- Total Asymmetric Transformations at Interfaces with Centrosymmetric Cristals: Role of Hydrophobic and Kinetic Effects in the Crystallization of the System Glycine/α-Amino Acids
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A model of generation and amplification of optical activity, using the centrosymmetric crystals of glycine as substrates for total separation of occluded α-amino acids into enantiomeric territories, is described.The principle is based on the enantioselective occlusion of these additives through the enantiotopic (010) and (00) faces of glycine cristals.Such crystals, when floating at the air/solution interface, and if correctly oriented, may incorporate only one of the two enantiomeric additives present in solution.We demonstrate that complete (010) or (00) orientation may be induced by both kinetic and "hydrophobic" effects.The former is achieved through inhibition of nucleation and growth of the say (010) oriented crystals , by (S) amino acids in solution, while the latter is due to induction of (00) orientation by (S) hydrophobic amino acids.By symmetry the enantiomers induce opposite orientation.The two effects are investigated separately, and possible mechanisms are proposed.Combimation of the two effects, which operate in the same direction, allows total orientation of glycin crystals and thus triggering of amplification starting with a solution containing leucine with an enantiomeric excess as low as 6percent.The relevance of such a mechanism to other systems and to nucleation in general is discussed.
- Weissbuch, I.,Addadi, L.,Leiserowitz, L.,Lahav, M.
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- Creation of a broad-range and highly stereoselective D-amino acid dehydrogenase for the one-step synthesis of D-amino acids
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Using both rational and random mutagenesis, we have created the first known broad substrate range, nicotinamide cofactor dependent, and highly stereoselective D-amino acid dehydrogenase. This new enzyme is capable of producing D-amino acids via the reductive amination of the corresponding 2-keto acid with ammonia. This biocatalyst was the result of three rounds of mutagenesis and screening performed on the enzyme meso-diaminopimelate D-dehydrogenase. The first round targeted the active site of the wild-type enzyme and produced mutants that were no longer strictly dependent on the native substrate. The second and third rounds produced mutants that had an increased substrate range including straight-and branched-aliphatic amino acids and aromatic amino acids. The very high selectivity toward the D-enantiomer (95 to >99% ee) was shown to be preserved even after the addition of the five mutations found in the three rounds of mutagenesis and screening. This new enzyme could complement and improve upon current methods for D-amino acid synthesis.
- Vedha-Peters, Kavitha,Gunawardana, Manjula,Rozzell, J. David,Novick, Scott J.
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- Characterization of d-amino acid aminotransferase from Lactobacillus salivarius
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We searched a UniProt database of lactic acid bacteria in an effort to identify d-amino acid metabolizing enzymes other than alanine racemase. We found a d-amino acid aminotransferase (d-AAT) homologous gene (UniProt ID: Q1WRM6) in the genome of Lactobacillus salivarius. The gene was then expressed in Escherichia coli, and its product exhibited transaminase activity between d-alanine and α-ketoglutarate. This is the first characterization of a d-AAT from a lactic acid bacterium. L. salivarius d-AAT is a homodimer that uses pyridoxal-5′-phosphate (PLP) as a cofactor; it contains 0.91 molecules of PLP per subunit. Maximum activity was seen at a temperature of 60 °C and a pH of 6.0. However, the enzyme lost no activity when incubated for 30 min at 30 °C and pH 5.5 to 9.5, and retained half its activity when incubated at pH 4.5 or 11.0 under the same conditions. Double reciprocal plots of the initial velocity and d-alanine concentrations in the presence of several fixed concentrations of α-ketoglutarate gave a series of parallel lines, which is consistent with a Ping-Pong mechanism. The Km values for d-alanine and α-ketoglutarate were 1.05 and 3.78 mM, respectively. With this enzyme, d-allo-isoleucine exhibited greater relative activity than d-alanine as the amino donor, while α-ketobutylate, glyoxylate and indole-3-pyruvate were all more preferable amino acceptors than α-ketoglutarate. The substrate specificity of L. salivarius d-AAT thus differs greatly from those of the other d-AATs so far reported.
- Kobayashi, Jyumpei,Shimizu, Yasuhiro,Mutaguchi, Yuta,Doi, Katsumi,Ohshima, Toshihisa
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- ω-Transaminase-catalyzed asymmetric synthesis of unnatural amino acids using isopropylamine as an amino donor
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Isopropylamine is an ideal amino donor for reductive amination of carbonyl compounds by ω-transaminase (ω-TA) owing to its cheapness and high volatility of a ketone product. Here we developed asymmetric synthesis of unnatural amino acids via ω-TA-catalyzed amino group transfer between α-keto acids and isopropylamine.
