Analysis enantioselective

In the case of chiral aroma substances, elucidation of the absolute configuration and determination of the enantiomeric ratio, which is usually given as the enantiomeric excess (ee), are of especial interest because the enantiomers of a compound can differ considerably in their odor quality and threshold. The compound 3a,4,5,7a- 

The determination of the ee value can be used to detect aromatization with a synthetic chiral aroma substance because in many cases one enantiomer is preferentially formed in the biosynthesis of chiral aroma substances (examples in Table 5.13). In contrast to biosynthesis, chemical synthesis gives the racemate which is usually not separated for economic reasons. The addition of an aroma sub- 

The method frequently applied to determine ee values is the enantioselective gas chromatographic analysis of the aroma substance on a chiral phase, e. g., peralkylated cyclodextrins. This method was used, e. g., to test raspberry fruit juice concentrates for unauthorized aromatization with trans-a-ionone. The gas chromatograms of trans-a-ionone from two different samples are shown in Fig. 5.13. The low excesses of the R-enantiomer of ee = 8% (concentrate A) and ee = 24% (B) can probably be put down to the addition of synthetic trans-a-ionone racemate to the fruit juice concentrate because in the natural aroma (C), the ee value is 92.4%. 

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Figure 10.1 Analysis of racemic 2,5-dimethyl-4-hydroxy-3[2H]-furanone (1) obtained from a strawbeny tea, flavoured with the synthetic racemate of 1 (natural component), using an MDGC procedure (a) dichloromethane extract of the flavoured strawbeny tea, analysed on a Carbowax 20M pre-column (60 m, 0.32 mm i.d., 0.25 p.m film thickness earner gas H2, 1.95 bar 170 °C isothermal) (b) chirospecific analysis of (1) from the sti awbeny tea exti act, ti ansfened foi stereoanalysis by using a pemiethylated /3-cyclodextrin column (47 m X 0.23 mm i.d. canier gas H2, 1.70 bar 110 °C isothemial). Reprinted from Journal of High Resolution Chromatography, 13, A. Mosandl et al., Stereoisomeric flavor compounds. XLIV enantioselective analysis of some important flavor molecules , pp. 660-662, 1990, with permission from Wiley-VCH.

In recent years, together with enantioselective analysis, the determination of the natural abundance of stable isotopes by means of stable isotope ratio mass spectrometry (TRMS) can be very useful for the assignment of the origin of foods and food ingredients, and of authenticity evaluation (24). 

A. Mosandl, G. Bmche, C. Askaii and H.-G. SclimaiT, Stereoisomeric flavor compounds. XLIV enantioselective analysis of some important flavor molecules , ]. High Resolut. Chromatogr. 13 660-662 (1990). 

Figure 13.2 MDGC-ECD chromatograms of PCB fractions from sediment samples, demonstrating the separation of the enantiomers of (a) PCB 95, (b) PCB 132, and (c) PCB 149 non-labelled peaks were not identified. Reprinted from Journal of Chromatography, A 723, A. Glausch et al, Enantioselective analysis of chiral polyclilorinated biphenyls in sediment samples by multidimensional gas cliromatography-electi on-capture detection after steam distillation-solvent exti action and sulfur removal , pp. 399-404, copyright 1996, with permission from Elsevier Science.

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... 

Lamprecht, G., Kraushofer, T., Stoschitzky, K., Lindner, W. (2000). Enantioselective analysis of (R)- and (S)-atenolol I urine samples by a high-performance liquid chromatography column-switching setup. J. Chromatogr. B 740, 219-226. 

Bortocan and Bonato [112] presented a capillary electrophoresis method for the enantioselective analysis of primaquine and its metabolite carboxyprimaquine. The method is used for the simultaneous determination of the drug and its metabolite, in... 

