- Synthesis of a novel constrained α-amino acid with quinoxaline side chain : 7-Amino-6,7-dihydro-8H-cyclopenta[g]quinoxaline-7-carbox-ylic acid
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A novel constrained 7-amino-6,7-dihydro-8H-cyclopenta[g]quinoxaline-7- carboxylic acid derivative was prepared starting from 4,5-dimethyl-o-phenylenediamine.
- Kotha, Sambasivarao,Brahmachary, Enugurthi,Kuki, Atsuo,Lang, Kamil,Anglos, Demetrios,Singaram, Bakthan,Chrisman, William
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- Rapid and sensitive determination of the intermediates of advanced glycation end products in the human nail by ultra-performance liquid chromatography with electrospray ionization time-of-flight mass spectrometry
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The resolution of the intermediate advanced glycation end products (AGEs) in the human nail was carried out by the combination of 4,5-dimethyl-1,2- phenylenediamine (DMPD) derivatives and ultra-performance liquid chromatography with electrospray ionization time-of-flight mass spectrometry (UPLC-ESI-TOF-MS). The reaction of the reagent with 3-deoxyglucosone (3-DG), methylglyoxal (MG), and glyoxal (GO) effectively proceeds at 60 °C for 2 h. The resulting derivatives were efficiently separated by a gradient program (a mixture of water and acetonitrile containing 0.1% formic acid) using a reversed-phase ACQUITY UPLC BEH C18 column (1.7 μm, 50 × 2.1 mm i.d.) and sensitively detected by TOF-MS. The detection limits (signal-to-noise ratio = 5) of the TOF-MS were 10 to 50 fmol. A good linearity was achieved from the calibration curve, which was obtained by plotting the peak area ratios of the analytes relative to the internal standard (IS) (i.e., 2,3-hexanedione) versus the injected amounts of 3-DG, MG, and GO (r2 > 0.999), and the intra- and interday assay precisions were less than 6.89%. The derivatives of the compounds in the human nail were successfully identified by the proposed procedure. As we know, these three kinds of dicarbonyl intermediates in the formation of AGEs - 3-DG, MG, and GO - were first found in human nail samples. Using these methods, the amounts of compound in the nails of healthy volunteers and diabetic patients were determined. When comparing the index from the diabetic patients with that from healthy volunteers, there is no significant difference in the content of the MG and GO in the nails. However, a statistically significant (P 0.001) correlation was observed between the 3-DG concentrations. Because the proposed method provides a good mass accuracy and the trace detection of the dicarbonyl intermediates of AGEs in the human nail, this analytical technique could be a noninvasive technique to assist in the diagnosis and assessment of disease activity in diabetic patients. Here we present a novel, sensitive, and simple method for the simultaneous determination of dicarbonyl compounds in the human nail.
- Min, Jun Zhe,Yamamoto, Makoto,Yu, Hai-Fu,Higashi, Tatsuya,Toyo'Oka, Toshimasa
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- Tetrabutylammonium Bromide-Catalyzed Transfer Hydrogenation of Quinoxaline with HBpin as a Hydrogen Source
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A metal-free environmentally benign, simple, and efficient transfer hydrogenation process of quinoxaline has been developed using the HBpin reagent as a hydrogen source. This reaction is compatible with a variety of quinoxalines offering the desired tetrahydroquinoxalines in moderate-to-excellent yields with Bu4NBr as a noncorrosive and low-cost catalyst.
- Guo, Qi,Chen, Jingchao,Shen, Guoli,Lu, Guangfu,Yang, Xuemei,Tang, Yan,Zhu, Yuanbin,Wu, Shiyuan,Fan, Baomin
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p. 540 - 546
(2021/12/27)
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- Iron-Catalyzed Hydrogen Transfer Reduction of Nitroarenes with Alcohols: Synthesis of Imines and Aza Heterocycles
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A straightforward and selective reduction of nitroarenes with various alcohols was efficiently developed using an iron catalyst via a hydrogen transfer methodology. This protocol led specifically to imines in 30-91% yields, with a good functional group tolerance. Noticeably, starting from o-nitroaniline derivatives, in the presence of alcohols, benzimidazoles can be obtained in 64-72% yields when the reaction was performed with an additional oxidant, DDQ, and quinoxalines were prepared from 1,2-diols in 28-96% yields. This methodology, unprecedented at iron for imines, also provides a sustainable alternative for the preparation of quinoxalines and benzimidazoles.
