Complexation gas chromatography

Metal Complex. Complexation gas chromatography was first introduced by V. Schurig in 1980 (118) and employs transition metals (eg, nickel, cobalt, manganese or rhodium) complexed with chiral terpenoid ketoenolate ligands such as 3-ttifluoroacetyl-lR-camphorate (6),... 

Figure 1-13. Chiral metal chelates for enantiomer resolution by complexation gas chromatography.

One of the most sophisticated methods is the use of chiral gas chromatographic capillary columns for the direct separation of volatile enantiomers. Complexation gas chromatography with enantioselec-tive transition metal fl-ketoenolates permits the stereochemical analysis of volatile oxygenated compounds in the nanogram range with high 44,45... 

Optically pure (3i )(—)-linalyl acetate was detected in the oils of clary sage Salvia sclarea). Salvia dominica, lavender and lavandin using H-NMR spectroscopy with a chiral lanthanide shift reagent, Eu(hfc)3. This enantiomer was also detected in the oils of lavender, lavandin and bergamot using complexation gas chromatography on Ni(hfc) 2, and... 

Schurig V. Enantiomer separation by complexation gas chromatography — Applications in chiral analysis of pheromones and flavours, in Schreier P (ed.), Bioflavour 87, Walter de Gruyter, Berlin, Germany, pp. 35—54, 1988. 

Weber R, Schurig V, Complexation gas chromatography— a valuable tool for the stereochemical analysis ofpheromones, Naturwissenschafien,7 AQi-A 5,1984. 

Determined by complexation gas chromatography on Ni(II) bis(2-heptafluoro-butyryl- S)-4-methy1thujan-3-onate) (ref 8). 

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. 

In general, enantiomer analysis by complexation gas chromatography can be performed without substrate derivatization. Aliphatic diols, however, have been separated as boronates or acetonides151. 

A limiting factor of complexation gas chromatography is the low temperature range (25-120°C). Therefore, improved thermostable polymeric stationary phases, e.g., Chirasil-Metal, in which the chiral metal chelates are chemically anchored to a polysiloxane backbone, have been prepared155 156. 

Examples for and have been observed under certain experimental conditions for reactive and/or strained chiral oxiranes which were separated by complexation gas chromatography (Figure 21)133. The first eluted peak was diminished in the separation of racemic 2-methyl-3-phenylo.xirane. In this case two enantioselective processes are mediated by the chiral metal chelate, i.e., chromatographic resolution and kinetic resolution (in favor of the first eluted enantiomer). Since two enantioselective processes are involved, the elution profile will be the same svhen the chirality of the metal chelate is inverted. 

Figure 21. A1) True racemic composition for enantiomer separation196 of frons-2,3-dimethyloxirane by complexation gas chromatography on nickel(II) bis[3-heptafluorobutanoyl-(D )-camphorale] at 80CC. Integration with a Spectra-Physics SP4100 instrument (peak areas are equal).

B) Deviation from the expected 1 1 ratio for a racemate (second peak diminished) upon enantiomer separation of 2-(chloromcthvl)oxirane on cobalt(Il) bis[3-(heplafluorobutanoyl)-(l/ )-camphorate] by complexation gas chromatography at 60 =C. 

Figure 22. Interconversion profiles due to inversion of configuration (enantiomerization) of 1-chloro-2,2-dimethylaziridine and 1,6-dioxaspiro[4.4]nonane determined by complexation gas chromatography on nickcl(II) bis[3-(heptafluorobutnnoyl)-(1 / )-camphorate] 148,203 boxed profile calculated chromatogram202.

Figure 23. Top temperature-dependent reversal of enantioselectivity for the enantiomers of (1-methyleth-yl)oxirane by complexation gas chromatography on nickel(II) bis[3-(heptafluorobutanoyl)-8-methylene-(1 /i)-camphorate]203. Bottom linear Van t Hoff plot and determination of the isoenantioselectivc temperature (89 °C).

Figure 27. Epoxide hydrolase catalyzed kinetic resolution of c/.v-2-ethyl-3-methyloxirane and formation of 2i ,3f -2,3-pentanediol as monitored by complexation gas chromatography on 0.08 M nickel(II) bis[3-(heptafluorobutanoyl)-(1 / )-camphorate] in methylpolysiloxane [25 m x 0.25 mm (i.d.) glass capillary column. 95CC, 1.1 bar nitrogen]191 2,3-pentanediol as acetonides 0.14 M nickel(ll) bis[3-(heptafluo-robutanoyl)-(l /t,2S)-pinan-4-onatc]151 in SE-30. Note that there is a change in the numbering of the chiral carbon atoms of the oxiranc vs. the diol due to nomenclature requirements.

Applications of enantiomer analysis by complexation gas chromatography in pheromone chemistry189 and in flavor research190 have been reviewed. The quantitative kinetic resolution of c -2-ethyl-3-methyloxirane by enzymatic hydrolysis to (21 ,3/ )-2,3-pentanediol, catalyzed... 

Various Chiral-Metal stationary phases used in complexation gas chromatography have been described192, as are racemates which have been successfully resolved6. 

Schurig, V. and Biirkle, W. (1982) Extending the scope of enantiomer resolution by complexation gas chromatography, J. Amer. Chem. Soc. 104, 7573-7580. 

Schurig, V. (1987) Semi-preparative enantiomer separation of l,6-dioxaspiro[4.4]nonanes by complexation gas chromatography, Naturwissenschaften 74, 190-191. 

Schurig, V. (2002) Practice and theory of enantioselective complexation gas chromatography. J. Chromatogr. A 965, 315-356. 

Weber, R. and Schurig V. (1984) Complexation gas chromatography - a valuable tool for the stereochemical analysis of pheromones. Naturwissenschaften 71, 408-413. 

Schurig V., Weber R. A., Nicholsen G. J., Oehlschlager A. C., Pierce H. D., Jr, Borden J. H. and Ryker L. C. (1983) Enantiomer composition of natural exo- and endo-brevicomin by complexation gas chromatography/selected ion mass spectrometry. Naturwissenschaften 70, 92-93. 

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