- Catalytic enantioselective synthesis of N,Cα,Cα-trisubstituted α-amino acid derivatives using 1H-imidazol-4(5H)-ones as key templates
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Abstract 1H-Imidazol-4(5H)-ones are introduced as novel nucleophilic α-amino acid equivalents in asymmetric synthesis. These compounds not only allow highly efficient construction of tetrasubstituted stereogenic centers, but unlike hitherto known templates, provide direct access to N-substituted (alkyl, allyl, aryl) α-amino acid derivatives. A BB method: 1H-imidazol-4(5H)-ones serve as effective and easily available α-amino acid surrogates for the catalytic and highly diastereo- and enantioselective direct construction of N-substituted quaternary α-amino acid derivatives. The reaction is catalyzed by a Br?nsted base (BB) and proceeds with different Michael acceptors. EWG=electron-withdrawing group.
- Etxabe, Julen,Izquierdo, Joseba,Landa, Aitor,Oiarbide, Mikel,Palomo, Claudio
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supporting information
p. 6883 - 6886
(2015/06/08)
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- Resolution of racemic N-benzyl α-amino acids by liquid-liquid extraction: A practical method using a lipophilic chiral cobalt(III) salen complex and mechanistic studies
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The efficient resolution of racemic N-benzyl α-amino acids (N-Bn-AA) has been achieved by a liquid-liquid extraction process using the lipophilic chiral salen-cobalt(III) complex [CoIII(3)(OAc)]. As a result of the resolution by extraction, one enantiomer (S) of the N-benzyl α-amino acid predominated in the aqueous phase, while the other enantiomer (R) was driven into the organic phase by complexation to cobalt. The complexed amino acid (R) was then quantitatively released by a reductive (CoIII→Co II) counter-extraction with aqueous sodium dithionite or L-ascorbic acid in methanol. The reductive cleavage allowed to recover the [Co II(3)] complex in good yield, which could be easily re-oxidized to [CoIII(3)(OAc)] with air/AcOH and reused with essentially no loss of reactivity and selectivity. Investigation on the nitrogen substitution indicates that the presence of a single benzyl group on the amino acid nitrogen is important to obtain high enantioselectivity in the extraction process. The kinetic vs. thermodynamic nature of the resolution process was also investigated with an enantiomeric exchange experiment, which shows that the liquid-liquid extraction with [CoIII(3)-(OAc)] is an equilibrium process operating under thermodynamic control. In the absence of a suitable crystal structure of the [CoIII(3)(N-Bn-AA)] complexes, computational and spectroscopic studies were used to investigate how the N-benzyl α-amino acids are accommodated in the "binding pocket" of the chiral cobalt complex. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Dzygiel, Pawel,Reeve, Toby B.,Piarulli, Umberto,Krupicka, Martin,Tvaroska, Igor,Gennari, Cesare
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supporting information; experimental part
p. 1253 - 1264
(2009/04/07)
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- Preparation of N-Z-protected N-methylated amino acids
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A process for preparing N-protected N-alkylated amino acids of the formula I: in which the substituents have the meanings stated in the description, comprises mixing a compound of the formula II with a solution of potassium tert-butanolate in a non-protic organic solvent, and subsequently adding a C1-2-alkyl halide.
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- Synthesis and utilization of a novel glycine derived chiral precursor, based on a recyclable L-prolinol auxiliary, for the enantioselective preparation of α-amino acids and their N-methyl derivatives
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α-Amino acids and their N-methyl derivatives are synthesized in fairly high optical purity employing a new glycine derived template based on a recyclable L-prolinol chiral auxiliary.
- Pandey,Reddy,Das
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p. 3175 - 3178
(2007/10/03)
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- REACTION OF ATOMIC CARBON WITH AMMONIA. THE MECHANISM OF FORMATION OF AMINO ACID PRECURSORS.
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The reaction of arc-generated carbon atoms with ammonia have been investigated. Primary reactions of C//1 are NH insertion and hydrogen abstraction. The NH insertion leads to methyleneamine (1) and HCN. The hydrogen abstraction proceeds in a stepwise manner to generate CH//2, which reacts with NH//3 to produce CH//3NH//2. Hydrolysis of the nonvolatile residue from this reaction produces the amino acids glycine, alanine, N-methylglycine, beta -alanine, and aspartic acid. Serine is also formed when H//2O is included with the reactants. The mechanism of formation of the amino acid precursors is discussed. Labeling experiments (**2H and **1**3C) rule out a hydrogen cyanide polymer as a major precursor to the amino acids. These studies may provide information on extraterrestrial amino acids. Refs.
- Shevlin,McPherson,Melius
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p. 488 - 491
(2007/10/02)
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- SYSTEMES DE STRECKER ET APPARENTES - XI FORMATION ET STABILITE DE L'α-CARBOXYAMINONITRILE. INTERMEDIAIRE ESSENTIEL DANS LA SYNTHESE DES HYDANTOINES SELON BUCHERER-BERGS
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The determination of the structure of the intermediate in the Bucherer-Bergs reaction (the transformation in aqueous solution of an aldehyde into the corresponding amino-acid via the hydantoin) showed that this reaction involved the formation of α-aminonitrile carbamate.The slow formation of the carbonic anhydride from the carbonate buffer limited the formation of that main intermediate which was in equilibrium with the α-aminonitrile.The variation of the stability of the carbamate vs pH is mainly determined by the concentration of CO2 dissolved in the mixture, but also by the equilibrated formation of products formed by the degradation of α-aminonitrile, i.e. the aminodinitrile and the cyanohydrin.
- Rousset, A.,Lasperas, M.,Taillades, J.,Commeyras, A.
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p. 2649 - 2661
(2007/10/02)
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