Showing papers by "Burkhard König published in 2012"
TL;DR: The general and easy procedure provides a transition-metal-free alternative for the formation of aryl-heteroaryl bonds in heteroarenes by a photoredox process.
Abstract: Visible light along with 1 mol % eosin Y catalyzes the direct C–H bond arylation of heteroarenes with aryl diazonium salts by a photoredox process. We have investigated the scope of the reaction for several aryl diazonium salts and heteroarenes. The general and easy procedure provides a transition-metal-free alternative for the formation of aryl–heteroaryl bonds.
617 citations
TL;DR: A review of physicochemical data of these reaction media and highlights recent advances in their use in organic synthesis and biotransformations can be found in this article, where the authors highlight the need to replace hazardous and harmful solvents with green or sustainable media.
539 citations
TL;DR: Heterogeneous inorganic semiconductors and chiral organocatalysts team up for the stereoselective photocatalytic formation of carbon–carbon bonds and the connection between the organic and inorganic catalysts should not be too tight.
Abstract: Dream team: Heterogeneous inorganic semiconductors and chiral organocatalysts team up for the stereoselective photocatalytic formation of carbon–carbon bonds. However, the connection between the organic and inorganic catalysts should not be too tight: Covalent immobilization inactivates the system.
227 citations
TL;DR: The photocatalytic reaction of o-methylthio-arenediazonium salts with alkynes yields substituted benzothiophenes regioselectively through a radical annulation process through green light irradiation of eosin Y.
204 citations
TL;DR: Visible light mediates efficiently the α-arylation of enol acetates by aryl diazonium salts under mild conditions using [Ru(bpy)(3)]Cl(2) as a photoredox catalyst.
Abstract: Visible light mediates efficiently the α-arylation of enol acetates by aryl diazonium salts under mild conditions using [Ru(bpy)3]Cl2 as a photoredox catalyst. The broad scope of the reaction toward various diazonium salts and enol acetates was explored. The application of this reaction in the concise synthesis of 2-substituted indoles was demonstrated
145 citations
TL;DR: Functionalized indoles are synthezised under mild conditions in a tartaric acid-dimethylurea melt and regioselectively in excellent yields in the synthesis of the hormone melatonin.
143 citations
TL;DR: Teaching old dogs new tricks: Visible light photoredox catalysis improves the classic Meerwein arylation protocol significantly and allows the light-controlled arylations of alkenes, alkynes and enones by diazonium salts.
Abstract: Teaching old dogs new tricks: Visible light photoredox catalysis improves the classic Meerwein arylation protocol significantly and allows the light-controlled arylation of alkenes, alkynes and enones by diazonium salts.
120 citations
TL;DR: In this paper, the photooxidation reaction scope includes aliphatic and aromatic sulfides including sterically hindered substrates, and was shown to be very effective in ethanol/water (95:5,v/v) mixture reaching a quantum yield of Φ=0.60.
Abstract: Chemoselective photooxidation: Tetra-O-acetylriboflavin and blue light mediate the selective oxidation of sulfides to sulfoxides without overoxidation to sulfones. Reaction is very effective in ethanol/water (95:5,v/v) mixture reaching a quantum yield of Φ=0.60. The photooxidation reaction scope includes aliphatic and aromatic sulfides including sterically hindered substrates.
102 citations
TL;DR: CdS is a suitable visible light photocatalyst for oxidative bond formation under anaerobic conditions and good to excellent yields of homocoupling products were obtained as mixtures of diastereomers.
Abstract: The oxidative coupling of sp3 hybridized carbon atoms by photocatalysis is a valuable synthetic method as stoichiometric oxidation reagents can be avoided and dihydrogen is the only byproduct of the reaction. Cadmium sulfide, a readily available semiconductor, was used as a visible light heterogeneous photocatalyst for the oxidative coupling of benzyl alcohols and benzyl amines by irradiation with blue light. Depending on the structure of the starting material, good to excellent yields of homocoupling products were obtained as mixtures of diastereomers. Cross-coupling between benzyl alcohols and benzyl amines gave product mixtures, but was selective for the coupling of tetrahydroisoquinolines to nitromethane. The results demonstrate that CdS is a suitable visible light photocatalyst for oxidative bond formation under anaerobic conditions.
