaped, and upon precipitation into water, readily assembled into stable nanoaggregates that transformed ciprofloxacin derivatives into AIE-active luminogens. The nanoaggregates displayed increased luminescence and were successfully used to image bacteria. In addition, these nanodrugs showed enhanced antibacterial activities, lowering the minimum inhibitory concentration (MIC) by more than one order of magnitude against both sensitive and resistant Escherichia coli. The study represents a strategy in the design and development of pure theranostic nanodrugs for combating drug-resistant bacterial infections.

  • 2624.
    Xie, Sheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Yan, Mingdi
    KTH, School of Chemical Science and Engineering (CHE), Chemistry. University of Massachusetts Lowell, United States.
    N,N-Diethylurea-Catalyzed Amidation between Electron-Deficient Aryl Azides and Phenylacetaldehydes2015In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 17, no 3, p. 636-639Article in journal (Refereed)
    Abstract [en]

    Urea structures, of which N,N-diethylurea (DEU) proved to be the most efficient, were discovered to catalyze amidation reactions between electron-deficient aryl azides and phenylacetaldehydes. Experimental data support 1,3-dipolar cycloaddition between DEU-activated enols and electrophilic phenyl azides, especially perfluoroaryl azides, followed by rearrangement of the triazoline intermediate. The activation of the aldehyde under near-neutral conditions was of special importance in inhibiting dehydration/aromatization of the triazoline intermediate, thus promoting the rearrangement to form aryl amides.

  • 2625.
    Xie, Sheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Yan, Mingdi
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. University of Massachusetts, United States .
    Photo-activatable switch-on fluorescence through intramolecular C-H insertion of azide derivativesManuscript (preprint) (Other academic)
  • 2626.
    Xie, Sheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Zhang, Yang
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Yan, Mingdi
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. University of Massachusetts, United States .
    Base-catalysed synthesis of aryl amides from aryl azides and aldehydesManuscript (preprint) (Other academic)
  • 2627.
    Xiong, Ruisheng
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Development of Novel Hydroporphyrins for Light Harvesting and Sensitising NIR Lanthanide Luminescence2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Chlorins, as the core structures of chlorophylls, have been extensively studied for harvesting solar energy, fluorescent imaging and photodynamic therapy against cancer. This thesis is concerned with design and synthesis of novel chlorins as antennae for harvesting light and sensitising near infrared lanthanide luminescence.

    In the first part, a series of chlorin monomers, dimers and polymers were synthesised and their photophysical properties were characterised. The chlorin monomers were substituted with five-membered heterocycles, such as thiophenes and furans. These heterocycles function as auxochromes analogous to the natural ones in chlorophylls, and extend chlorin absorption and emission strongly to the red (up to λem = 680 nm). A borylation method was developed to prepare borylated chlorins, which gave access to directly linked chlorin dimers through Suzuki coupling reaction. Different regioisomers of chlorin dimer were prepared, including β-meso homodimers, meso-meso homodimers and heterodimers. The dimerisation resulted in red-shifted absorption and emission. Chlorin polymerisations were performed both electrochemically and chemically. Bis-thienylchlorins yielded chlorin films and an organic solvent soluble copolymer with hexylthiophene, respectively. These polymers from both polymerisations have red absorptions beyond 700 nm, and might be used as light-harvesting antennae.

    In the second part, chlorins were used as chromophores to sensitise near infrared lanthanide luminescence. Two types of chlorin-lanthanide dyads were prepared through lanthanide coordination with cyclen derivatives and dipicolinic acids (DPA). The cyclen-based dyads were poorly soluble in water, thus their near infrared emissions were not observed. The other type of complexes was fully soluble in H2O and THF. Both Nd and Yb emission were recorded even upon excitation into the Q bands of chlorins. In the dyads with free base chlorins, the singlet state of chlorins might be involved in the sensitisation of lanthanide luminescence. These DPA-based dyads presented two-color emission based on one chlorin and two-color excitation based on one lanthanide ion. These dyads would enable in theory 4-color imaging.

    In the last part, a microwave-assisted two-step synthesis was described to prepare dipyrromethanes, which are the key intermediates in the chlorin synthesis. This mild method took advantage of the nucleophilicity of pyrrole and the electrophilicity of N,N-dimethylaminomethyl pyrroles. The usually used acid catalysis is detrimental to many functionalities, thus our methods enable the synthesis of dipyrromethanes with acid sensitive groups or a formyl group.

