Home About us Contact
|
Home About us Contact | ||
|
|
||
Quinoxaline
Terms modified by Quinoxaline Selected AbstractsNMR Study of L-Shaped (Quinoxaline)platinum(II) Complexes , Crystal Structure of [Pt(DMeDPQ)(bipy)](PF6)2EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2004Enrico Rotondo Abstract A 1H and 13C NMR study of nine PtII complexes of DMeDPQ [6,7-dimethyl-2,3-bis(2-pyridyl)quinoxaline] and BDPQ [2,3-bis(2-pyridyl)benzo[g]quinoxaline], and the crystal structure of one of them, are reported. The results are consistent with Cs symmetry of "L-shaped square-planar complexes". The rigid seven-membered chelated quinoxaline ligand holds the fused aromatic rings nearly perpendicular to the PtII coordination plane, generating the peculiar L-shaped structure. Ancillary ligands in the residual coordination sites are: a) bidentate flexible-planar 2,2,-bipyridine (bipy; complexes 1 and 2); b) bidentate rigid-planar dipyrido[3,2- a:2,3,- c]phenazine (dppz) or benzo[b]dipyrido[3,2- h:2,,3,- j]phenazine (bdppz; complexes 3,6); or c) 3-substituted monodentate pyridines (3-Rpy; complexes 7,9). The L-shaped geometry has been exploited to gain insight into the steric and dynamic features that regulate the noncovalent interactions of these square-planar complexes with DNA. We have shown previously, for [Pt(bipy)(n -Rpy)2]2+, that bipy twisting can be frozen out on the NMR timescale below 260 K. Preservation of the Cs symmetry at low temperature indicates a lack of bipy fluxionality within these L-shaped structures. The static butterfly-like symmetric orientation of the quinoxaline pyridyl rings accounts for the hampered twisting of Pt(bipy), which is otherwise assisted by the synchronous "windscreen wiper" conrotatory rocking of the ancillary pyridine rings. The L-geometry can also be used to monitor the ancillary n -Rpy rotation by NMR spectroscopy. The quasi-vertical quinoxaline pyridyl rings alignment leave room in the coordination plane for the crossing of the opposite pyridine rings, thereby reducing their rotational barriers about the Pt,N bond. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Quinoxaline 1,4-dioxides: Hypoxia-selective therapeutic agentsMOLECULAR CARCINOGENESIS, Issue 4 2002Mona Diab-Assef Abstract A problem that confronts clinicians in the treatment of cancer is the resistance of hypoxic tumors to chemotherapy and radiation therapy. Thus, the development of new drugs that are toxic to hypoxic cells found in solid tumors is an important objective for effective anticancer chemotherapy. We recently showed that the heterocyclic aromatic N-oxides, quinoxaline 1,4-dioxides (QdNOs), are cytotoxic to tumor cells cultured under hypoxia. In this study, we evaluated the hypoxia-selective toxicity of four diversely substituted QdNOs and determined their effect on the expression of hypoxia inducible factor (HIF) 1, in the human colon cancer cell line T-84. The various QdNOs were found to possess a 50- to 100-fold greater cytotoxicity to T-84 cells cultured under hypoxia compared with oxia. Interestingly, the hypoxia cytotoxicity ratio (HCR), the ratio of equitoxic concentrations of the drug under aerobic/anoxic conditions, was highly structure related and depended on the nature of the substituents on the QdNO heterocycle. The most cytotoxic 2-benzoyl-3-phenyl-6,7-dichloro derivative of QdNO (DCQ) was potent at a dose of 1 ,M with an HCR of 100 and significantly reduced the levels of HIF-1, transcript and protein. The 2-benzoyl-3-phenyl derivative (BPQ) had a hypoxia potency of 20 ,M and an HCR of 40. By contrast, the 2-aceto-3-methyl and the 2,3-tetramethylene (TMQ) derivatives of QdNO were much less cytotoxic under hypoxia (HCRs of 8.5 and 6.5, respectively) and reduced the expression of HIF-1, mRNA to a much lesser extent. Because the nonchlorinated analogue BPQ did not demonstrate behavior similar to that of DCQ, we hypothesize that the C-6, C-7-chlorine of DCQ might play a significant role in the selective hypoxic cytotoxicity of the drug. © 2002 Wiley-Liss, Inc. [source] Quinoxaline,Benzimidazole Rearrangement in the Synthesis of Benzimidazole-Based Podands.CHEMINFORM, Issue 13 2007V. A. Mamedov Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis of New 2-Acetyl and 2-Benzoyl Quinoxaline 