- Click. Coordinate. Catalyze. Using CuAAC Click Ligands in Small-Molecule Model Chemistry of Tyrosinase
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Three triazolylmethylpyridine ligands are synthesized using the copper-catalyzed azide-alkyne cycloaddition (CuAAC). The corresponding copper(I) complexes are investigated as catalysts for the oxygenation of several monophenols, in analogy to the enzyme tyrosinase. Importantly, they show a higher catalytic activity than previously investigated systems. This is ascribed to the lower charge donation of the electron-poor triazole heterocycle, supporting the hydroxylation of phenolic substrates by an electrophilic substitution mechanism.
- Herzigkeit, Benjamin,Fl?ser, Benedikt M.,Mei?ner, Nadja E.,Engesser, Tobias A.,Tuczek, Felix
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p. 5402 - 5405
(2018/11/27)
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- Tyrosinase Model Systems Supported by Pyrazolylmethylpyridine Ligands: Electronic and Steric Factors Influencing the Catalytic Activity and Impact of Complex Equilibria in Solution
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Two new copper(I) complexes supported by pyrazolylmethylpyridine (PMP) ligands are synthesized and investigated regarding their ability to catalyze the oxygenation of several monophenolic substrates. The PMP ligands containing a pyridine and a pyrazole donor group represent hybrids between dipyridylmethane (DPM) and bis(pyrazolyl)methane (BPM) ligands. The catalytic activity of the two new [Cu(MeCN)2PMP]PF6 complexes is found to be intermediate between that of catalytically inactive [Cu(MeCN)2DPM]PF6 and highly active [Cu(MeCN)2BPM]PF6, suggesting that the electronic properties of a multidentate ligand can be designed in a modular fashion. DFT calculations are used to explore the differences in reactivity between the two systems. Regarding the behavior of these complexes in solution, evidence for an equilibrium between homoleptic and heteroleptic forms is presented. The crystal structure of a dinuclear complex exhibiting two homoleptic CuII units bridged by a fluorido ligand is obtained, which might represent one of the decay products of PMP-type catalysts after prolonged reaction times.
- Herzigkeit, Benjamin,Fl?ser, Benedikt M.,Engesser, Tobias A.,N?ther, Christian,Tuczek, Felix
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supporting information
p. 3058 - 3069
(2018/07/29)
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- Tyrosinase and catechol oxidase activity of copper(I) complexes supported by imidazole-based ligands: structure–reactivity correlations
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Four new imidazole-based ligands, 4-((1H-imidazol-4-yl)methyl)-2-phenyl-4,5-dihydrooxyzole (LOL1), 4-((1H-imidazol-4-yl)methyl)-2-(tert-butyl)-4,5-dihydrooxyzole (LOL2), 4-((1H-imidazol-4-yl)methyl)-2-methyl-4,5-dihydrooxyzole (LOL3), and N-(2,2-dimethylpropylidene)-2-(1-trityl-1H-imidazol-4-yl-)ethyl amine (Limz1), have been synthesized. The corresponding copper(I) complexes [Cu(I)(LOL1)(CH3CN)]PF6 (CuLOL1), [Cu(I)(LOL2)(CH3CN)]PF6 (CuLOL2), [Cu(I)(LOL3)(CH3CN)]PF6 (CuLOL3), [Cu(I)(Limz1)(CH3CN)2]PF6 (CuLimz1) as well as the Cu(I) complex derived from the known ligand bis(1-methylimidazol-2-yl)methane (BIMZ), [Cu(I)(BIMZ)(CH3CN)]PF6 (CuBIMZ), are screened as catalysts for the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC-H2) to 3,5-di-tert-butylquinone (3,5-DTBQ). The primary reaction product of these oxidations is 3,5-di-tert-butylsemiquinone (3,5-DTBSQ) which slowly converts to 3,5-DTBQ. Saturation kinetic studies reveal a trend of catalytic activity in the order CuLOL3?≈?CuLOL1?>?CuBIMZ?>?CuLOL2?>?CuLimz1. Additionally, the catalytic activity of the copper(I) complexes towards the oxygenation of monophenols is investigated. As substrates 2,4-di-tert-butylphenol (2,4-DTBP-H), 3-tert-butylphenol (3-TBP-H), 4-methoxyphenol (4-MeOP-H), N-acetyl-l-tyrosine ethyl ester monohydrate (NATEE) and 8-hydroxyquinoline are employed. The oxygenation products are identified and characterized with the help of UV/Vis and NMR spectroscopy, mass spectrometry, and fluorescence measurements. Whereas the copper complexes with ligands containing combinations of imidazole and imine functions or two imidazole units (CuLimz1 and CuBIMZ) are found to exhibit catalytic tyrosinase activity, the systems with ligands containing oxazoline just mediate a stoichiometric conversion. Correlations between the structures of the complexes and their reactivities are discussed.
