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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of some racemicγ-fluoro-α-amino acids (1997)
    Springer
    Amino acids 12 (1997), S. 363-372 
    Details
    ISSN: 1438-2199
    Keywords: Fluorinated amino acids ; Alkylation ; tert-Butyl N-(diphenylmethylene)glycinate ; 1-Bromo-2-fluoroalkanes ; Phase transfer catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Versatile three-step procedures for syntheses of seven racemiγ-fluoro-a-amino acids are described. Alkylation oftert-butyl N-(diphenylmethylene) glycinate with 1-bromo-2-fluoroalkanes gave N-protected aminoacid esters both in anhydrous medium using lithium-diisopropylamide as base at low temperature or in a two phase system of 50% aqueous sodium hydroxide and methylene chloride with triethylbenzylammonium chloride as the phase transfer catalyst at room temperature. Subsequent two-step deprotection with citric acid and hydrochloric acid gave the title compounds in 13–33% overall yields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01373016
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Syntheses ofγ-fluoro-α-amino acids (1996)
    Springer
    Amino acids 11 (1996), S. 409-424 
    Details
    ISSN: 1438-2199
    Keywords: Amino acids ; Fluorinated amino acids ; Alkylation ; Glycine esters ; 1-Bromo-2-fluoroalkanes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Methods for the synthesis of racemic and optically active title compounds are presented. Key step of these four-step procedures is the alkylation with 1-bromo-2-fluoroalkanes of glycine-ester-derived imines in anhydrous medium using lithium diisopropylamide as a base at low temperature or phase transfer catalyzed alkylation with 50% NaOH and triethylbenzylammoniumchloride as the phase transfer catalyst, respectively. Subsequent three-step deprotection gave the free acids in 13–33% overall yield. Deracemization ofγ-fluoro-α-aminobutyric acid methyl and ethyl esters withα-chymotrypsin was shown to give the (−)-enantiomers of the esters and (+)-γ-fluoro-α-aminobutyric acid in 〉98% ee, while from thetert-butylester the opposite stereochemical result was observed giving the (−)-acid with 88% ee. Optically activeγ-fluoro-α-amino acids were synthesized alternatively by phase transfer catalysis with N-benzyl-cinchonium chloride or using an auxiliary-directed asymmetric alkylation of the imine derived from (R)-(+)-camphor or (R)-(+)-2-hydroxypinan-3-one. These processes gave different enantiomers ofγ-fluoro-α-aminobutyric acid via a monomeric lithium enolate in the first or a dimeric lithium enolate in the second case, respectively. The enantiomeric excess can be improved by lithium/magnesium exchange.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807945
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Structure-retention correlations of hydrocarbons in gas-liquid and gas-solid chromatography. Cycloalkenes and cycloalkadienes (1987)
    Springer
    Chromatographia 23 (1987), S. 590-594 
    Details
    ISSN: 1612-1112
    Keywords: Gas-liquid chromatography ; Gas-solid chromatography ; Retention index data ; Cycloalkanes ; Cycloalkenes ; Cycloalkadienes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention indices of cycloalkenes and cycloalkadienes with C6–C13 rings are determined by gas-liquid chromatography (GLC) on glass capillary columns coated with OV-1 and Ucon LB 550X and by gas-solid chromatography (GSC) on a microcolumn packed with uncoated graphitized thermal carbon black (GTCB). Structure — retention correlations are derived on using index differences such as HOV, HGTCB and ΔI values, considering the differences in the stereochemistry of these compounds. It is shown that the combined application of index increments obtained in GLC and GSC provides more detailed structure informations. The value of the retention index units agree with the most stable conformations of the alicyclic compounds. The high value for the energy equivalent to an index unit (ΔGI.U.=4.18kJ/mol) confirmes that graphitized thermal carbon black causes much stronger dispersive interactions than any nonpolar liquid phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02324870
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    Paper (German National Licenses)
    Fulltext
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