1,4-Di-N-oxide Derivatives as anti-Mycobacterium tuberculosis Agents.CHEMINFORM, Issue 7 2004Andres Jaso Abstract For Abstract see ChemInform Abstract in Full Text. [source] Molecular Iodine Stabilization in an Extended N···I,I···N AssemblyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2009Francesco Isaia Abstract The adduct [bis(quinoxaline)-2,2,,3,3,-disulfide·I2], (Q2S2·I2), (1) can be easily synthesised from the reaction of Q2S2 and I2 in CH2Cl2 or, in the absence of any solvent, through diffusion of I2 vapours at 60 °C. X-ray diffraction analysis shows the presence of an extended N···I,I···N assembly in which each I2 molecule links a Q2S2 molecule at both ends through a nitrogen atom to form a polymeric species; the d(I,I) and d(N,I) bond lengths confirm a very weak nitrogen,iodine interaction at the base of the N···I,I···N assembly. DFT calculations provide optimised distances for the N···I and I,I bonds and explanation for the zigzag chain formation: the mPW1PW functional and the B3LYP hybrid functional with a variety of basis sets for the I atomic species [CRENBL, LANL2DZ, LANL2DZ(d,p), LANL08(d), SBKJC, SBKJC polarised-LFK and Stuttgart RLC] have been tested. Compound 1 proved stable up to nearly 100 °C, and the stability is to be mainly attributed to the lattice energy of its polymeric structure then to donor,acceptor stabilisation. The facile insertion of molecular iodine into the Q2S2 network makes this compound an interesting iodine sponge, suitable for I2 storage; moreover, Q2S2 can easily collect and release I2(g) by a temperature-controlled process (60 and 97 °C, respectively). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] NMR Study of L-Shaped (Quinoxaline)platinum(II) Complexes , Crystal Structure of [Pt(DMeDPQ)(bipy)](PF6)2EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2004Enrico Rotondo Abstract A 1H and 13C NMR study of nine PtII complexes of DMeDPQ [6,7-dimethyl-2,3-bis(2-pyridyl)quinoxaline] and BDPQ [2,3-bis(2-pyridyl)benzo[g]quinoxaline], and the crystal structure of one of them, are reported. The results are consistent with Cs symmetry of "L-shaped square-planar complexes". The rigid seven-membered chelated quinoxaline ligand holds the fused aromatic rings nearly perpendicular to the PtII coordination plane, generating the peculiar L-shaped structure. Ancillary ligands in the residual coordination sites are: a) bidentate flexible-planar 2,2,-bipyridine (bipy; complexes 1 and 2); b) bidentate rigid-planar dipyrido[3,2- a:2,3,- c]phenazine (dppz) or benzo[b]dipyrido[3,2- h:2,,3,- j]phenazine (bdppz; complexes 3,6); or c) 3-substituted monodentate pyridines (3-Rpy; complexes 7,9). The L-shaped geometry has been exploited to gain insight into the steric and dynamic features that regulate the noncovalent interactions of these square-planar complexes with DNA. We have shown previously, for [Pt(bipy)(n -Rpy)2]2+, that bipy twisting can be frozen out on the NMR timescale below 260 K. Preservation of the Cs symmetry at low temperature indicates a lack of bipy fluxionality within these L-shaped structures. The static butterfly-like symmetric orientation of the quinoxaline pyridyl rings accounts for the hampered twisting of Pt(bipy), which is otherwise assisted by the synchronous "windscreen wiper" conrotatory rocking of the ancillary pyridine rings. The L-geometry can also be used to monitor the ancillary n -Rpy rotation by NMR spectroscopy. The quasi-vertical quinoxaline pyridyl rings alignment leave room in the coordination plane for the crossing of the opposite pyridine rings, thereby reducing their rotational barriers about the Pt,N bond. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] A New Donor,Acceptor,Donor Polyfluorene Copolymer with Balanced Electron and Hole Mobility,ADVANCED FUNCTIONAL MATERIALS, Issue 18 2007A. Gadisa Abstract A new alternating polyfluorene copolymer poly[2,7-(9,9-dioctylfluoren)- alt -5,5-(5,,8,-di-2-thienyl-(2,,3,-bis-(3,,-octyloxyphenyl)-quinoxaline))] (APFO-15), which has electron donor,acceptor,donor units in between the fluorene units, is synthesized and characterized. This polymer has a strong absorption and emission in the visible range of the solar spectrum. Its electroluminescence and photoluminescence emissions extend from about 560 to 