A Guide to the Analysis of Chiral Compounds by …

1 Inside:Definitions ofChirality and ChiralChromatographyChiral ColumnsOffer UniqueSelectivityOptimizationof ChiralSeparationsChiral SpecificApplications ofEssential Oils,Flavors, an dPharmaceuticalsA Guide to th eAnalysis of ChiralCompounds by GCTechnical Guide2 The Rt - DEXsm and Rt - DEXsechiral capillary columns offe rextensive enantiomeric separationof monoterpenes, monoterpen ealcohols, an d monoterpene ketonesthat cannot be matched bype rmethylated -cyclodextrincolumns. Rt - DEXsp and Rt - DEXsa are secondary columnsthat best resolve specific flavor an dfragrance Chiral components. Th eRt - DEXcst provides excellentresolution of some complex flavorcompounds and has demonstratedgreat potential with pharmaceuticalsubstances as :Definitions of Chirality an dChiral Chromatography.

2 3 Chiral Columns Offe rUnique Selectivity ..5 Optimization of Specific Applicationsof Essential Oils, Flavors, an team of researchers at th eUniversity of Neuch teldeveloped -cyclodextrins withsuperb enantiomericse lectivi ty . They joined forceswith Restek, a manufacturer oftop quali ty columns, to provid ea unique line of commerciallyavailable -cyclodextrinstationary phases withenhanced capabilities fo rchiral capillary ga Raphael TabacchiBorn in Ticino, Switzerland,Dr. Tabacchi has been aprofessor for Analytical an dOrganic St ructure at th eUniversity of Neuch tel,Switzerland, since 1978. Hi sresearch interests focusedupon natural productchemistry, and developmentof HPLC and GC stationaryphases.

3 He has developed -cyclodextrins with uniquesubstitutions to create novelchiral phases for Georges Claude SaturninBorn in St. Joseph,Martinique, Dr. Saturninbecame a Senior Assistantand Assistant Professor in1990 at the University ofNeuch tel. He is involved inth e devel opment of HPLC phases. His focus is th esynthesis of these ne wcyclodextrin materials thatcharacterize the new BitzerAfter completing he rChemistry degree at WestVirginia University in 1995,Lori joined Restek as a FusedSilica ManufacturingChemist. She is involved withthe design and production ofnew pr odu cts includingcapillary Chiral columns. Loriensures product quality an dconsistency that ar echaracteristic of all SponslerSherry is an ApplicationsChemist and has been withRestek since 1990.

4 Sheconducts method and productdevelopment for Analysis offoods, flavors and fragrances,as well as some pharmaceuti-cal samples. Frequentcommunication withcustomers has helped Sherryto identify many importantchiral applications in theseindustries. She has demon-strated many of these ke yseparations, especially fo rfragrances and amphet-amines, using the ne wcyclodextrin Bieder mannMaurus has been with Grob s GC/LCGC group at the KantonalesLaborat or y Zurich (OfficialFood Control Authority inSwitzerland) since 1990 an dhas participated in th edevelopment of severalLCGC methods for foodanalysis. During hi ssabbatical at Restek, hedemonstrated the ab ili ty ofthese new and unique chiralphases for many applicationssuch as the authenticity ofessential oils, natural flavor extracts, and th eanalysis of drugs fo renantiomeric PorretBorn in Neuch tel, Switzer-land, Ms.

5 Porret waspreviously a technician atNestl and joined s team in 1991. Sheis also involved in th esynthesis of organiccompounds and with th edevelopment of GC an dHPLC stationary phases. 3 Linalool is a Chiral compound because it contains an assymmetric carboncenter. The mirror images are not superimposable and so they are configurationEnantiomers can be distinguished by configuration. Following groups fromhigh to low priority in the clockwise direction is denoted R, and S for thecounterclockwise configurationFigure 1 ALinalool oxides have two Chiral centers at carbon numbers 2 and 5 andexist as four 1B2S, 5R(+)-cis-linalool oxide2R, 5S(-)-cis-linalool oxide2S, 5S(-)-trans-linalool oxide2R, 5R(+)-trans-linalool oxideWHAT ARE CHIRALCOMPOUNDS?

