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  • 1.
    Adrian Meredith, Jenny
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Design and Synthesis of Inhibitors Targeting the Aspartic Proteases HIV-1 PR and BACE-12009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis describes the synthesis of molecules designed for inhibition of two aspartic proteases, viral HIV-1 PR and human BACE-1. It also reports on the structure activity relationships of the targeted enzyme inhibitors.

    It is estimated that currently 33 million people are infected with HIV, the causative agent of AIDS. The virus targets T-lymphocytes and macrophages of the human immune system. The HIV-1 PR plays an important role in the viral replication, and by inhibiting the enzyme the disease progression can be slowed down or even halted.

    Herein is reported the design and synthesis of a series of HIV-1 PR inhibitors with novel P2 substituents of which several inhibit the enzyme in the nanomolar range. The aim of the second work was to further develop the inhibitors by the introduction of fluorine. Several attempts were performed to fluorinate different P2-substituents.

    Alzheimer’s disease (AD) is neurodegenerative, progressive and fatal disorder of the brain. It is associated with accumulation of plaques and tangles that cause impairment and functional decline of brain tissue which result in loss of memory and cognition. The plaques are mainly constituted of amyloid-β peptides that are generated in two steps from the amyloid precursor protein (APP). The cleavage sequence is initiated by the aspartic protease BACE-1, which makes the enzyme a key target in the effort of finding a therapy that aim to slow down the progression of AD.

    Herein are enclosed the development of two series of potent BACE-1 inhibitors. In the first work a synthetic strategy was developed to truncate a previously reported hydroxyethylene core structure in order to generate more drug-like inhibitors. This generated a series of truncated inhibitors where two amide bonds have been replaced with an ether - or alternatively a secondary amine linkage. A number of these inhibitors show potency against BACE-1. In the second part of the work the aim was investigate the effect of alterations in the P1 position. Five scaffolds with new P1 substituents were designed, synthesized and coupled with two different P2-P3 substituents. This resulted in a series of potent inhibitors that inhibit BACE-1 in the nanomolar range.

  • 2.
    Ahlford, Katrin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ekström, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Zaitsev, Alexey B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ryberg, Per
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Asymmetric Transfer Hydrogenation of Ketones Catalyzed by Amino Acid Derived Rhodium Complexes: On the Origin of Enantioselectivity and Enantioswitchability2009Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, nr 42, s. 11197-11209Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Amino acid based thioamides, hydroxamic acids, and hydrazides have been evaluated as ligands in the rhodium-catalyzed asymmetric transfer hydrogenation of ketones in 2-propanol. Catalysts containing thioamide ligands derived from L-valine were found to selectively generate the product with an R configuration (95 % ee), whereas the corresponding L-valine-based hydroxamic acids or hydrazides facilitated the formation of the (S)-alcohols (97 and 91 % ee, respectively). The catalytic reduction was examined by performing a structure–activity correlation investigation with differently functionalized or substituted ligands and the results obtained indicate that the major difference between the thioamide and hydroxamic acid based catalysts is the coordination mode of the ligands. Kinetic experiments were performed and the rate constants for the reduction reactions were determined by using rhodium–arene catalysts derived from amino acid thioamide and hydroxamic acid ligands. The data obtained show that the thioamide-based catalyst systems demonstrate a pseudo-first-order dependence on the substrate, whereas pseudo-zero-order dependence was observed for the hydroxamic acid containing catalysts. Furthermore, the kinetic experiments revealed that the rate-limiting steps of the two catalytic systems differ. From the data obtained in the structure–activity correlation investigation and along with the kinetic investigation it was concluded that the enantioswitchable nature of the catalysts studied originates from different ligand coordination, which affects the rate-limiting step of the catalytic reduction reaction.

  • 3.
    Ahlford, Katrin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Livendahl, Madeleine
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Fine-tuning catalytic activity and selectivity-[Rh(amino acid thioamide)] complexes for efficient ketone reduction2009Ingår i: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 50, nr 46, s. 6321-6324Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Amino acid-derived thioamides are prepared and evaluated as ligands in the rhodium-catalyzed asymmetric transfer hydrogenation of ketones in 2-propanol. It is found that increasing the steric bulk at the C-terminus of the ligand had a positive impact on both activity and selectivity in the reduction reaction. In order to find the optimum catalyst, a study is performed on a series of thioamide ligands having substituents of varying size.