Hiihnerfuss, H. BiselU, S. Gaterman, R. 2004, Enantioselective Analysis of Polycyclic Musks as a Versatile Tool for the Understanding of Environmental Processes. The Handbook of Environmental Chemistry, Springer-Verlag Heidelberg, Germany Vol. 3X, pp. 213-231. 

Marchelli R, Dossena A, Pala G, The potential of enantioselective analysis as a quality control tool. Trends Food Sci Technol7, 1996. 

Shellie R, Marriott P, Cornwell C, Application of comprehensive two-dimensional gas chromatography (GC GC) to the enantioselective analysis of essential oils, J Sep Sci 24 823-830, 2001. 

Kreck, M., Scharrer, A., Bilke, S., Mosandl, A. (2002) Enantioselective analysis of monoter-pene compounds in essential oils by stir bar sorptive extraction (SBSE)-enantio-MDGC-MS. Flavour Fragrance ]. 17 32-40. 

If optimum chiral separation conditions and high-efficiency sample cleanup are properly employed, the first priorities in enantioselective analysis have been achieved. The ideal detector is universal yet selective, sensitive and structurally informative. MS currently provides the closest realisation to this ideal. 

The combination of enantio-MDGC with high-resolution MS or mass-selective detectors, both used in full scan or (at least) in the multiple ion monitoring (MIM) mode is currently the most potent analytical tool in enantioselective analysis of chiral compounds from complex mixtures. 

Fig. 17.5 Enantioselective analysis of germacrene D from the essential oil of different Solidago canadensis plants, using the enantio-MDGC-mass spectrometry (MS) technique [21]...

For that reason enantioselective analysis of linalool and linalyl acetate proved to be a powerful tool to detect adulterations with synthetic racemates of linalool and linalyl acetate, respectively [56, 75]. 

A reliable authenticity assessment is concluded from the simultaneous consideration of multielement IRMS and enantioselective analysis. The differences of the stable isotope ratios of linalool and linalyl acetate are depicted as a three-dimensional plot of A values (d values of linalool minus d values of linalyl acetate for oxygen, hydrogen and carbon) (Fig. 17.15). This plot shows that the commercial samples S1-S5 are different from all the other samples investigated. Linalool and linalyl acetate of S1-S5 definitely are not genuine lavender oil compounds. 

Mosandl A, Bruche G, Askari C, Schmarr H-G (1990) Steroisomeric flavor compoimds XLIV Enantioselective analysis of some important flavor molecules. J High Resolut Chromatogr... 

Bicchi C, Cordero C, lori C, Rubiolo P, Sandra P (2000) Headspace sorptive extraction (HSSE) in the headspace analysis of aromatic and medicinal plants. J High Resol Chromatogr 23 539 KreckM, Scharrer A, Bilke S, Mosandl A (2001) Stir bar sorptive extraction (SBSE)—enantio-MDGC-MS, a rapid method for the enantioselective analysis of chiral flavour compoimds in strawberries. Eur Food Res Technol 213 389... 

The main principle for enantioselective analysis using EPME is to find the lock for the key. The key is the enantiomer that must be analysed and the lock is a substance with a special architecture that can bind enantioselectively with the enantiomer. Accordingly, the principle can be defined as enantioselective binding. 

A. Glausch, G. P. Blanch and V. Schurig, Enantioselective analysis of chiral polychlorinated biphenyls in sediment samples by multidimensional gas chromatography-electron-capture detection after steam distihation-solvent extraction and sulfur removal , J. Chromatogr. 723 399 -404 (1996). 

Polychlorobiphenyls were recovered from sediments in another investigation by steam distillation/solvent extraction, followed by enantioselective analysis using multidimensional electron capture gas chromatography [189]. 

Rocha A, Marques MP, Coelho EB et al (2007) Enantioselective analysis of citalopram and demethylcitalopram in human and rat plasma by chiral LC-MS/MS application to pharmacokinetics. Chirality 19 793-801... 