6 Any carbon atom that is bonded tofour different functional groups istermed a Chiral or an assymetric car-bon. Molecules containing one ormore of these carbon centers are con-sidered Chiral molecules. Chiral cen-ters can exist in two forms calledenantiomers. These two forms arenon-superimposable mirror images ofeach other, but both have similarproperties. For example, both enan-tiomers will have the same boilingpoint, densities, and reaction rates asachiral molecules. They do, however,generally possess different aroma andflavor characteristics; more impor-tantly, they possess differences intoxicity and biological are also known as opti-cal isomers because they rotate planepolarized light in different isomers that rotate plane po-larized light to the right, or clockwise,are termed dextrorotary {denoted as(d) or (+)}, Optical isomers that rotatein the left direction are termed levoro-tary {denoted (l) or (-)}.

7 Enantiomers can be denoted by thespecific configuration around thechiral center. Groups on the carboncenter are assigned a priority basedon atomic number of the first bondedatom (Cahn-Ingold-Prelog rules). Thegroup with the highest atomic num-ber is rated first. If priority cannot beestablished with the first atom, workoutward until priority differences canbe determined. Once priorities havebeen established for all four groups,specific configuration can be deter-mined. An R configuration is desig-nated when the priority around theassymmetric carbon is in a clockwisedirection, whereas a counterclockwisedirection is denoted as S. (Figure 1A)1A Chiral compound can possess mul-tiple Chiral centers and many combi-nations of configurations.

8 Linalooloxides possess two Chiral centers, re-sulting in four enantiomers. (Figure1B) Note that configuration (R or S) isindependent from optical activity (+ or-) or interaction with (CH2)3CH2CH2(CH2)3CH3 CHCH2CH2 CHOHHOWHAT ARE CHIRALCOMPOUNDS?Any carbon atom that isbonded to four different groupsis termed a Chiral or anassymetric carbon. Moleculescontaining one or more ofthese carbon centers are con-sidered Chiral centers can exist in twoforms called two forms are non-superimposable mirror imagesof each other, but both havesimilar properties. 4 Figure 2 Restek s Chiral columns demonstrate exceptional lifetime and stability formore than 250 injections without loss of 102030min.

9 1020301,234895671011121314151,2348567101 1121314159 Chiral chromatography is theseparation of enantiomericcompounds. Common liquidstationary phases do notpossess adequate selectivityfor enantiomeric of derivatizedcyclodextrin macromoleculesto common stationary phasescreates capillary columns withthe ability to separatemany (-) -pinene2. (+) -pinene3. decane4. (-) 2,3-butanediol5. (+) 2,3-butanediol30m, ID, m Rt- DEXsa (cat.# 13108)Oven temp.: 40 C (hold 1 min.) to 230 C @ 2 C/min.;Carrier gas: hydrogen; 80cm/sec. set @ 40 C; Detector: FID set @ 220 CWHAT IS CHIRALCHROMATOGRAPHY? Chiral chromatography is the separa-tion of enantiomeric liquid stationary phasesused in gas chromatography resolvecomponents from one another, butthey do not possess adequate selec-tivity for enantiomeric of derivatized cyclodextrinmacromolecules to common station-ary phases creates capillary columnswith the ability to separate enanti-omers as permethylated derivative of beta-cyclodextrin in cyanopropyl-dim-ethylpolysiloxane liquid stationaryphase is commonly used for such ste-reochemical separations, but it exhib-its limited applications.

10 Beta-cyclodextrins derivatized with alkylsubstituents can enhance the enan-tiomeric resolution of various com-pound classes. Restek s five capillarycolumns incorporate various combi-nations of alkylated beta-cyclodex-trins into a cyanopropyl-dimethylpolysiloxane liquid stationary phaseto achieve significant columns also exhibit stabilityand extended lifetime. From the firstinjection to the 250th injection on achiral column, enantiomeric separa-tion is maintained with almost no lossin resolution (Figures 2A and B).A: 1st injectionB: 250th injection6. undecane7. nonanal8. 1-octanol9. 2,6-dimethylphenol10. (+) phenylethanol11. (-) phenylethanol12. methyl decanoate13. dicyclohexylamine14.