Chiral Stationary Phases CSPs cyclodextrins from

The separation of enantiomers can be effected either by transforming them into diastereoisomers using a chiral reagent and separating them on conventional phases or by separating the enantiomers on chiral phases. The utilization of chiral phases has not yet become routine, but studies of enantiomeric dipeptides have been carried out (115,116). Pirkle et al. (117) and Hyun et al. (118) separated enantiomeric di- and tripeptides (methyl esters of /V-3-5-dinitrobenzoyl derivatives) on chiral stationary phases (CSPs) derived from (R)-a-arylalkylamines, (S)-N-(2-naphthyl) valine, or (S)-1 -(6,7-dimethyl-1 -naphthyl) isobutylamine. These workers were able to separate four peaks for each dipeptide derivative, corresponding to the two enantiomeric pairs (R,R)/(S,S) and (R,S)/(S,R). Cyclodextrin-bonded stationary phases and chiral stationary immobilized a-chymotrypsin phases were used to separate enantiomeric peptides (118a,b). 

The most popular and commonly used chiral stationary phases (CSPs) are polysaccharides, cyclodextrins, macrocyclic glycopeptide antibiotics, Pirkle types, proteins, ligand exchangers, and crown ether based. The art of the chiral resolution on these CSPs has been discussed in detail in Chapters 2-8, respectively. Apart from these CSPs, the chiral resolutions of some racemic compounds have also been reported on other CSPs containing different chiral molecules and polymers. These other types of CSP are based on the use of chiral molecules such as alkaloids, amides, amines, acids, and synthetic polymers. These CSPs have proved to be very useful for the chiral resolutions due to some specific requirements. Moreover, the chiral resolution can be predicted on the CSPs obtained by the molecular imprinted techniques. The chiral resolution on these miscellaneous CSPs using liquid chromatography is discussed in this chapter. 

Aroma compounds originate from biosynthetic pathways inside an animal, a botanical body, and other life-forms as well as enzymes and thus frequently carry chiral components within the molecule. Determination of such enantiomeric properties can, in many cases, be accomplished using a GC column with a chiral stationary phase (CSP) application.75-79 These columns, usually called chiral GC column, will provide diastereometric interaction that could lead to resolution of enantiomers. Commercially available chiral GC columns predominantly utilize cyclodextrin derivatives as CSPs. Chiral columns consisting of multiple cyclodextrin derivatives intending synergic effect in resolution property80 are also successful in the market. In practice, these columns are mainly operated as secondary columns in MDGC technique. 

Chromatographic enantioseparation of chiral xenobiotics and their metabolites is a versatile tool for process studies in marine and terrestrial ecosystems [235]. In 1994, three papers focused on the enantioselective determination of toxaphene components [120,236,237]. Buser and Muller found that technical toxaphene mixtures are not necessarily racemic [237]. This observation was supported after isolation of non-racemic B7-1453 from the product Melipax which had an excess of ca. 25% of the dextrorotary enantiomer [27, 238]. The enantioselective separation of toxaphene components is almost restricted to chiral stationary phases (CSPs) based on randomly derivatized ferf-butyldimethyl-silylated /1-cyclodextrin (commercially available from BGB Analytik, Adliswil, Switzerland). So far, only a few toxaphene components were enantioseparated on other CSPs [239, 240]. Some of these CSPs are not well defined as well, and for this reason a test mixture called CHIROTEST X was suggested for initial column testing [241],... 

The use of chiral stationary phases (CSP) in liquid chromatography continues to grow at an impressive rate. These CSPs contain natural materials such as cellulose and starch as well as totally synthetic materials, utilizing enantioselective and retentive mechanisms ranging from inclusion complexation to Ti-electron interactions. The major structural features found in chiral stationary phases include cellulose, starch, cyclodextrins, synthetic polymers, proteins, crown ethers, metal complexes, and aromatic w-electron systems. 

Enantiomeric analysis of a new antiinflammatory agent in rat plasma using a chiral p-cyclodextrin stationary phase" (71). The R,R S,S enantiomers of the investigational antiinflammatory agent trans-6,6a,7,10, 10a,ll-hexahydro-8,9-dimethyl-U-oxodibenz[b,e]-oxepin-3-acetic add (HOA) were resolved on the p-CD CSP after extraction from rat plasma. The mobUe phase was a mixture of 0.05 M potassium dihydrogenphosphate (pH 5.3) and methanol (35 65, v/v) the flow rate was 1.0 mL/min and the temperature was 22 1 C. The results of the study indicated that the inactive (—) enantiomer was cleared from the plasma more rapidly than the active (+) isomer. 

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