- Helix-forming propensity of aliphatic urea oligomers incorporating noncanonical residue substitution patterns
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Aliphatic N,N′-linked oligoureas are peptidomimetic foldamers that adopt a well-defined helical secondary structure stabilized by a collection of remote three-center H-bonds closing 12- and 14-membered pseudorings. Delineating the rules that govern helix formation depending on the nature of constituent units is of practical utility if one aims to utilize this helical fold to place side chains in a given arrangement and elaborate functional helices. In this work, we tested whether the helix geometry is compatible with alternative substitution patterns. The central -NH-CH(R)-CH2-NH-CO- residue in a model oligourea pentamer sequence was replaced by guest units bearing various substitution patterns [e.g., -NH-CH2-CH2-NH-CO-, -NH-CH2-CH(R)-NH-CO-, and -NH-CH(R1)-CH(R 2)-NH-CO-], levels of preorganization (cyclic vs acyclic residues), and stereochemistries, and the helix formation was systematically assessed. The extent of helix perturbation or stabilization was primarily monitored in solution by Fourier transform IR, NMR, and electronic circular dichroism spectroscopies. Our results indicate that although three new substitution patterns were accommodated in the 2.5-helix, the helical urea backbone in short oligomers is particularly sensitive to variations in the residue substitution pattern (position and stereochemistry). For example, the trans-1,2- diaminocyclohexane unit was experimentally found to break the helix nucleation, but the corresponding cis unit did not. Theoretical calculations helped to rationalize these results. The conformational preferences in this series of oligoureas were also studied at high resolution by X-ray structure analyses of a representative set of modified oligomers.
- Pendem, Nagendar,Douat, Celine,Claudon, Paul,Laguerre, Michel,Castano, Sabine,Desbat, Bernard,Cavagnat, Dominique,Ennifar, Eric,Kauffmann, Brice,Guichard, Gilles
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supporting information
p. 4884 - 4892
(2013/05/09)
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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; 59
(2010/12/31)
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- Use of enantiomerically pure 7-azabicyclo[2.2.1]heptan-2-ol as a chiral template for the synthesis of aminocyclitols
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(Chemical Equation Presented) Using enantiopure 7-azabicyclo[2.2.1]heptane- 2-ol, the synthesis of cis- as well as trans-2-aminocyclohexanols, dihydroconduramine E-1, and ent-conduramine F-1 has been described.
- Pandey, Ganesh,Tiwari, Keshri Nath,Puranik
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supporting information; scheme or table
p. 3611 - 3614
(2009/05/07)
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- Resolution of racemic 2-aminocyclohexanol derivatives and their application as ligands in asymmetric catalysis
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A preparatively easy and efficient protocol for the resolution of racemic 2-aminocyclohexanol derivatives is described, delivering both enantiomers with >99% enantiomeric excess (ee) by sequential use of (R)- and (S)-mandelic acid. A simple aqueous workup procedure permits the isolation of the amino alcohols in analytically pure form and the almost quantitative recovery of mandelic acid. Debenzylation of enantiopure trans-2-(N-benzyl)amino-1- cyclohexanol by hydrogenation and subsequent derivatization give access to a broad variety of diversely substituted derivatives. Furthermore, the corresponding cis isomers are readily available. Applications of these optically active aminocyclohexanols in catalyzed asymmetric phenyl transfer reactions to benzaldehydes and transfer hydrogenations of aryl ketones lead to products with up to 96% ee.
- Schiffers, Ingo,Rantanen, Toni,Schmidt, Frank,Bergmans, Werner,Zani, Lorenzo,Bolm, Carsten
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p. 2320 - 2331
(2007/10/03)
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- Kinetic resolution of amino alcohol derivatives with a chiral nucleophilic catalyst: Access to enantiopure cyclic cis-amino alcohols
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Acylative kinetic resolution of racemic cyclic cis-amino alcohol derivatives with a chiral nucleophilic catalyst proceeds enantioselectively (s = 10-21) at ambient temperature to give enantiopure recovered materials, and the % conversion of the acylation can be readily controlled by the amount of acid anhydride.
- Kawabata,Yamamoto,Momose,Yoshida,Nagaoka,Fuji
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p. 2700 - 2701
(2007/10/03)
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- Lipase-catalyzed Kinetic Resolution of (+/-)-trans- and cis-2-Azidocycloalkanols
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The lipase-catalyzed kinetic resolution of trans- and cis-2-azidocycloalkanols and the preparation of enantiomerically pure trans- and cis-2-aminocycloalkanols are described. Four kinds of lipases were screened for the acetylation of trans- and cis-2-azidocycloalkanols. Among them, Pseudomonas sp. lipases (lipase PS and lipase AK, Amamo Pharmaceutical Co.) showed the highest enantioselectivity. These products were converted to the corresponding 2-aminocycloalkanols to determine their enantiomeric excess (ee) and absolute configurations by HPLC and CD analyses, using (S)-TBMB carboxylic acid [(S)-2-tert-butyl-2-methyl-1,3-benzodioxole-4-carboxylic acid] as the chiral conversion reagent. The results of the CD analysis proved N,O-bis-(S)-TBMB carboxylated cis-2-aminocycloalkanols to adopt a predominantly N-equatorial conformation. The partially resolved trans- and cis-2-aminocycloalkanols, except for trans-2-aminocyclopentanol, were recrystallized from ethyl acetate to give enantiomerically pure forms.
- Ami, Ei'ichi,Ohrui, Hiroshi
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p. 2150 - 2156
(2007/10/03)
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- Diastereo- and enantioselective synthesis of cis-2- hydroxycyclohexanamine and corresponding ethers by asymmetric reductive amination
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A series of homochiral cis-2-alkoxy- and 2-aryloxyeyclohexanamines 5b- 5e has been synthesised by means of asymmetric reductive amination of the corresponding racemic 2-oxygenated cyclohexanones 2 with ee-values ranging from 95 to >99%. The respective 2-hydroxy and 2-cyclohexyl derivatives 5g-5h have been prepared from the 2-phenoxycyclohexanamine 4e. Relative and absolute stereochemistry has been elucidated.
- Lauktien, Gerhard,Volk, Franz-J,Frahm, August W.
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p. 3457 - 3466
(2007/10/03)
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