  • 2628.
    Xiong, Ruisheng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Andres, Julien
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Scheffler, Kira
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Borbas, Eszter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Synthesis and characterisation of lanthanide-hydroporphyrin dyads2015In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, p. 2541-2553Article in journal (Refereed)
    Abstract [en]

    Fluorescence spectroscopy is in many ways the ideal tool for the interrogation of complex biological systems, as it is non-invasive, sensitive, and offers high spatiotemporal resolution. For biomedical imaging luminescent probes absorbing and emitting in the red-to-near infrared (NIR) region are best suited to maximise tissue penetration and minimise damage to cellular components. NIR-emitting lanthanides (Ln) sensitised with red-absorbing antennae are promising candidates for these applications, assuming the challenges of poor photophysical properties and tedious syntheses of the complexes are overcome. Chlorins are porphyrin-type tetrapyrroles with intense red absorption. Recently chlorins have been shown to sensitise Yb and Nd emission when incorporated into Ln-complexes. Here we expand on our previous work, and explore the effect of chlorin structure, metallation state, chlorin-Ln-complex linker length and mode of attachment on the properties of chlorin-Ln complexes. As chlorin absorption bands are approximately 20 nm fwhm and readily tunable, a deeper understanding of structure-property relationships would enable the use of chlorin-Ln complexes in multicolour imaging using antenna-specific excitation. A detailed description of antenna and complex syntheses and photophysical characterisation is given. A number of challenges were identified, which will have to be addressed in future studies to enable multicolour imaging using the NIR-emitting lanthanides.

  • 2629.
    Xiong, Ruisheng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Arkhypchuk, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Kovacs, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Orthaber, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Borbas, Eszter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Directly linked hydroporphyrin dimers2016In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 52, p. 9056-9058Article in journal (Refereed)
    Abstract [en]

    Directly linked hydroporphyrin (chlorin) dimers were accessed regioselectively from bromochlorins. Versatile 15-borylated chlorins were prepared in excellent yield via Miyaura borylation. Suzuki coupling yielded meso-meso-linked homo- and heterodimers, and meso-beta-linked dimers. The photophysical and electrochemical properties of the dimers are reported.

  • 2630.
    Xiong, Ruisheng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Borbas, Eszter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Mild Microwave-Assisted Synthesis of Dipyrromethanes and Their Analogues2014In: Synlett: Accounts and Rapid Communications in Synthetic Organic Chemistry, ISSN 0936-5214, E-ISSN 1437-2096, Vol. 26, p. 484-488Article in journal (Refereed)
    Abstract [en]

    The Mannich reaction between pyrroles or indoles and Eschenmoser’s salt (dimethylmethylideneammonium iodide) forms N,N-dimethylamino-methylated derivatives in good to excellent yields. The reaction is highly regioselective, and for pyrroles both 2- and 3-sub- stituted derivatives could be obtained. The N,N-dimethylaminometh- ylpyrroles and indoles underwent substitution with pyrrole under mi- crowave irradiation, affording the appropriate dipyrromethanes, N- confused, and indolo-dipyrromethanes in moderate to excellent overall yield. 

  • 2631.
    Xiong, Ruisheng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Bornhof, Anna-Bea
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Arkhypchuk, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Orthaber, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Borbas, Eszter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Furan- and Thiophene-Based Auxochromes Red-shift Chlorin Absorptions and Enable Oxidative Chlorin Polymerizations2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 17, p. 4089-4095Article in journal (Refereed)
    Abstract [en]

    The de novo syntheses of chemically stable chlorins with five-membered heterocyclic (furane, thiophene, formylfurane and formylthiophene) substituents in selected meso- and beta-positions are reported. Heterocycle incorporation in the 3- and 13-positions shifted the chlorin absorption and emission to the red (up to lambdaem =680 nm), thus these readily incorporated substituents function analogously to auxochromes present in chlorophylls, for example, formyl and vinyl groups. Photophysical, theoretical and X-ray crystallographic experiments revealed small but significant differences between the behavior of the furan- and the thiophene-based auxochromes. Four regioisomeric bis-thienylchlorins (3,10; 3,13, 3,15 and 10,15) were oxidatively electropolymerized; the chlorin monomer geometry had a profound impact on the polymerization efficiency and the electrochemical properties of the resulting material. Chemical co-polymerization of 3,13-bis-thienylchlorin with 3-hexylthiophene yielded an organic-soluble red-emitting polymer.

