- Analysis of crystallographic structures of Ni(II) complexes of α-amino acid Schiff bases: Elucidation of the substituent effect on stereochemical preferences
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In this study, we performed critical analysis of 13 crystallographic structures of various Ni(ii) complexes of amino acid Schiff bases. The major finding of this work is the significance of a parallel displaced type of aromatic interactions between o-amino-benzophenone and Pro N-benzyl rings. The quality of these aromatic interactions was shown to control the steric environment around the amino acid side-chain, rendering variously substituted Ni(ii) complexes of different thermodynamic stabilities. The discovered structural trend holds true for aliphatic, aromatic and sterically bulky amino acids and can be used for the rational design of new and more efficient chiral ligands for general asymmetric synthesis of tailor-made α-amino acids.
- Nian, Yong,Wang, Jiang,Moriwaki, Hiroki,Soloshonok, Vadim A.,Liu, Hong
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- The use of 4,4,4-trifluorothreonine to stabilize extended peptide structures and mimic β-strands
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Pentapeptides having the sequence R-HN-Ala-Val-X-Val-Leu-OMe, where the central residue X is L-serine, L-threonine, (2S, 3R)-L-CF3-threonine and (2S, 3S)-L-CF3-threonine were prepared. The capacity of (2S, 3S)- and (2S, 3R)-CF3
- Xu, Yaochun,Correia, Isabelle,Ha-Duong, Tap,Kihal, Nadjib,Soulier, Jean-Louis,Kaffy, Julia,Crousse, Beno?t,Lequin, Olivier,Ongeri, Sandrine
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p. 2842 - 2853
(2018/01/17)
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- Synthesis of a Chiral Nickel(II) Complex of an Electrophilic Glycinate, and its Use for Asymmetric Preparation of α-Amino Acids
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A chiral NiII complex of a Schiff's base derived from (S)-o-benzophenone and α-bromoglycine has been obtained and its stereoselective reaction with nucleophiles studied; the synthesis of aspartic acid with 80percent optical purity is described.
- Belokon', Yuri N.,Popkov, Aleksander N.,Chernoglazova, Nina I.,Saporovskaya, Marina B.,Bakhmutov, Vladimir I.,Belikov, Vasili M.
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p. 1336 - 1338
(2007/10/02)
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- General Method of Diastereo- and Enantioselective Synthesis of β-Hydroxy-α-amino Acids by Condensation of Aldehydes and Ketones with Glycine
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The condensation of formaldehyde with a Ni(II) complex of glicyne Schiff base with (S)-2-acetophenone (1) or (S)-2-benzophenone (2) in CH3OH at 25 deg C in the presence of Et3N yields (S)-Ser with an enantiomeric excess (ee) of 80-90percent.The same reaction gives rise to (R)-Ser with an ee greater than 80percent in the presence of more than 0.2 N CH3ONa, α-(hydroxymethyl) serine being formed in negligible quantities.The reaction of benzaldehyde, 3,4-(methilenedioxy)benzaldehyde, and acetaldehyde with these Gly complexes in 0.2 N CH3ONa at 25 deg C yields β-hydroxy-α-amino acids: (R)-β-phenylserine, (R)-3,4-(methylenedioxy)-β-phenylserine, and (R)-threonine, respectively, with a threo/allo ratio ranging from 10:1 up to over 50:1 and ee more than 80percent.Condensation with acetone yields (R)-β-hydroxyvaline with an enantiomeric purity of 70percent.The enantiomerically pure β-hydroxy-α-amino acids can be obtained from pure diastereomers, isolated by chromatography on silica or Toyopearl HW-60.The initial reagents 1 and 2 were recovered with 60-98percent yield.The stereochemical mechanism of the reaction is discussed.
- Belokon, Yuri N.,Bulychev, Alexander G.,Vitt, Sergei V.,Struchkov, Yuri T.,Batsanov, Andrei S.,et al.
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p. 4252 - 4259
(2007/10/02)
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