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  • 1.
    Akkarasamiyo, Sunisa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sawadjoon, Supaporn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Orthaber, Andreas
    Samec, Joseph S. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tsuji-Trost Reaction of Non-Derivatized Allylic Alcohols2018Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, nr 14, s. 3488-3498Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Palladium-catalyzed allylic substitution of non-derivatized enantioenriched allylic alcohols with a variety of uncharged N-, S-, C- and O-centered nucleophiles using a bidentate BiPhePhos ligand is described. A remarkable effect of the counter ion (X) of the XPd[kappa(2)-BiPhePhos][kappa(3)-C3H5] was observed. When ClPd[kappa(2)-BiPhePhos][eta(3)-C3H5] (complexI) was used as catalyst, non-reproducible results were obtained. Study of the complex by X-ray crystallography, (PNMR)-P-31 spectroscopy, and ESI-MS showed that a decomposition occurred where one of the phosphite ligands was oxidized to the corresponding phosphate, generating ClPd[kappa(1)-BiPhePhosphite-phosphate][eta(3)-C3H5] species (complexII). When the chloride was exchanged to the weaker coordinating OTf- counter ion the more stable Pd[kappa(2)-BiPhePhos][eta(3)-C3H5](+)+[OTf] (-) (complexIII) was formed. ComplexIII performed better and gave higher enantiospecificities in the substitution reactions. ComplexIII was evaluated in Tsuji-Trost reactions of stereogenic non-derivatized allylic alcohols. The desired products were obtained in good to excellent yields (71-98%) and enantiospecificities (73-99%) for both inter- and intramolecular substitution reactions with only water generated as a by-product. The methodology was applied to key steps in total synthesis of (S)-cuspareine and (+)-lentiginosine. A reaction mechanism involving a palladium hydride as a key intermediate in the activation of the hydroxyl group is proposed in the overall transformation.

  • 2.
    Bartholomeyzik, Teresa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pendrill, Robert
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lihammar, Richard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Jiang, Tuo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kinetics and Mechanism of the Palladium-Catalyzed Oxidative Arylating Carbocyclization of Allenynes2018Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, nr 1, s. 298-309Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pd-catalyzed C-C bond-forming reactions under oxidative conditions constitute a class of important and widely used synthetic protocols. This Article describes a mechanistic investigation of the arylating carbocyclization of allenynes using boronic acids and focuses on the correlation between reaction conditions and product selectivity. Isotope effects confirm that either allenic or propargylic C-H activation occurs directly after substrate binding. With an excess of H2O, a triene product is selectively formed via allenic C-H activation. The latter C-H activation was found to be turnover-limiting and the reaction zeroth order in reactants as well as the oxidant. A dominant feature is continuous catalyst activation, which was shown to occur even in the absence of substrate. Smaller amounts of H2O lead to mixtures of triene and vinylallene products, where the latter is formed via propargylic C-H activation. The formation of triene occurs only in the presence of ArB(OH)(2). Vinylallene, on the other hand, was shown to be formed by consumption of (ArBO)(3) as a first-order reactant. Conditions with sub-stoichiometric BF3 center dot OEt2 gave selectively the vinylallene product, and the reaction is first order in PhB(OH)(2). Both C-H activation and transmetalation influence the reaction rate. However, with electron-deficient ArB(OH)(2), C-H activation is turnover-limiting. It was difficult to establish the order of transmetalation vs C-H activation with certainty, but the results suggest that BF3 center dot OEt2 promotes an early transmetalation. The catalytically active species were found to be dependent on the reaction conditions, and H2O is a crucial parameter in the control of selectivity.

  • 3. Betterley, Nolan M.
    et al.
    Kerdphon, Sutthichat
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Chaturonrutsamee, Suppisak
    Kongsriprapan, Sopanat
    Surawatanawong, Panida
    Soorukram, Darunee
    Pohmakotr, Manat
    Andersson, Pher G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Reutrakul, Vichai
    Kuhakarn, Chutima
    Bi(OTf)(3) Enabled C-F Bond Cleavage in HFIP: Electrophilic Aromatic Formylation with Difluoro(phenylsulfanyl)methane2018Ingår i: Asian Journal of Organic Chemistry, ISSN 2193-5807, Vol. 7, nr 8, s. 1642-1647Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bismuth(III) trifluoromethanesulfonate [Bi(OTf)(3)] mediated mild electrophilic aromatic formylation utilizing difluoro(phenylsulfanyl)methane (PhSCF2H) as a formylating agent in hexafluoro-2-propanol (HFIP) as a recyclable ionizing solvent has been developed. The active formylating species was generated via C-F bond cleavage and was characterized to be a bis(phenylsulfanyl)methyl cation by experimental and computational H-1 and C-13 NMR.

  • 4.
    Binh, Khanh Mai
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán J
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mechanisms of Rh-Catalyzed Oxyfluorination and Oxytrifluoromethylation of Diazocarbonyl Compounds with Hypervalent Fluoroiodine2018Ingår i: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, nr 5, s. 4483-4492Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The reaction mechanisms of rhodium-catalyzed geminal oxyfluorination and oxytrifluoromethylation of diazo-carbonyl compounds with fluoro-benziodoxole and Togni reagents are investigated by means of density functional theory calculations. It is shown that the two reactions follow very similar mechanisms, involving N-2 dissociation to form a Rh-carbene intermediate, alcohol insertion and proton transfer resulting in a stable Rh-enol intermediate, and concerted proton transfer/electrophilic addition of the hypervalent iodine reagent to the enol. Isomerization of the hypervalent iodine takes then place before a ligand coupling affords the final product. The role of the dirhodium catalyst in facilitating the various steps of the reaction is discussed. The presented mechanisms are consistent with available experimental information, and the obtained insights allow for extension to other reactions involving hypervalent iodine reagents.

  • 5.
    Brea, Oriana
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Luna, Alberto
    Diaz, Cristina
    Corral, Ines
    Molecular Modelling of the H-2-Adsorptive Properties of Tetrazolate-Based Metal-Organic Frameworks: From the Cluster Approach to Periodic Simulations2018Ingår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 19, nr 11, s. 1349-1357Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hydrogen has been proposed as a long-term non-fossil fuel to be used in a future ideal carbon-neutral energetic economy. However, its low volumetric energy density hinders its storage and transportation. Metal-organic frameworks (MOFs) represent very promising materials for this purpose due to their very extended surface areas. Azolates, in particular tetrazolates, are - together with carboxylate functionalities - very common organic linkers connecting metallic secondary building units in MOFs. This study addresses, from a theoretical perspective, the H-2 adsorptive properties of tetrazolate linkers at the molecular level, following a size-progressive approach. Specifically, we have investigated how the physisorption energies and geometries are affected when changing the environment of the linker by considering the azolates in the gas phase, immersed in a finite cluster, or being part of an infinite extended crystal material. Furthermore, we also study the H-2 adsorptive capacity of these linkers within the cluster model.

