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Wiesław Wiczk - One of the best experts on this subject based on the ideXlab platform.
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Influence of alkyl group on amide Nitrogen Atom on fluorescence quenching of tyrosine amide and N-acetyltyrosine amide
Biophysical Chemistry, 2004Co-Authors: Justyna Mrozek, Alicja Rzeska, Katarzyna Guzow, Jerzy Karolczak, Wiesław WiczkAbstract:Abstract The steady-state and time-resolved fluorescence spectroscopy was applied to determine the influence of an alkyl substituent(s) (methyl or ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, or t-butyl) on amide Nitrogen Atom on photophysical properties of tyrosine and N-acetyltyrosine amides in water. Generally, the amide group strongly quenches the fluorescence of tyrosine, however, the size and number of substituents on amide Nitrogen Atom modify the quenching process only in small degree. The fluorescence intensity decays of all amides studied are bi-exponential. The contribution of both components (αi) to the fluorescence decay undergoes irregular change. An introduction of alkyl substituent on amide Nitrogen Atom causes an increase of the fluorescence lifetime of tyrosine derivative compared to the unsubstituted amide for both N-acetyltyrosine and tyrosine with the protonated amino group. Calculated, basing on the fluorescence quantum yield (QY) and average lifetime, the radiative rate constants (kf) are similar, which indicates that the substituent(s) does not have substantial influence on radiative process of the deactivation of the excited state of the phenol chromophore for all compounds studied regardless the amino group status as well as the number and type of substituent (linear or branched). The comparison of the ground-state rotamer populations of tyrosine amides and N-acetyltyrosine amides with different alkyl substituent on amide Nitrogen Atom obtained from 1H NMR with the value of pre-exponential factors indicates that not the rotamer populations, but specific hydration of a whole molecule of the amino acid including chromophore and amino acid moiety, seems to be the main reason of the heterogenous fluorescence intensity decay of tyrosine derivatives.
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Influence of a substituent on amide Nitrogen Atom on fluorescence efficiency quenching of Tyr(Me) by amide group
Journal of Photochemistry and Photobiology A-chemistry, 2001Co-Authors: Joanna Łukomska, Alicja Rzeska, Joanna Malicka, Wiesław WiczkAbstract:An amide group quenches the O-methyl-tyrosine fluorescence with higher efficiency than that of tyrosine because of a lower ionization potential of the former. The influence of methyl substituents on an amide Nitrogen Atom of Tyr(Me) amide, as well as distance dependence of the efficiency of fluorescence quenching by an additional amide group in Tyr(Me)-Gly dipeptide supported suggestion that the photo-induced electron transfer from the excited fluorophore to an amide group is responsible for the fluorescence quenching of aromatic amino acid residue by an amide (peptide) group. The mono-exponential fluorescence intensity decay of Tyr(Me)-NHMe and much lower quenching efficiency than that observed for other Tyr(Me) derivatives studied, indicate that specific hydration of the whole molecule plays a crucial role in the fluorescence quenching process.
M. A. Yurovskaya - One of the best experts on this subject based on the ideXlab platform.
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synthesis of 2 phenyl 4 5 6 7 tetrahydro 1h indoles with a chiral substituent at the Nitrogen Atom
Chemistry of Heterocyclic Compounds, 2012Co-Authors: Ivan A Andreev, Alexander V. Kurkin, I O Ryzhkov, M. A. YurovskayaAbstract:An efficient method has been developed for the enantioselective synthesis of 2-phenyl-4,5,6,7-tetra-hydro-1H-indoles containing chiral substituents at the Nitrogen Atom. It is based on opening of the epoxide fragment of 1-phenylethynyl-7-oxabicyclo[4.1.0]heptane with chiral amines and/or amino acid esters followed by intramolecular, metal catalyzed cyclization.
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Synthesis of imidazo[4,5-b]pyridines with a chiral substituent at the Nitrogen Atom and their conversion to piperazine derivatives
Chemistry of Heterocyclic Compounds, 2012Co-Authors: K. V. Bukhryakov, Alexander V. Kurkin, M. A. YurovskayaAbstract:Imidazopyridine and benzimidazole derivatives have been prepared with chiral substituents at the Nitrogen Atom and have been converted to the corresponding condensed structures fused with a piperazine ring. A method has been developed for the synthesis of novel class of compounds – 6,7,8,9-tetra-hydropyrido[3',2':4,5]imidazo[1,2-a]pyrazine derivatives.