  • 4.
    Ahlsten, Nanna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Martín-Matute, Belén
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Rhodium-catalysed coupling of allylic, homoallylic, and bishomoallylic alcohols with aldehydes and N-tosylimines: insights into the mechanism2009Ingår i: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 351, nr 16, s. 2657-2666Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The isomerisation of alkenols followed by reaction with aldehydes or N-tosylimines catalysed by rhodium complexes has been studied. The catalytically active rhodium complex is formed in situ from commercially available (cyclooctadiene)rhodium(l) chloride dimer [Rh(COD)Cl](2). The tandem process affords aldol and Mannich-type products in excellent yields. The key to the success of the coupling reaction is the activation of the catalysts by reaction with postassium tert-butoxide (t-BuOK), which promotes a catalytic cycle via alkoxides rather than rhodium hydrides. This mechanism minimises the formation of unwanted by-products. The mechanism has been studied by (1)H NMR spectroscopy and deuterium labelling experiments.

  • 5. Andersson, Samir
    et al.
    Zou, Dapeng
    Zhang, Rong
    Sun, Shiguo
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Sun, Licheng
    Selective positioning of CB[8] on two linked viologens and electrochemically driven movement of the host molecule2009Ingår i: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, nr 8, s. 1163-1172Artikel i tidskrift (Refereegranskat)
  • 6.
    Aydin, Juhanes
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Novel Pincer Complex-Catalyzed Transformations: Including Asymmetric Catalysis2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis is focused on the development of new pincer complex-catalyzed transformations. Optimization of the catalytic properties (fine-tuning) was directed to increase the catalytic activity as well as the chemo-, stereo- and enantioselectivity of the complexes. This was achieved by varying the heteroatoms in the terdentate pincer ligand, by changing the electronic properties of the coordinated aryl moiety and by implementing chiral functionalities in the pincer complexes.

    In the cross-coupling reaction of vinyl epoxides and aziridines with organoboronic acids the chemoselectivity of the reaction could be increased by employment of pincer complexes instead of commonly used Pd(0) catalysts. Furthermore, the introduction of a methoxy substituent in the aromatic subunit of the complex considerably increased the activity of the pincer complex catalyst.

    Fine-tuning of the enantioselectivity in electrophilic allylation reactions was achieved by using a wide variety of new BINOL- and biphenanthrol-based pincer complexes. The highest enantioselectivity (85% ee) was obtained by applying biphenanthrol-based pincer complexes.

    Stereoselective pincer complex-catalyzed condensation of sulfonylimines with isocyanoacetate could be achieved under mild reaction conditions. By application of chiral PCP catalysts, 2-imidazolines could be obtained with up to 86% ee.

    A new pincer complex-catalyzed C-H bond functionalization based reaction between organonitriles and sulfonylimines affords homoallylic amines and beta-aminonitriles in high yields. The asymmetric version of this process affords beta-aminonitriles with up to 71% ee.

    In the last chapter, a pincer complex-catalyzed redox coupling reaction is described. In this highly regio- and stereoselective process the integrity of the pincer catalysts is fully retained. This catalytic reaction proceeds with a high level of functional group tolerance, as allylic acetate and aryl halide functionalities are retained.

  • 7.
    Aydin, Juhanes
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Larsson, Johanna M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Selander, Nicklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pincer complex-catalyzed redox coupling of alkenes with iodonium salts via presumed palladium(IV) intermediates2009Ingår i: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 11, nr 13, s. 2852-2854Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Palladium pincer complexes directly catalyze the redox coupling reactions of functionalized alkenes and iodonium salts. The catalytic process, which is suitable for mild catalytic functionalization of allylic acetates and electron-rich alkenes, probably occurs through Pd(IV) intermediates. Due to the strong metal−ligand interactions, the oxidation of phosphine and amine ligands of the pincer complexes can be avoided in the presented reactions.

  • 8.
    Aydin, Juhanes
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Larsson, Johanna M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Szabó, Kálmán J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pincer Complex-Catalyzed Coupling Reactions via Palladium (IV) Intermediates2009Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 11, nr 13, s. 2852-2854Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Palladium pincer complexes directly catalyze the redox coupling reactions of functionalized alkenes and iodonium salts. The catalytic process, which is suitable for mild catalytic functionalization of allylic acetates and electron-rich alkenes, probably occurs through Pd(IV) intermediates. Due to the strong metal−ligand interactions, the oxidation of phosphine and amine ligands of the pincer complexes can be avoided in the presented reactions.