  • 6.
    Brea, Oriana
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mó, Otilia
    Yáñez, Manuel
    Merced Montero-Campillo, M.
    Alkorta, Ibon
    Elguero, José
    Are beryllium-containing biphenyl derivatives efficient anion sponges?2018Ingår i: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 24, nr 1, artikel-id 16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structures and stabilities of 2,2'-diBeX-1,1'-biphenyl (X = H, F, Cl, CN) derivatives and their affinities for F-, Cl-, and CN- were theoretically investigated using a B3LYP/6-311 + G(3df, 2p)//B3LYP/6-31 + G(d,p) model. The results obtained show that the 2,2'-diBeX-1,1'-biphenyl derivatives (X = H, F, Cl, CN) exhibit very high F-, Cl-, and CN- affinities, albeit lower than those reported before for their 1,8-diBeX-naphthalene analogs, in spite of the fact that the biphenyl derivatives are more flexible than their naphthalene counterparts. Nevertheless, some of the biphenyl derivatives investigated are predicted to have anion affinities larger than those measured for SbF5, which is considered one of the strongest anion capturers. Therefore, although weaker than their naphthalene analogs, the 2,2'-diBeX-1,1'-biphenyl derivatives can still be considered powerful anion sponges. This study supports the idea that compounds containing -BeX groups in chelating positions behave as anion sponges due to the electron-deficient nature and consequently high intrinsic Lewis acidity of these groups.

  • 7.
    Colas, Kilian
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mendoza, Abraham
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Iterative Synthesis of Pluripotent Thioethers through Controlled Redox Fluctuation of Sulfur2018Ingår i: Synlett: Accounts and Rapid Communications in Synthetic Organic Chemistry, ISSN 0936-5214, E-ISSN 1437-2096, Vol. 29, nr 10, s. 1329-1333Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Target- and diversity-oriented syntheses are based on diverse building blocks, whose preparation requires discrete design and constructive alignment of different chemistries. To enable future automation of the synthesis of small molecules, we have devised a unified strategy that serves the divergent synthesis of unrelated scaffolds such as carbonyls, olefins, organometallics, halides, and boronic esters. It is based on iterations of a nonelectrophilic Pummerer-type C-C coupling enabled by turbo -organomagnesium amides that we have recently reported. The pluripotency of sulfur allows the central building blocks to be obtained by regulating C-C bond formation through control of its redox state.

  • 8.
    Cortés González, Miguel A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Nordeman, Patrik
    Bermejo Gómez, Antonio
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. AstraZeneca PET Centre at Karolinska Institutet, Sweden.
    Meyer, Denise N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Antoni, Gunnar
    Schou, Magnus
    Szabó, Kálmán J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    [F-18]fluoro-benziodoxole: a no-carrier-added electrophilic fluorinating reagent. Rapid, simple radiosynthesis, purification and application for fluorine-18 labelling2018Ingår i: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, nr 34, s. 4286-4289Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Operationally simple radiosynthesis and purification of [F-18]fluoro-benziodoxole was developed starting from a cyclotron produced [F-18]F- precursor, [F-18]TBAF, and tosyl-benziodoxole. The synthetic utility of [F-18]fluoro-benziodoxole was demonstrated by electrophilic fluorocyclization of o-styrilamides proceeding with high RCC (typically 50-90%) and high molar activity (up to 396 GBq mol(-1)).

  • 9. Daikoku, S.
    et al.
    Pendrill, Robert
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kanie, Y.
    Ito, Y.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kanie, O.
    Synthesis and structural investigation of a series of mannose-containing oligosaccharides using mass spectrometry2018Ingår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 16, nr 2, s. 228-238Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of compounds associated with naturally occurring and biologically relevant glycans consisting of alpha-mannosides were prepared and analyzed using collision-induced dissociation (CID), energy-resolved mass spectrometry (ERMS), and H-1 nuclear magnetic resonance spectroscopy. The CID experiments of sodiated species of disaccharides and ERMS experiments revealed that the order of stability of mannosyl linkages was as follows: 6-linked > 4-linked >= 2-linked > 3-linked mannosyl residues. Analysis of linear trisaccharides revealed that the order observed in disaccharides could be applied to higher glycans. A branched trisaccharide showed a distinct dissociation pattern with two constituting disaccharide ions. The estimation of the content of this ion mixture was possible using the disaccharide spectra. The hydrolysis of mannose linkages at 3- and 6-positions in the branched trisaccharide revealed that the 3-linkage was cleaved twice as fast as the 6-linkage. It was observed that the solution-phase hydrolysis and gas-phase dissociation have similar energetics.

  • 10. Dorau, Robin
    et al.
    Görbe, Tamás
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Svedendahl Humble, Maria
    Improved Enantioselectivity of Subtilisin Carlsberg Towards Secondary Alcohols by Protein Engineering2018Ingår i: ChemBioChem (Print), ISSN 1439-4227, E-ISSN 1439-7633, Vol. 19, nr 4, s. 338-346Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Generally, the catalytic activity of subtilisin Carlsberg (SC) for transacylation reactions with secondary alcohols in organic solvent is low. Enzyme immobilization and protein engineering was performed to improve the enantioselectivity of SC towards secondary alcohols. Possible amino-acid residues for mutagenesis were found by combining available literature data with molecular modeling. SC variants were created by site-directed mutagenesis and were evaluated for a model transacylation reaction containing 1-phenylethanol in THF. Variants showing high E values (>100) were found. However, the conversions were still low. A second mutation was made, and both the E values and conversions were increased. Relative to that shown by the wild type, the most successful variant, G165L/M221F, showed increased conversion (up to 36 %), enantioselectivity (E values up to 400), substrate scope, and stability in THF.

  • 11.
    Erbing, Elis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sanz-Marco, Amparo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Vazquez-Romero, Ana
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Malmberg, Jesper
    Johansson, Magnus J.
    Gomez-Bengoa, Enrique
    Martín-Matute, Belén
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Base- and Additive-Free Ir-Catalyzed ortho-Iodination of Benzoic Acids: Scope and Mechanistic Investigations2018Ingår i: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, nr 2, s. 920-925Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A protocol for the C-H activation/iodination of benzoic acids catalyzed by a simple iridium complex has been developed. The method described in this paper allows the ortho-selective iodination of a variety of benzoic acids under extraordinarily mild conditions in the absence of any additive or base in 1,1,1,3,3,3-hexafluoroisopropanol as the solvent. The iridium catalyst used tolerates air and moisture, and selectively gives ortho-iodobenzoic acids with high conversions. Mechanistic investigations revealed that an Ir(III)/Ir(V) catalytic cycle operates, and that the unique properties of HFIP enables the C-H iodination using the carboxylic moiety as a directing group.

  • 12.
    González Miera, Greco
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Martínez-Castro, Elisa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Martín-Matute, Belén
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Acceptorless Alcohol Dehydrogenation: OH vs NH Effect in Bifunctional NHC–Ir(III) Complexes2018Ingår i: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 37, nr 5, s. 636-644Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bifunctional complexes bearing N-heterocyclic carbene (NHC) ligands functionalized with hydroxy or amine groups were synthesized to measure the beneficial effect of different modes of metal–ligand cooperation in the acceptorless dehydrogenation of alcohols. In comparison to complexes with an amine moiety, hydroxy-functionalized iridium catalysts showed superior activity. In contrast to alcohols, 1,4-diols underwent cyclization to give the corresponding tetrahydrofurans without involving dehydrogenation processes. Mechanistic investigations to rationalize the “OH effect” in these types of complexes have been undertaken.

