Preparative displacement chromatographic

Quintero, G., Vo, M., Farkas, G., and Vigh, G. (1995). Series of homologous displacers for preparative chiral displacement chromatographic separations on Cyclobond II columns. J. Chromatogr. 693, 1-5. 

Cholestenone. Place a mixture of 1 0 g. of purified cholesterol and 0-2 g. of cupric oxide in a test-tube clamped securely at the top, add a fragment of Dry Ice in order to displace the air by carbon dioxide, and insert a plug of cotton wool in the mouth of the tube. Heat in a metal bath at 300-315° for 15 minutes and allow to cool rotate the test-tube occasionally in order to spread the melt on the sides. Warm with a few ml. of benzene and pour the black suspension directly into the top of a previously prepared chromatographic column (1) rinse the test-tube with a little more benzene and pour the rinsings into the column. With the aid of shght suction (> 3-4 cm. of mercury), draw the solution into the alumina column stir the top 0 -5 cm. or so with a stout copper wire to... 

A chromatographic separation can be developed in three ways, by displacement development, by frontal analysis, and by elution development, the last being almost universally used in all analytical chromatography. Nevertheless, for the sake of completeness, and because in preparative chromatography (under certain conditions of mass overload) displacement effects occur to varying extents, all three development processes will be described. 

Supernatants were chromatographed over a column of Sephadex G-10, G-25, and G-50, and aliquots of collected fractions were assessed for their ability to displace 3H-PCP from binding sites in rat brain preparations. Results indicated that the endogenous material has a molecule weight of about 3,000. 

SUMMARY. The frontal technique does not lend itself to many analytical applications because of the overlap of the bands and the requirement of a large amount of sample. However, it may be used to study phase equilibria (isotherms) and for preparative separations. (Many of the industrial chromatographic techniques use frontal analysis.) Displacement development has applications for analytical LC (e.g. it may be used as an initial concentrating step in GC for trace analysis). This technique may also be used in preparative work. The outstanding disadvantage of both of these techniques is that the column still contains sample at the conclusion of the separation. Thus, regeneration of the column is necessary before it can be used again. 

In concomitance with the displacement observed by i.r., an evolution of the catalytic activity has been observed while studying the liquid-phase epoxidation of cyclohexene in the presence of (EGDA)- Mo(VI), freshly prepared or after four months of conditioning at room temperature under inert atmosphere. As usual, the appearance of epoxide was followed by gas chromatographic analyses or by direct titration of oxirane oxygen and the disappearance of hydroperoxide was monitored by iodometric titration. In figure we report concentration-time for typical runs in ethylbenzene at 80°C obtained with the experimental procedure already described (ref. 9). It may be seen that with a freshly prepared catalyst an induction period is observed which lowers the initial catalytic activity. Our modified Michaelis-Menten type model equation (ref. 9) cannot adequately fit the kinetic curves obtained due to the absence of kinetic parameters which account for the apparent initial induction period (see Figure). 

Carrying out the benzhydrylpiperazine formation via nucleophilic displacement as depicted in Scheme 2 using the enantiopure (—)-(2R,5S)-l -allyl-2,5-dimethylpiperazine provides two stereoisomers, epimeric at the benz-hydryl position. These epimers are separable by common chromatographic techniques (although these are sometimes difficult separations), and the absolute stereochemistry of the products has been proven via x-ray crystallography [19,23,40,41]. For large-scale preparation, a stereoselective approach to the final products is preferred to minimize waste and reduce costs. Two distinct stereoselective routes to benzhydrylpiperazines have been described. 

Displacement chromatography has also been carried out in dye affinity chromatographic systems for the purification of lactate dehydrogenase (LDH).59 In that study, polyethyleneimine (PEI) was employed as a displacer on dye affinity matrices prepared by immobilizing Cibacron Blue 3GA or Procion Red HE-3B. 

Preparative Methods obtained by reaction of (—)-menthol with p-toluenesulfinyl chloride. This esterification showed no particular stereoselectivity, giving an equal amount of the two sulfinate diastereomers. In order to avoid a chromatographic separation, it is possible to epimerize these sulfinate esters in acidic medium and displace the resulting equilibrium towards the less soluble isomer, (—)-menthyl (5)-p-toluenesulfinate, in 80% yield (eq 1). This procedure was later extended to large scale preparation. ... 

Availability. Although commercially available via the degradation of pantothenic acid, (i )-pantolactone is also conveniently prepared by enantioselective reduction of its corresponding keto lactone employing homogeneous catalysis," " or by microbial methods. The (5)-enantiomer has been prepared by inversion of the natural product in 90% yield and 97% ee via triflate activation, acetate displacement, and Lithium Hydroxide hydrolysis. The enantiomers were also prepared by resolution of the race-mate with (R)- and (5)-phenethylamine. A gas chromatographic method exists for ee determination. ... 

The chromatographic separation of enantiomers, often referred to as enantioseparation, has received a great deal of attention in recent years. Both liquid (LC) and gas (GC) chromatographic procedures are used. The former is extremely useful for enantioseparations because of the available variations in scale, mechanism, and technique. It has been used in enantioseparations from analytical to preparative in scale, taking advantage of various modes of diastereoisomeric interactions andusing elution and displacement techniques. All the chromatographic methods involve diastereoisomeric interactions between the enantiomers of interest and... 

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