Ulrich Koert

Philipps University of Marburg, Marburg, Hesse, Germany

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Publications (188)689.93 Total impact

  • Jan Rossbach, Klaus Harms, Ulrich Koert
    ChemInform 10/2014; 45(43).
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    ABSTRACT: The reaction of tetrahydrofuran (THF), an otherwise inert solvent molecule, on Si(001) was experimentally studied in ultrahigh vacuum. Using scanning tunneling microscopy (STM) and photoelectron spectroscopy at variable temperature, we could both isolate a datively bound intermediate state of THF on Si(001), as well as the final configuration that bridges two dimer rows of the Si(001) surface after ether cleavage. The latter configuration implies splitting of the O-C bond, which is typically kinetically suppressed. THF thus exhibits a hitherto unknown reactivity on Si(001).
    ChemPhysChem 09/2014; · 3.35 Impact Factor
  • Tobias Seitz, Klaus Harms, Ulrich Koert
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    ABSTRACT: A synthesis of the title compound (I) is presented, in which a vicinal tricarbonyl compound functioned as key intermediate.
    ChemInform 07/2014; 45(29).
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    ABSTRACT: The total synthesis of the heptacyclic natural product isoquinocyclinone has been achieved. A Hauser annulation was used to assemble the anthraquinone core structure. The unique 2,4,5,6-tetrahydropyrrolo[2,3-b]pyrrole substructure was prepared by alkyne addition to a lactone intermediate and subsequent Ni0-mediated cyanide addition, the conversion of an O,O- into an N,O-acetal, and final intramolecular N-alkylation.
    Chemistry - A European Journal 07/2014; · 5.93 Impact Factor
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    ABSTRACT: A 2-unsubstituted indole adds under Cu-box-catalysis to mesoxalic ester amides with high enantioselectivity, whereas low enantiomeric excess is obtained for 2-substituted indoles. A mesoxalic ester amide is used as key component in the total syntheses of alkaloids cladoniamide G and cladoniamide F. The natural product syntheses involve Suzuki cross-coupling to a 2,2′-biindole, arylation of the vic-tricarbonyl compound, and intramolecular lactam formation.
    Annalen der Chemie und Pharmacie 07/2014; · 3.10 Impact Factor
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    ABSTRACT: Porins, like the outer membrane protein G (OmpG) of Escherichia coli, are ideal templates amongst ion channels for protein and chemical engineering due to their robustness and simple architecture. OmpG shows fast transitions between open and closed states, which were attributed to loop 6 (L6). As flickering limits single-channel based applications, we pruned L6 by either 8 or 12 amino acids. While the open probabilities of both L6 variants resemble that of native OmpG, their gating frequencies were reduced by 63% and 81% respectively. Using the 3.2 Å structure of the shorter L6 variant in the open state we engineered a minimal porin (220 aa), where all remaining extramembranous loops were truncated. Unexpectedly, this minimised porin still exhibited gating albeit fivefold less frequent than OmpG. The residual gating of the minimal pore is hence independent of L6 rearrangements and involves narrowing of the ion conductance pathway most probably driven by global stretching-flexing deformations of the membrane-embedded β-barrel.
    Biochemistry 07/2014; · 3.38 Impact Factor
  • Jan Roßbach, Klaus Harms, Ulrich Koert
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    ABSTRACT: The Passerini reaction of vic‐diketo amides with a variety of isocyanides and carboxylic acids has been examined. α‐Acyloxy β‐keto carboxamides were formed regioselectively as the major products. For the Passerini reactions with electron‐withdrawing‐group‐substituted acetic acids, a one‐pot Passerini–Knoevenagel reaction was accomplished by the addition of triethylamine. vic‐Diketo amides react with a variety of isocyanides and carboxylic acids in a regioselective Passerini three‐component reaction (P‐3CR) to give good to excellent yields of α‐acyloxy‐β‐keto‐carboxamides. In the case of Passerini reactions with electron‐withdrawing‐group‐substituted acetic acids, a one‐pot Passerini–Knoevenagel reaction was accomplished by the addition of triethylamine.
    European Journal of Organic Chemistry 01/2014; 2014(5). · 3.34 Impact Factor
  • Philipp Reiß, Ulrich Koert
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    ABSTRACT: Ion channels provide a conductance pathway for the passive transport of ions across membranes. These functional molecules perform key tasks in biological systems such as neuronal signaling, muscular control, and sensing. Recently, function-oriented synthesis researchers began to focus on ion channels with the goal of modifying the function of existing ion channels (ion selectivity, gating) or creating new channels with novel functions. Both approaches, ion channel engineering and de novo design, have involved synthetic chemists, biochemists, structural biologists, and neurochemists. Researchers characterize the function of ion channels by measuring their conductance in samples of biological membranes (patch clamp) or artificial membranes (planar lipid bilayers). At the single molecule level, these measurements require special attention to the purity of the sample, a challenge that synthetic