  • 2632.
    Xiong, Ruisheng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Deun, Rik Van
    Gent University.
    Borbas, Eszter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Excitation- and emission wavelength-based multiplex imaging using red-absorbing near infrared-emitting lanthanide complexesManuscript (preprint) (Other academic)
    Abstract [en]

    : Multiplex luminescence imaging in the red and near infrared (NIR) should be an enabling tool for the real-time investigation of complex biological systems. Current probes have numerous limitations including low photostability, short luminescent lifetime, overlapping absorption and emission bands, and small Stokes shift, the combination of which limits multiplexing in this region to two colors. Here we report emitters based on near infrared (NIR) emitting luminescent lanthanides (Ln) sensitized by hydroporphyin antennae. The narrow and intense absorption bands of hydroporphyrins are in the red, and their porisiotns are readily tunable. These dyads enable both emission- and excitation-based multiplexing; the former by combining either the same antenna with different Ln’s, the latter by attaching chlorin antennae with non-overlapping absorptions to the same Ln-complex. Up to 4 different species could be discerned without tedious data manipulation.

  • 2633.
    Xu, Chao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Afewerki, Samson
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Córdova, Armando
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    A Cyclopalladated Microporous Azo-linked Polymer as a Heterogeneous Catalyst for Eco-friendly Suzuki and Heck Coupling ReactionsManuscript (preprint) (Other academic)
  • 2634.
    Xu, Quan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kerdphon, Sutthichat
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    C-C Coupling of Ketones with Methanol Catalyzed by a N-Heterocyclic Carbene-Phosphine Iridium Complex2015In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 21, p. 3576-3579Article in journal (Refereed)
    Abstract [en]

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

  • 2635.
    Xu, Quan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kerdphon, Sutthichat
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Rujirawanich, Janjira
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Krajangsri, Suppachai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Andersson, Pher
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Highly Active Cationic NHC, Phosphine Iridium Catalysts for Base Free Asymmetric Hydrogenation of KetonesManuscript (preprint) (Other academic)
  • 2636.
    Xu, Yunhua
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis and Photoinduced Electron Transfer of Donor-Sensitizer-Acceptor Systems2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

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

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

  • 2637. Xu, Yunhua
    et al.
    Duan, Lele
    Tong, Lianpeng
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    Visible light-driven water oxidation catalyzed by a highly efficient dinuclear ruthenium complex2010In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 46, no 35, p. 6506-6508Article in journal (Refereed)
  • 2638.
    Xu, Yunhua
    et al.
    Royal Institute of Technology (KTH).
    Duan, Lele
    Royal Institute of Technology (KTH).
    Åkermark, Torbjörn
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tong, Lianpeng
    Royal Institute of Technology (KTH).
    Lee, Bao-Lin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zhang, Rong
    Dalian University of Technology (DUT), (P.R. China).
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    Royal Institute of Technology (KTH), Department of Organic Chemistry.
    Synthesis and catalytic water oxidation activities of ruthenium complexes containing neutral ligands2011In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, no 34, p. 9520-9528Article in journal (Refereed)
    Abstract [en]

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

  • 2639. Xu, Yunhua
    et al.
    Fischer, Andreas
    Duan, Lele
    Tong, Lianpeng
    Gabrielsson, Erik
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    Chemical and light-driven oxidation of water catalyzed by an efficient dinuclear ruthenium complex2010In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 49, no 47, p. 8934-8937Article in journal (Refereed)
  • 2640.
    Yan J, Naeslund C, Al-Madhoun A.S, Wang J, Ji W, Cosquer G.Y, Johnsamuel J, Sjöberg S, Eriksson S, Tjarks W
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry.
    Synthesis and Biological Evaluation of 3'-Carboranyl Thymidine Analogues2002In: Biorg Med Chem Lett, no 12, p. 2209-2212Article in journal (Other scientific)
  • 2641.
    Yan, Jiajie
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry.
    Regenerable Organochalcogen Antioxidants: An Explorative Study2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Antioxidants are widely used to protect organic materials from damages caused by autoxidation, an oxidation process that occurs under normal aerobic conditions. In this thesis, novel multifunctional organoselenium and organotellurium antioxidants were designed, synthesized, and evaluated in search for compounds with better radical-trapping capacity, regenerability, and hydroperoxide-decomposing ability.

