Enantiomers chromatographic separation using

Interactions even weaker than ionic bonds can be used to separate enantiomers. Chromatographic separation relies on a difference in affinity between a stationary phase (often silica) and a mobile phase (the solvent travelling through the stationary phase, known as the eluent) mediated by, for example, hydrogen bonds or van der Waals interactions. If the stationary phase is made chiral by bonding it with an enantiomerically pure compound (often a derivative of an amino acid), chromatography can be used to separate enantiomers. 

Most chiral chromatographic separations are accompHshed using chromatographic stationary phases that incorporate a chiral selector. The chiral separation mechanisms are generally thought to involve the formation of transient diastereomeric complexes between the enantiomers and the stationary phase chiral ligand. Differences in the stabiHties of these complexes account for the differences in the retention observed for the two enantiomers. Often, the use of a... 

Since all the physical properties of two given enantiomers are the same in the absence of a chiral, or optically active, medium, their chromatographic resolution needs a different approach from the relatively simple separation of geometrical isomers, stereoisomers or positional isomers. Two methods are used. The older technique of indirect resolution, requires conversion of the enantiomers to diastereoisomers using a suitable chiral reagent, followed by separation of the diastereoisomers on a non-chiral GC or LC stationary phase. This technique has now been largely superseded by direct resolution, using either a chiral mobile phase (in LC) or a chiral stationary phase. A variety of types of chiral stationary phase have been developed for use in GC, LC and SFC(21 23). 

A wide variety of CSPs have been synthesizsed and several of them are commercially available. Their use is nowadays the most favored chromatographic technique used to separate enantiomeric drugs by means of HPLC. In the case of CSPs, the enantiomers that form a stronger association with the chiral selector will be more strongly retained. Interaction... 

For the separation of crystalline diastereomeric p,n-pairs, the same principles as for enantiomers are followed. Similar to the chromatographic resolution of enantiomers, the scale may vary significantly, but, in general, the separations of diastereomeric pairs are more reliable. For example, acids and lactones which may be separated via their phenylglycinol amide derivatives by MPLC on silica gel. Some examples with their derivatives and chromatographic method used for separation arc listed in Table 10. 

Takahisa E, Engel K-H (2005) 2,3-Di-0-methoxymethyl-6-0-tert-butyldimethysilyl-)6-cyclo-dextrin, a useful stationary phase for gas chromatographic separation of enantiomers. J Chromatogr A 1076 148... 

The original racemic patents described the use of resolution to give a chiral oxirane, such as 25, as an intermediate or the use of a chiral auxiliary (20) to produce the salmeterol enantiomers. Alkylation of chiral amine 20 with 2-benzyloxy-5-(2-bromo-acetyl)-benzoic acid methyl ester, followed by diastereoselective reduction of the ketone with lithium borohydride furnished intermediate 21 after chromatographic separation of the diasteromers. Removal of the benzyl group and the chiral auxiliary was... 

The use of sulfoximines in the syntheses of optically active compounds has been reported [429]. A remarkable ketone methylcnation with optical resolution was realized. A highly selective diastereofacial addition of an enantiopure sulfoximine to a racemic ketone, chromatographic separation of the two diastereoisomers and reductive cleavage yielded both enantiomers of p-panasinsene [430], isolated from the root of ginseng, a herb used in Chinese folk medicine. 

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