chemists should be aware of. Ideally, researchers study the function of channels while also acquiring structural data (X-ray, NMR) to understand and predict how synthetic modifications alter channel function. Long-term oriented researchers would like to apply synthetic ion channels to single molecule sensing and to implantat these synthetic systems in living organisms as tools or for the treatment of channelopathies. In this Account, we discuss our own work on synthetic ion channels and explain the shift of our research focus from a de novo design of oligo-THFs and oligo-THF-amino acids to ion channel engineering. We introduce details about two biological lead structures for ion channel engineering: the gramicidin β(6,3) helix as an example of a channel with a narrow ion conductance pathway and the outer membrane porins (OmpF, OmpG) with their open β-barrel structure. The increase and the reversal of ion selectivity of these systems and the hydrophobic match/mismatch of the channel with the phospholipid bilayer are of particular interest. For engineering ion channels, we need to supplement the single-point attachment of a synthetic modulator with the synthesis of a more challenging two-point attachment. The successful function-oriented synthesis of ion channels will require interdisciplinary efforts that include new electrophysiology techniques, efficient synthesis (peptide/protein/organic), and good structural analysis.
    Accounts of Chemical Research 05/2013; · 20.83 Impact Factor
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    ABSTRACT: A total synthesis of the proposed structures of fulicineroside and its aglycone fulicinerine is reported. The tetrasubstituted dibenzofuran substructure was accessible either through a Pd-mediated ortho-metalation or by an Ir-catalyzed meta-borylation. The synthesis of the β,β,α-linked trisaccharide consisting of D-olivose, L-rhodinose, and L-rhamnose was challenged by the unprecedented β-linked rhodinose. A Pd-catalyzed β-selective glycosylation of a 4-epi-rhodinose and a subsequent Mitsunobu inversion provided selectively the β-linked L-rhodinose-L-rhamnose disaccharide. Comparison with the reported data for the natural product and the aglycone suggests a misassignment of the structure of the natural product.
    Chemistry - A European Journal 04/2013; · 5.93 Impact Factor
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    ABSTRACT: 6,13-Disubstituted pentacenes were synthesized. Their electrochemical and optical properties, in addition to their packing motifs in the solid state, were determined. Treatment of pentacenequinone with TMSCF3 (Ruppert's reagent) and deprotection led to 6,13-bis(trifluoromethyl)pentacene-6,13-diol, which was aromatized to 6,13-bis(trifluoromethyl)pentacene by using PBr3. 6,13-Dialkoxypentacenes were accessible by alkylation of the corresponding hydroquinopentacenes by using dialkyl sulfates. 6,13-Bis(trifluoromethyl)pentacene and 6,13-dimethoxypentacene exhibit slipped face-to-face π stacking in the solid state, whereas 6,13-diethoxypentacene forms pairs of π-stacking molecules in the solid state.
    Annalen der Chemie und Pharmacie 03/2013; 2013(9). · 3.10 Impact Factor
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    ABSTRACT: Crotylboration of vic-diketoamides and vic-diketo esters was achieved with high diastereoselectivity and complementary regioselectivity. Whereas (E)-crotylboration of α,β-diketoamides resulted in high yields (91–99 %) of β-crotylated products obtained as a single diastereomer (anti), Lewis acid promoted crotylboration of α,β-diketo esters yielded the α-crotylated species with the anti product as main diastereomer.
    Annalen der Chemie und Pharmacie 02/2013; 2013(4). · 3.10 Impact Factor
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    ABSTRACT: Adsorption of cyclooctyne on Si(0 0 1) was investigated by means of scanning tunneling microscopy. Two different adsorption configurations were identified for the chemisorbed molecules which exhibit a tendency for clustering along the dimer rows. At high coverage well ordered adsorbate structures are formed. The adsorption behavior was observed to be similar at room temperature and at low surface temperature of 50 K. Moreover, it was found to be insensitive to distorted, hydrogen induced dangling-bond configurations. Our results suggest a direct adsorption pathway for cyclooctyne on Si(0 0 1) most likely governed by the molecule’s triple bond in combination with its high ringstrain.
    Chemical Physics Letters 01/2013; 556:70-76. · 2.15 Impact Factor
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    ABSTRACT: A synthesis of the AB-ring substructure of granaticin A was developed. The pyranolactone moiety was stereoselectively accessed by Sharpless asymmetric dihydroxylation and subsequent oxa-Pictet–Spengler cyclization. The use of BF3·OEt2 resulted in the formation of the cis pyranolactone, whereas the combination of BF3·OEt2 with trifluoroacetic acid led to the trans isomer. The resulting hydroquinones were selectively cleaved by ozonolysis to dicarboxylic acids. An aryl Grignard reagent could be regioselectively added to unsymmetrical anhydrides. As an alternative strategy for the construction of the B-ring, a benzyne–furan cycloaddition could be established.
    European Journal of Organic Chemistry 01/2013; · 3.34 Impact Factor