97 citations
TL;DR: The novel state (1T) inhibitor Zn(2+)-BPA (BPA = bis(2-picolyl)amine) binds outside the nucleotide binding pocket but nevertheless allosterically stabilizes state’1(T) and thus inhibits the Ras-Raf interaction.
Abstract: Allosteric interactions: Metal(II) cyclens inhibit Ras-effector interactions by stabilizing a weak effector-binding state of Ras, state 1(T), and binding directly in the active site. The novel state (1T) inhibitor Zn(2+) -BPA (BPA=bis(2-picolyl)amine) binds outside the nucleotide binding pocket but nevertheless allosterically stabilizes state 1(T) and thus inhibits the Ras-Raf interaction
60 citations
TL;DR: In this article, anorganische Halbleiter und chirale Organokatalysatoren bilden ein gutes Team in der stereoselektiven photokatalytischen Knupfung von Kohlenstoff-Kohlenstoffs Bindungen.
Abstract: Eine gute Mischung: Heterogene anorganische Halbleiter und chirale Organokatalysatoren bilden ein gutes Team in der stereoselektiven photokatalytischen Knupfung von Kohlenstoff-Kohlenstoff Bindungen. Allerdings sollte die Bindung zwischen organischem und anorganischem Katalysator nicht zu eng sein: Die kovalente Immobilisierung auf dem heterogenen Substrat desaktiviert den Katalysator.
TL;DR: Dynamic molecular recognition events at biological membrane receptors play a key role in cell signaling and artificial membranes have been prepared with embedded synthetic receptors which dynamically arrange and selectively respond to external stimuli like small peptide ligands.
Abstract: Dynamic molecular recognition events at biological membrane
receptors play a key role in cell signaling. Artificial membranes have been prepared with embedded synthetic receptors which
dynamically arrange and selectively respond to external stimuli like small peptide ligands.
TL;DR: The synthetic protocol for the reduction of alcohols to hydrocarbons by using hydriodic acid, first described by Kiliani more than 140 years ago, was improved to be more applicable to organic synthesis.
Abstract: The synthetic protocol for the reduction of alcohols to hydrocarbons by using hydriodic acid, first described by Kiliani more than 140 years ago, was improved to be more applicable to organic synthesis. Instead of a strongly acidic, aqueous solution, a biphasic toluene–water reaction medium was used, which allowed the conversion of primary, secondary and tertiary benzylic alcohols, in good yields and short reaction times, into the corresponding hydrocarbons. Red phosphorous was used as the stoichiometric reducing agent. Keto, ester, amide or ether groups are tolerated, and catalytic amounts of hydriodic acid (0.2 equiv) in the presence of 0.6 equiv phosphorous are sufficient to achieve conversion.
TL;DR: Two-dimensional nuclear magnetic resonance spectroscopy demonstrated the binding of AR71 to the MIA dimerization domain, in agreement with in vitro and in vivo data revealing reduced cell migration, reduced formation of metastases and increased immune response after AR71 treatment.
Abstract: Melanoma is the most aggressive form of skin cancer, with fast progression and early dissemination mediated by the melanoma inhibitory activity (MIA) protein. Here, we discovered that dimerization of MIA is required for functional activity through mutagenesis of MIA which showed the correlation between dimerization and functional activity. We subsequently identified the dodecapeptide AR71, which prevents MIA dimerization and thereby acts as a MIA inhibitor. Two-dimensional nuclear magnetic resonance (NMR) spectroscopy demonstrated the binding of AR71 to the MIA dimerization domain, in agreement with in vitro and in vivo data revealing reduced cell migration, reduced formation of metastases and increased immune response after AR71 treatment. We believe AR71 is a lead structure for MIA inhibitors. More generally, inhibiting MIA dimerization is a novel therapeutic concept in melanoma therapy.
TL;DR: In this article, the authors reported the combinatorial synthesis and screening of phosphorescent iridium complexes as solution processable emitters for OLEDs, which can be easily applied to other metal complexes or organic dyes for various applications.