- Wu, Jiajun,Darcel, Christophe
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p. 1023 - 1036
(2021/01/09)
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- Iron-catalyzed Minisci acylation of N-heteroarenes with α-keto acids
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An efficient and mild protocol has been developed for the Minisci acylation reactions of nitrogen-containing heteroarenes with α-keto acids. Distinct from the conventional Minisci acylation conditions, the chemistry was performed using non-noble metal Fe(II), instead of expensive Ag(I) salt, as catalyst. A wide range of substrates, including aliphatic or aromatic α-keto acids, as well as various N-heteroarenes, proved to be compatible with the protocol. Scale-up experiment also demonstrates the practicality of the approach.
- Wang, Xiu-Zhi,Zeng, Cheng-Chu
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supporting information
p. 1425 - 1430
(2019/02/01)
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- Meta C-H Arylation of Electron-Rich Arenes: Reversing the Conventional Site Selectivity
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Controlling site selectivity of C-H activation without using a directing group remains a significant challenge. While Pd(II) catalysts modulated by a mutually repulsive pyridine-type ligand have been shown to favor the relatively electron-rich carbon centers of arenes, reversing the selectivity to favor palladation at the relatively electron-deficient positions has not been possible. Herein we report the first catalytic system that effectively performs meta C-H arylation of a variety of alkoxy aromatics including 2,3-dihydrobenzofuran and chromane with exclusive meta site selectivity, thus reversing the conventional site selectivity governed by native electronic effects. The identification of an effective ligand and modified norbornene (NBE-CO2Me), as well as taking advantage of the statistics, are essential for achieving the exclusive meta selectivity.
- Liu, Luo-Yan,Qiao, Jennifer X.,Yeung, Kap-Sun,Ewing, William R.,Yu, Jin-Quan
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supporting information
p. 14870 - 14877
(2019/10/02)
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- Efficient synthesis of quinoxalines from 2-nitroanilines and vicinal diols via a rutheniumcatalyzed hydrogen transfer strategy
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Via a ruthenium-catalyzed hydrogen transfer strategy, we have demonstrated a one-pot method for efficient synthesis of quinoxalines from 2-nitroanilines and biomass-derived vicinal diols for the first time. In such a synthetic protocol, the diols and the nitro group serve as the hydrogen suppliers and acceptors, respectively. Hence, there is no need for the use of external reducing agents. Moreover, it has the advantages of operational simplicity, broad substrate scope and the use of renewable reactants, offering an important basis for accessing various quinoxaline derivatives.
- Xie, Feng,Zhang, Min,Jiang, Huanfeng,Chen, Mengmeng,Lv, Wan,Zheng, Aibin,Jian, Xiujuan
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supporting information
p. 279 - 284
(2018/04/16)
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- Ruthenium(II) η6-arene complexes containing a dinucleating ligand based on 1,8-naphthyridine
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Ruthenium arene complexes, [(η6-p-cymene)2Ru2(L)Cl2](PF6)2 [3b, L = 2, 7-bis(di-2-pyridinyl)-1,8-naphthyridine] and [(η6-p-cymene)Ru(L′)Cl](PF6) [4, L′ = tri(2-pyridinyl)amine], were synthesized and characterized by spectroscopic and analytical techniques. The molecular structure of [(η6-p-cymene)2Ru2(L)Cl2]Cl2 (3a) was further determined by single-crystal X-ray analysis. The use of these ruthenium complexes as pre-catalysts for oxidative coupling of 1,2-diols/1,2-aminoalcohol with o-phenylenediamines leading to quinoxalines was investigated. Complex 3b appeared to be a good catalyst for this transformation.
