- 2,4,5-Trimethylimidazolium Scaffold for Anion Recognition Receptors Acting Through Charge-Assisted Aliphatic and Aromatic C-H Interactions
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A series of two-armed 2,4,5-trimethylimidazolium-based oxoanion receptors, which incorporate two end-capped photoactive anthracene rings, being the central core an aromatic or heteroaromatic ring, has been designed. In the presence of HP2O73-, H2PO4-, and SO42- anions, 1H- and 31P NMR spectroscopical data clearly indicate the simultaneous occurrence of several charge-assisted aliphatic and aromatic C-H noncovalent interactions, i.e., significant downfield shifts were observed for the imidazolium C(2)-CH3 protons, the methylene N-CH2 protons, and the inner aromatic proton or the outer heteroaromatic protons. Density functional theory calculations confirm the occurrence of these noncovalent interaction and suggest that the interaction between the anions and the receptors is mainly electrostatic in nature.
- Sabater, Paula,Zapata, Fabiola,Caballero, Antonio,Fernández, Israel,Ramirez De Arellano, Carmen,Molina, Pedro
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- Lewis Pair Polymerization of Epoxides via Zwitterionic Species as a Route to High-Molar-Mass Polyethers
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A dual catalytic setup based on N-heterocyclic olefins (NHOs) and magnesium bis(hexamethyldisilazide) (Mg(HMDS)2) was used to prepare poly(propylene oxide) with a molar mass (Mn) >500 000 g mol?1, in some cases even >106 g mol?1, as determined by GPC/light scattering. This is achieved by combining the rapid polymerization characteristics of a zwitterionic, Lewis pair type mechanism with the efficient epoxide activation by the MgII species. Transfer-to-monomer, traditionally frustrating attempts at synthesizing polyethers with a high degree of polymerization, is practically removed as a limiting factor by this approach. NMR and MALDI-ToF MS experiments reveal key aspects of the proposed mechanism, whereby the polymerization is initiated via nucleophilic attack by the NHO on the activated monomer, generating a zwitterionic species. This strategy can also be extended to other epoxides, including functionalized monomers.
- Walther, Patrick,Krau?, Annabelle,Naumann, Stefan
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supporting information
p. 10737 - 10741
(2019/07/04)
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- Syntheses of polyalkylated imidazoles
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We have developed improved general simple methods for large-scale preparation of polyalkylated imidazoles by improved multicomponent synthesis from commercially available starting materials. A large range of NH- and N-alkyl-polyalkylimidazoles (40 in total, including novel compounds) has been synthesized.
- Evjen, Sigvart,Fiksdahl, Anne
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supporting information
p. 1392 - 1399
(2017/07/25)
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- Phosphine Supported Ruthenium Nanoparticle Catalyzed Synthesis of Substituted Pyrazines and Imidazoles from α-Diketones
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A new methodology has been developed for the synthesis of highly substituted nitrogen heterocycles such as pyrazines and imidazoles starting from α-diketones using phosphine supported ruthenium nanoparticles (RuNPs) as catalysts. Ruthenium nanoparticles Ru1-Ru4 supported with different phosphines such as dbdocphos, dppp, DPEphos, and Xantphos are screened, of which Ru1 and Ru4 are found to be the most active. Interestingly, aryl-substituted and alkyl-substituted α-diketones produced different products: namely, pyrazine and imidazoles, respectively. This reaction methodology has been applied to the synthesis of a key intermediate (2m) of the marine cytotoxic natural product Dragmacidin B and an estrogen receptor (2l). This work represents the first examples of pyrazines prepared by RuNPs.
- Ganji, Prasad,Van Leeuwen, Piet W. N. M.
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p. 1768 - 1774
(2017/02/10)
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- One-pot synthesis of polysubstituted imidazoles from arylaldehydes in water catalyzed by nhc using microwave irradiation
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A simple, high yielding synthesis of tri (3a-i) and tetrasubstituted (4a-g) imidazols from aldehydes is described. The cornerstone of this methodology involves the condensation of NH4OAc, substituted aldehydes, and benzoin, which is synthesized in situ from aldehydes catalyzed by N-heterocyclic carbine (NHC), under microwave irradiation in water to afford trisubstituted imidazoles (3a-i). If arylamine is added in the solution, tetrasubstituted imidazoles (4a-g) can be obtained. Lepidilines B and trifenagrel are also synthesized in high yield using this procedure. All the experiment deta are in agreement with the literature.
- Wu, Lei,Jing, Xiaobi,Zhu, Hongxiang,Liu, Yinlin,Yan, Chaoguo
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p. 1204 - 1207
(2013/03/28)
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- QUINOLONES USEFUL AS INDUCIBLE NITRIC OXIDE SYNTHASE INHIBITORS
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The present invention relates to novel quinolones of Formula I that inhibit inducible NOS synthase together with methods of synthesizing and using the compounds including methods for inhibiting or modulating nitric oxide synthesis and/or lowering nitric oxide levels in a patient by administering the compounds for the treatment of disease.