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New strategies for the synthesis of N-alkylated indoles (Review)
Chemistry of Heterocyclic Compounds, 2012Co-Authors: A. V. Karchava, Ferdinand S Melkonyan, M. A. YurovskayaAbstract:New data, mostly published in the last five years, on methods for the synthesis of N -alkylated indoles both as a result of direct introduction of the alkyl substituent at the Nitrogen Atom and by construction of the indole heterocyclic system are reviewed. Only examples of indole derivatives containing branched, sterically hindered, and chiral alkyl substituents at the Nitrogen Atom are discussed.
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Use of the α-amination reaction for the synthesis of pyrazole derivatives containing carbo- and heterocyclic substituents on the Nitrogen Atom
Chemistry of Heterocyclic Compounds, 2012Co-Authors: A. A. Utkina, A. V. Kurkin, M. A. YurovskayaAbstract:A method has been developed for the synthesis of pyrazoles with carbo- and heterocyclic substituents on the Nitrogen Atom based on the α-amination reaction of carbo- and heterocyclic ketones, using azodicarboxylate–L-proline system with subsequent interaction with malonodialdehyde tetramethyl-acetal. In the case of carbocyclic ketones and tetrahydro-γ-pyranone, the reaction occurs stereo-selectively to give chiral hydrazines and pyrazoles. With derivatives of piperidin-4-one, α-amination is accompanied by racemization.
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Comparative study of the different approaches to the synthesis of isatins with a chiral substituent at the Nitrogen Atom
Chemistry of Heterocyclic Compounds, 2011Co-Authors: Alexander V. Kurkin, Anna A. Bernovskaya, M. A. YurovskayaAbstract:Through a comparative study of three different routes to the synthesis of isatins with a chiral substituent on the Nitrogen Atom it has been shown that better results for preparing the isatins are achieved using the Sandmeyer (>99% ee , yield 50%) rather than the Stolle method (95% ee , yield 16%). The procedure proposed by Gassman for preparing isatins was unsuitable for the compounds described.
Toshiaki Murai - One of the best experts on this subject based on the ideXlab platform.
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thioamide dianions derived from n arylmethyl thioamides generation and application as carbon nucleophiles adjacent to the Nitrogen Atom
Pure and Applied Chemistry, 2010Co-Authors: Toshiaki MuraiAbstract:This review illustrates the ready availability of thioamide dianions and their versa- tility as carbon nucleophiles adjacent to the Nitrogen Atom. The products derived from the ad- dition of thioamide dianions to a range of electrophiles can participate in a cyclization reac- tion to form Nitrogen-containing heterocycles. The electronic properties of thioamide dianions are also considered.
Kang Zhao - One of the best experts on this subject based on the ideXlab platform.
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intramolecular functionalization of benzylic methylene adjacent to the ring Nitrogen Atom in n aryltetrahydroisoquinoline derivatives
Journal of Organic Chemistry, 2016Co-Authors: Liu Yang, Daisy Zhangnegrerie, Kang ZhaoAbstract:Functionalization at the benzylic methylene group that is adjacent to the ring Nitrogen Atom in a series of N-aryltetrahydroisoquinoline compounds has been realized through intramolecular cross-dehydrogenative coupling reactions. The presented transformation provided straightforward access to the formation of C(sp3)–Y (Y = C, N or O) bond via I(III) reagent.
Shinji Murai - One of the best experts on this subject based on the ideXlab platform.
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ru3 co 12 catalyzed coupling reaction of sp3 c h bonds adjacent to a Nitrogen Atom in alkylamines with alkenes
Journal of the American Chemical Society, 2001Co-Authors: Naoto Chatani, Taku Asaumi, Shuhei Yorimitsu, Tsutomu Ikeda, And Fumitoshi Kakiuchi, Shinji MuraiAbstract:Catalytic reactions which involve the cleavage of an sp3 C−H bond adjacent to a Nitrogen Atom in N-2-pyridynyl alkylamines are described. The use of Ru3(CO)12 as the catalyst results in the addition of the sp3 C−H bond across the alkene bond to give the coupling products. A variety of alkenes, including terminal, internal, and cyclic alkenes, can be used for the coupling reaction. The presence of directing groups, such as pyridine, pyrimidine, and an oxazoline ring, on the Nitrogen of the amine is critical for a successful reaction. This result indicates the importance of the coordination of the Nitrogen Atom to the ruthenium catalyst. In addition, the nature of the substituents on the pyridine ring has a significant effect on the efficiency of the reaction. Thus, the substitution of an electron-withdrawing group on the pyridine ring as well as a substitution adjacent to the sp2 Nitrogen in the pyridine ring dramatically retards the reaction. Cyclic amines are more reactive than acyclic ones. The choice o...
