- Insights into the hydronium-ion storage of alloxazine in mild electrolyte
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Here, it is shown for the first time that alloxazine (ALO) can reversibly store hydronium ions in 1 M Mg(NO3)2 electrolyte. Comprehensive analyses confirm that Mg2+ ions, which possess catalytic properties, can promote hydronium-ion transfer by forming a
- Hou, Xuesen,Liang, Jing,Liu, Chang,Nian, Qingshun,Sun, Tianjiang,Tao, Zhanliang,Xu, XiuFang,Zheng, Shibing
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Read Online
- Novel riboflavin-inspired conjugated bio-organic semiconductors
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Flavins are known to be extremely versatile, thus enabling routes to innumerable modifications in order to obtain desired properties. Thus, in the present paper, the group of bio-inspired conjugated materials based on the alloxazine core is synthetized using two efficient novel synthetic approaches providing relatively high reaction yields. The comprehensive characterization of the materials, in order to evaluate the properties and application potential, has shown that the modification of the initial alloxazine core with aromatic substituents allows fine tuning of the optical bandgap, position of electronic orbitals, absorption and emission properties. Interestingly, the compounds possess multichromophoric behavior, which is assumed to be the results of an intramolecular proton transfer.
- Richtar, Jan,Heinrichova, Patricie,Apaydin, Dogukan Hazar,Schmiedova, Veronika,Yumusak, Cigdem,Kovalenko, Alexander,Weiter, Martin,Sariciftci, Niyazi Serdar,Krajcovic, Jozef
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- Discovery of isoalloxazine derivatives as a new class of potential anti-Alzheimer agents and their synthesis
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This article describes discovery of a novel and new class of cholinesterase inhibitors as potential therapeutics for Alzheimer's disease. A series of novel isoalloxazine derivatives were synthesized and biologically evaluated for their potential inhibitory outcome for both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). These compounds exhibited high activity against both the enzymes AChE as well as BuChE. Of the synthesized compounds, the most potent isoalloxazine derivatives (7m and 7q) showed IC50 values of 4.72 μM and 5.22 μM respectively against AChE; and, 6.98 μM and 5.29 μM respectively against BuChE. These two compounds were further evaluated for their anti-aggregatory activity for β-amyloid (Aβ) in presence and absence of AChE by performing Thioflavin-T (ThT) assay and Congo red (CR) binding assay. In order to evaluate cytotoxic profile of these two potential compounds, cell viability assay of SH-SY5Y human neuroblastoma cells was performed. Further, to understand the binding behavior of these two compounds with AChE and BuChE enzymes, docking studies have been reported.
- Kanhed, Ashish M.,Sinha, Anshuman,Machhi, Jatin,Tripathi, Ashutosh,Parikh, Zalak S.,Pillai, Prakash P.,Giridhar, Rajani,Yadav, Mange Ram
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- Synthesis of riboflavines, quinoxalinones and benzodiazepines through chemoselective flow based hydrogenations
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Robust chemical routes towards valuable bioactive entities such as riboflavines, quinoxalinones and benzodiazepines are described. These make use of modern flow hydrogenation protocols enabling the chemoselective reduction of nitro group containing building blocks in order to rapidly generate the desired amine intermediates in situ. In order to exploit the benefits of continuous processing the individual steps were transformed into a telescoped flow process delivering selected benzodiazepine products on scales of 50 mmol and 120 mmol respectively.
- Baumann, Marcus,Baxendale, Ian R.,Hornung, Christian H.,Ley, Steven V.,Rojo, Maria Victoria,Roper, Kimberley A.
