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  • 1
    ISSN: 0899-0042
    Keywords: enantiomeric separation ; chiral phase ; ovomucoid ; octahydrobenzo(g) quinoline ; chiral recognition mechanism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomeric resolution of six closely related hexa- and octa-hydrobenzo(g) quinoline racemates by HPLC on an ovomucoid column (Ultron ES-OVM) is described. First, the influence of uncharged mobile phase additives (with different hydrogen bonding properties) and pH on retention and enantioselectivity is investigated. It is shown that an optimum pH of around 6 for the given separations is much more important than the choice of modifier. Second, the influence on enantioselectivity of small differences in molecular structure is examined. In one case a large difference is obtained for diastereomeric racemates depending on the cis- or trans-configuration of the quinoline skeleton. Higher flexibility of the solute seen in the cis enantiomers seems to improve enantioselectivity. © 1993 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0899-0042
    Keywords: amylose ; 3,5-dimethylphenyl-carbamate ; polysaccharide phase ; tert-butyl 2-tert-butyl-4-methoxy-2,5-dihydro-1,3-imidazole-1-carboxylate; amino acid ester synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparative separation of the enantiomers of the title compound, a versatile chiral building block for the synthesis of unnatural amino acid esters, by high performance liquid chromatography on a chiral stationary phase (CSP), is reported for the first time. The CSP consists of amylose-(3,5-dimethylphenyl-carbamate), which has been coated onto the surface of macroporous aminopropyl-functionalized silica gel. The effect of mobile phase composition and the amount of amylose derivative on the silica gel has been thoroughly investigated. Using 2-propanol as organic modifier in hexane as mobile phase, on a semi-preparative column (200 mm × 40 mm ID, containing 192 g of stationary phase) about 200 mg of the racemate was separated per injection. Running the equipment under automatic conditions with repetitive injection mode allowed for the separation of 30 g per day. Both enantiomers were obtained with enantiopurities >99.75:0.25. Chirality 10:217-222, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0935-6304
    Keywords: HPLC ; Chiral stationary phase ; Poly(triphenylmethacrylate) ; Enantiomer separation ; Calcium antagonist ; Dihydropyridines ; Isradipine ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0935-6304
    Keywords: Capillary GC ; Chiral stationary phase ; Chirasil-Val ; Cyclodextrins ; Perfluoroacylation ; Enantiomeric separation ; Amino alcohols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic amino alcohols have been separated as perfluoroacylated derivatives by gas chromatography using either improved Chirasil-Val or heptakis(2,6-di-O-methyl-3-O-pentyl)-β-cyclodextrin as stationary phase. Using Chirasil-Val all the amino alcohols investigated were separated to baseline (α values between 1.03 and 1.08) whereas only a few amino alcohols were resolved on the modified cyclodextrin column. The enantioselectivity obtained on the latter phase was, however, significantly higher.The separations were performed as trifluoroacetyl, pentafluoropropionyl, and heptafluorobutyryl derivatives and the chiral discrimination observed for the different derivatives was significantly different for both stationary phases.In oder to obtain a better understanding of the separation mechanism, the Gibbs-Helmholtz parameters Δ(R,S)ΔH° and Δ(R,S)ΔS° were determined. The most extraordinary result was obtained for the trifluoroacetyl derivative of allo-threoninol. In addition to the order of elution of the enantiomers being the opposite of that for the other compounds, the separation seems to be entropy controlled (the sign Δ(R,S)ΔH° is positive), i.e. the separation improved at higher temperatures.
    Additional Material: 4 Ill.
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  • 5
    ISSN: 0935-6304
    Keywords: Enantiomer separation ; Chiral stationary phase ; Binaphthalene stationary phase ; S-3,3′-Dicarboxy-2,2′-dihydroxy-1,1′-binaphthyl (S-DDBN) ; Effect of structure on chiral resolution ; Dopamine D1 receptor agonists ; Benzergoline derivatives ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel chiral stationary phase (CSP) derived from the atropisomeric enantiomer S-3,3′-dicarboxy-2,2′-dihydroxy-1,1′-binaphthyl (S-DDBN) has been synthesized and its use for the separation of enantiomers demonstrated. The chiral selector is covalently bonded to amino-functionalized silica gel, thus enabling the use of alcohols as mobile phases. Good chiral discrimination was obtained for the pharmacologically interesting class of benzergoline derivatives which act as selective dopamine D1 receptor agonists. This paper reports the successful separtion of fifteen structurally related benzergoline racemates with separation factors up to 3.5. The influence of small differences in molecular structure on chiral discrimination was examined.
    Additional Material: 5 Ill.
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  • 6
    ISSN: 0899-0042
    Keywords: simulated moving bed technology ; chiral separation ; cellulose triacetate ; preparative scale liquid chromatography ; racemic epoxide ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The feasibility of using simulated moving bed technology (SMB) for chiral separation on cellulose triacetate is demonstrated on the preparative scale: 1 kg of a chiral epoxide has been separated. On comparing SMB technology with conventional liquid chromatography it turns out that the main advantage of SMB lies in the significant reduction of mobile phase consumption. The process design for SMB is made theoretically and the predictions are confirmed by our pilot study. © 1993 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0899-0042
    Keywords: cellulose ; regioselective derivatization ; chiral stationary phases ; liquid chromatography ; enantioseparation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various cellulose-2,3-bis-arylcarbamate-6-O-arylesters and cellulose-2,3-bis-arylester-6-O-arylcarbamates, designed to test the possible combined effects of the known tris-arylcarbamate and tris-arylester classes, were synthesized with high regioselectivity at O-C(6), and their use as CSPs in liquid chromatography for enantiomeric separations was investigated. The separations obtained with the synthesized CSPs were compared to the separations achieved on a self-packed reference column, consisting of cellulose-tris-(3,5-dimethylphenyl-carbamate) as CSP standard. Among the synthesized, regioselectively substituted cellulose derivatives, 2,3-bis-O-(3,5-dimethylphenylcarbamate)-6-O-benzoate-cellulose and 2,3-bis-O-(benzoate)-6-O-(3,5-dichlorophenylcarbamate)-cellulose gave the best CSPs for the separation of the test racemates. CSPs from regioselectively substituted cellulose derivatives seem to exhibit higher selectivities than cellulose-tris-(3,5-dimethylphenylcarbamate) for certain classes of racemic compounds. Chirality 10:294-306, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
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  • 8
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A stereoselective total synthesis of the racemic form of the 2,6-dimethylergolin-8ã-amine derivative III, previously obtained semi-synthetically from lysergic acid, is described. Starting from the commercially available tricyclic lactam 1, the 9,10-didehydroergoline skeleton containing an angular Me group in position 3 (see 18) is built up in several steps applying a Woodward D-ring annelation sequence. The introduction of the 8-amino group is achieved with complete diastereoselectivity to give exclusively the 8ã-derivative 22. Subsequently, a Wagner-Meerwein-type migration of the angular Me group yields the 2-methylated 9,10-didehydroergoline derivative 31. The feasibility of this key transformation was tested on the two model systems 4 and 7 prior to the evaluation of the total synthesis. A stereoselective Birch reduction to the trans-fused ergoline, and deacetylation/acylation conclude the total synthesis of the racemic target compound 34.In addition, the resolution of an early intermediate (see 3) by chromatography on a chiral stationary phase is presented which demonstrates that the described total synthesis could also be used for the preparation of the biologically active (5R,8S,10R)-enantiomer III.
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