900 nm. Moreover, solar cells with efficiencies in excess of 3.5,% have been realized from blends of APFO-15 and an electron acceptor molecule, a methanofullerene [6,6]-phenyl-C61 -butyric acid methyl ester (PCBM). It has also been observed that electron and hole transport is balanced both in the pure polymer phase and in polymer/PCBM bulk heterojunction films, which makes this material quite attractive for applications in opto-electronic devices. [source] Synthesis of some novel imidazolidine derivatives and their metal complexes with biological and antitumor activityHETEROATOM CHEMISTRY, Issue 7 2006Shaya Y. Al-Raqa Halogenated imidazo(pyrazine,[1,4]diazocine and quinoxaline), 9,10-anthraquinone- [6,7-e], phenanthroline[5,6-e] {imidazo[4,5-b]pyrazine}, and naphtho[1,8-ef]imidazo[4,5-b][1,4] diazipen were obtained through interaction of imidazolidineiminothiones with the corresponding diamino compounds. Imidazo[4,5-e] triazine and pyrrolo[2,3-d]imidazole were prepared when the iminothiones were reacted with thiocarbohydrazide and with ethylphenyl acetate, separately. Some of the synthesized compounds exhibited better biological and antitumor activities. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:634,647, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20244 [source] Substituent effect on local aromaticity in mono and di-substituted heterocyclic analogs of naphthaleneJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2010Afshan Mohajeri Abstract A quantitative study on local aromaticity has been performed on a series of mono- and di-substituted biheterocycles (quinoline, isoquinoline, quinoxaline, quinazoline). Three electronically based indices (PDI, ATI, and FLU) have been employed to investigate the substituent effect on the , -electron delocalization in both heterocycle and benzenoid rings. Three typical substituents (Cl, OCH3, and CN) with different inductive and resonance power have been selected. Generally, substituent causes a reduction in aromaticity irrespective of whether it is electron attracting or electron donating. It is shown that the maximum aromaticity exhibits a similar trend of Cl,>,CN,>,OCH3 for all the studied rings. Moreover, it is found that the substituent situation with respect to the heteroatom has a significant influence on the aromaticity. It results from our study that in di-substituted derivatives, irrespective of whether the two substituents form a meta or para isomer, they preferably choose the position which leads to the maximum aromaticity character. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of colloidal self-assemblies on the basic hydrolysis of 2-(4-bromophenoxy)quinoxalineJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2003Angela Cuenca Abstract In the presence of cationic surfactants (C16H33NR3Cl; R,=,Me, n-Pr, n-Bu), the shape of rate versus surfactant concentration profiles for the basic hydrolysis of 2-(4-bromophenoxy)quinoxaline depends on substrate concentration. At low substrate concentration there is a single rate maximum and with a 10-fold substrate concentration increase a double rate maximum is observed. The first rate maximum is ascribed to reaction occurring in premicellar aggregates and the second to reaction in micelles. At low substrate concentration the effect of surfactant head group size was examined. Second-order rate constants in the micellar pseudophase increase with increasing head group size. Copyright © 2003 John Wiley & Sons, Ltd. [source] Synthesis and properties of new dialkoxyphenylene quinoxaline-based donor-acceptor conjugated polymers and their applications on thin film transistors and solar cellsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2009Mei-Hsiu Lai Abstract Synthesis, properties, and optoelectronic device applications of four new bis-[4-(2-ethyl-hexyloxy)-phenyl]quinoxaline(Qx(EHP))-based donor-acceptor conjugated copolymers are reported, in which the donors are thiophene(T), dithiophene(DT), dioctylfluorene(FO), and didecyloxyphenylene(OC10). The optical band gaps (Eg) of PThQx(EHP), PDTQ(EHP), POC10DTQ(EHP), and PFODTQ(EHP) estimated from the onset absorption are 1.57, 1.65, 1.77, and 1.92 eV, respectively. The smallest Eg of PThQx(EHP) among the four copolymers is attributed to the balanced