  • 9.
    Ayesa, Susana
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lindquist, Charlotta
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Agback, Tatiana
    Benkestock, Kurt
    Classon, Björn
    Henderson, Ian
    Hewitt, Ellen
    Jansson, Katarina
    Kallin, Anders
    Sheppard, Dave
    Samuelsson, Bertil
    Solid-phase parallel synthesis and SAR of 4-amidofuran-3-one inhibitors of cathepsin S: Effect of sulfonamides P3 substituents on potency and selectivity.2009Ingår i: Bioorganic & Medicinal Chemistry, ISSN 0968-0896, E-ISSN 1464-3391, Vol. 17, nr 3, s. 1307-1324Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Highly potent and selective 4-amidofuran-3-one inhibitors of cathepsin S are described. The synthesis and structure–activity relationship of a series of inhibitors with a sulfonamide moiety in the P3 position is presented. Several members of the series show sub-nanomolar inhibition of the target enzyme as well as an excellent selectivity profile and good cellular potency. Molecular modeling of the most interesting inhibitors describes interactions in the extended S3 pocket and explains the observed selectivity towards cathepsin K.

  • 10.
    Bartoszewicz, Agnieszka
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Building molecular complexity via tandem Ru-catalyzed reactions of allylic alcohols2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 11.
    Bartoszewicz, Agnieszka
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Martín-Matute, Belén
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Building molecular complexity via tandem Ru-catalyzed isomerization/C-H activation2009Ingår i: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 11, nr 8, s. 1749-1752Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A tandem isomerization/C-H activation of allylic alcohols was performed using a catalytic amount of RUCl(2)(PPh(3))(3). A variety of ortho alkylated ketones have been obtained in excellent yields. This tandem process relies on an in situ generation of a carbonyl functional group that directs the ortho C-H bond activation.

  • 12.
    Bielawski, Marcin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Olofsson, Berit
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Efficient one-pot synthesis of bis(4-tert-butylphenyl)iodonium triflate2009Ingår i: Organic Syntheses, ISSN 0078-6209, Vol. 86, s. 308-314Artikel i tidskrift (Refereegranskat)
  • 13.
    Björklund, Catarina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Design and Synthesis of BACE-1 Inhibitors: Novel Compounds Targeting an Aspartic Protease Important in the Pathogenesis of Alzheimer’s Disease2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis deals with the design and synthesis of protease inhibitors targeting the aspartic protease BACE-1 (β-site APP cleaving enzyme-1), an enzyme important in the pathogenesis of Alzheimer’s disease. The inhibitors are evaluated with respect to inhibition data, in a structure-activity relationship part.

    Alzheimer’s disease is a disabling, progressive and ultimately fatal form of dementia afflicting approximately 40 percent of the population over 80 years, with over 30 million people suffering from Alzheimer’s disease worldwide. This makes Alzheimer’s disease the most common form of dementia. The identification of the amyloid-β peptide (Aβ) as the main constituent of extracellular plaques, which characterize Alzheimer’s disease, suggests that Aβ plays a vital role in the pathology of Alzheimer’s disease. The formation of Aβ occurs when amyloid-β precursor protein (APP) is cleaved by β-secretase (BACE-1) and γ-secretase, which differ in length by 39-42 amino acids. This suggests that β-secretase is a suitable target for the development of therapeutics against Alzheimer’s disease.

    The synthetic work of this thesis comprises development of BACE-1 inhibitors containing a hydroxyethylene (HE) central core transition state isostere. The target molecules were readily synthesized from chiral carbohydrate starting materials. Highly potent inhibitors were produced by varying the substituents coupled to the HE central core. Selecting an aryloxymethyl P1 side-chain and a methoxy P1’ side-chain resulted in exceptionally potent BACE-1 inhibitors that also exhibit high selectivity over cathepsin D. In a further development, the ether oxygen linkage in the P1 side-chain was removed, resulting in a carba analogue, providing improved potency in a cell-based assay.