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    ABSTRACT: The BCD-ring substructure of granaticin A was synthesised following a new approach for the construction of the naphthoquinone moiety. The 2-oxabicyclo[2.2.2]oct-5-ene substructure was accessible stereoselectively using a Sharpless asymmetric dihydroxylation and a diastereoselective ketone reduction in combination with Yoshii's route. The naphthoquinone B-ring was prepared by addition of an aryllithium intermediate to an anhydride followed by a Friedel–Crafts cyclisation mediated by AlCl3 and Mg(OTf)2. The success of the Friedel–Crafts cyclisation relied on the conversion of the ketone-carboxylic acid into a lactone acetal.
    Annalen der Chemie und Pharmacie 11/2012; 2012(33). · 3.10 Impact Factor
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    ABSTRACT: A convergent total synthesis of the structurally unprecedented alkaloid lodopyridone was achieved using a cross-coupling of an iodopyridone fragment with a quinolinethiazolylstannane. Key features of the syntheses of the pentasubstituted 4-pyridone were a regioselective bromination of a 4-pyridone derived from kojic acid, a subsequent Cu-mediated introduction of the thioether, and a directed lithiation/iodination step. A chemoselective Negishi cross-coupling of a dibromothiazole and a quinolinylzinc reagent was used to assemble the chloroquinolinethiazol moiety.
    Organic Letters 08/2012; 14(17):4674-7. · 6.14 Impact Factor
  • Malte Wohlfahrt, Klaus Harms, Ulrich Koert
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    ABSTRACT: The total synthesis of (+)-awajanomycin has been achieved by asymmetric allylboration of a vicinal tricarbonyl compound as the key step. A substrate-controlled dihydroxylation and subsequent differentiation of diastereotopic ester groups were used to synthesize the γ-lactone substructure. After formation of the δ-lactam, the bicyclic core structure was established. The synthetic strategy and overall efficacy is compared with Huang's route to awajanomycin.
    Annalen der Chemie und Pharmacie 04/2012; 2012(11). · 3.10 Impact Factor
  • Niels Münster, Klaus Harms, Ulrich Koert
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    ABSTRACT: A novel directed S(N)2 reaction of conformationally biased gem-dibromides and an arenesulfinate anion is described. The reaction results in the diastereoselective formation of α-bromosulfones. The selectivity originates from pre-coordination of the nucleophile to a free hydroxyl group in the γ-position.
    Chemical Communications 02/2012; 48(13):1866-7. · 6.38 Impact Factor
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    ABSTRACT: Since the solution of the molecular structures of members of the voltage dependent anion channels (VDACs), the N-terminal α-helix has been the main focus of attention, since its strategic location, in combination with its putative conformational flexibility, could define or control the channel's gating characteristics. Through engineering of two double-cysteine mVDAC1 variants we achieved fixing of the N-terminal segment at the bottom and midpoint of the pore. Whilst cross-linking at the midpoint resulted in the channel remaining constitutively open, cross-linking at the base resulted in an "asymmetric" gating behavior, with closure only at one electric field´s orientation depending on the channel's orientation in the lipid bilayer. Additionally, and while the native channel adopts several well-defined closed states (S1 and S2), the cross-linked variants showed upon closure a clear preference for the S2 state. With native-channel characteristics restored following reduction of the cysteines, it is evident that the conformational flexibility of the N-terminal segment plays indeed a major part in the control of the channel's gating behavior.
    PLoS ONE 01/2012; 7(10):e47938. · 3.53 Impact Factor
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    ABSTRACT: Poly(L-menthyl methacrylate) (PMenMA) is synthesized by atom transfer radical polymerization (ATRP) of methyl L-mentholacrylate using bis[2-(2-bromoisobutyrooxy)ethyl]disulfide] ((BiBOE)2)S2) as the ATRP coinitiator. Reduction of hydrogen tetrachloroaureate(III) (HAuCl4 ·3 H2O) by Super-Hydride in the presence of PMenMA yields gold nanoparticles (AuNP)–PMenMA conjugates in the size range of 2–20 nm, depending on the ratio of PMenMA and HAuCl4. AuNP–PMenMA is characterized by TEM, NMR, IR-, and UV-spectroscopy. The correlation of the ratio of (AuNP)–PMenMA conjugates and free PMenMA is analyzed by gel permeation chromatography (GPC).
    Macromolecular Chemistry and Physics 12/2011; 212(23). · 2.39 Impact Factor
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    Malte Wohlfahrt, Klaus Harms, Ulrich Koert
    Angewandte Chemie 11/2011; 123(46).

Publication Stats

606 Citations
689.93 Total Impact Points

Institutions

  • 1993–2014
    • Philipps University of Marburg
      • Faculty of Chemistry
      Marburg, Hesse, Germany
  • 2010
    • Goethe-Universität Frankfurt am Main
      • Institute of Biochemistry
      Frankfurt, Hesse, Germany
  • 1999–2010
    • Humboldt-Universität zu Berlin
      • Department of Chemistry
      Berlín, Berlin, Germany
  • 2007
    • Moscow State Textile University
      Moskva, Moscow, Russia
  • 2005
    • Yarmouk University
      • Department of Chemistry
      Arbēla, Irbid, Jordan
  • 1997
    • Ludwig-Maximilians-University of Munich
      München, Bavaria, Germany