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p. 9736 - 9759
(2014/08/05)
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- Electron-deficient alloxazinium salts: Efficient organocatalysts of mild and chemoselective sulfoxidations with hydrogen peroxide
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A series of substituted alloxazinium perchlorates has been prepared and tested as catalysts for the oxidation of sulfides to sulfoxides with hydrogen peroxide. The logarithms of the observed rate constants of thioanisole oxidation correlate with the Hammett σ constants of the substituents on the alloxazinium catalysts, as well as with their reduction potentials E 0′ and their pKR+ values, representing the alloxazinium salt/pseudobase equilibrium. The stronger the electron-withdrawing substituent, the more efficient is the alloxazinium catalyst. The alloxazinium salts with a cyano or trifluoromethyl group in position 8 proved to be the most efficient, operating at room temperature at small loadings, down to 0.1 mol%, achieving turnover number values of up to 640 and acceleration by a factor of 350 relative to the non-catalyzed oxidation. The 8-cyanoalloxazinium perchlorate was evaluated as the best catalyst; however, due to its relatively good accessibility, the 8-(trifluoromethyl)alloxazinium perchlorate seems to be the catalyst of choice for sulfoxidations with hydrogen peroxide. It was successfully tested for the sulfoxidation of a series of aliphatic and aromatic sulfides on a preparative scale. It produced the corresponding sulfoxides in quantitative conversions and with high isolated yields (87-98%). No over-oxidation to sulfone was ever observed. Copyright
- Menova, Petra,Dvorakova, Hana,Eigner, Vaclav,Ludvik, Jiri,Cibulka, Radek
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p. 3451 - 3462
(2013/12/04)
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- Organocatalytic Dakin oxidation by nucleophilic flavin catalysts
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Flavin catalysts perform the first organocatalytic Dakin oxidation of electron-rich arylaldehydes to phenols under mild, basic conditions. Catechols are readily prepared, and the oxidation of 2-hydroxyacetophenone was achieved. Aerobic oxidation is displayed in the presence of Zn(0) as a reducing agent. This reactivity broadens the scope of biomimetic flavin catalysis in the realm of nucleophilic oxidations, providing a framework for mechanistic investigations for related oxidations, such as the Baeyer-Villiger oxidation and Weitz-Scheffer epoxidation.
- Chen, Shuai,Hossain, Mohammad S.,Foss, Frank W.
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supporting information; experimental part
p. 2806 - 2809
(2012/08/07)
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- Aerobic organocatalytic oxidation of aryl aldehydes: Flavin catalyst turnover by Hantzsch's ester
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The first Dakin oxidation fueled by molecular oxygen as the terminal oxidant is reported. Flavin and NAD(P)H coenzymes, from natural enzymatic redox systems, inspired the use of flavin organocatalysts and a Hantzsch ester to perform transition-metal-free, aerobic oxidations. Catechols and electron-rich phenols are achieved with as low as a 0.1 mol % catalyst loading, 1 equiv of Hantzsch ester, and O2 or air as the stoichiometric oxidant source.
- Chen, Shuai,Foss, Frank W.
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supporting information
p. 5150 - 5153,4
(2020/09/15)
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- Turning a riboflavin-binding protein into a self-sufficient monooxygenase by cofactor redesign
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By cofactor redesign, self-sufficient monooxygenases could be prepared. Tight binding of N-alkylated flavins to riboflavin-binding protein results in the creation of artificial flavoenzymes capable of H2O 2-driven enantioselective sulfoxidations. By altering the flavin structure, opposite enantioselectivities could be achieved, in accordance with the binding mode predicted by in silico flavin-protein docking of the unnatural flavin cofactors. The study shows that cofactor redesign is a viable approach to create artificial flavoenzymes with unprecedented activities.
- De Gonzalo, Gonzalo,Smit, Christian,Jin, Jianfeng,Minnaard, Adriaan J.,Fraaije, Marco W.