  • 14.
    Borén, Linnéa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Leijondahl, Karin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Dynamic Kinetic Asymmetric Transformation of 1,4-diols and Preparation of Trans-2,5-Disubstituted pyrrolidines2009Ingår i: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 50, nr 26, s. 3237-3240Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dynamic kinetic asymmetric transformation (DYKAT) of a series of 1,4-diols is carried out with Candida antarctica lipase B (CALB), Pseudomonas cepacia lipase II (PS-C II), and a ruthenium catalyst. A β-chloro-substituted 1,4-diol is successfully transformed into an optically pure 1,4-diacetate, which is a highly useful synthetic intermediate. The usefulness of the optically pure 1,4-diacetates is demonstrated by the synthesis of enantiopure 2,5-disubstituted pyrrolidines.

  • 15.
    Buitrago, Elina
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Zani, Lorenzo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Fe/NHC-catalyzed hydrosilylation of aromatic ketones2009Ingår i: Abstracts of Papers, 238th ACS National Meeting, Washington, DC, United States, August 16-20, 2009, Washington, DC: American Chemical Society , 2009Konferensbidrag (Övrigt vetenskapligt)
  • 16.
    Burkhardt, Anja
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Eriksson, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Avdelningen för strukturkemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Cumpstey, Ian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    (Z)-1,2:5,6-di-O-isopropylidene-α-D-ribo-hexofuranos-3-ulose O-benzyloxime2009Ingår i: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. E65, nr Part 3, s. o633-o633Artikel i tidskrift (Refereegranskat)
  • 17.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Catalytic asymmetric synthesis via combined metal and enzyme catalysis2009Ingår i: 3rd Hellenic Symposium on Organic Synthesis, October 15-17, 2009, Athens, Greece: Abstracts of papers, Athens, 2009Konferensbidrag (Övrigt vetenskapligt)
  • 18.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Palladium- and ruthenium-catalyzed redox reactions in selective organic synthesis2009Ingår i: Abstract of LOST II Symposium in honour of Prof. Alain Krief, March 18-20, 2009, Namur, Belgium, 2009Konferensbidrag (Övrigt vetenskapligt)
  • 19.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pd- and Ru-catalyzed redox reactions in catalysis. Application to the combination with enzyme catalysis2009Ingår i: Abstract of 42nd Jahrestreffen Deutscher Katalytiker, March 11-13, 2009, Weimar, Germany, 2009Konferensbidrag (Övrigt vetenskapligt)
  • 20.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Recent advances in the combination of metal and enzyme catalysis2009Ingår i: Abstract of the 10th Netherlands Catalysis and Chemistry Conference (NCCC-X), March 2-4, 2009, Noordwijkerhout, the Netherlands, 2009Konferensbidrag (Övrigt vetenskapligt)
  • 21. Cribiù, Riccardo
    et al.
    Borbas, K. Eszter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Cumpstey, Ian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    On the synthesis of vinyl and phenyl C-furanosides by stereospecific debenzylative cycloetherification2009Ingår i: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 65, nr 10, s. 2022-2031Artikel i tidskrift (Refereegranskat)
  • 22.
    Cumpstey, Ian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthesis of carbasugar-containing non-glycosidically linked pseudodisaccharides and higher pseudooligosaccharides2009Ingår i: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 344, nr 17, s. 2285-2310Artikel, forskningsöversikt (Refereegranskat)
  • 23.
    Cumpstey, Ian
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Alonzi, Dominic S.
    Butters, Terry D.
    Carbasugar-thioether pseudodisaccharides related to N-glycan biosynthesis2009Ingår i: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 344, nr 4, s. 454-459Artikel i tidskrift (Refereegranskat)
  • 24.
    Córdova, Armando
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Rios, Ramón
    The University of Barcelona, Departament Química Orgànica.
    Highly Z- and enantioselective ring-opening/cross-metathesis reactions and Z-selective ring-opening metathesis polymerization2009Ingår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 48, nr 47, s. 8827-8831Artikel i tidskrift (Refereegranskat)
  • 25. Daikoku, Shusaku
    et al.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Kanie, Osamu
    Analysis of a series of isomeric oligosaccharides by energy-resolved mass spectrometry: a challenge on homobranched trisaccharides2009Ingår i: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 23, nr 23, s. 3713-3719Artikel i tidskrift (Refereegranskat)
  • 26.
