Chiral cyclodextrin column

The curves relate log(k ) against 1/T for two pairs of enantiomers on a chiral BBP column containing 1,6-dipentyl-buteryl cyclodextrin that was 20 m long, 250 pm... 

Figure 3.7 [continued) (b) Chromatograms of (iii) the dichloromethane extract of strawberry fruit yoghurt analysed with an apolar primary column, with the heart-cut regions indicated, and (iv) a non-racemic mixture of y-deca-(Cio) and 7-dodeca-Cj2 lactones isolated by heart-cut transfer, and separated by using a chiral selective modified cyclodextrin column. Reproduced from A. Mosandl, et al J. High Resol. Chromatogr. 1989, 12, 532 (39f. 

Figure 3.8 Second-dimension chiral cyclodextrin capillary column separation of a non-racemic pair of nonachlorobomane compounds extracted from dolphin blubber, shown with expanded attenuation in the inset. The primary separation (not shown) was performed on an apolar primary capillary column. Reproduced from H.-J. de Geus et al. J. High Resol. Chromatogr. 1998, 21, 39 (59).

GC using chiral columns coated with derivatized cyclodextrin is the analytical technique most frequently employed for the determination of the enantiomeric ratio of volatile compounds. Food products, as well as flavours and fragrances, are usually very complex matrices, so direct GC analysis of the enantiomeric ratio of certain components is usually difficult. Often, the components of interest are present in trace amounts and problems of peak overlap may occur. The literature reports many examples of the use of multidimensional gas chromatography with a combination of a non-chiral pre-column and a chiral analytical column for this type of analysis. 

Figure 10.3 Gas cliromatograms of a cold-pressed lemon oil obtained (a) with an SE-52 column in the stand-by position and (b) with the same column showing the five heart-cuts (c) shows the GC-GC chiral chromatogram of the ti ansfeired components. The asterisks in (b) indicate electric spikes coming from the valve switcliing. The conditions were as follows SE-52 pre-column, 30 m, 0.32 mm i.d., 0.40 - 0.45 p.m film tliickness cairier gas He, 90 KPa (stand-by position) and 170 KPa (cut position) oven temperature, 45 °C (6 min)-240 °C at 2 °C/min diethyl-tert-butyl-/3-cyclodextrin column, 25 m X 0.25 mm i.d., 0.25 p.m film thickness cairier gas He, 110 KPa (stand-by position) and 5 KPa (cut position) oven temperature, 45 °C (6 min), rising to 90 °C (10 min) at 2 °C/min, and then to 230 °C at 2 °C/min. Reprinted from Journal of High Resolution Chromatography, 22, L. Mondello et al, Multidimensional capillary GC-GC for the analysis of real complex samples. Part IV. Enantiomeric distribution of monoterpene hydrocarbons and monoterpene alcohols of lemon oils , pp. 350-356, 1999, with permission from Wiley-VCH.

Recently, multidimensional GC has been employed in enantioselective analysis by placing a chiral stationary phase such as a cyclodextrin in the second column. Typically, switching valves are used to heart-cut the appropriate portion of the separation from a non-chiral column into a chiral column. Heil et al. used a dual column system consisting of a non-chiral pre-column (30 m X 0.25 mm X 0.38 p.m, PS-268) and a chiral (30 m X 0.32 mm X 0.64 p.m, heptakis(2,3-di-(9-methyl-6-(9-tert-butyldimethylsilyl)-(3-cyclodextrin) (TBDM-CD) analytical column to separate derivatized urinary organic acids that are indicative of metabolic diseases such as short bowel syndrome, phenylketonuria, tyrosinaemia, and others. They used a FID following the pre-column and an ion trap mass-selective detector following the... 

Phenylthiocarbamoyl derivatives of 18 chiral amino acids were separated on a C8 column connected in series to a phenylcarbamoylated (3-cyclodextrin column (Iida et al., 1997). The Cg column separated the derivatized amino acids from one another entering the chiral column. Under this configuration several enantiomers of adjacent amino acids coeluted resulting in poor resolution. However, this configuration was successful in determining the amino acid sequence and chirality of the amino acids in a D-amino acid containing peptide. 

Like plasma and urine, matrixes from plant or environmental sources contain a vast diversity of components. Thus, achiral-chiral LC-LC is also useful for analysis involving samples from these sources. Stalcup et al. (1991) studied the enantiomeric purity of scopolamine extracted from Datura sanguinea in both homogenized plant leaves and commercial extracts. A reverse-phase separation on a C j g column separated the scopolamine from other alkaloid and matrix components while the enantiomeric separation (also in the reverse-phase mode) was carried out on two coupled [3-cyclodextrin columns or a single acetylated (3-cyclodextrin column. The single... 

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. 

