Cyclodextrin derivatives application

The type of CSPs used have to fulfil the same requirements (resistance, loadabil-ity) as do classical chiral HPLC separations at preparative level [99], although different particle size silica supports are sometimes needed [10]. Again, to date the polysaccharide-derived CSPs have been the most studied in SMB systems, and a large number of racemic compounds have been successfully resolved in this way [95-98, 100-108]. Nevertheless, some applications can also be found with CSPs derived from polyacrylamides [11], Pirkle-type chiral selectors [10] and cyclodextrin derivatives [109]. A system to evaporate the collected fractions and to recover and recycle solvent is sometimes coupled to the SMB. In this context the application of the technique to gas can be advantageous in some cases because this part of the process can be omitted [109]. 

Gas chromatography (GC) has also been used for preparative purposes, but is restricted to relatively volatile racemates such as anesthetics, pheromones or monoterpenes and, therefore, very few applications are reported. Nevertheless, in the cases to which GC may be applied, it could be considered as an economical alternative to HPLC. Most of the resolutions of enantiomers were performed on cyclodextrin-derived CSPs [109, 144-153], and only on very few occasions were other chiral selectors used [153]. 

A chiral GC column is able to separate enantiomers of epoxy pheromones in the Type II class, but the applications are very limited as follows a custom-made column packed with a p-cyclodextrin derivative as a liquid phase for the stereochemical identification of natural 3,4- and 6,7-epoxydienes [73, 74] and a commercialized column of an a-cyclodextrin type (Chiraldex A-PH) for the 3,4-epoxydiene [71] (See Table 3). The resolution abilities of chiral HPLC columns have been examined in detail, as shown in Table 7 and Fig. 14 [75,76, 179]. The Chiralpak AD column operated under a normal-phase condition separates well two enantiomers of 9,10-epoxydienes, 6,7-epoxymonoenes and 9,10-epoxymonoenes. Another normal-phase column, the Chiralpak AS column, is suitable for the resolution of the 3,4-epoxydienes. The Chiralcel OJ-R column operated under a reversed-phase condition sufficiently accomplishes enantiomeric separation of the 6,7-epoxydienes and 6,7-epoxymonoenes. 

Only the silica-based stationary phases with covalently bonded alkyl chain, cyano and propylamino ligands have found practical applications in HPLC. Besides these common ligands, the experimental use of naphthalene, pyrene and nitroaromatic as ligands has also been reported. Silica-based stationary phases with covalently bonded cyclodextrins or cyclodextrin derivatives have been frequently employed in the separation and quantitative determination of isomer pairs. 

Even more generally applicable are GC columns with chiral metal chelates as stationary phases (complexation gas chromatography)26 (Table 6). Quite recently, chiral GC methods have been developed on the basis of cyclodextrin derived stationary phases27. 

Frijlink, H.W., et al. 1992. The effects of cyclodextrins on drug release from fatty suppository bases. III. Application of cyclodextrin derivatives. Eur J Pharm Biopharm 38 174. 

Bicchi, C., Balbo, C., D Amato, A., Manzin, V., Schreier, P., Rozenblum, A., and Brunerie, P. (1998) Cyclodextrin derivatives in GC separation of racemic mixtures of volatiles - Part XIV Some applications of thick-film wide-bore columns for enantiomer GC micropreparation. J. High Resol. Chromatogr. 21, 103-106. 

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. 

Uekama, K. Hirayama, F. Irie, T. Pharmaceutical uses of cyclodextrin derivatives. In High Performance Biomaterials, A Comprehensive Guide to Medical and Pharmaceutical Applications Szyeher, M., Ed. Technomic Lancaster, PA, 1991 789-806. 

The review articles dealing with the application of cyclodextrin derivatives for a direct gas chromatographic separation of optically active components in the essential oils have been published by Bicchi et al. [15, 16]. 

Menard FA, Dedhiya MG, Rhodes CT. Potential pharmaceutical applications of a new beta cyclodextrin derivative. Drug Dev Ind Pharm 1988 14(11) 1529-1547. 

Stella V. SBE7-p-CD, a new, novel and safe polyanionic p-cyclodextrin derivative characterization and biomedical applications. In Szejtli... 

The developments of the Lewis base-modified zirconia and mixed-oxide containing zirconia as stationary phases for high-performance liquid chromatography (HPLC) are reviewed. In this context, the preparation methods of porous spherical zirconia, and zirconia supports for HPLC based on modification with fluoride, phosphate, phos-phonate, carboxylic acid, phenols, and protein, as well as cyclodextrin derivative, are covered. The application of modified-zirconia in capillary electrochromatography (CEC) is also discussed. 

Smith et have prepared 11 chiral calix[4]arenes, calix[4]resorcarenes, and anionic cyclodextrin derivatives and investigated the properties of their lanthanide (Yb, Dy +) complexes as chiral lanthanide shift reagents (LSR). Baldovini et alP report an application of a camphor-derived chiral complex, Yb(hfc)3 (hfc = tris[3-(heptafluoropropylhydroxymethylene)-(- -)-camphorate]) to differentiate the C NMR spectra of enantiomers of bornyl acetate. 

Juza et al. [31] described the application of the SMB technique in gas chromatography for the separation of the highly volatile enantiomers of enflurane at 323 K in glass and stainless steel columns packed with cyclodextrine derivatives. 

Photoisomerization of azobenzenes has been widely developed as photochromic compounds. Lots of papers sriU appeared in this subject from basic chemisty to applications. Some examples were described. Harada et al., reported the effect of cyclodextrin derivatives bearing photo-isomerized stilbene moiety. Single molecule conductance of E- and Z-4, 4 -(ethane-l,2-diyl)dibenzoic acids (E-l and Z-1) was determined using scanning tunnelling microscopy (STM). The dynamics of photoisomerization of E- and Z-urocanic acids (E- and Z-2) driven by Hg-free... 

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