  • 13.
    Gudmundsson, Arnar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Gustafson, Karl P. J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Yang, Bin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Efficient Formation of 2,3-Dihydrofurans via Iron-Catalyzed Cycloisomerization of alpha-Allenols2018Ingår i: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, nr 1, s. 12-16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Herein, we report a highly efficient iron-catalyzed intramolecular nucleophilic cyclization of alpha-allenols to furnish substituted 2,3-dihydrofurans under mild reaction conditions. A highly diastereoselective variant of the reaction was developed as well, giving diastereomeric ratios of up to 98:2. The combination of the iron-catalyzed cycloisomerization with enzymatic resolution afforded the 2,3-dihydrofuran in high ee. A detailed DFT study provides insight into the reaction mechanism and gives a rationalization for the high chemo-and diastereoselectivity.

  • 14.
    Gustafson, Karl P. J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Studies on Metalloenzymatic Dynamic Kinetic Resolutions and Iron-Catalyzed Reactions of Allenes2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The main focus of this thesis lies in the development of new transition metal-catalyzed chemoenzymatic dynamic kinetic resolutions (DKR) of both alcohols and amines. The first part of the thesis deals with the development of new heterogeneous systems for the DKR of amines. The racemization catalysts in these different systems are all composed of palladium nanoparticles supported on either mesoporous silica or incorporated in a biocomposite that is composed of a bioactive cross-linked enzyme aggregate. 

    The second part of the thesis deals with the development of a homogeneous iron catalyst in the racemization of sec-alcohols for the implementation in a chemoenzymatic DKR. Two protocols for the racemization of sec-alcohols are reported. The first one could not be combined with a chemoenzymatic kinetic resolution, although this was overcome in the second iron based protocol. 

    Following the successful iron catalyzed chemoenzymatic DKR of sec-alcohols, the iron catalyst was used in the cyclization of α-allenic alcohols and N-protected amines to furnish 2,3-dihydrofurans and 2,3-dihydropyrroles, respectively. The cyclization is proceeding in a diastereoselective manner.

    The last part of the thesis deals with attempts to further elucidate the mechanism of activation of a known ruthenium racemization catalyst. X-ray absorption spectroscopy using synchrotron radiation was used for this purpose.

  • 15.
    Görbe, Tamás
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Heterogeneous catalysis in racemization and kinetic resolution along a journey in protein engineering2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The first part of my thesis concerns the use of heterogeneous acidic resins for racemization of tert-alcohols without any side-product formation. The focus was to develop a system which can be further extended to a DKR protocol consisting of an enzymatic KR reaction. Based on our knowledge of the resins, an unexpected migratory DKR protocol turned out to be an efficient method for the synthesis of carbocyclic allylic carbinols.

    The development of enzyme and metal catalyst hybrids was already an ongoing theme in our group. A supporter-free biohybrid catalyst was developed which can be used in several different types of reactions. The Pd(0)-CalB CLEA catalyst was applied in a two-step-cascade transformation and in the DKR of benzylic primary amines. The catalyst was characterized by different analytical techniques, to understand its composition and structure.

    The enzymes have always been the main focus of the studies and therefore wild type enzymes were initially utilized. However, these natural biocatalysts are associated with certain limitations. In contrast, protein engineering allows for enzymes to be modified and optimized. We have used the technique to create a subtilisin Carlsberg mutant, which was studied both by modeling and in vitro. The mutant was found to catalyze the (S)-selective transesterification of sec-alcohols containing long aliphatic carbon chains, and it also exhibited higher performance in organic solvent.

    The last project concerned the protein engineering of CalA enzyme towards tert-alcohols. The kinetic resolution of tert-alcohols with this enzyme is very slow but it occurs with good enantioselectivity. The aim was therefore to improve the activity of CalA via protein engineering. Seven amino acids were mutated close to the active site and a library was created based on our prediction. Throughout the screening, a few variants showed higher activity, which were sequenced and further analyzed in the transesterification of tert-alcohols.

  • 16.
    Görbe, Tamás
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lihammar, Richard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Heterogeneous Acid-Catalyzed Racemization of Tertiary Alcohols2018Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, nr 1, s. 77-80Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tertiary alcohols are important structural motifs in natural products and building blocks in organic synthesis but only few methods are known for their enantioselective preparation. Chiral resolution is one of these approaches that leaves one enantiomer (50% of the material) unaffected. An attractive method to increase the efficiency of those resolutions is to racemize the unaffected enantiomer. In the present work, we have developed a practical racemization protocol for tertiary alcohols. Five different acidic resin materials were tested. The Dowex 50WX8 was the resin of choice since it was capable of racemizing tertiary alcohols without any byproduct formation. Suitable solvents and a biphasic system were investigated, and the optimized system was capable of racemizing differently substituted tertiary alcohols.

  • 17.
    Heshmat, Mojgan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Privalov, Timofei
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Structurally Flexible Oxocarbenium/Borohydride Ion Pair: Dynamics of Hydride Transfer on the Background of Conformational Roaming2018Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, nr 23, s. 5098-5106Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We apply Born-Oppenheimer molecular dynamics to the practically significant [dioxane-H(+)-acetone]-[(C6F5)(3)B-H(-)] and [Et2O-H(+)-OCPr2][(C6F5)(3)B-H(-)] ion pair intermediates. Dynamics of hydride transfer in cation/anion ion pair takes place on the background of large amplitude configurational changes. Geometry of oxocarbenium/borohydride ion pairs is flexible, meaning that we uncover significant actual structural disorder at a finite temperature. Therefore, although the starting structure can be fairly close to the configurational area of the hydride transfer transition state (TS) and despite a low potential energy barrier (ca. 1.5 kcal/mol, according to the literature), already at T approximate to 325 K the system can remain ignorant of the TS region and move round and about (roam) in the configurational space for a period of time in the range between 10 and 100 ps. This indicates structural flexibility of oxocarbenium/borohydride ion pair on apparently a flat potential energy landscape of cation/anion interaction, and this has not been taken into consideration by the free energy estimations in static considerations made thus far. The difference between the dynamics-based representation of the system versus the static representation amounts to the difference between quasi-bimolecular versus unimolecular descriptions of the hydride transfer step.

  • 18.
    Heshmat, Mojgan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Privalov, Timofei
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Surprisingly Flexible Oxonium/Borohydride Ion Pair Configurations2018Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, nr 15, s. 3713-3727Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the geometry of oxonium/borohydride ion pairs [ether-H(+) ether] [LA-H(-)] with dioxane, THF, and Et2O as ethers and B(C6F5)(3) as the Lewis acid (LA). The question is about possible location of the disolvated proton [ether -H(+) -ether], with respect to the hydride of the structurally complex [LA -H(-)] anion. Using Born Oppenheimer molecular dynamics and a comparison of the potential and free energies of the optimized configurations, we show that herein considered ion pairs are much more flexible geometrically than previously thought. Conformers with different locations of cations with respect to anions are governed by a flat energy -landscape. We found a novel configuration in which oxonium is below [LA-11((-))], with respect to the direction of borane -> hydride vector, and the proton -hydride distance is ca. 6 A. With calculations of the vibrational spectra of [ether-H(+)-ether][(C6F5)(3)B-H(-)] for dioxane, THF, and Et2O as ethers, we investigate the manifestation of SSLB-type (short, strong, low -barrier) hydrogen bonding in the OHO motif of an oxonium cation.

