- A Simple Chiral Cu(II) Complex as an Effective Phase-Transfer Catalyst for the Enantioselective Alkylation of Dissymmetric Glycinate Ketimines
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Catalytic asymmetric benzylation of a dissymmetric tert-butylglycinate ketimine, incorporating 1-naphthyl and phenyl groups as the Schiff base substituents, under phase-transfer conditions was investigated. It was interesting to note that the sense of asymmetric induction of the alkylation of Z-imine stereoisomer is opposite to that of the corresponding E stereoisomer with a similar degree of enantioselectivity. More interestingly, the chiral Cu(II) complex of the Schiff base derived from (R)-2-phenylglycinol and 2-hydroxy-1-naphthaldehyde was found to catalyze the same reaction under solid-liquid conditions with comparable enantioselectivity (up to 60% ee) with respect to known cinchona alkaloid catalysts. The solvent/base-system parameter was shown to control the optimal catalytic activity. Chirality 27:944-950, 2015.
- Bafqiren, Hanane,Zouihri, Hafid,Gmouh, Said,Jamal Eddine, Jamal
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p. 944 - 950
(2015/11/16)
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- COMPOSITIONS AND METHODS FOR CYCLOFRUCTANS AS SEPARATION AGENTS
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The present invention relates to derivatized cyclofructan compounds, compositions comprising derivatized cyclofructan compounds, and methods of using compositions comprising derivatized cyclofructan compounds for chromatographic separations of chemical species, including enantiomers. Said compositions may comprise a solid support and/or polymers comprising derivatized cyclofructan compounds.
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Page/Page column 45-49; 60
(2010/12/31)
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- Chiral salen-metal complexes as novel catalysts for the asymmetric synthesis of α-amino acids under phase transfer catalysis conditions
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Chiral salen-metal complexes have been tested as catalysts for the C-alkylation of Schiff's bases of alanine and glycine esters with alkyl bromides under phase-transfer conditions (solid sodium hydroxide, toluene, ambient temperature, 1-10 mol% of the catalyst). The best catalyst, which was derived from a Cu(II) complex of (1R, 2R or 1S,2S)-[N,N′-bis(2′-hydroxybenzylidene)]-1,2-diaminocyclohexane, gave α-amino and α-methyl-α-amino acids with enantiomeric excesses of 70-96%.
- Belokon, Yuri N,North, Michael,Churkina, Tatiana D,Ikonnikov, Nikolai S,Maleev, Victor I
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p. 2491 - 2498
(2007/10/03)
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- STUDIES ON AMINO ACIDS AND PEPTIDES X. HPLC-MEDIATED TEST OF 2,4-BIS(4-METHOXYPHENYL)-1,3,2,4-DITHIADIPHOSPHETANE 2,4-DISULFIDE (LAWESSONS'S REAGENT) AS A RACEMIZATIONFREE COUPLING REAGENT IN PEPTIDE SYNTHESIS
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The easily available 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (Lawesson's Reagent), 1, has been tested as a coupling reagent for racemization in peptide synthesis.The assay procedure is separation of stereomeric products by HPLC.Z-S-Pro-S-Val-S-Pro-OtBu and Z-S-Leu-S-Phe-S-Val-OtBu have been used as test peptides in 2+1 segment couplings, and only a small amount of epimerization (0.5 and 0.1percent, respectively) has been observed.
- Thorsen, M.,Andersen, T. P.,Pedersen, U.,Yde, B.,Lawesson, S.-O.,Hansen. H. F.
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p. 5633 - 5636
(2007/10/02)
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