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Page/Page column 109
(2008/12/06)
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- Efficient synthesis of imidazoles from aldehydes and 1,2-diketones using microwave irradiation
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A simple, high-yielding synthesis of 2,4,5-trisubstituted imidazoles from 1,2-diketones and aldehydes in the presence of NH4OAc is described. Under microwave irradiation, alkyl-, aryl-, and heteroaryl-substituted imidazoles are formed in yields ranging from 80 to 99%. Short syntheses of lepidiline B and trifenagrel illustrate the utility of this approach.
- Wolkenberg, Scott E.,Wisnoski, David D.,Leister, William H.,Wang, Yi,Zhao, Zhijian,Lindsley, Craig W.
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p. 1453 - 1456
(2007/10/03)
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- Synthesis, acidity and 19F NMR characteristics of imidazoles bearing 1-fluorinated substituents with potential application as probes for intracellular pH determination.
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A series of 1-substituted imidazoles containing fluorine have been prepared. These compounds were identified as potentially useful probes for intracellular pH determination based on 19F NMR. Key parameters including pK(a), 19F NMR chemical shift sensitivity, water solubility and low toxicity were identified and included in the target molecule selection process. The pK(a) and 19F NMR parameters of the molecules are reported and trends analysed.
- Harper, Jacquie L.,Smith, Robin A. J.,Bedford, Jennifer J.,Leader, John P.
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p. 8211 - 8224
(2007/10/03)
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- Synthesis and Reactions of 1,2,4,5-Tetramethylimidazole; the Crystal Structure of Pentamethylimidazolium Iodide
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1,2,4,5-Tetramethylimidazole Derivatives, Synthesis, X-Ray1,2,4,5-Tetramethylimidazole (3) is obtained by metalation of 2,4,5-trimethylimidazole (2) with sodium in liquid ammonia and subsequent addition of methyl iodide. 3 reacts with Lewis acids to form the compounds Me4C3N2*BH3 (8) and Me4C3N2*E+ (4, 5, 7, 10; E = Me, H, SiMe3, C(O)Me).The X-ray structure reveals the ionic nature of pentamethylimidazolium iodide (4) in the solid state.
- Kuhn, Norbert,Henkel, Gerald,Kreutzberg, Joerg
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p. 1706 - 1712
(2007/10/02)
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- Hydrolysis of Imidazole-Containing Amide Acetals
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N-(Dialkoxymethyl)imidazoles (amide acetals 1a-c) are shown to hydrolyze by a common mechanism between pH 1 and pH 11 that involves preequilibrium protonation of the imidazole distal N, followed by rate-llimiting C - N cleavage.The Broensted plot of the log C - N cleavage rate vs. pKa of the parent imidazole has a slope of -1.0 and suggest a transition sate in which (+) is nearly completely transferred to the departing dialkoxymethyl group.Throughout the pH range studied, C - N cleavage is the dominant process.The bicyclic amide acetal 2 formed from 4(5)-(hydroxyethyl)imidazole and triethyl orthoformate behaves similarly to the acyclic cases at pHs > 5 except that the observed rate of C - N cleavage for the former is depressed by (1 - 2) x 102-fold.This apparent reduction of C - N cleavage rate is analyzed in terms of reversibility of the ring opening.Such reversal is demonstrated by the ability of good nucleophiles such as N3- or H2NOH to trap the open ion, preventing reversal and hence increasing the apparent rate of loss of 2.From pH 0 to pH 5, an additional sigmoidal event in the pH/log kobsd profile for 2 is observed, which is analyzed as a protonation of the imidazole of the open ion.Such a protonation prevents the reversible reclosure and concomitantly increases the kobsd.Bicyclic 2 can be taken as a model for the tetrahedral intermediate formed during intramolecular alcoholysis of an N-acylimidazole or intramolecular attack of an imidazole on an ester.
- Brown, R. S.,Ulan, J. G.
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p. 2382 - 2388
(2007/10/02)
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- Application of the Bucherer Hydantoin Synthesis to Diacetyl Mono-oxime. The Mechanism of the Bucherer Reaction, and the Constitution of the Hypothetical 'Dimethylbishydantoin' of Bucherer and Lieb
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The major product obtained when the Bucherer conditions for hydantoin synthesis were applied to diacetyl mono-oxime was (3aRS,6aSR)-6-amino-1,3,3a,6a-tetrahydro-1-hydroxy-3a,6a-dimethylpyrroloimidazole-2,4-dione (3).Two minor products (7) and (9) are related to (3) but a third, the imidazole 1-oxide (10), is not.Compound (10) was obtained from diacetyl mono-oxime and ammonium carbonate in the absence of cyanide.It is proposed that 4,4-disubstituted 5-imino-oxazolidin-2-ones (18), postulated by Bucherer and Steiner to be intermediates in hydantoin syntheses, rearrange to hydantoins by a base catalysed E1cB mechanism.It is further proposed that (3) is the hypothetical 'dimethylbishydantoin' (35) reported by Bucherer and Lieb in 1934.
- Bowness, W. Gary,Howe, Ralph,Rao, Balbir S.
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p. 2649 - 2653
(2007/10/02)
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