    Deska, Jan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Enzymatic kinetic resolution of primary allenic alcohols. Application to the total synthesis and stereochemical assignment of striatisporolide A2009Ingår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 7, nr 17, s. 3379-3381Artikel i tidskrift (Refereegranskat)
  • 27.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bartoszewicz, Agnieszka
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Inorganic ammonium salts as catalysts for direct aldol reactions in the presence of water2009Ingår i: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 50, nr 52, s. 7242-7245Artikel i tidskrift (Refereegranskat)
  • 28.
    Dziedzic, Pawel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Schyman, Patric
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Avdelningen för fysikalisk kemi.
    Kullberg, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Córdova, Armando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Highly enantioselective organocatalytic addition of aldehydes to N-(phenylmethylene)benzamides: Asymmetric synthesis of the paclitaxel side chain and its analogues2009Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, nr 16, s. 4044-4048Artikel i tidskrift (Refereegranskat)
  • 29.
    Frigell, Jens
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Cumpstey, Ian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthesis of carbadisaccharide mimics of galactofuranosides2009Ingår i: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 50, nr 36, s. 5142-5144Artikel i tidskrift (Refereegranskat)
  • 30.
    Gao, Yan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Åkermark, Torbjörn
    Liu, Jianhui
    Sun, Licheng
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Nucleophilic attack of hydroxide on a MnV oxo complex: a model of the O-O bond formation in the oxygen evolving complex of photosystem II2009Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, nr 25, s. 8726-8727Artikel i tidskrift (Refereegranskat)
  • 31. Georgieva, Polina
    et al.
    Wu, Qian
    McLeish, Michael J.
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    The reaction mechanism of phenylethanolamine N-methyltransferase: A density functional theory study2009Ingår i: Biochimica et Biophysica Acta, ISSN 0006-3002, E-ISSN 1878-2434, Vol. 1794, nr 12, s. 1831-1837Artikel i tidskrift (Refereegranskat)
  • 32. Hernández-Toribio, Jorge
    et al.
    Gómez Arrayás, Ramón
    Martín-Matute, Belén
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Carretero, Juan C.
    Catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides with α,β-unsaturated ketones2009Ingår i: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 11, nr 2, s. 393-396Artikel i tidskrift (Refereegranskat)
  • 33.
    Jalalian, Nazli
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Olofsson, Berit
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Asymmetric α-arylation of carbonyl compounds with chiral diaryliodonium salts2009Ingår i: Abstracts of Papers, 238th ACS National Meeting, Washington, DC, United States, August 16-20, 2009, Washington, D.C.: American Chemical Society , 2009Konferensbidrag (Övrigt vetenskapligt)
  • 34.
    Johnston, Eric
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Biomimetic oxidation methods: Efficient reoxidation of palladium and ruthenium by the use of a hybrid electron transfer catalyst.2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 35.
    Johnston, Eric V.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Karlsson, Erik A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lindberg, Staffan A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Efficient reoxidation of palladium by a hybrid catalyst in aerobic palladium-catalyzed carbocyclization of enallenes2009Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, nr 28, s. 6799-6801Artikel i tidskrift (Refereegranskat)
  • 36.
    Johnston, Eric V.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Karlsson, Erik A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Tran, Lien-Hoa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Åkermark, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Efficient synthesis of hybrid (hydroquinone-Schiff base)cobalt oxidation catalysts2009Ingår i: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, nr 23, s. 3973-3976Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hybrid catalysts A and B have recently been found to efficiently transfer electrons from a metal catalyst to molecular oxygen in biomimetic oxidations. In the present work hybrid catalysts A and B were synthesized in high yield from inexpensive starting materials. The key step is an efficient Suzuki cross-coupling, which allows the use of unprotected aldehyde 5. The new synthesis of the title hybrid catalysts is easy to carry out and can be scaled up.