donor/acceptor ratio and backbone coplanarity, leading to a strong intramolecular charge transfer. The hole mobilities obtained from the thin film transistor (TFT) devices of PThQx(EHP), PDTQ(EHP), POC10DTQ(EHP), and PFODTQ(EHP) are 2.52 × 10,4, 4.50 × 10,3, 4.72 × 10,5, and 9.31 × 10,4 cm2 V,1 s,1, respectively, with the on-off ratios of 2.00 × 104, 1.89 × 103, 4.07 × 103, and 2.30 × 104. Polymer solar cell based on the polymer blends of PFODTQ(EHP), PThQx(EHP), POC10DTQ(EHP), and PDTQ(EHP) with [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) under illumination of AM1.5 (100 mW cm,2) solar simulator exhibit power conversion efficiencies of 1.75, 0.92, 0.79, and 0.43%, respectively. The donor/acceptor strength, molecular weight, miscibility, and energy level lead to the difference on the TFT or solar cell characteristics. The present study suggests that the prepared bis[4-(2-ethyl-hexyloxy)-phenyl]quinoxaline donor-acceptor conjugated copolymers would have promising applications on electronic device applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 973,985, 2009 [source] Novel two-dimensional donor,acceptor conjugated polymers containing quinoxaline units: Synthesis, characterization, and photovoltaic propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2008Lijun Huo Abstract Novel two-dimensional donor,acceptor (D,A) structured conjugated polymers, P1,P4, were designed and synthesized by introducing electron-deficient quinoxaline as core and electron-rich alkoxyl-phenylenevinylene in side chains and p -phenylenevinylene, triphenylamine, or thiophene in main chain. Benefited from the D,A structures, the polymers possess low bandgaps of 1.75 eV, 1.86 eV, 1.59 eV, and 1.58 eV for P1, P2, P3, and P4, respectively, and show broad absorption band in the visible region: the shorter wavelength absorption peak at ,400 nm ascribed to the conjugated side chains and the longer wavelength absorption peak between 500 nm and 750 nm belonging to the absorption of the conjugated main chains. Especially, the absorption band of P4 film covers the whole visible range from 300 nm to 784 nm. The power conversion efficiencies of the polymer solar cells based on P1,P4 as donor and PCBM as acceptor are 0.029%, 0.14%, 0.46%, and 0.57%, respectively, under the illumination of AM 1.5, 100 mW/cm2. The polymers with the low bandgap and broad absorption band are promising photovoltaic materials. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4038,4049, 2008 [source] Competitive AMPA receptor antagonistsMEDICINAL RESEARCH REVIEWS, Issue 2 2007Daniela Catarzi Abstract Glutamic acid (Glu) is the major excitatory neurotransmitter in the mammalian central nervous system (CNS) where it is involved in the physiological regulation of different processes. It has been well established that excessive endogenous Glu is associated with many acute and chronic neurodegenerative disorders such as cerebral ischaemia, epilepsy, amiotrophic lateral sclerosis, Parkinson's, and Alzheimer's disease. These data have consequently added great impetus to the research in this field. In fact, many Glu receptor antagonists acting at the N -methyl- D -aspartic acid (NMDA), 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA), and/or kainic acid (KA) receptors have been developed as research tools and potential therapeutic agents. Ligands showing competitive antagonistic action at the AMPA type of Glu receptors were first reported in 1988, and the systemically active 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo[f]quinoxaline (NBQX) was first shown to have useful therapeutic effects in animal models of neurological disease in 1990. Since then, the quinoxaline template has represented the backbone of various competitive AMPA receptor antagonists belonging to different classes which had been developed in order to increase potency, selectivity and water solubility, but also to prolong the "in vivo" action. Compounds that present better pharmacokinetic properties and less serious adverse effects with respect to the others previously developed are undergoing clinical evaluation. In the near future, the most important clinical application for the AMPA receptor antagonists will probably be as neuroprotectant in neurodegenerative diseases, such