  • 19. Ibrahem, Ismail
    et al.
    Iqbal, Muhammad Naeem
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Verho, Oscar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Eivazihollagh, Alireza
    Olsén, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Edlund, Håkan
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Norgren, Magnus
    Johnston, Eric V.
    Copper Nanoparticles on Controlled Pore Glass and TEMPO for the Aerobic Oxidation of Alcohols2018Ingår i: ChemNanoMat, ISSN 2199-692X, Vol. 4, nr 1, s. 71-75Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Herein, we report on the facile synthesis of a heterogeneous copper nanocatalyst and its combination with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) for the aerobic oxidation of alcohols to their corresponding carbonyl compounds. This low cost copper nanocatalyst was found to exhibit excellent recyclability, making it a highly attractive catalytic system from an economical and environmental point of view. Extensive characterization of the catalyst by a number of techniques revealed that it was comprised of well-dispersed Cu(I/II) nanoparticles with an average size of around 6nm.

  • 20.
    Jiang, Yan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Deiana, Luca
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Alimohammadzadeh, Rana
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Liu, Leifeng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Sun, Junliang
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Cordova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Highly Diastereo- and Enantioselective Cascade Synthesis of Bicyclic Lactams in One-Pot2018Ingår i: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, nr 9, s. 1158-1164Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A versatile and highly stereoselective synthetic route to functionalized bi- and tricyclic lactams (up to > 20:1 dr and 99% ee) in one pot from simple starting materials (allylic alcohols, enals, diamines and amino alcohols) using cascade transformations promoted by chiral amine/BrOnsted or metal/chiral amine/BrOnsted relay catalysis is disclosed. Here molecular oxygen is employed as the terminal oxidant for the latter relay catalysis approach.

  • 21. Jo, Sunhwan
    et al.
    Myatt, Daniel
    Qi, Yifei
    Doutch, James
    Clifton, Luke A.
    Im, Wonpil
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Multiple Conformational States Contribute to the 3D Structure of a Glucan Decasaccharide: A Combined SAXS and MD Simulation Study2018Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, nr 3, s. 1169-1175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The inherent flexibility of carbohydrates is dependent on stereochemical arrangements, and characterization of their influence and importance will give insight into the three-dimensional structure and dynamics. In this study, a beta-(1 -> 4)/beta-(1 -> 3)-linked glucosyl decasaccharide is experimentally investigated by synchrotron small-angle X-ray scattering from which its radius of gyration (R-g) is obtained. Molecular dynamics (MD) simulations of the decasaccharide show four populated states at each glycosidic linkage, namely, syn- and anti-conformations. The calculated R-g values from the MD simulation reveal that in addition to syn-conformers the presence of anti-psi conformational states is required to reproduce experimental scattering data, unveiling inherent glycosidic linkage flexibility. The CHARMM36 force field for carbohydrates thus describes the conformational flexibility of the decasaccharide very well and captures the conceptual importance that anti-conformers are to be anticipated at glycosidic linkages of carbohydrates.

  • 22.
    Kazemi, Masoud
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. Uppsala University, Sweden.
    Socan, Jaka
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Åqvist, Johan
    Mechanistic alternatives for peptide bond formation on the ribosome2018Ingår i: Nucleic Acids Research, ISSN 0305-1048, E-ISSN 1362-4962, Vol. 46, nr 11, s. 5345-5354Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The peptidyl transfer reaction on the large ribosomal subunit depends on the protonation state of the amine nucleophile and exhibits a large kinetic solvent isotope effect (KSIE similar to 8). In contrast, the related peptidyl-tRNA hydrolysis reaction involved in termination shows a KSIE of similar to 4 and a pH-rate profile indicative of base catalysis. It is, however, unclear why these reactions should proceed with different mechanisms, as the experimental data suggests. One explanation is that two competing mechanisms may be operational in the peptidyl transferase center (PTC). Herein, we explored this possibility by re-examining the previously proposed proton shuttle mechanism and testing the feasibility of general base catalysis also for peptide bond formation. We employed a large cluster model of the active site and different reaction mechanisms were evaluated by density functional theory calculations. In these calculations, the proton shuttle and general base mechanisms both yield activation energies comparable to the experimental values. However, only the proton shuttle mechanism is found to be consistent with the experimentally observed pH-rate profile and the KSIE. This suggests that the PTC promotes the proton shuttle mechanism for peptide bond formation, while prohibiting general base catalysis, although the detailed mechanism by which general base catalysis is excluded remains unclear.

  • 23.
    Kerdphon, Sutthichat
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    NHC,P- and N,P-Iridium Catalysts for Hydrogenations and Hydrogen Transfer Reactions2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The work described in this thesis is focused on hydrogenation and hydrogen transfer reactions using iridium catalysts. The first part concerns the use of N-heterocyclic carbene-phosphine iridium complexes in alkylation reactions (Chapters 2 and 3) and the hydrogenation of ketones (Chapter 4). A number of N-heterocyclic carbene-phosphine iridium complexes have been prepared and evaluated as catalysts for C-N bond formation of amides using alcohols as the electrophile. This catalytic system can be used with a wide range of substrates at low catalyst loading (only 0.5 mol%) to furnish the desired products in up to 98% isolated yield. The achiral N-heterocyclic carbene-phosphine iridium complexes were also found to catalyze the methylation of ketones with methanol under mild conditions to afford the mono-methylated products in up to 98% isolated yield with low catalyst loading (1.0 mol%). Additionally, several chiral N-heterocyclic carbene-phosphine iridium complexes were synthesized and evaluated in asymmetric hydrogenation of ketones. The reactions were carried out at room temperature under base-free conditions to obtain the chiral alcohols in up to 96% ee in 30 minutes.

    The second part of this thesis (Chapter 5) details the preparation of new N,P-iridium complexes which were found to be highly efficient catalysts for the asymmetric hydrogenation of challenging tetrasubstituted olefins. This catalytic system results in optically active compounds of high enantiomeric excess (up to 98% ee) as the single diasteroisomer.

  • 24.
    Kervefors, Gabriella
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Becker, Antonia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Dey, Chandan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Olofsson, Berit
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Metal-free formal synthesis of phenoxazine2018Ingår i: Beilstein Journal of Organic Chemistry, ISSN 2195-951X, E-ISSN 1860-5397, Vol. 14, s. 1491-1497Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A transition metal-free formal synthesis of phenoxazine is presented. The key step of the sequence is a high-yielding O-arylation of a phenol with an unsymmetrical diaryliodonium salt to provide an ortho-disubstituted diaryl ether. This species was cyclized to acetylphenoxazine in moderate yield. The overall yield in the three-step sequence is 72% based on recovered diaryl ether. An interesting, unusually stable iodine(III) intermediate in the O-arylation was observed by NMR and could be converted to the product upon longer reaction time.

  • 25. Kiss, Anita
    et al.
    Herman, Bianka Edina
    Görbe, Tamás
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mernyak, Erzsebet
    Molnar, Barnabas
    Wolfling, Janos
    Szecsi, Mihaly
    Schneider, Gyula
    Synthesis of novel 17-triazolyl-androst-5-en-3-ol epimers via Cu(I)-catalyzed azide-alkyne cycloaddition and their inhibitory effect on 17 alpha-hydroxylase/ C-17,C-20-lyase2018Ingår i: Steroids, ISSN 0039-128X, E-ISSN 1878-5867, Vol. 135, s. 79-91Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The regioselective Cu(I)-catalyzed 1,3-dipolar cycloaddition of 17 alpha- and 17 beta-azidoandrost-5-en-3 beta-ol epimers (3b and 5b) with different terminal alkynes afforded novel 1,4-substituted triazolyl derivatives (8a-k and 9a-k). For the preparation of 5'-iodo-l',2',3'-triazoles (8m-n and 9m-n), an improved method was developed, directly from steroidal azides and terminal alkynes, in reaction mediated by Cul and IC1 as iodinating agents. Acetolysis and subsequent hydrolysis of 8n and 9n yielded 5'-hydroxy-l',2',3'-triazoles 8o and 9o. The inhibitory effect of 8a-o, 9a-o, 3, and 5 on rat testicular C-17,C-20-lyase was investigated by means of an in vitro radioincubation technique. The results revealed that the C-17 epimers of steroidal triazoles influence the C-17,C-20-lyase effect. Inhibitors were found only in the 17 alpha-triazolyl series (8a-o), whereas in the C-17 azide pair the 17 beta compound (5b) was more potent.