- Wendt, Franziska,N?ther, Christian,Tuczek, Felix
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p. 777 - 792
(2016/08/26)
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- Development of enantioselective synthetic routes to the hasubanan and acutumine alkaloids
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We describe a general strategy to prepare the hasubanan and acutumine alkaloids, a large family of botanical natural products that display antitumor, antiviral, and memory-enhancing effects. The absolute stereochemistry of the targets is established by an enantioselective Diels-Alder reaction between 5-(trimethylsilyl)cyclopentadiene (36) and 5-(2-azidoethyl)-2,3- dimethoxybenzoquinone (24). The Diels-Alder adduct 38 is transformed to the tetracyclic imine 39 by a Staudinger reduction-aza-Wittig sequence. The latter serves as a universal precursor to the targets. Key carbon-carbon bond constructions include highly diastereoselective acetylide additions to the N-methyliminium ion derived from 39 and Friedel-Crafts and Hosomi-Sakurai cyclizations to construct the carbocyclic skeleton of the targets. Initially, this strategy was applied to the syntheses of (-)-acutumine (4), (-)-dechloroacutumine (5), and four hasubanan alkaloids (1, 2, 3, and 8). Herein, the synthetic route is adapted to the syntheses of six additional hasubanan alkaloids (12, 13, 14, 15, 18, and 19). The strategic advantage of 5-(trimethylsilyl)cyclopentadiene Diels-Alder adducts is demonstrated by site-selective functionalization of distal carbon-carbon π-bonds in the presence of an otherwise reactive norbornene substructure. Evaluation of the antiproliferative properties of the synthetic metabolites revealed that four hasubanan alkaloids are submicromolar inhibitors of the N87 cell line.
- Calandra, Nicholas A.,King, Sandra M.,Herzon, Seth B.
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supporting information
p. 10031 - 10057
(2013/11/06)
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- Preparation and structure-activity relationships of novel asterriquinone derivatives
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Asterriquinone (ARQ, la) is an antitumor metabolite of Aspergillus terreus IFO 6123. To gain insight into the structure-activity relationships of ARQ, a series of chemically modified derivatives (1 - 6), the ARQ analogues (b - e) and the 2,5-dihydroxy-p-benzoquinone analogues (f - h), were prepared, and cytotoxic activity against mouse leukemia P388 cells investigated. Results indicated that: 1) at least one hydroxy group or acetoxy group in the p-benzoquinone moiety is important to exhibit cytotoxicity; 2) in the p-benzoquinone moiety, a single methoxy group and/or one acetoxy group substitution showed more potent cytotoxicity than when two hydroxy groups are substituted (1); 3) the indole ring is important for the cytotoxicity of ARQ analogues; 4) the 1,1-dimethyl-2-propenyl group in the indole ring is not important for the cytotoxic activity of ARQ.
- Kaji, Akira,Kimura, Kengo,Teranishi, Masanori,Kiriyama, Noriki,Nomura, Masaaki,Miyamoto, Ken-Ichi
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p. 1325 - 1329
(2007/10/03)
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- Transformation of asterriquinone diacetatetoasterriquinone monoalkyl ether via its monoacetal
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Asterriquinone (ARQ) diacetate; 2,5-bis[1-(1,1-dimethyl-2-propenyl)- 1H-indol-3-yl]-3,6-diacetoxy-2,5-cyclohexadiene-1,4-dione (3), was converted into ARQ monoalkyl ether (6) by treatment with a mixture of alcohol and K2CO3 under hea
- Kaji,Saito,Shinbo,Kiriyama
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p. 2340 - 2341
(2007/10/03)
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- Partial deacetylation of asterriquinone diacetate by aqueous sodium bicarbonate in pyridine
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Asterriquinone (ARQ); 2,5 -bis[1-(1,1-dimethyl-2-propenyl)-1H-indol-3- yl]-3,6-dihydroxy-2,5-cyclohexadiene-1,4-dione and ARQ monoacetate are metabolites from mycelium of Aspergillus terreux IFO 6123. ARQ diacetate was convened into ARQ monoacetate by treatment with 5% aq. NaHCO3 in pyridine at 80°C for 5 min, and the yield was 93.4%. Similarly, by treatment with 5% aq. NaHCO3 in acetone at room temperature, 2,5-diacetoxy-p-xyloquinone and 2,5- diacetoxy-p-benzoquinone were convened into 2-acetoxy-5-hydroxy-p-xyloquinone (yield, 85.8%) and 2-acetoxy-5-hydroxy-p-benzoquinone (yield, 66.7%), respectively.
- Kaji,Kimura,Iwata,Kiriyama
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p. 1818 - 1820
(2007/10/03)
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- NOUVELLE TRANSPOSITION ACIDO-CATALYSEE DE DIALCOXY-ORTHOBENZOQUINONES
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The paramethoxyphenoxyl group of 4-paramethoxyphenoxy 5-methoxy orthobenzoquinone (2) is readily substituted in basic medium by alcohols ROH (3b-k).The alkyl component R of the 4-alkoxy (OR) substituent of the 4-alkoxy 5-methoxy orthobenzoquinones (4 b-k)
- Reinaud, Olivia,Capdevielle, Patrice,Maumy, Michel
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p. 4167 - 4176
(2007/10/02)
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