as epilepsy, for the treatment of patients not responding to current therapies. The present review reports the history of competitive AMPA receptor antagonists from 1988 up to today, providing a systematic coverage of both the open and patent literature. © 2006 Wiley Periodicals, Inc. [source] Quinoxaline 1,4-dioxides: Hypoxia-selective therapeutic agentsMOLECULAR CARCINOGENESIS, Issue 4 2002Mona Diab-Assef Abstract A problem that confronts clinicians in the treatment of cancer is the resistance of hypoxic tumors to chemotherapy and radiation therapy. Thus, the development of new drugs that are toxic to hypoxic cells found in solid tumors is an important objective for effective anticancer chemotherapy. We recently showed that the heterocyclic aromatic N-oxides, quinoxaline 1,4-dioxides (QdNOs), are cytotoxic to tumor cells cultured under hypoxia. In this study, we evaluated the hypoxia-selective toxicity of four diversely substituted QdNOs and determined their effect on the expression of hypoxia inducible factor (HIF) 1, in the human colon cancer cell line T-84. The various QdNOs were found to possess a 50- to 100-fold greater cytotoxicity to T-84 cells cultured under hypoxia compared with oxia. Interestingly, the hypoxia cytotoxicity ratio (HCR), the ratio of equitoxic concentrations of the drug under aerobic/anoxic conditions, was highly structure related and depended on the nature of the substituents on the QdNO heterocycle. The most cytotoxic 2-benzoyl-3-phenyl-6,7-dichloro derivative of QdNO (DCQ) was potent at a dose of 1 ,M with an HCR of 100 and significantly reduced the levels of HIF-1, transcript and protein. The 2-benzoyl-3-phenyl derivative (BPQ) had a hypoxia potency of 20 ,M and an HCR of 40. By contrast, the 2-aceto-3-methyl and the 2,3-tetramethylene (TMQ) derivatives of QdNO were much less cytotoxic under hypoxia (HCRs of 8.5 and 6.5, respectively) and reduced the expression of HIF-1, mRNA to a much lesser extent. Because the nonchlorinated analogue BPQ did not demonstrate behavior similar to that of DCQ, we hypothesize that the C-6, C-7-chlorine of DCQ might play a significant role in the selective hypoxic cytotoxicity of the drug. © 2002 Wiley-Liss, Inc. [source] Cocrystals of 2,3,5,6-tetrafluorobenzene-1,4-diol with diaza aromatic compoundsACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Agnieszka Czapik 2,3,5,6-Tetrafluorobenzene-1,4-diol easily forms cocrystals with heteroaromatic bases containing the pyrazine unit. In the 1:1 complexes with pyrazine, C6H2F4O2·C4H4N2, (I), and quinoxaline, C6H2F4O2·C8H6N2, (II), the crystal components are linked via O,H...N hydrogen bonds into one-dimensional chains. With the largest base, phenazine, the 1:2 benzenediol,phenazine complex, C6H2F4O2·2C12H8N2, (III), was obtained, with the molecules linked via O,H...N interactions into a discrete heterotrimer. In all three cocrystals, the two types of molecules are organized into layers via softer C,H...O and C,H...F interactions and ,,, stacking interactions, with stronger hydrogen bonds linking molecules of adjacent layers. In (II) and (III), molecules are arranged into heterostacks, whereas in (I) separate stacks are formed by the heterocyclic base and the benzenediol molecule. [source] Lack of a Dose-response Relationship for Carcinogenicity in the Rat Liver with Low Doses of 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline or N-NitrosodiethylamineCANCER SCIENCE, Issue 10 2002Shoji Fukushima For a long period, it has been generally considered that carcinogens, particularly genotoxic ones, have no threshold in exerting their potential for cancer induction. However, the non-threshold theory can be challenged with regard to assessment of cancer risk to humans. Here we show that a food-derived, genotoxic hepatocarcinogen, 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline, forms DNA adducts at low doses, but does not induce glutathione S-transferase placental form (GST-P)-positive foci (considered to be preneoplastic lesions) or 8-hydroxy-2,-deoxyguanosine in rat liver. Moreover a N -nitroso compound, N -nitrosodiethylamine, at low doses was also found not to induce GST-P-positive foci in rat liver. These results imply that there is a no-observed effect level for hepatocarcinogenesis by