  • 26.
    Krajangsri, Suppachai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Development of Asymmetric Iridium Catalysed Hydrogenation Reactions2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The focus of the work presented in this thesis is the development of iridium-catalysed asymmetric hydrogenation reactions.

    The first part of this thesis covers the development of dynamic kinetic resolution in asymmetric hydrogenation of chiral, racemic secondary allylic alcohols, which are converted to chiral saturated alcohols with high dr and ee. In this study, a wide range of substrates was successfully hydrogenated to give good results, with up to 95:5 dr and 99% ee. Moreover, a number of different allylic alcohol derivatives were also investigated and found to undergo the DKR of hydrogenation with good results.

    The second part of this thesis is directed towards the development of regioselective asymmetric mono-hydrogenation of 1,4- and 1,5-disubstituted 1,4-cyclohexadienes. Under optimized hydrogenation conditions, high yield of regioselective mono-hydrogenated products and excellent enantioselectivity were observed in most cases. The usefulness of the reaction was demonstrated in the preparation of important chiral α,β-unsaturated ketones in good yield and excellent ee of up to 96%. Our novel method provides a general route to this important class of compounds.

    The third part concerns the development of asymmetric hydrogenation of β-hydroxy silanes. It was observed that under hydrogenation conditions, β-hydroxy silanes undergo Peterson olefination to form terminal olefins which are then hydrogenated using an Ir catalyst. A new class of Ir-N,P catalysts were prepared and provided high yield with excellent ee in up to 99%. In addition, the reaction was highly chemoselective and could be tuned to hydrogenate either an olefin or a β-hydroxy silane depending on the choice of catalyst and reaction conditions.

    The final part describes the asymmetric hydrogenation of enamides. A variety of oxazolidinone-enamides were prepared and evaluated in this reaction. High yields, (up to 99%) and excellent ee, (up to 99%) were obtained.

  • 27.
    Krajangsri, Suppachai
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Yang, Jianping
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Massaro, Luca
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Andersson, Pher
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Iridium-Catalysed Enantioselective Hydrogenation of Enamides2018Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    A variety of oxazolidinone-enamides were prepared and evaluated in this reaction. High yields, (up to 99%) and excellent ee, (up to 99%) were obtained.

  • 28.
    Kumaniaev, Ivan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Samec, Joseph S. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Valorization of Quercus suber Bark toward Hydrocarbon Bio-Oil and 4-Ethylguaiacol2018Ingår i: ACS sustainable chemistry and engineering, ISSN 2168-0485, Vol. 6, nr 5, s. 5737-5742Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A reductive fractionation process for the valorization of Quercus suber bark toward hydrocarbons in gasoline and diesel ranges and optionally 4-ethylguaiacol has been developed. The procedure involves three steps: (1) tandem hydrogen-free Pd/C-catalyzed transfer hydrogenolysis of lignin where the carbohydrates serve as an inherent hydrogen donor under slightly alkaline conditions to also facilitate the depolymerization of suberin, (2) optional distillation, to isolate the 4-ethylguaiacol, (3) hydrodeoxygenation of the mixture from the first step by a Pt-MoO3/TiO2 catalyst generated hydrocarbons in gasoline and diesel ranges. The yield of 4-ethylguaiacol (90% purity) is 2.6% of dry bark weight (12% of acid insoluble lignin), and yield of hydrocarbon bio-oil is 42% of dry bark weight. This corresponds to a theoretical maximum yield of 77% for lignin and suberin. The carbon yield of the obtained bio-oil is thereby 64% from the total initial bark.

  • 29.
    Lati, Monireh Pourghasemi
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. University of Zanjan, Iran.
    Naeem, Muhammad Iqbal
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Alinia-Asli, Mokhtar
    Shirini, Farhad
    Rezvani, Mohammad Ali
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Johnston, Eric
    Verho, Oscar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Palladium Nanoparticles Immobilized on an Aminopropyl-functionalized Silica-Magnetite Composite as a Recyclable Catalyst for Suzuki-Miyaura Reactions2018Ingår i: Chemistryselect, ISSN 2365-6549, Vol. 3, nr 27, s. 7970-7975Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Herein, we describe the straightforward synthesis and thorough characterization of a magnetically-separable heterogeneous catalyst comprised of 1-3nm-sized Pd nanoparticles immobilized on a mesoporous silica-magnetite composite (Pd-0-AmP-SMC). Catalytic evaluations were conducted using Suzuki-Miyaura cross-couplings as the model reactions, for which this Pd nanocatalyst exhibited high performance in an environmentally-friendly solvent mixture. Additionally, this Pd nanocatalyst could be re-used up to five cycles without any observable loss of activity, and separation of the catalyst could be conveniently done by a magnet.

  • 30.
    Margarita, Cristiana
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Rabten, Wangchuk
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Andersson, Pher G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Transition-Metal-Catalyzed Regioselective Asymmetric Mono-Hydrogenation of Dienes and Polyenes2018Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, nr 32, s. 8022-8028Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Organic compounds containing multiple C=C bonds are attractive substrates for catalytic asymmetric hydrogenation. The full saturation of prochiral double bonds, controlling the creation of two or more stereocenters in one step, is obviously a remarkable goal. However, another fascinating and useful option is to selectively introduce a new defined stereogenic center while leaving other double bonds untouched. Thus, the retained functionalities can be further exploited in synthesis. Examples of regio- and enantioselective mono-hydrogenations of polyolefins are highlighted in this Concept article, and are divided according to the nature of the reduced double bond and the transition-metal catalyst used. Alkenes bearing coordinating functional groups are often preferentially hydrogenated by Rh- and Ru-complexes, while the more recently developed Ir-based catalysts promote the selective saturation on alkyl-substituted olefins. Relevant applications of this effective methodology in the synthesis of natural products are included to demonstrate its value in organic synthesis.