- Tang, Wei-Hung,Liu, Yi-Hung,Peng, Shie-Ming,Liu, Shiuh-Tzung
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- The syntheses of pyrazino-containing sultines and their application in Diels-Alder reactions with electron-poor olefins and [60]fullerene
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The Diels-Alder reactions of heterocyclic o-quinodimethanes, generated in situ from 6,7-disubstituted quinoxalino[2,3-d]-[1,2λ4]oxathiine 2-oxides (6a-c), 2,3-disubstituted-8,9-dihydro-6H-8λ 4-[1,2]oxathiino[4,5-g]quinoxalin-8-one (7a-c) (sultines), and pyrazinosultine (22), with electron-poor olefins and [60]fullerene are described. The heterocyclic-fused sultines 7a-c and 22 are readily prepared from the corresponding dibromides 9a-c and 24 with the commercially available Rongalite (sodium formaldehyde sulfoxylate). When heated in the presence of electron-poor dienophiles and [60]fullerene, all of the sultines underwent extrusion of SO2, and the resulting heterocyclic o-quinodimethanes (3a-d, 4a-c, and 25) were intercepted as the 1:1 adducts in good to excellent yields. The temperature-dependent 1H NMR spectra of fullerene derivatives 31-38 show a dynamic process for the methylene protons. The activation free energies (ΔGc?) determined for the boat-to-boat inversion of these pyrazino-containing C60 compounds (31-34 and 38) are found to be in the range of 14.1-14.8 kcal/mol, but they are in the range of 15.2 to >17.1 kcal/mol for adducts 35-37. The activation free energies (ΔGC?) are significantly affected by (1) the orientations and (2) the substituents of the quinoxaline rings and (3) the extended benzannulation in the arenes of C60 adducts (see Table 2), which implies that both electronic interactions and steric effects between the aromatic addends and C60 are important. Tautomerization of methylquinoxaline to its enamine is invoked as a rationalization for the lowering of ΔGC? in some of the fulleroadducts.
- Liu, Jing-Horng,Wu, An-Tai,Huang, Ming-Hwei,Wu, Chein-Wei,Chung, Wen-Sheng
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p. 3395 - 3403
(2007/10/03)
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- Elemental fluorine. Part 10.1 Selective fluorination of pyridine, quinoline and quinoxaline derivatives with fluorine-iodine mixtures
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Selective fluorination of a range of pyridine and quinoline substrates to give corresponding 2-fluoro-derivatives can be readily achieved in high yield at room temperature using elemental fluorine-iodine mixtures. Reaction of fluorine with iodine forms, in situ, systems that function like sources of both iodonium and fluoride ions and fluorination of heterocyclic derivatives is suggested to proceed by fluoride ion attack on intermediate W-iodo-heterocyclic species. Quinoxaline derivatives react under similar conditions to give either the 2-fluoro- or 2,3-difluoro-quinoxaline derivatives depending on the ratio of fluorine passed through the solution. In related processes, pyridine can be alkoxylated upon reaction of an appropriate alcohol and fluorine.
- Chambers, Richard D.,Parsons, Mandy,Sandford, Graham,Skinner, Christopher J.,Atherton, Malcolm J.,Moilliet, John S.
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p. 803 - 810
(2007/10/03)
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- Potent Quinoxaline-Spaced Phosphono α-Amino Acids of the AP-6 Type as Competitive NMDA Antagonists: Synthesis and Biological Evaluation
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A series of α-amino-3-(phosphonoalkyl)-2-quinoxalinepropanoic acids was synthesized and evaluated for NMDA receptor affinity using a CPP binding assay.Functional antagonism of the NMDA receptor complex was evaluated in vitro using a stimulated TCP binding assay and in vivo by empolying an NMDA-induced seizure model.Some analogues also were evaluated in the -glycine binding assay.Several compounds of the AP-6 type show potent and selective NMDA antagonistic activity both in vitro and in vivo.In particular α-amino-7-chloro-3-(phosphonomethyl)-2-quinoxalinepropanoic acid (1) d isplayed an ED50 of 1.1 mg/kg ip in the NMDA lethality model.Noteworthy is α-amino-6,7-dichloro-3-(phosphonomethyl)-2-quinoxalinepropanoic acid (3) with a unique dual activity, displaying in the NMDA receptor binding assay an IC50 of 3.4 nM and in the glycine binding assay an IC50 of 0.61 μM.