these genotoxic carcinogens. [source] ChemInform Abstract: A Straightforward Synthesis of Pyridopyrazino[2,3-b]indoles and Indolo[2,3-b]quinoxaline.CHEMINFORM, Issue 36 2001France-Aimee Alphonse Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Novel Bridgehead Nitrogen Heterocyclic Systems: Synthesis and Antimicrobial Activity of Imidazo[2,1-b]-1,3,4-thiadiazolo[2,3-c]-s-triazoles, s-Triazolo[3,4-b][1,3,4]thiadiazolo[3,2-b]imidazo[4,5-b]quinoxaline and Bis-(s-triazolo[3,4-b][1,3,4]thiadiazolo[3,2-b][imidazo [4,5-b]-cyclohexane]-5a,6a-diene).CHEMINFORM, Issue 31 2001Jag Mohan Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Some Nucleophilic Reactions with 6-Benzoyl-2,3-dichloroquinoxaline: Synthesis of Tetrazolo[1,5-a]quinoxaline, 2-Methylidene-1,3-dithiolo[4,5-b]quinoxalines, Quinoxalino[2,3-b]quinoxalines and Pyrazolo[1,,5,:1,2]imidazolo[4,5-b]quinoxalines.CHEMINFORM, Issue 26 2001M. S. A. El-Gaby Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Pyrazino[2.3- g]quinoxaline-Bridged Indole-Based Building Blocks: Design, Synthesis, Anion-Binding Properties, and Phosphate-Directed Assembly in the Solid StateCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2010Ting Wang Abstract Strategies for exploring anionic templates to direct sophisticated supramolecular assembly have attracted attention. Herein, a series of new anion receptors 1,3 containing two indole-based binding sites bridged by linking spacer pyrazino[2.3- g]quinoxaline (PQ) have been rationally designed and prepared from the precursors 2,3-diindol-3,-yl quinoxaline (DIQ) and 5,6-dihydrodiindolo[3,2- a:2,,3,- c]phenazine (DIPZ). X-ray analyses showed a self-connected network and dimeric packing through hydrogen bonding and ,,, stacking interaction in the solid state in the structures of 1 and 2, respectively. All three receptors exhibited a series of prominent absorption bands from the expanded ,,system. The indole-based expanded receptors were found to strongly and selectively bind F,, AcO,, and H2PO4, among the tested anions (F,, Cl,, Br,, AcO,, H2PO4,, HSO4,, NO3,, and ClO4,), and operated as efficient colorimetric sensors for naked-eye detection of fluoride anions in DMSO. These tailored building blocks captured two anions located at far-spaced binding sites, and adopted noninterfering anion-binding processes to guarantee the anion-binding affinity, topology, and dimensionality. Solid-state studies elucidated that the neutral 1,3 interacted with the tetrahedral dihydrogen phosphate anion in proper proportions and designed topologies, thus leading to the formation of a series of multidimensional networks by self-assembly in the solid state. The observations showed a well-characterized phosphate-directed assembly of multidimensional metal-free coordination polymers in the solid state, in which the formed phosphate aggregates, including dimer encapsulated in an indole-mediated hydrogen-bonded pocket and an infinite chain, behaved as anionic templates to direct the self-assembly. However, no evidence proved the presence of such phosphate-directed infinite coordination polymers in solution. [source] Dipyrrolyl-Functionalized Bipyridine-Based Anion Receptors for Emission-Based Selective Detection of Dihydrogen PhosphateCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2007Patrick Plitt Dr. Abstract New cationic anion receptors, based on the use of pyrrole-substituted bipyridine and coordinated to transition metals, are described. Specifically, polypyridine,ruthenium and ,rhodium cores have been functionalized to generate an anion binding site. The design was chosen to probe the influence of the pyrrole-to-pyrrole separation on anion-binding affinities and selectivities; this distance is greater in the new systems of this report (receptors 1 and 2) relative to that present in related dipyrrolyl quinoxaline based receptors 3 and 4. Solution-phase anion-binding studies, carried out by means of 1H,NMR spectroscopic titrations in [D6]DMSO and isothermal titration calorimetry (ITC) in DMSO, reveal that 1 and 2 bind most simple anions with substantially higher affinity than either 3 or 4. In the case of chloride anion, structural studies, carried out by means of single-crystal X-ray diffraction analyses, are consistent with the solution-phase results