All aldehydes used in the experiment were freshly distilled or washed with aqueous NaHC03 solution to minimize the amount of free acid. Chiral HPLC was performed using a chiral OJ-H column (0.46 cm x 25 cm, Daicel industries) with a water 717 auto sampler and a UV-vis detector (254 nm). The eluting solvent used was different ratios of hexane and 2-propanol. Chiral gas chromatography analysis was performed in a Shimadzu auto sampler with cyclodextrins columns as chiral stationary phase (fused-silica capillary column, 30 m X 0.25 mm x 0.25 gm thickness, /3-Dex-120 and /3-Dex-325 from Supelco, USA) using He as a carrier gas (detector temperature 230 °C and injection temperature 220 °C). 

The optical purity was determined by chiral GC, using a 20 % permethylated cyclodextrin column, after esterification of the pure product with (CF3C0)20 in dry CH2CI2 (65 °C isothermal carrier gas N2, pressure 70 kPa). T r = 26.305 min (>99%, (3R,45)-3-allyl-4-hydroxy-2-pentanone). The enantiomeric purity was estimated to be >99 % and the diastereomeric purity >99 %. 

Extensive comparisons between GC and SFC have been reported in chiral separation [63-66]. Zoltan investigated the performance of SFC and GC using the same chiral capillary columns coated with cyclodextrin-based stationary phases. It was observed that chiral selectivity was higher in GC than in SFC using the same open tubular column at the identical temperature (e.g., >100°C). However, the selectivity in SFC was significantly increased at low temperatures, especially for polar compounds [67]. 

Ravid U, Putievsky E, Katzir I, Ikan R, Determination of the enantiomeric composition of terpinen-4-ol in essential oils using a permethylated 3-cyclodextrin coated chiral capillary column. Flavour Fragr/7 49—52, 1992. 

Supelco. 1998. Chiral Cyclodextrin Capillary GC Columns. Sigma-Aldrich, Bellefonte, Penn. 

Complexes of unsymmetrically substituted conjugated dienes are chiral. Racemic planar chiral complexes are separated into their enantiomers 84 and 85 by chiral HPLC on commercially available /f-cyclodextrin columns and used for enantioseletive synthesis [25]. Kinetic resolution was observed during the reaction of the meso-type complex 86 with the optically pure allylboronate 87 [26], The (2R) isomer reacted much faster with 87 to give the diastereomer 88 with 98% ee. The complex 88 was converted to 89 by the reaction of meldrum acid. Stereoselective Michael addition of vinylmagnesium bromide to 89 from the opposite side of the coordinated Fe afforded 90, which was converted to 91 by acetylation of the 8-OH group and displacement with EtjAl. Finally, asymmetric synthesis of the partial structure 92 of ikarugamycin was achieved [27],... 

As a further test of the etched open tubular approach for the analysis of optical isomers, another column was fabricated based on the selector naphthylethylamine that had been attached to porous silica by the silanization/hydrosilation method for use in HPLC [70]. As in the HPLC experiments, this column was best suited for the resolution of the optical isomers of dinitrobenzoyl methyl esters of amino acids. The best separation (a = 1.14) was obtained for the alanine derivative. In addition, the peak symmetry and efficiency for the naphthylethylamine column was significantly better than that obtained on the cyclodextrin column. However, as shown in HPLC experiments, changes in the amino acid moiety (replacing alanine with valine, etc.) often results in a loss of chiral resolution. In the case of optical isomers, the separation mechanism in HPLC and CEC modes is identical since only interaction between the solute and the bonded phase can result in resolution of the enantiomers. 

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. 

Figure 3b. Enantiodifferentiation of methionol-S-oxide (6) on a chiral GC column coated with diacetyl tert. butyl silyl-P-cyclodextrin.

The efficiency of chiral stationary phase (CSP) is crucial in chromatographic technique. Recently, a new p-cyclodextrin phenyl isocyanate bonded chiral stationary phase (CSP) was developed. This CSP is quite stable and can be used in most of HPLC solvents. Many drug enantiomers that do not have enantioseparation effect on native P-cyclodextrin column in reversed phase were separated very well on this new CSP. 

An advanced HPLC system has been developed to separate cisltrans isomers of tocotrienols using a chiral permethylated P-cyclodextrin column and an acetonitrile/ water eluent mixture (Drotleff and Temes, 1999). 

Furthermore, enantio-MDGC, employing heart-cutting techniques from DB-1701 as the preseparation column on to heptakis (3-0-acetyl-2,6-di-0-pentyl)-P-cyclodextrin as the chiral main column, was described by Mosandl et al. /2S7 as a powerful tool in the direct enantiomer separation of chiral y-lactones from complex matrices without any further clean-up or derivatization procedures. 

Two-dimensional GC in the direct enantiomer separation of menthone, isomenthone and menthol with Ni(HFC)2 as the chiral main column has been reported by Bicchi et al. [92]. Werkhoff et al. [68] isolated these compounds from peppermint oils before stereoanalysis with permethylated p-cyclodextrin. 

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