  • 37.
    Jonsson, K. Hanna M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Weintraub, Andrej
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Structural determination of the O-antigenic polysaccharide from Escherichia coli O742009Ingår i: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 344, nr 12, s. 1592-1595Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structure of the O-antigen polysaccharide (PS) from Escherichia coli O74 has been determined. Component analysis, together with 1H and 13C NMR spectroscopy as well as 1H,15N-HSQC experiments were employed to elucidate the structure. Inter-residue correlations were determined by 1H,1H-NOESY and 1H,13C-heteronuclear multiple-bond correlation experiments. The PS is composed of tetrasaccharide repeating units with the following structure:

    Full-size image (5K)

    Cross-peaks of low intensity from an α-linked N-acetylglucosamine residue were present in the NMR spectra, and spectral analysis indicates that they originate from the penultimate residue in the polysaccharide. Consequently, the biological repeating unit has a 3-substituted N-acetyl-d-glucosamine residue at its reducing end. The 1H, 13C and 15N NMR chemical shifts of the α- and β-anomeric forms of d-Fucp3NAc are also reported. The repeating unit of the E. coli O74 O-antigen is identical to that of the capsular polysaccharide from E. coli K45.

  • 38.
    Kalek, Marcin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Jezowska, Martina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Stawinski, Jacek
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Preparation of arylphosphonates by palladium(0)-catalyzed cross-coupling in the presence of acetate additives: Synthetic and mechanistic studies2009Ingår i: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 351, nr 18, s. 3207-3216Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An efficient protocol for the synthesis of arylphosphonate diesters via a palladium-catalyzed cross-coupling of H-phosphonate diesters with aryl electrophiles, promoted by acetate ions, was developed. A significant shortening of the cross-coupling time in the presence of the added acetate ions was achieved for bidentate and monodentate supporting ligands, and for different aryl electrophiles (iodo, bromo and triflate derivatives). The reaction conditions were optimized in terms of amount of the catalyst, supporting ligands, and source of the acetate ion used. Various arylphosphonates, including those of potential biological significance, were synthesized using this newly developed protocol. Some mechanistic aspects of the investigated reactions are also discussed.

  • 39.
    Kalek, Marcin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Stawinski, Jacek
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Efficient synthesis of mono-and diarylphosphinic acids: a microwave-assisted palladium-catalyzed cross-coupling of aryl halides with phosphinate2009Ingår i: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 65, nr 50, s. 10406-10412Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A general, efficient method for the microwave-assisted synthesis of mono- and diarylphosphinic acids from anilinium phosphinate and aryl halides, using Pd(0) and Xantphos as a supporting ligand, was developed.

  • 40.
    Karlsson, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Catalytic Oxidation Methods. Use of inexpensive and environmentally friendly Oxidants in organic Synthesis.2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 41.
    Karlsson, Erik A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Privalov, Timofei
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Oxidation of ethers, alcohols, and unfunctionalized hydrocarbons by the methyltrioxorhenium/H2O2 system: a computational study on catalytic C-H bond activation2009Ingår i: Abstracts of Papers, 238th ACS National Meeting, Washington, DC, United States, August 16-20, 2009, Washington DC: American Chemical Society , 2009Konferensbidrag (Övrigt vetenskapligt)
  • 42.
    Karlsson, Erik A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Privalov, Timofei
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Oxidation of ethers, alcohols, and unfunctionalized hydrocarbons by the methyltrioxorhenium/H2O2 system: a computational study on catalytic C-H bond activation2009Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, nr 8, s. 1862-1869Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A concerted mechanism that does not involve an ionic intermediate was revealed by a DFT study on oxidation of ethers, alcohols, and unfunctionalized hydrocarbons by methyltrioxorhenium/H2O2. Instead, CH insertion occurs through hydride transfer and then turns into a hydroxide transfer/rebound in a concerted fashion. The picture shows selected frames from an intrinsic reaction coordinate scan from the transition state to the product for the oxidation of cis-1,2-dimethylcyclohexane.

    The potential-energy surfaces (PESs) of methyltrioxorhenium (MTO)-catalyzed CH insertion reactions in the presence of hydrogen peroxide were studied by accurate DFT methods for a series of substrates including unsaturated hydrocarbons, an ether, and an alcohol. Based on the comprehensive analysis of transition states and intrinsic reaction coordinate (IRC) scans, CH insertion was found to proceed by a concerted mechanism that does not require, as previously thought, a side-on or a butterfly-like transition state. We found that a typical transition state follows requirements of the SN2 reaction instead. Furthermore, by exploring the PESs of several CH insertion reactions, we discovered that no ionic intermediate is formed even in a polar solvent. The latter was modeled within the self-consistent reaction field approach in a polarizable continuum model (PB-SCRF/PCM). According to our study, CH insertion occurs by a concerted but highly asynchronous mechanism that first proceeds by hydride transfer and then turns into hydroxide transfer/rebound. For the oxidation of alcohols, CH bond cleavage occurs without formation of alkoxide intermediates on the dominant pathway. The computed deuterium kinetic isotope effect of 2.9 for the hydride-transfer transition state for alcohol oxidation is in good agreement with the experimental kH/kD ration of 3.2 reported by Zauche and Espenson. As confirmed by IRC and PES scans in different solvents, the OH-rebound phase of the CH insertion pathway demonstrates strong similarities with the rebound mechanism that was previously proposed for cytochrome P450 and metalloporphyrin-catalyzed oxidations.