    Selenium was incorporated into ebselenols and hydroxy-2,3-dihydrobenzo[b]selenophenes and tellurium into diaryl disulfides and aryltellurophenols. All newly developed antioxidants were evaluated in a chlorobenzene/water two-phase lipid peroxidation system containing suitable co-antioxidants in the aqueous phase. Ebselenol carrying a hydroxyl group (OH) ortho to selenium showed a two-fold longer inhibition time than the reference α-tocopherol in the presence of aqueous-phase ascorbic acid. 2,3-Dihydrobenzo[b]selenophenes carrying a 5- or 7-OH outperformed α-tocopherol both when it comes to radical-trapping capacity and regenerability. Alkyltellurothiophenols, in situ formed from their corresponding disulfides by tris(2-carboxyethyl)phosphine, were also efficient regenerable radical-trapping antioxidants. The consumption of N-acetylcysteine in the water phase was followed and found to be limiting for the duration of the inhibition. The hydroperoxide-decomposing ability of all organoselenium antioxidants was evaluated. Ebselenols were often better glutathione peroxidase mimics than the parent.

    In an effort to find out more about antioxidant mechanisms, aryltellurophenols carrying electron donating and electron withdrawing groups in the phenolic or aryltelluro parts were synthesized and OH bond dissociation enthalpies, BDEO-Hs, were calculated. Compounds carrying electron donating groups in the phenolic or aryltelluro part of the molecule showed the best radical-trapping capacity. Deuterium labelling experiments suggested that hydrogen atom transfer could be the rate-limiting step in the antioxidant mechanism.  

  • 2642.
    Yan, Jiajie
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Poon, Jia-fei
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Singh, Vijay P
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Gates, Paul
    Engman, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Regenerable thiophenolic radical-trapping antioxidants2015In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 17, no 24, p. 6162-6165Article in journal (Refereed)
    Abstract [en]

    Diphenyl disulfides carrying alkyltelluro groups in the o-, m-, and p-positions were prepared using ortho-lithiation and lithium halogen exchange reactions. The novel antioxidants showed only minimal inhibitory effect on the azo-initiated peroxidation of linoleic acid in chlorobenzene until reduced to the corresponding thiophenols by tris(2-carboxyethyl)phosphine (TCEP). The best in situ generated thiophenol (from 7c) under these conditions quenched peroxyl radicals more efficiently than α-tocopherol with an almost 3-fold increase in inhibition time.

  • 2643.
    Yang, Bin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic Stereoselective Formation of C–O, C–C and C–B Bonds: A Voyage from Asymmetric Reactions Enabled by Lipases to Stereoselective Palladium-Catalyzed Oxidative Transformations of Enallenes2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

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

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

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

  • 2644.
    Yang, Bin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lihammar, Richard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Investigation of the Impact of Water on the Enantioselectivity Displayed by CALB in the Kinetic Resolution of δ-Functionalized Alkan-2-ol Derivatives2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 42, p. 13517-13521Article in journal (Refereed)
    Abstract [en]

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

  • 2645.
    Yang, Bin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Qiu, Youai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Control of Selectivity in Palladium(II)-Catalyzed Oxidative Transformations of Allenes2018In: Accounts of Chemical Research, ISSN 0001-4842, E-ISSN 1520-4898, Vol. 51, no 6, p. 1520-1531Article, review/survey (Refereed)
    Abstract [en]

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

  • 2646.
    Yang, Bin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Qiu, Youai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jiang, Tuo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Wulff, William D.
    Yin, Xiaopeng
    Zhu, Can
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Enantioselective Palladium-Catalyzed Carbonylative Carbocyclization of Enallenes via Cross-Dehydrogenative Coupling with Terminal Alkyne: Efficient Construction of a-Chirality of Ketones2017In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 56, no 16, p. 4535-4539Article in journal (Refereed)
    Abstract [en]

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

  • 2647.
    Yang, Bin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zhu, Can
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Qiu, Youai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Enzyme- and Ruthenium-Catalyzed Enantioselective Transformation of alpha-Allenic Alcohols into 2,3-Dihydrofurans2016In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 55, no 18, p. 5568-5572Article in journal (Refereed)
    Abstract [en]

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

  • 2648.
    Yang, Hai-Bin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pathipati, Stalin R.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selander, Nicklas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nickel-Catalyzed 1,2-Aminoarylation of Oxime Ester-Tethered Alkenes with Boronic Acids2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 12, p. 8441-8445Article in journal (Refereed)
    Abstract [en]

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

  • 2649.
    Yang, Hai-Bin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selander, Nicklas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    A redox-economical synthesis of trifluoromethylated enamides with the Langlois reagent2017In: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 15, no 8, p. 1771-1775Article in journal (Refereed)
    Abstract [en]

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

  • 2650.
    Yang, Hai-Bin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selander, Nicklas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Divergent Iron-Catalyzed Coupling of O-Acyloximes with Silyl Enol Ethers2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 8, p. 1779-1783Article in journal (Refereed)
    Abstract [en]

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

50515253545556 2601 - 2650 of 2768
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