LC-MS-based procedures for chiral and enantioselective analysis of mammalian samples are discussed in the Sects. 3.2 and 3.2.2 [47-50], Detailed data on biotransformation in vivo especially in man are quite rare. LC-ESI MS/MS procedures are referred that allowed metabolite identification in animals in in vivo and in vitro models [51, 52],... 

Fig. 4 Scheme of enzymatic plasma sample preparation for enantioselective analysis of S- and fChyoscyamine. Atropine-containing plasma samples are mixed either with human serum (procedure A) or with rabbit serum (procedure B). The latter one contains atropinesterase (AtrE) whereas human serum does not. AtrE catalyses the stereoselective hydrolysis of S-Hyo, whereas f -Hyo remains unaffected. 

Following procedure A the concentration of total Hyo was determined and following procedure B only the remaining i -Hyo portion was measured. 5-Hyo was calculated by the difference of both concentrations. Enantioselective analysis was performed according to John et al. [49]... 

Flavour and off-flavour compounds of black and white pepper (P. nigrum L.) were evaluated by Jagella and Grosch (1999a,b). Enantioselective analysis of optically active monoterpenes indicated ( )-linalool, (+)-a-phellandrene, (-)-limonene, myrcene, (-)-a-pinene, 3-methylbutanal and meth-ylpropanal as the most potent odorants of black pepper. Additionally, 2-isopropyl-3-methoxypyrazine and 2,3-diethyl-5-meth-ylpyrazine were detected as important odorants of the black pepper sample from Malaysia, which had a mouldy, musty off-flavour. Omission tests indicated a-and (3-pinene, myrcene, a-phellandrene, limonene, linalool, methylpropanal, 2- and 3-methylbutanal, butyric acid and 3-meth-ylbutyric acid as key odorants. A storage experiment revealed that for ground black pepper, losses of a-pinene, limonene and 3-methylbutanal were mainly responsible for deficits in the pepper-like, citrus-like, terpene-like and malty notes after 30 days at room temperature. The musty/mouldy off-flavour of a sample of black pepper was caused by a mixture consisting of 2,3-diethyl-5-methylpyrazine (2.9pg/kg) and 2-isopropyl-3-methoxypyrazine (0.2 (xg/kg). 

The reaction of 3,4-dihydroisoquinoline A-oxide (74) and methacrylonitrile in the presence of cationic half-sandwich rhodium and iridium complexes containing a chiral diphosphine ligand was analyzed. The cycloadditions occurred with excellent regio- and diastereoselectivity and low-to-moderate enantioselectivity. Analysis of the catalytic system showed the formation of two epimeric complexes 75 containing the dipolarophile methacrylonitrile. The reaction of one of the isolated diastereopure complexes 75 with 74 afforded cycloadduct 76 with high enantioselectivity. A recycling procedure was developed in order to increase the adduct/catalyst ratio <07CEJ9746>. 

Vetter, W. Maruya, K. A., Congener and enantioselective analysis of toxaphene in sediment and food web of a contaminated estuarine wetland Environ. Sci. Technol 2000, 34, 1627-1635. 

Vetter, W. Krock, B. Klobes, U. Luckas, B., Enantioselective analysis of a heptachlorobomane isolated from the technical product Malipax by gas chromatography/mass spectrometry J. Agric. Food Chem. 1997, 45, 4866-4870. 

Wiberg, K. Oehme, M. Haglund, R Karlsson, H. Olsson, M. Rappe, C., Enantioselective analysis of organochlorine pesticides in herring and ringed seal from the Swedish marine environment Mar. Poll. Bull. 1998, 36, 345-353. 

Lanchote, V.L., Bonato, P.S., Cerqueira, P.M., Pereira, V.A., Cesarino, E.J. Enantioselective analysis of metoprolol in plasma using highperformance liquid chromatographic direct and indirect separations applications in pharmacokinetics. J. Chromatogr. B 738, 27-37 (2000)... 

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