  • 31. Martínez-Gómez, Estrella
    et al.
    Ståhle, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Gil-Ramírez, Yolanda
    Zúñiga-Ripa, Amaia
    Zaccheus, Mona
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Moriyón, Ignacio
    Iriarte, Maite
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Conde-Álvarez, Raquel
    Genomic Insertion of a Heterologous Acetyltransferase Generates a New Lipopolysaccharide Antigenic Structure in Brucella abortus and Brucella melitensis2018Ingår i: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 9, artikel-id 1092Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Brucellosis is a bacterial zoonosis of worldwide distribution caused by bacteria of the genus Brucella. In Brucella abortus and Brucella melitensis, the major species infecting domestic ruminants, the smooth lipopolysaccharide (S-LPS) is a virulence factor. This S-LPS carries a N-formyl-perosamine homopolymer O-polysaccharide that is the major antigen in serodiagnostic tests and is required for virulence. We report that the Brucella O-PS can be structurally and antigenically modified using wbdR, the acetyl-transferase gene involved in N-acetyl-perosamine synthesis in Escherichia coli O157:H7. Brucella constructs carrying plasmidic wbdR expressed a modified O-polysaccharide but were unstable, a problem circumvented by inserting wbdR into a neutral site of chromosome II. As compared to wild-type bacteria, both kinds of wbdR constructs expressed shorter O-polysaccharides and NMR analyses showed that they contained both N-formyl and N-acetyl-perosamine. Moreover, deletion of the Brucella formyltransferase gene wbkC in wbdR constructs generated bacteria producing only N-acetyl-perosamine homopolymers, proving that wbdR can replace for wbkC. Absorption experiments with immune sera revealed that the wbdR constructs triggered antibodies to new immunogenic epitope(s) and the use of monoclonal antibodies proved that B. abortus and B. melitensis wbdR constructs respectively lacked the A or M epitopes, and the absence of the C epitope in both backgrounds. The wbdR constructs showed resistance to polycations similar to that of the wild-type strains but displayed increased sensitivity to normal serum similar to that of a per R mutant. In mice, the wbdR constructs produced chronic infections and triggered antibody responses that can be differentiated from those evoked by the wild-type strain in S-LPS ELISAs. These results open the possibilities of developing brucellosis vaccines that are both antigenically tagged and lack the diagnostic epitopes of virulent field strains, thereby solving the diagnostic interference created by current vaccines against Brucella.

  • 32.
    Mobarak, Hani
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthesis and analysis of carbohydrates related to bacterial polysaccharides2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The outer surface of bacteria is composed of around 75% carbohydrates, which are vital for the bacteria to survive and communicate with the host biological system. The thesis discusses different properties of carbohydrates that are essential for understanding the bacterial behavior in biological systems. The first three chapters give an overview of carbohydrates.

    The fourth chapter discusses the synthesis of four amide-substituted 3,6-dideoxy-α-D-galactopyranosides, namely, methyl α-3,6-dideoxy-3-formamido-, acetamido-, (R)-3-hydroxybutyramido-, and (4-hydroxybutyramido)-D-galactopyranoside. These sugars were found as components of some bacterial O-antigens; the study is a step toward the synthesis of oligosaccharides that contain them. The fifth chapter describes the exchange kinetics of the formyl and acetyl derivatives that were synthesized. Both of them have two conformational states for the amide side-chain. 13C-NMR saturation transfer experiments are utilized for these measurements to reveal more about their properties in solution.

    In chaptr six, NMR and conformational analysis of oligosaccharides related to the O-antigen of Yersinia enterocolitica O:3 bacteria were carried out to obtain more information regarding their 3D structure.

    Chapter seven is focusing on the development of CASPER, a program for rapid assignment of 1H- and 13C-NMR chemical shifts of bacterial lipopolysaccharides, by adding more sugars into its database and testing it for naturally occurring LPS as well as extending the scope for synthetic carbohydrates, which is planned to be developed further in the future.

  • 33.
    Olsén, Peter
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Morvan, Jennifer
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sawadjoon, Supaporn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Shatskiy, Andrey
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Johnston, Eric V.
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Cyclic allylic carbonates as a renewable platform for protecting chemistry in water2018Ingår i: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 20, nr 14, s. 3186-3190Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present work explores different cyclic allylic carbonates as a potential class of allylcarbamate precursors. The 5-membered carbonate formed a carbamate with very good thermal and pH stability, which could be cleanly deprotected in aqueous solution, in just 30 min with 2 mol% Pd(OAc)(2) as catalyst. The polar nature of the installed motif made it possible to deprotect highly unpolar substrates in water as solvent.

  • 34.
    Olsén, Peter
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Oschmann, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Johnston, Eric V.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthesis of highly functional carbamates through ring-opening of cyclic carbonates with unprotected alpha-amino acids in water2018Ingår i: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 20, nr 2, s. 469-475Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present work shows that it is possible to ring-open cyclic carbonates with unprotected amino acids in water. Fine tuning of the reaction parameters made it possible to suppress the degree of hydrolysis in relation to aminolysis. This enabled the synthesis of functionally dense carbamates containing alkenes, carboxylic acids, alcohols and thiols after short reaction times at room temperature. When Glycine was used as the nucleophile in the ring-opening with four different five membered cyclic carbonates, containing a plethora of functional groups, the corresponding carbamates could be obtained in excellent yields (> 90%) without the need for any further purification. Furthermore, the orthogonality of the transformation was explored through ring-opening of divinylenecarbonate with unprotected amino acids equipped with nucleophilic side chains, such as serine and cysteine. In these cases the reaction selectively produced the desired carbamate, in 70 and 50% yield respectively. The synthetic design provides an inexpensive and scalable protocol towards highly functionalized building blocks that are envisioned to find applications in both the small and macromolecular arena.

  • 35. Orebom, Alexander
    et al.
    Verendel, J. Johan
    Samec, Joseph S. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi. RenFuel AB, Sweden.
    High Yields of Bio Oils from Hydrothermal Processing of Thin Black Liquor without the Use of Catalysts or Capping Agents2018Ingår i: ACS omega, ISSN 2470-1343, Vol. 3, nr 6, s. 6757-6763Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Black liquor (BL) from the kraft pulping process has been treated at elevated temperatures (380 degrees C) in a batch reactor to give high yields of a bio oil comprising monomeric phenolic compounds that were soluble in organic solvents and mineral oil and a water fraction with inorganic salts. The metal content in the product was < 20 ppm after a simple extraction step. A correlation between concentration, temperature, and reaction time with respect to yield of desired product was found. At optimal reaction conditions (treating BL with 16 wt % dry substance at 380 degrees C for 20 min), the yield of extractable organics was around 80% of the original lignin with less than 7% of char. The product was analyzed by gel permeable chromatography, mass spectroscopy, nuclear magnetic resonance, elemental analysis, and inductively coupled plasma. It was found that a large fraction composed of mainly cresols, xylenols, and mesitols. This process provides a pathway to convert a major waste stream from a pulp mill into a refinery feed for fuel or chemical production, whereas at the same time the inorganic chemicals are recovered and can be returned back to the pulp mill.

  • 36.
    Pathi Pati, Stalin Reddy
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Development of new Catalytic Methods for the Selective Synthesis of Heterocycles2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In the field of organic chemistry, the development of new catalytic methods for the synthesis of complex molecules from simple precursors is a top priority. The main focus of this thesis concerns the diastereoselective synthesis of heterocyclic compounds using main group elements as Lewis acid catalysts.

    The first part of this thesis deals with an annulation reaction of nitrones with oxiranes, aziridines, and thiiranes using Al(III) or In(III) catalysts. From this protocol, 1,4,2-dioxazinanes, 1,2,4-oxadiazinanes, and 1,4,2-oxathiazinanes were obtained in moderate to high yields with excellent diastereoselectivity. The transformation was found to be stereospecific and proceed via an SN2-mechanism.

    The second and third parts concern the development of In(III)-catalyzed annulation of carbonyl compounds, amines, and alkynyl enones. InBr3 was found to be an efficient catalyst for the activation of alkynyl enones in a multicomponent reaction with aldehydes and amines. The method affords cyclopenta[c]furans in high yields and in good to excellent diastereomeric ratios. Bicyclo[3.n.1]alkenone derivatives were formed via a double Michael addition reaction of cyclic ketones, amines, and alkynyl enones, in the presence of InCl3. The utility of these protocols was also demonstrated by sequential transformations.