and reveal that receptors 1 and 2 are both able to stabilize complexes with this halide anion in the solid state. [source] Photophysical Properties of Heteroleptic Iridium Complexes Containing Carbazole-Functionalized ,-DiketonatesCHEMPHYSCHEM, Issue 4 2008Zhiwei Liu Abstract Twelve iridium complexes with general formula of Ir(C^N)2(LX) [C^N represents the cyclometalated ligand, i.e. 2-(2,4-difluorophenyl) pyridine (dfppy), 2-phenylpyridine (ppy), dibenzo{f, h}quinoxaline (DBQ); LX stands for ,-diketonate, i.e. acetyl acetonate (acac), 1-(carbazol-9-yl)-5,5-dimethylhexane-2,4-diketonate (CBDK), 1-(carbazol-9-yl)-5,5,6,6,7,7,7-heptafluoroheptane-2,4-diketonate (CHFDK), 1-(N-ethyl-carbazol-3-yl)-4,4,5,5,6,6,6-heptafluorohexane-1,3-diketonate (ECHFDK)] are synthesized, characterized and their photophysical properties are systemically studied. In addition, crystals of Ir(DBQ)2(CHFDK) and Ir(DBQ)2(acac) are obtained and characterized by single crystal X-ray diffraction. The choice of these iridium complexes provides an opportunity for tracing the effect of the triplet energy level of ancillary ligands on the photophysical and electrochemical behaviors. Data show that if the triplet energy level of the ,-diketonate is higher than that of the Ir(C^N)2 fragment and there is no superposition on the state density map, strong 3LC or 3MLCT-based phosphorescence can be obtained. Alternatively, if the state density map of the two parts are in superposition, the 3LC or 3MLCT-based transition will be quenched at room temperature. Density functional theory calculations show that these complexes can be divided into two categories. The lowest excited state is mainly determined by C^N but not ,-diketonate when the difference between the triplet energy levels of the two parts is large. However, when this difference is very small, the lowest excited state will be determined by both sides. This provides a satisfactory explanation for the experimental observations. [source] Hydrothermal Synthesis, Crystal Structures and Photoluminescence of Two Novel Metal-organic Supramolecular Frameworks Based on Mixed Ligands of Dipyrazino[2,3- f:2,,3,-h]quinoxaline and Pyridine-2,5-dicarboxylic AcidCHINESE JOURNAL OF CHEMISTRY, Issue 9 2008Xiu-Li WANG Abstract Two novel metal-organic frameworks [Zn2(Dpq)2(2,5-pda)2(H2O)2]·2H2O (1) (dipyrazino[2,3- f:2,3,- h]quinoxaline=Dpq) and [Cd2(Dpq)2(2,5-pda)2]·2H2O (2) (pyridine-2,5-dicarboxylic acid=2,5-H2pda) have been obtained from hydrothermal reactions of two different metal(II) nitrates with the same mixed ligands Dpq and 2,5-H2pda, and structurally characterized by elemental analyses, TG, IR spectroscopy, and single-crystal X-ray diffraction analyse. Single-crystal X-ray analyses show that the metal ions are bridged by different coordination modes of 2,5-pda to form a dimer in 1, 2D rhombic grid in 2, respectively. In the compound 1, adjacent dimers are packed through hydrogen bonds and - aromatic stacking interactions to form a distorted , -Po supramolecular structure. In the compound 2, adjacent polymer layers are further linked by hydrogen bonds to form a distorted , -Po 3D supramolecular framework stabilized by - stacking interactions. The different structures of compounds 1 and 2 illustrate the influence of the metal ions and ligands on the self-assembly of polymeric coordination architectures. In addition, the title compounds exhibit blue emission in the solid state at room temperature. [source] Syntheses of Triostin A Antibiotic and Nucleobase-Functionalized Analogs as New DNA BindersEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 28 2009Anmol Kumar Ray Abstract A total synthesis of the natural product triostin A, wherein the N -methylated depsipeptide scaffold is constructed by solution-phase peptide chemistry followed by disulfide formation and macrocyclization, is described. Finally, the quinoxalines were attached to provide the DNA bisintercalator. Analogs of triostin A were obtained by the successive functionalization of the cyclic depsipeptide with pyrimidine or purine recognition units. The attachment of functional units was achieved by the orthogonal protection of the respective side chain amino functionalities. The nucleobase-functionalized triostin analogs have the potential to recognize double-stranded DNA by hydrogen bonding. The interaction with DNA was investigated by UV spectroscopy and fluorescence intercalator displacement. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] A New Synthesis of Push-Pull Pyrroles, Their Oxidation to Stable 3H -Pyrroles and an Unexpected Anellation ReactionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2009Gunther Buehrdel Abstract A new synthesis of push-pull pyrroles of type 5 was developed starting from bis(imidoyl chlorides) 1 and various iminodiacetic acid derivatives 3. The use of appropriate N -trifluoroacetyl residues as protecting/activating group proved to be the method of choice for the straightforward preparation of the 3,4-diarylamino-1H -pyrroles 5. When benzothiazole substructures are present in 2,5-position of heterocycles 5, a two-electron oxidation leads to 3H -pyrroles of type 6 in excellent yields. However, in the case of cyano or ester groups, a further oxidative process immediately led to the new 3H -pyrrolo[3,4- b]quinoxalines 7 via intramolecular ring anellation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Iridium-Difluorphos-Catalyzed Asymmetric Hydrogenation of 2-Alkyl- and 2-Aryl-Substituted Quinoxalines: A General and Efficient Route into TetrahydroquinoxalinesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Damien Cartigny Abstract A highly efficient and general iridium-difluorphos-catalyzed asymmetric hydrogenation of diverse 2-alkyl- and 2-aryl-substituted quinoxalines into biologically and pharmaceutically relevant 2-substituted-1,2,3,4-tetrahydroquinoxaline units has been developed. High isolated yields and excellent enantioselectivities of up to 95% for 2-alkyl-substituted quinoxalines and of up to 94% for 2-aryl-substituted quinoxalines were obtained. [source] Copper(I)-Catalyzed Synthesis of Novel 4-(Trifluoromethyl)-[1,2,3]triazolo[1,5- a]quinoxalines via Cascade Reactions of N -(o -Haloaryl)alkynylimine with Sodium AzideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 8 2010Zixian Chen Abstract Novel tricyclic 4-(trifluoromethyl)-[1,2,3]triazolo[1,5- a]quinoxalines were readily prepared from N -(o -haloaryl)alkynylimines and sodium azide via copper(I)-catalyzed tandem reactions. This synthetic strategy provides an efficient way to access a library of novel heterocyclic compounds that are of interest in drug discovery. [source] Asymmetric Hydrogenation of Quinoxalines Catalyzed by Iridium/PipPhosADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2009Abstract A catalyst made in situ from the (cyclooctadiene)iridium chloride dimer, [Ir(COD)Cl]2, and the monodentate phosphoramidite ligand (S)-PipPhos was used in the enantioselective hydrogenation of 2- and 2,6-substituted quinoxalines. In the presence of piperidine hydrochloride as additive full conversions and enantioselectivities of up to 96% are obtained. [source] Quinoxalines X,. a new and convenient synthesis of 1H -Pyrazolo [3,4- b] quinoxalines (Flavazoles)JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2001Gerhard Sarodnick Dedicated to Professor Gerhard Kempter on the occasion of his 70th birthday Quinoxaline-2-aldoximes and -ketoximes (6) react with hydrazine, alkylhydrazines or arylhydrazines under acidic conditions to afford lH -pyrazolo[3,4- b]quinoxalines (flavazoles) (1). Since the oximes (6) are easily available from phenylenediamine, the herein described methodology provides a convenient two step entry to various functionalized flavazoles. Furthermore, acylation and alkylation of the 1-unsubstituted lH -pyrazolo[3,4- b]quinoxalines 7 proceeds smoothly and in good yield to afford 31 different flavazoles 11 and 12. [source] Synthesis and properties of some 2,3-disubstituted 6-fluoro-7-(4-methyl-1-piperazinyl)quinoxalinesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2000Raid J. Abdel-Jalil The 2,3-disubstituted 6-fluoro-7-(4-methyl-1-piperazinyl)-quinoxalines (3,11) were synthesized for bioassay via reaction of 1.2-diamino-4-fluoro-5-(4-methyl-1-piperazinyl)benzene (2) with the appropriate 1,2-dicarbonyl compounds. However, none of the tested compounds 3,11 showed significant in vitro activ ity against E. coli ATCC11229, S. aureus ATCC6538 and C.albicans SATCC10231. [source] | |||||||||||||||||||||||||||||||