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supporting information; experimental part
p. 11050 - 11052
(2011/12/01)
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- Quantitative cascade condensations between o-phenylenediamines and 1,2-dicarbonyl compounds without production of wastes
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o-Phenylenediamines 1 underwent a series of cascade condensations with 1,2-dicarbonyl compounds to afford quantitative yields (eight cases) of heterocycles in solid-state syntheses that avoided waste formation. The products were produced in pure form and did not require purifying workup. The components were ball-milled in stoichiometric ratio, or in exceptional cases they were melted together and heated in the absence of solvents (some of them giving quantitative yields). Benzils and 2-hydroxy-1,4-naphthoquinone afforded quinoxaline derivatives 3 and 5, 2-oxoglutaric acid gave a 3-oxodihydroquinoxaline 7, and oxalic acid afforded the dihydroquinoxaline-2,3-dione 9. This last condensed with la in the melt, to afford a mixture of bis(benzimidazolyl) 10 and fluoflavin 11. Alloxane hydrate provided a 100% yield of the 3-oxodihydroquinoxaline-2-carbonylureas 15/16 at room temperature. Parabanic acid required a melt reaction providing a 78% yield of 3-oxodihydroquinoxalinyl-2-urea 22 and side products. Despite numerous reaction steps, most of these uncatalyzed stoichiometric reactions proceeded quantitatively in the solid state to give only one product (plus water), with unsurpassed atom economy. If catalysis with HCl was tried, the results were inferior. If melt reactions were required it appeared to be advantageous to have the products crystallize directly at the reaction temperature. The synthetic results have been interpreted mechanistically and compared to some similar solution reactions that do not exhibit the benefits of the solid-state techniques. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002).
- Kaupp, Gerd,Naimi-Jamal, M. Reza
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p. 1368 - 1373
(2007/10/03)
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- Mild and Efficient Flavin-Catalyzed H2O2 Oxidation of Tertiar Amines to Amine N-Oxides
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A mild and highly effective H2O2 oxidation of tertiary amines has been developed by the use of flavin catalysis. Eight aliphatic amines were oxidized to their corresponding N-oxides in fast and selective reactions. For all substrates a considerable rate enhancement was observed compared to the noncatalyzed reactions. The product N-oxides were isolated in good yields using this mild oxidation system based on the environmentally attractive oxidant H2O2. As the catalyst, an N1N5- dialkylated flavin was used as an analogue of the biologically important flavin redox cofactor. The catalytic cycle proposed for the flavin catalysis accounts for the observation that, in addition to the hydrogen peroxide oxidant, molecular oxygen is required for the initiation of the process.
- Bergstad, Katarina,B?ckvall, Jan-E.
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p. 6650 - 6655
(2007/10/03)
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- Tyrphostins. 5. Potent inhibitors of platelet-derived growth factor receptor tyrosine kinase: Structure-activity relationships in quinoxalines, quinolines, and indole tyrphostins
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A series of 3-indoleacrylonitrile tyrphostins, 2-chloro-3- phenylquinolines, and 3-arylquinoxalines were prepared and tested for inhibition of platelet-derived growth factor receptor tyrosine kinase (PDGF- RTK) activity. The potency of the inhibitors was found to be quinoxalines > quinolines > indoles. Lipophilic groups (methyl, methoxy) in the 6 and 7 positions and phenyl at the 3 position of quinoxalines and quinolines were essential for potency, in contrast to the hydrophilic catechol group in tyrphostins active against EGFR kinase inhibition at different sites. The inhibitors showed selectivity for PDGF and were not active against EGF receptor and HER-2/c-ErbB-2 receptor.
- Gazit, Aviv,App, Harald,McMahon, Gerald,Chen, Jefferey,Levitzki, Alexander,Bohmer, Frank D.
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p. 2170 - 2177
(2007/10/03)
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- Synthesis of quinoxalines under focussed microwave irradiation
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Quinoxalines were obtained by the condensation of α-diones with o-diaminobenzenes without solvent under focussed microwave irradiation.
- Villemin,Martin
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p. 2319 - 2326
(2007/10/02)
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- Synthesis of some new condensed pyrimidines: Thienopteridine and purine derivatives
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7-Hydroxypteridine (3) and its isomeric 6-hydroxypteridine (4) were prepared by condensation of 5,6-diaminouracil (1) with ethyl thienoylpyruvate (2) in pyridine and hydrochloric acid, respectively. Compounds 3 and 4 were converted into the corresponding thienopteridines 8 and 9 upon treatment with phosphorus pentasulphide. The synthesis of pteridines 12 and 13 was achieved from nitrosouracil (10). Also, the purine 15 and condensed purine 18 were prepared.
- El-Farargy,Assy,Hassanien
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p. 109 - 119
(2007/10/02)
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