Chiral stationary phases chromatographic studies

Polarimetric detection of enantiomers eluted from liquid chromatographic columns employing chiral stationary phases has been described 57 58 and interesting applications have been report-ed 59-60, for example, the study of enantiomerizations during chromatography and the evaluation of optica] purity despite incomplete chromatographic enantiomer separation. By this deconvolution method, based on Beer s and Biot s expressions, optical purities rather than enantiomeric purities are determined60. 

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],... 

Measurement of underivatized propranolol enantiomers in serum using a celluIose-tris(3,5-dimethylphenylcarbamate) high performance liquid chromatographic (HPLC) chiral stationary phase" (54). A method for the direct measurement of the enantiomers of propranolol in human serum was developed using the OD CSP and a mobile phase composed of hexane 2-propranol W,W-dimethyloctylamine (92 8 0.01, v/v/ v). The assay was validated for use in pharmacokinetic and metabolic studies and was subsequently used in the investigation of the effect of cimetidine on the metallism and clearance of propranolol enantiomers (60). 

There has been no systematic study of chromatographic properties, but the enantiomers of the spiro sulfurane (24) have been separated using liquid chromatography on a commercially available chiral stationary phase <93TA2329>. 

One of the most studied polymerization systems employs alkyllithium initiators that are modified by chiral amine ligands for the polymerization of sterically bulky methacrylates [8,38,39,40,41], acrylates [42],crotonates [43], and acrylamides [44]. A primary example is the reaction of triphenylmethyl methacrylate with an initiator derived from 9-fluorenyllithium and (-)-sparteine (3) at -78 °C (Scheme 4). The resultant isotactic polymer is optically active, and is postulated to adopt a right-handed helix as it departs from the polymerization site. This polymer has been particularly successful as a chiral stationary phase for the chromatographic resolution of atropisomers [8]. Many modifications of the or-ganolithium initiator/chiral ligand system have been explored. Recently, Okamo-to has applied enantiopure radical initiators for the enantioselective polymerization of bulky methacrylate monomers [45]. 

Of course for new classes of compounds being studied on a chiral stationary phase, that a mixture of enantiomers are separable must be proven by analyzing a racemate, and the order of elution must be established by correlation with compounds of known configuration. In certain instances, derivatization may be necessary to improve chromatographic behavior and/or detectability. 

Hayball, P.J. Holman, J.W. Nation, R.L. Influence of octanoic acid on the reversible protein binding of ketorolac enantiomers to human serum albumin (HSA) comparative liquid chromatographic studies using a HSA chiral stationary phase. J.ChromatognB, 1994, 662, 128-133 [chiral]... 

After successful application of enantioselective GC to the analysis of enantiomeric composition of monoterpenoids in many essential oils (e.g., Werkhoff et al., 1993 Bicchi et al., 1995 and references cited therein), the studies have been extended to the sesquiterpene fraction. Standard mixtures of known enantiomeric composition were prepared by isolation of individual enantiomers from numerous essential oils by preparative GC and by preparative enantioselective GC. A gas chromatographic separation of a series of isolated or prepared sesquiterpene hydrocarbon enantiomers, showing the separation of 12 commonly occurring sesquiterpene hydrocarbons on a 2,6-methyl-3-pentyl-P-cyclodextrin capillary column has been presented by Konig et al. (1995). Further investigations on sesquiterpenes have been published by Konig et al. (1994). However, due to the complexity of the sesquiterpene pattern in many essential oils, it is often impossible to perform directly an enantioselective analysis by coinjection with standard samples on a capillary column with a chiral stationary phase alone. Therefore, in many cases two-dimensional GC had to be performed. 

Another current problem in environmental studies is the chromatographic separation of enantiomers of marine pollutants (Huhnerfuss and Kallenbom, 1992). HPLC with chiral stationary phases is a new tool to investigate the fate of chiral organic compounds and their degradation products in the environment Ludwig et al., 1992). 

The molecular imprinting strategy can be applied for the recognition of different kinds of templates from small organic molecules to biomacromolecules as proteins. Some examples of separations investigated with MIP monoliths in CEC and LC are shown in Table 2. The influence of the imprinted monolithic phase preparation procedure and of the separation conditions on the selectivity and chromatographic efficiency have been widely studied [154, 157, 161, 166, 167, 192]. The performance of imprinted monoliths as chromatographic stationary phase has also been compared to that of the traditional bulk polymer packed column [149, 160]. It was shown that the monolithic phases yielded faster analyses and improved chiral separations. 

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