  • 43.
    Krumlinde, Patrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Transition metal- and lipase-catalyzed reactions: Dynamic resolutions, hydrogen transfer and enzyme engineering2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis mainly focuses on chemoenzymatic processes and can be divided into three parts: The first part of the thesis, chapters 2-4, is devoted to the development of combined ruthenium- and enzyme-catalyzed dynamic processes. In these processes the metal catalyst racemizes (epimerizes) the alcohol substrate via hydrogen transfer and the enzyme transforms the substrate into enantiomerically enriched product. Chapter 2 focuses on bicyclic diols, where a process was developed to provide the enantiomerically pure product diacetates in high yield. The diacetates were then hydrolyzed using various protocols to yield the corresponding enantio- and diastereoenriched diols. Two of the substrates were mono-oxidized to yield the enantioenriched hydroxyketones in high yield. One of the hydroxyketones was subsequently employed in the formal synthesis of Sertraline in a highly enantioselective manner. Chapter 3 deals with the application of dynamic kinetic resolution in the synthesis of a pesticide derivative, which is obtained in high yield and high enantiomeric excess. Chapter 4 describes the use of dynamic kinetic resolution to set the configuration of a non-activated stereocenter in primary alcohols by taking advantage of the intermediate aldehydes intrinsic enolization behavior. A wide range of primary alcohols with a stereogenic center in β-position were dynamically resolved using this approach.

    The second part, chapters 5-6, deals with different types of enzyme engineering. In chapter 5, a lipase from Pseudomonas aeruginosa was mutated using directed evolution to increase the enantioselectivity of the lipase towards an allenic substrate. In chapter 6, a racemization catalyst was anchored to the active site of both cutinase and Candida Antarctica lipase.

    In the last part, chapter 7, an immobilized transition metal catalyst was used in transfer hydrogenation, a process which is closely related to the racemization of alcohols. The catalyst was used to reduce carbonyl compounds to the corresponding alcohols and was applicable to a wide range of substrates.

  • 44.
    Krumlinde, Patrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bogár, Krisztián
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthesis of a neonicotinoide pesticide derivative via chemoenzymatic dynamic kinetic resolution2009Ingår i: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 74, nr 19, s. 7407-7410Artikel i tidskrift (Refereegranskat)
  • 45.
    Landström, Jens
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Structure, dynamics and interactions of biomolecules: Investigations by NMR spectroscopy and computational methods2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this thesis, the structure, dynamics and interactions of proteins and carbohydrates are investigated using mainly NMR spectroscopy and computer simulations.

    Oligosaccharides representing a Salmonella O-antigen have been synthesized and their dynamic behavior and interaction with the bacteriophage P22 tail-spike protein have been studied by NMR spectroscopy, MD and docking simulations. A binding mechanism between the protein and the O-antigen has been proposed.

    Transient hydrogen bonds have been defined and examined in an E. coli polysaccharide and in a pentasaccharide representing the repeating unit, using MD simulation and NMR spectroscopy.

    Conformational dynamics of a trisaccharide representing the repeating unit of an A. salmonicida O-antigen have been investigated by MD simulations. The simulation together with relaxation matrix calculations reveals a conformational exchange on a ns timescale and explains an unusual NOE.

    A fragment-based screening for inhibitors of the glycosyltransferase GTB acceptor site has been performed using NMR spectroscopy and SPR. IC50 values of the binding fragments are reported. Complex structures of the fragments and GTB have been proposed using docking simulations.

    A fragment-based screening for inhibitors of the WaaG glycosyltransferase donor site has been performed using NMR spectroscopy and three compounds were selected. Structures of the WaaG-fragment complexes have been suggested from docking simulations. Binding of natural substrates and activity has also been investigated by NMR spectroscopy. MD simulations have been carried out on WaaG with and without bound donor substrate. The simulation revealed a conformational change upon substrate binding.

