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  • 1
    Electronic Resource
    Electronic Resource
    Amphiphilic proline and prolylproline derivatives in the rhodium(I)-catalyzed asymmetric hydrogenation in water: Chiral induction as indication of the location of reactants within the micelle (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 754-759 
    Details
    ISSN: 0899-0042
    Keywords: solubilization ; enhanced enantioselectivity ; chiral induction ; critical micellar concentration ; reaction place ; function of proline ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proline and prolylproline dipeptide derived surfactants promote the asymmetric hydrogenation of (Z)-methyl α-acetamidocinnamate in water in the presence of the catalytic system [Rh(cod)2]BF4 + BPPM. Activity and enantioselectivity are enhanced significantly and the results in water are similar to those obtained with organic solvents. The possibility of a chiral induction was investigated in the presence of the optically active amino acid and peptide amphiphiles and an achiral rhodium catalyst [Rh(bdpb)(cod)]BF4. The analysis of the low optical induction gave some indications of the site where the reaction takes place within the micelle. Selected critical micelle concentrations (cmc) of the new prepared surfactants were determined by surface tension measurements. Chirality 10:754-759, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Asymmetric Hydrogenation of Amino Acid Precursors promoted by a new type of cholesterol amphiphiles: Investigation of aggregation behaviour and stereoselective effects (1996)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 338 (1996), S. 614-619 
    Details
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of 2-hydroxyethanesulfonic acid sodium salt, 3-hydroxypropanesulfonic acid sodium salt or 2-aminoethanesulfonic acid sodium salt with cholest-5-en-3β-ol-3-chloroformate yields the chiral amphiphilic compounds 2-(cholest-5-en-3β)oxy-carbonyloxy-ethanesulfonic acid sodium salt 1, 2-(cholest-5-en-3β)oxy-carbonyloxy-propanesulfonic acid sodium salt 2 and 2-(cholest-5-en-3β)oxy-carbonylaminoethanesulfonic acid sodium salt 3, respectively. Another chiral amphiphile 2-(cholest-5-en-3β)oxy-carbonylethanesulfonic acid sodium salt 4 was synthesized by treating cholest-5-en-3β-ol with sulfopropionic acid anhydride. The surfactants form vesicles in aqueous solutions, as shown by electron microscopy. Stepwise destruction of these vesicles by addition of ethanol or methanol was proved by Circular Dichroism (CD) measurements. Especially compound 3 shows pronounced induced CD effects with the achiral dye 3,6-diamino-acridine-sulfate (proflavine). The synthesized chiral amphiphiles were used in the asymmetric hydrogenation reaction of methyl (Z)-α-acetamidocinnamate. In the case of an achiral rhodium complex as catalyst the prepared surfactants 1, 2, and 4 are able to provide an enantiomer excess by themselves. The best ee-value reached was 8.5% methyl (R)-N-acetylphenyl-alaninate in connection with compound 4.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.199633801118
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  • 3
    Electronic Resource
    Electronic Resource
    Polymeric surfactant systems in the asymmetric hydrogenation of amino acid precursors with a rhodium complexDedicated to Prof. Dr. rer. nat., Dr.-Ing. E.h. Hansjörg Sinn on the occasion of his 65th birthday. (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 195 (1994), S. 3289-3301 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The synthesis of new types of soluble and insoluble amphiphilic systems is described, being polysoaps, crosslinked polysoaps, an amphiphilised ion exchanger, and ion exchangers loaded with ionic surfactants. It was possible to synthesise insoluble polymeric systems which nevertheless showed micellar properties. The polymers were tested as aids in the stereospecific hydrogenation of (Z)-methyl α-acetamidocinnamate to the methyl ester of N-acetylphenylalanine (R) by means of an optically active rhodium complex in water. With linear polysoaps the effect on the reaction was dependent on the structure of the soap molecules. The enantioselectivity of the reaction with monomeric surfactants in water was almost attained. Crosslinked polysoaps showed the same effects on the hydrogenation as linear polysoaps with an analogous structure. Macromolecular ion exchangers loaded with amphiphilic counterions gave in hydrogenation almost the same effect as these counterions give when they are not bound to an insoluble carrier. Enantioselectivities and reaction rates were usually slightly lower than with monomeric surfactants. However, there is an advantage in the separation of catalyst and product after reaction. It was shown that the rhodium-containing amphiphilic ion exchangers could be reused for up to 9 times.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1994.021951001
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    Paper (German National Licenses)
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