- Park, Eul-Soo,Dong, Joo-Young,Shin, Jong-Shik
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- Asymmetric Transamination of α-Keto Acids Catalyzed by Chiral Pyridoxamines
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A new type of novel chiral pyridoxamines 3a-g containing a side chain has been developed. The pyridoxamines displayed catalytic activity and promising enantioselectivity in biomimetic asymmetric transamination of α-keto acids, to give various α-amino acids in 47-90% yields with up to 87% ee's under very mild conditions. An interesting effect of the side chain on enantioselectivity was observed in the reaction.
- Lan, Xiaoyu,Tao, Chuangan,Liu, Xuliang,Zhang, Aina,Zhao, Baoguo
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supporting information
p. 3658 - 3661
(2016/08/16)
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- Synthesis of α-Amino Acids via Asymmetric Phase Transfer-Catalyzed Alkylation of Achiral Nickel(II) Complexes of Glycine-Derived Schiff Bases
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Achiral, diamagnetic Ni(II) complexes 1 and 3 have been synthesized from Ni(II) salts and the Schiff bases, generated from glycine and PBP (7) and PBA (11), respectively, in MeONa/MeOH solutions. The requisite carbonyl-derivatizing agents pyridine-2-carboxylic acid(2-benzoyl-phenyl)-amide 7 (PBP) and pyridine-2-carboxylic acid(2-formyl-phenyl)-amide 11 (PBA) were readily prepared from picolinic acid and o-aminobenzophenone or picolinic acid and methyl o-anthranilate, respectively. The structure of 1 was established by X-ray crystallography. Complexes 1 and 3 were found to undergo C-alkylation with alkyl halides under PTC conditions in the presence of β-naphthol or benzyltriethylammonium bromide as catalysts to give mono- and bis-alkylated products, respectively. Decomposition of the complexes with aqueous HCI under mild conditions gave the required amino acids, and PBP and PBA were recovered. Alkylation of 1 with highly reactive alkyl halides, carried out under the PTC conditions in the presence of 10% mol of (S)- or (R)-2-hydroxy-2′ -amino-1,1′-binaphthyl 31a (NOBIN) and/or its N-acyl derivatives and by (S)- or (R)-2-hydroxy-8′-amino-1,1′-binaphthyl 32a (iso-NOBIN) and its N-acyl derivatives, respectively, gave rise to α-amino acids with high enantioselectivities (90-98.5% ee) in good-to-excellent chemical yields at room temperature within several minutes. An unusually large positive nonlinear effect was observed in these reactions. The Michael addition of acrylic derivatives 37 to 1 was conducted under similar conditions with up to 96% ee. The 1H NMR and IR spectra of a mixture of the sodium salt of NOBIN and 1 indicated formation of a complex between the two components. Implications of the association and self-association of NOBIN for the observed sense of asymmetric induction and nonlinear effects are discussed.
- Belokon, Yuri N.,Bespalova, Natalia B.,Churkina, Tatiana D.,Cisarova, Ivana,Ezernitskaya, Marina G.,Harutyunyan, Syuzanna R.,Hrdina, Radim,Kagan, Henri B.,Kocovsky, Pavel,Kochetkov, Konstantin A.,Larionov, Oleg V.,Lyssenko, Konstantin A.,North, Michael,Polasek, Miroslav,Peregudov, Alexander S.,Prisyazhnyuk, Vladimir V.,Vyskocil, Stepan
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p. 12860 - 12871
(2007/10/03)
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- Highly efficient catalytic synthesis of α-amino acids under phase-transfer conditions with a novel catalyst/substrate pair
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A facile and fast enantioselective synthesis of α-amino acids with high ee values was achieved by the asymmetric alkylation of the glycine derivative 1 under phase-transfer conditions with (R)-2-amino-2′-hydrozy-1,1′-binaphthyl (NOBIN; see sceme). The ee value of the amino acid products. This occures as a results of a significant positive nonlinear effect in the alkylation reaction.
- Belokon, Yuri N.,Kochetkov, Konstantin A.,Churkina, Tatiana D.,Ikonnikov, Nikolai S.,Larionov, Oleg V.,Harutyunyan, Syuzanna R.,Vyskocil, Stepan,North, Michael,Kagan, Henri B.
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p. 1948 - 1951
(2007/10/03)
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- ASYMMETRIC SYNTHESIS OF α-AMINO ACIDS FROM α-HALOGENATED 10-SULFONAMIDO-ISOBORNYL ESTERS.
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Treatment of chiral α-haloesters 2 with NaN3 gave azidoesters 3 wich on successive transesterification and hydrogenolysis furnished α-amino acids 5 and 9 in high e.e.
- Oppolzer, Wolfgang,Pedrosa, Rafael,Moretti, Robert
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p. 831 - 834
(2007/10/02)
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