    Interactions between HEWL and carbohydrate ligands have been investigated, using a combination of weak affinity chromatography, NMR spectroscopy and computer simulations. KDs of the ligands have been presented as well as the solution structures of two HEWL-disaccharide complexes.

  • 46.
    Lavén, Gaston
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Stawinski, Jacek
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Palladium(0)-catalyzed benzylation of H-phosphonate diesters: An efficient entry to benzylphosphonates2009Ingår i: Synlett: Accounts and Rapid Communications in Synthetic Organic Chemistry, ISSN 0936-5214, E-ISSN 1437-2096, nr 2, s. 225-228Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new, efficient method for the synthesis of benzylphosphonate diesters via a palladium(0)-catalyzed cross-coupling reaction between benzyl halides and H-phosphonate diesters, using Pd(OAc)2 as a palladium source and Xantphos as a supporting ligand, has been developed.

  • 47.
    Lavén, Gaston
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Stawinski, Jacek
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Synthetic studies on the preparation of nucleoside 5'-H-phosphonate monoesters under the Mitsunobu reaction conditions2009Ingår i: ARKIVOC, ISSN 1424-6376, nr 3, s. 20-27Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A reaction of suitably protected nucleosides with phosphonic acid in the presence of diethyl azodicarboxylate and triphenylphosphine in pyridine provided in good yields the corresponding 5’-H-phosphonate monoesters.

  • 48.
    Leijondahl, Karin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Borén, Linnéa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Braun, Roland
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Bäckvall, Jan-Erling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Enzyme- and ruthenium-catalyzed dynamic kinetic asymmetric transformation of 1,5-diols: Application to the synthesis of (+)-Solenopsin A2009Ingår i: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 74, nr 5, s. 1988-1993Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dynamic kinetic asymmetric transformation (DYKAT) of 1,5-diols via combined lipase and ruthenium catalysis provides enantiomerically pure diacetates in high diastereoselectivity, which can serve as intermediates in natural product synthesis. This is demonstrated by the synthesis of (+)-Solenopsin A.

  • 49.
    Liao, Rong-Zhen
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Yu, Jian-Guo
    Liu, Ruo-Zhuang
    Theoretical study of the RNA hydrolysis mechanism of the dinuclear zinc enzyme RNase Z2009Ingår i: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, Vol. 2009, nr 20, s. 2967-2972Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    RNase Z is a dinuclear zinc enzyme that catalyzes the removal of the tRNA 3'-end trailer. Density functional theory is used to investigate the phosphodiester hydrolysis mechanism of this enzyme with a model of the active site constructed on the basis of the crystal structure. The calculations imply that the reaction proceeds through two steps. The first step is a nucleophihc attack by a bridging hydroxide coupled with protonation of the leaving group by a Glu-His diad. Subsequently, a water molecule activated by the same Glu-His diad makes a reverse attack, regenerating the bridging hydroxide. The second step is calculated to be the rate-limiting step with a barrier of 18 kcal/mol, in good agreement with experimental kinetic studies. Both zinc ions participate in substrate binding and orientation, facilitating nucleophilic attack. In addition, they act as electrophilic catalysts to stabilize the pentacoordinate trigonal-bipyramidal transition states.

  • 50.
    Liao, Rong-Zhen
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Yu, Jian-Guo
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Reaction Mechanism of the Dinuclear Zinc Enzyme N-Acyl-l-homoserine Lactone Hydrolase: A Quantum Chemical Study2009Ingår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 48, nr 4, s. 1442-1448Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    N-acyl-L-homosedne lactone hydrolase (AHL lactonase) is a dinuclear zinc enzyme responsible for the hydrolytic ring opening of AHLs, disrupting quorum sensing in bacteria. The reaction mechanism is investigated using hybrid density functional theory. A model of the active site is designed on the basis of the X-ray crystal structure, and stationary points along the reaction pathway are optimized and analyzed. Two possible mechanisms based on two different substrate orientations are considered. The calculations give support to a reaction mechanism that involves two major chemical steps: nucleophilic attack on the substrate carbonyl carbon by the bridging hydroxide and ring opening by direct ester C-O bond cleavage, The roles of the two zinc ions are analyzed. Zn1 is demonstrated to stabilize the charge of the tetrahedral intermediate, thereby facilitating the nucleophilic attack, while Zn2 stabilizes the charge of the alkoxide resulting from the ring opening, thereby lowering the barrier for the C-O bond cleavage.

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