    In the fourth part, AgOTf and CuI were found to be efficient catalysts for the activation of pyridine-substituted enynes towards enamines, providing indolizine derivatives in high yield and good diastereomeric ratios.

    In the last part of the thesis, 1,2-aminoarylation of γ,δ-unsaturated oxime esters with arylboronic acids using Ni catalysis is discussed. The protocol demonstrates the potential of Ni-catalysts for the generation of iminyl radicals to furnish functionalized pyrroline derivatives. The utility of this protocol was exemplified by transforming the pyrroline products to the corresponding pyrrole and pyrrolidine derivatives. 

  • 37.
    Pathipati, Stalin R.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    van der Werf, Angela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Selander, Nicklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Diastereoselective Synthesis of Polycyclic Indolizines with 2-(2-Enynyl)pyridines and Enamines2018Ingår i: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 20, nr 12, s. 3691-3694Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A diastereoselective metal-catalyzed reaction of 2-(2-enynyl)pyridines and cyclic enamines is reported. The method provides access to a variety of substituted indolizine derivatives by variation of the enyne component and the reaction conditions. Performing the reaction using a preformed enamine led to the formation of polycyclic indolizines. With in situ generated enamines, ketone-containing indolizine derivatives were obtained. An asymmetric reaction of 2-(2-enynyl)pyridines and enamines generated from an aldehyde and a catalytic amount of amine is presented.

  • 38.
    Planas, Ferran
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sheng, Xiang
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    McLeish, Michael J.
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    A Theoretical Study of the Benzoylformate Decarboxylase Reaction Mechanism2018Ingår i: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 6, artikel-id 205Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density functional theory calculations are used to investigate the detailed reaction mechanism of benzoylformate decarboxylase, a thiamin diphosphate (ThDP)-dependent enzyme that catalyzes the nonoxidative decarboxylation of benzoylformate yielding benzaldehyde and carbon dioxide. A large model of the active site is constructed on the basis of the X-ray structure, and it is used to characterize the involved intermediates and transition states and evaluate their energies. There is generally good agreement between the calculations and available experimental data. The roles of the various active site residues are discussed and the results are compared to mutagenesis experiments. Importantly, the calculations identify off-cycle intermediate species of the ThDP cofactor that can have implications on the kinetics of the reaction.

  • 39. Pope, Giovanna M.
    et al.
    Hung, Ivan
    Gan, Zhehong
    Mobarak, Hani
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Harper, James K.
    Exploiting C-13/N-14 solid-state NMR distance measurements to assign dihedral angles and locate neighboring molecules2018Ingår i: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, nr 49, s. 6376-6379Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The RESPDOR NMR method rapidly provides multiple C-13/N-14 distance measurements in natural abundance solids. In this study, C-13/N-14 RESPDOR information is shown, for the first time, to provide accurate molecular conformation and to locate non-bonded neighboring molecules.

  • 40.
    Posevins, Daniels
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Qiu, Youai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Highly Diastereoselective Palladium-Catalyzed Oxidative Carbocyclization of Enallenes Assisted by a Weakly Coordinating Hydroxyl Group2018Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, nr 9, s. 3210-3214Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A highly diastereoselective palladium-catalyzed oxidative carbocyclization-borylation of enallenes assisted by a weakly coordinating hydroxyl group was developed. The reaction afforded functionalized cyclo-hexenol derivatives, in which the 1,3-relative stereo chemistry is controlled (d.r. > 50:1). Other weakly coordinating oxygen-containing groups (ketone, alkoxide, acetate) also assisted the carbocyclization toward cyclo-hexenes. The reaction proceeds via a ligand exchange on Pd of the weakly coordinating group with a distant olefin group. The high diastereoselectivity of the hydroxyl directed reaction could be rationalized by a face-selective coordination of the distant olefin. It was demonstrated that the primary coordination of the close-by oxygen containing functionality was necessary for the reaction to occur and removal of this functionality shut down the reaction.

  • 41.
    Qiu, Youai
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mendoza, Abraham
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Posevins, Daniels
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kalek, Marcin
    Bäckvall, Jan E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mechanistic Insight into Enantioselective Palladium-Catalyzed Oxidative Carbocyclization-Borylation of Enallenes2018Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, nr 10, s. 2433-2439Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The asymmetric palladium-catalyzed oxidative carbocyclization-borylation of enallenes, employing a chiral phosphoric acid as co-catalyst, constitutes an efficient and convenient entry into functionalized building blocks with cyclopentene scaffolds in high enantiopurity. Up till now there has been a lack of knowledge concerning the origin of enantioselectivity of this reaction as well as the absolute configuration of the product. Herein, we report the crystal structure of one of the compounds generated via this carbocyclization, providing the link between the configuration of the products and the configuration of the chiral phosphoric acid used in the reaction. Furthermore, the origin of the enantioselectivity is thoroughly investigated with density functional theory (DFT) calculations. By careful examination of different possible coordination modes, it is shown that the chiral phosphoric acid and the corresponding phosphate anion serve as ligands for palladium during the key stereoselectivity-determining cyclization step. In addition, we examine reactions wherein an extra chiral reagent, a p-benzoquinone containing a chiral sulfoxide, is used. The combined experimental and theoretical studies provide insight into the details of complexation of palladium with various species present in the reaction mixture, furnishing a general understanding of the factors governing the stereoselectivity of this and related catalytic reactions.

  • 42.
    Rabten, Wangchuk
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    The Use of N,P-Iridium and N,P-Palladium Complexes in Asymmetric Synthesis2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The work presented in this thesis concerns asymmetric catalysis using chiral N,P-ligands and iridium or palladium transition metals. The first part  (Chapters 2 and 3) highlights the N,P-iridium catalyzed asymmetric hydrogenation of 1,4-cyclohexadienes having functionalized or unfunctionalized substituents, including allylsilane side chains. A series of N,P-iridium catalysts were synthesized and screened on a number of cyclohexadienes. The developed N,P-iridium catalysts have provided excellent chemo-, regio- and enantioselectivity for most of the products obtained. For substrates having an allylsilane sidechain, the chiral cyclic allylsilane products were used to induce stereocontrol in a subsequent Hosomi-Sakurai reaction using TiCl4 as Lewis acid and aldehydes as electrophiles. The corresponding homoallylic alcohols were obtained in good to excellent diastereoselectivity. 

    The second part (Chapter 4) describes the N,P-iridium catalyzed asymmetric hydrogenation of various vinyl fluorides. A number of tri- and tetrasubstituted vinyl fluorides were synthesized and evaluated for the asymmetric hydrogenation. The corresponding saturated chiral fluoro compounds were obtained in very high enantioselectivity (up to 99% ee). The defluorination, usually known to occur under the catalytic hydrogenation conditions, were not observed for the majority of the substrates. 

    Finally, Chapter 5 describes the application of N,P-ligands in the asymmetric cycloisomerization of 1,6-enynes using a palladium precatalyst. The enantioselectivities for the products were found to depend both on the substrate as well as the hydrogen source. These developed catalytic reactions provide attractive methods to create multiple stereogenic centers in a molecule in relatively few steps from readily available starting materials.