Abstract: This work reports the combinatorial synthesis and screening of phosphorescent iridium complexes as solution processable emitters for OLEDs. The approach taken here allows for the rapid synthesis, isolation, spectroscopic characterization and identification of the libraries based on chromatographic methods. Subsequent analysis of the irradiation induced degradation provides insight on the stability of the complexes under continuous excitation. The method is versatile and can easily be applied to other metal complexes or organic dyes for various applications, e.g., in electroluminescence, photovoltaics and sensing.
TL;DR: A series of substituted diaryltriazoles resemble a molecular structure similar to established terphenyl-alpha-helix peptide mimics and have therefore the potential to act as selective inhibitors for protein–protein interactions.
Abstract: A series of substituted diaryltriazoles was prepared by a solid-phase-synthesis protocol using a modified Wang resin. The copper(I)- or ruthenium(II)-catalyzed 1,3-cycloaddition on the polymer bead allowed a rapid synthesis of the target compounds in a parallel fashion with in many cases good to excellent yields. Substituted diaryltriazoles resemble a molecular structure similar to established terphenyl-alpha-helix peptide mimics and have therefore the potential to act as selective inhibitors for protein–protein interactions.
TL;DR: The interaction of EF with a series of 18 2′,3′-O-mono- and bis-(M)ANT-substituted nucleotides, recently shown to be very potent inhibitors of the AC toxin from Bordetella pertussis, CyaA, is examined to provide a basis for future studies aiming at the development of potent EF inhibitors with high selectivity relative to mammalian ACs.
Abstract: Bacillus anthracis causes anthrax disease and exerts its deleterious effects by the release of three exotoxins, i.e. lethal factor, protective antigen and edema factor (EF), a highly active calmodulin-dependent adenylyl cyclase (AC). Conventional antibiotic treatment is ineffective against either toxaemia or antibiotic-resistant strains. Thus, more effective drugs for anthrax treatment are needed. Our previous studies showed that EF is differentially inhibited by various purine and pyrimidine nucleotides modified with N-methylanthraniloyl (MANT)- or anthraniloyl (ANT) groups at the 2′(3′)-O-ribosyl position, with the unique preference for the base cytosine (Taha et al., Mol Pharmacol 75:693 (2009)). MANT-CTP was the most potent EF inhibitor (K
i, 100 nM) among 16 compounds studied. Here, we examined the interaction of EF with a series of 18 2′,3′-O-mono- and bis-(M)ANT-substituted nucleotides, recently shown to be very potent inhibitors of the AC toxin from Bordetella pertussis, CyaA (Geduhn et al., J Pharmacol Exp Ther 336:104 (2011)). We analysed purified EF and EF mutants in radiometric AC assays and in fluorescence spectroscopy studies and conducted molecular modelling studies. Bis-MANT nucleotides inhibited EF competitively. Propyl-ANT-ATP was the most potent EF inhibitor (K
i, 80 nM). In contrast to the observations made for CyaA, introduction of a second (M)ANT-group decreased rather than increased inhibitor potency at EF. Activation of EF by calmodulin resulted in effective fluorescence resonance energy transfer (FRET) from tryptophan and tyrosine residues located in the vicinity of the catalytic site to bis-MANT-ATP, but FRET to bis-MANT-CTP was only small. Mutations N583Q, K353A and K353R differentially altered the inhibitory potencies of bis-MANT-ATP and bis-MANT-CTP. The nucleotide binding site of EF accommodates bulky bis-(M)ANT-substituted purine and pyrimidine nucleotides, but the fit is suboptimal compared to CyaA. These data provide a basis for future studies aiming at the development of potent EF inhibitors with high selectivity relative to mammalian ACs.
TL;DR: Quantitative and reversible extraction of riboflavin (vitamin B2) from aqueous solutions and a vitamin dietary supplement is achieved retaining high efficacy for six consecutive cycles.
Abstract: Fishing for riboflavin: Highly magnetic polymer-coated Fe/C nanoparticles are used as supports for zinc(II)–cyclen complexes. Quantitative and reversible extraction of riboflavin (vitamin B2) from aqueous solutions and a vitamin dietary supplement is achieved retaining high efficacy for six consecutive cycles. Applying an external magnetic field readily recycles the nanobeads.