Chiral capillary columns

For experiments conducted in Liverpool GC was performed on a Shimadzu GC-14A gas chromatograph using a SE30 capillary column with the injector and detector set to 250 °C chiral GC was performed with chiral capillary columns (Lipodex E and C as indicated) with the injector and detector set to 250 °C. HPLC was performed on a Gilson chromatograph equipped with chiral columns Daicel Chiralpack AD and OD (wavelength 254 nm). 

This technology was extended to the preparation of chiral capillary columns [ 138 -141 ]. For example, enantioselective columns were prepared using a simple copolymerization of mixtures of O-[2-(methacryloyloxy)ethylcarbamoyl]-10,11-dihydro quinidine, ethylene dimethacrylate, and 2-hydroxyethyl methacrylate in the presence of mixture of cyclohexanol and 1-dodecanol as porogenic solvents. The porous properties of the monolithic columns can easily be controlled through changes in the composition of this binary solvent. Very high column efficiencies of 250,000 plates/m and good selectivities were achieved for the separations of numerous enantiomers [140]. 

Extensive comparisons between GC and SFC have been reported in chiral separation [63-66]. Zoltan investigated the performance of SFC and GC using the same chiral capillary columns coated with cyclodextrin-based stationary phases. It was observed that chiral selectivity was higher in GC than in SFC using the same open tubular column at the identical temperature (e.g., >100°C). However, the selectivity in SFC was significantly increased at low temperatures, especially for polar compounds [67]. 

Ravid U, Putievsky E, Katzir I, Ikan R, Determination of the enantiomeric composition of terpinen-4-ol in essential oils using a permethylated 3-cyclodextrin coated chiral capillary column. Flavour Fragr/7 49—52, 1992. 

The preceding 12-step sequence was the first published enantiose-lective synthesis of (-)-u-thujone (1). With the aid of gas chromatography over a chiral capillary column it was established that the enantiomeric excess (ee) in the resulting natural product 1 was >99.2%. 

The major advantage of using the urinary S R ratio as a phenotypic trait for assessing CYP2C19 activity is that the method is fairly robust with regard to any incompleteness of urine collection or noncompliance with respect to dose administration. This is because the R-enantiomer serves as an in vivo internal standard. On the other hand, the required enantiospecific assay uses chiral capillary column gas chromatography with a nitrogen-specific detector, and such instmmentation is not commonly available. For this reason, an alternative phenotypic trait measure based on the formation and urinary elimination of 4 -hydroxymephenytoin has also been frequently used. 

The (25) absolute configuration and enantiomeric purities (up to 99 % ee) of the crude amino acids 37 were readily determined by GC comparison (using a chiral capillary column) of their (jV-trifluoroacetyl)-n-propyl esters with those of racemic and enantiomerically pure authentic samples and were further supported by chiroptic comparison. 

Hepatotoxins were isolated as new hepatotoxic compounds from the cyanobacterium Nostoc sp. strain 152 and assigned structures based on their high resolution FAB (fast atom bombardment) MS/MS, H and C NMR spectra, amino acid analysis and gas chromatography on a chiral capillary column by Namikoshi et al ... 

Essential oils - Analysis by gas chromatography on chiral capillary columns - General method... 

Enantioselective hydrogenation of ethyl pyruvate was carried out in a 300 ml stirred autoclave (Parr Instruments, Illinois) at 20 °C and the pressure kept constant at 60 bar with a high pressure H2 burette. Reaction rates were determined from the drop in H2 pressure measured in the burette. Conversion and enantiomeric excess were determined by quantitative analysis by a GC equipped with a chiral capillary column for enantiomeric separation (for details see [6]). 

Acetoxypropanal [Asymmetric Hydroformylation of a Vinyl Ester under Homogeneous Conditions]. " A solution of vinyl acetate (532.3 mg, 6.19 mmol), Rh(acac)(CO)2 (4.0 mg, 1.55 X 10 mmol), and (/ ,5 )-BINAPHOS (89) (17.7 mg, 3.34 X 10 mmol) in benzene (10 mL) placed in a Schlenk tube was degassed by freeze-thaw cycles. It was then transferred into a 50 mL autoclave, and the mixture was stirred at 60° for 36 hours under hydrogen and carbon monoxide pressure (1 1 ratio, total 100 atm). H NMR analysis of the reaction mixture showed that the conversion was >99% and the branched and normal aldehydes (2-acetoxypropanal and 3-acetoxypropanal) were formed in 86 14 ratio. The enantiomeric excess of (5)-2-acetoxypropanal (92%) was determined by GC using a chiral capillary column. 

Hydrogenation studies All reactions were carried out in a three-phase slurry reactor with magnetic stirring (ca. 1000 rpm), at 25-30°C and 70-100 bar. The reactions were run to completion and the conversion was checked by gas chromatography (column OV 101, 2m, 50°C) after esterification of the hydroxyacids (EtOH, HCl, RT). For technical reasons, the time (minutes) required for the uptake of 100% hydrogen is given as a qualitative measure of the catalyst activity. Optical yields were determined by gas chromatography on a chiral capillary column (Chirasil-(L)-Val, 50 m, 150°C) after derivatization of the hydroxyesters with isopropyl-isocyanate. 

In the case of the crotylation of benzaldehyde, it is necessary to methylate the product alcohols and determine their enantiomeric excesses by gas chromatography (GC) using a Supelco 3-Dex 120 chiral capillary column (30 m, 0.25 mm (diameter), 0.25 rm). GC... 

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