  • 43.
    Rabten, Wangchuk
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Margarita, Margarita
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Andersson, Pher G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ir-Catalyzed Asymmetric and Regioselective Hydrogenation of Cyclic Allylsilanes and Generation of Quaternary Stereocenters via the Hosomi-Sakurai Allylation2018Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, nr 7, s. 1681-1685Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A number of cyclic dienes containing the allylsilane moiety were prepared via Birch reduction and subjected to iridium-catalyzed regioselective and asymmetric hydrogenation, which provided chiral allylsilanes in high conversion and enantiomeric excess (up to 99 % ee). The compounds were successively used in the Hosomi-Sakurai allylation with various aldehydes employing TiCl4 as Lewis acid, providing adducts with two additional stereogenic centers in excellent diastereoselectivity.

  • 44.
    Reitti, Marcus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Gurubrahamam, Ramani
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Walther, Melanie
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lindstedt, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Olofsson, Berit
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthesis of Phenols and Aryl Silyl Ethers via Arylation of Complementary Hydroxide Surrogates2018Ingår i: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 20, nr 7, s. 1785-1788Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two transition-metal-free methods to access substituted phenols via the arylation of silanols or hydrogen peroxide with diaryliodonium salts are presented. The complementary reactivity of the two nucleophiles allows synthesis of a broad range of phenols without competing aryne formation, as illustrated by the synthesis of the anesthetic Propofol. Furthermore, silyl-protected phenols can easily be obtained, which are suitable for further transformations.

    Publikationen är tillgänglig i fulltext från 2019-03-14 01:00
  • 45.
    Rukkijakan, Thanya
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Akkarasamiyo, Sunisa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sawadjoon, Supaporn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Samec, Joseph S. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pd-Catalyzed Substitution of the OH Group of Nonderivatized Allylic Alcohols by Phenols2018Ingår i: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 83, nr 7, s. 4099-4104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nonactivated phenols have been employed as nucleophiles in the allylation of nonderivatized allylic alcohols to generate allylated phenolic ethers with water as the only byproduct. A Pd[BiPhePhos] catalyst was found to be reactive to give the O-allylated phenols in good to excellent yields in the presence of molecular sieves. The reactions are chemo-selective in which the kinetically favored O-allylated products are formed exclusively over the thermodynamically favored C-allylated products.

  • 46. Santoro, Stefano
    et al.
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mechanism and selectivity of rhodium-catalyzed CH bond arylation of indoles2018Ingår i: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 118, nr 9, artikel-id e25526Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density functional theory calculations are used to study the reaction mechanism and origins of C2-selectivity in a rhodium-catalyzed arylation of indole. It is shown that the reaction is catalyzed by an anionic Rh(III)-intermediate that activates the substrate through a concerted-metalation deprotonation. Dissociation of pivalic acid and subsequent reductive elimination generate the arylated indole product. Oxidative addition of the aryl iodide and a subsequent ligand exchange regenerates the active catalytic species. The origin of the regioselectivity is found to be the more favorable interaction between the 2-indolyl fragment and the metal center compared to the 3-indolyl fragment. Moreover, the better interaction of the pivalate ligands with the substrate in the transition state for the activation of C2H compared to the transition state for the C3H activation further favors the C2-selectivity.

  • 47.
    Sanz-Marco, Amparo
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Martinez-Erro, Samuel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Martín-Matute, Belén
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Selective Synthesis of Unsymmetrical Aliphatic Acyloins through Oxidation of Iridium Enolates2018Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, nr 45, s. 11564-11567Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The first method to access unsymmetrical aliphatic acyloins is presented. The method relies on a fast 1,3-hydride shift mediated by an Ir-III complex in allylic alcohols followed by oxidation with TEMPO+. The direct conversion of allylic alcohols into acyloins is achieved in a one-pot procedure. Further functionalization of the C alpha' of the alpha-amino-oxylated ketone products gives access to highly functionalized unsymmetrical aliphatic ketones, which further highlights the utility of this transformation.

  • 48.
    Sheng, Xiang
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Patskovsky, Yury
    Vladimirova, Anna
    Bonanno, Jeffrey B.
    Almo, Steven C.
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Raushel, Frank M.
    Mechanism and Structure of gamma-Resorcylate Decarboxylase2018Ingår i: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 57, nr 22, s. 3167-3175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    gamma-Resorcylate decarboxylase (gamma-RSD) has evolved to catalyze the reversible decarboxylation of 2,6-dihydroxybenzoate to resorcinol in a nonoxidative fashion. This enzyme is of significant interest because of its potential for the production of gamma-resorcylate and other benzoic acid derivatives under environmentally sustainable conditions. Kinetic constants for the decarboxylation of 2,6-dihydroxybenzoate catalyzed by gamma-RSD from Polaromonas sp. JS666 are reported, and the enzyme is shown to be active with 2,3-dihydroxybenzoate, 2,4,6-trihydroxybenzoate, and 2,6-dihydroxy-4-methylbenzoate. The three-dimensional structure of gamma-RSD with the inhibitor 2-nitroresorcinol (2-NR) bound in the active site is reported. 2-NR is directly ligated to a Mn2+ bound in the active site, and the nitro substituent of the inhibitor is tilted significantly from the plane of the phenyl ring. The inhibitor exhibits a binding mode different from that of the substrate bound in the previously determined structure of gamma-RSD from Rhizobtum sp. MTP-10005. On the basis of the crystal structure of the enzyme from Polaromonas sp. JS666, complementary density functional calculations were performed to investigate the reaction mechanism. In the proposed reaction mechanism, gamma-RSD binds 2,6-dihydroxybenzoate by direct coordination of the active site manganese ion to the carboxylate anion of the substrate and one of the adjacent phenolic oxygens. The enzyme subsequently catalyzes the transfer of a proton to Cl of y-resorcylate prior to the actual decarboxylation step. The reaction mechanism proposed previously, based on the structure of gamma-RSD from Rhizobtum sp. MTP-10005, is shown to be associated with high energies and thus less likely to be correct.

  • 49.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    A Major Structural Change of the Homocitrate Ligand of Probable Importance for the Nitrogenase Mechanism2018Ingår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, nr 3, s. 1090-1095Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mo-containing nitrogenase is the main enzyme that is able to take N-2 from the air and form ammonia. The active-site cofactor of the enzyme, termed FeMoco, is unique in nature. It has seven Fe and one Mo atoms connected by S bridges, with a C atom in the center of the cofactor. Another unusual feature is that it has a large homocitrate ligand known to be of importance for catalysis. In the present computational study, the role of the homocitrate ligand is investigated. It is found that a large structural change, which makes Mo-III five coordinated, is energetically favorable in the more reduced states. This is of probable importance for the nitrogenase mechanism.

  • 50.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Is there computational support for an unprotonated carbon in the E-4 state of nitrogenase?2018Ingår i: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 39, nr 12, s. 743-747Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the key enzyme for nitrogen fixation in nature, nitrogenase, the active site has a metal cluster with seven irons and one molybdenum bound by bridging sulfurs. Surprisingly, there is also a carbon in the center of the cluster, with a role that is not known. A mechanism has been suggested experimentally, where two hydrides leave as a hydrogen molecule in the critical E-4 state. A structure with two hydrides, two protonated sulfurs and an unprotonated carbon has been suggested for this state. Rather recently, DFT calculations supported the experimental mechanism but found an active state where the central carbon is protonated all the way to CH3. Even more recently, another DFT study was made that instead supported the experimentally suggested structure. To sort out the origin of these quite different computational results, additional calculations have here been performed using different DFT functionals. The conclusion from these calculations is very clear and shows no computational support for an unprotonated carbon in E-4.

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