- Baudy, Reinhardt B.,Greenblatt, Lynne P.,Jirkovsky, Ivo L.,Conklin, Mary,Russo, Ralph J.,et al.
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p. 331 - 342
(2007/10/02)
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- Electrochemical and Spectroscopic Characterization of N,N'-Dialkylquinoxalinium Redox Systems
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The outstanding position of the 1,4-isomer, quinoxaline, among the diazanaphthalenes is confirmed by comparing LUMO energies from HMO perturbation calculations.Diquaternary salts +)2(quin)>(X-)2, R = Me, Et; quin = quinoxaline, 2,3- and 6,7-dimethyl- and 2,3,6,7-tetramethylquinoxaline, X = BF4- or SbCl6- (4a-g), were isolated and characterized as compounds which are sensitive to reduction and hydrolysis.Cyclic voltammetry of the two-step redox systems of the Weitz type showed two reversible one-electron reductions with an extraordinarily stable radical cation intermediate (lg Kc > 12).The redox potentials are less negative than those of the 4,4'-bipyridinium systems but also less positive in comparison to the values of N,N'-dialkylphenazinium compounds.The radical cation intermediates which include a TCNQ- radical salt cannot only be characterized by ESR, but also by absorption spectroscopy in comparison to the respective dications.
- Schulz, Andreas,Kaim, Wolfgang
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p. 129 - 139
(2007/10/02)
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- Flavosemiquinone Model Systems. Part 2. Methyl-substituted Quinoxaline Radical Ions
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2,3-Dimethyl-, 6,7-dimethyl-, and 2,3,6,7-tetramethyl-quinoxaline were reduced in aprotic (THF) and acidic media (DMF - HClO4) to yield the corresponding quinoxaline radical anions and 1,4-dihydroquinoxaline radical cations.Analysis of their e.s.r. spectra was accomplished by computer simulation; a consistent assignment of coupling constants in quinoxaline radical ions could be made on the basis of the methyl substitution pattern.The hyperfine splitting is in agreement with Hueckel MO correlations and may be used to explain the spin distribution in flavosemiquinones.
- Kaim, Wolfgang
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p. 1767 - 1770
(2007/10/02)
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- 13C Nuclear Magnetic Resonance Spectra of Quinoxaline Derivatives
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The 13C n.m.r. spectra of a series of 5-, 6-, and 2-substituted quinoxalines have been analysed by consideration of their 1H coupled spectra.Typical values of the coupling constants are: C(2,3), 1JCH 181.9, 2JCH 11.4, C(5,8), 1JCH 162.6, 3JCH 6.5, C(6.7), 1JCH 159.4, 3JCH 9.1; C(9), 3JCH(2) = 3JCH(7) = 10.0, 3JCH(5) 5.4; C(10), 3JCH(3) = 3JCH(6) = 10.0, 3JCH(8) 5.4 Hz.The magnitudes of the coupling constants in the benzenoid ring are similar to these for the corresponding positions in naphthalene, but application of naphthalene chemical shift substitutions effects leads in some cases to the wrong peak sequence in the related quinoxalines.Within the quinoxaline series itself, however, acceptable additivity of substituent effects is found (+/- 0.8 p.p.m.), provided that the reference compounds are carefully chosen.Analysis of mixtures of quinoxalines from substituted o-phenylenediamines and α-oxo-aldehydes is possible by consideration of the multiplicity of the ring-junction quaternary carbon signals in the fully coupled spectra.
- McNab, Hamish
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p. 357 - 364
(2007/10/02)
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