Chiral Capillary Column Research Articles

Enantioselective epoxidation reaction of non-functionalised prochiral alkenes using optically resolved [brucine]( R)-[Ru(PDTA-H)Cl] and [brucine]( S)-[Ru(PDTA-H)Cl] complexes

The racemic metal complex K[Ru(PDTA-H)Cl] 1 PDTA=Propylene diaminetetraacetic acid. 1 has been resolved into its optical isomers using brucine as the resolving agent counter ion, [brucine]( S)-[Ru(PDTA-H)Cl] ( 1) and [brucine]( R)-[Ru(PDTA-H)Cl] ( 2) and their structures are determined by single crystal X-ray methods. Longer Ru–Cl bonds in both the complexes (2.3974(13)A in 1 and 2.415(6) in 2 along with one relatively weaker and strained chelation ring could be responsible for their catalytic activity. The CD pattern of the complex 1 shows the presence of the two isomers λ and δ with more contribution of λ form while the complex 2 acquire only λ conformation. Catalytic activity of 1 and 2 for enantioselective epoxidation of non-functionalised alkenes viz. styrene, 4-chloro-, 4-methyl-, 4-nitrostyrene, 1,2-dihydronaphthalene and indene was accomplished by using molecular oxygen and iodosyl benzene as terminal oxidant. Excellent conversions (85–89%) were obtained in case of 1,2-dihydronaphthalene with both the catalysts while catalyst 2 gave good conversion with styrene and 4-methylstyrene. The enantiomeric excess of the epoxide was determined by 1 H NMR using chiral shift reagent Eu(hfc) 3/ by chiral capillary column. The extent of enantioselectivity with respect to the substituents on substrate is shown on Hammet plot. A possible mechanism at the oxo transfer stage is also envisaged.

Chiral Ru(II) Schiff base complex-catalysed enantioselective epoxidation of styrene derivatives using iodosyl benzene as oxidant. II

Six-coordinated chiral Ru(II) Schiff base complexes of the type [RuLX(Y) 2] where L=terdentate chiral Schiff bases derived from l-tyrosine, l-phenylalanine with salicylaldehyde, 3- tertiary-butyl-, 3,5-di- tertiary-butyl-, 3,5-dichloro- and 3,5-dinitrosalicylaldehyde, X=PPh 3 and Y=H 2O have been investigated as catalysts for enantioselective epoxidation of styrene, 4-chloro-, 4-nitro- and 4-methylstyrene in fluorobenzene in order to explore the efficiency of catalytic system by varying the substituents on the ligand moiety of the catalysts as well as on the substrates using iodosyl benzene as terminal oxidant. Much better results were obtained with catalyst 5 and 10 with 4-nitrostyrene. The enantiomeric excess of the resulting epoxide was evaluated by chiral capillary column.

Enantiomeric analysis of D- and L-pipecolic acid in plasma using a chiral capillary gas chromatography column and mass fragmentography.

Enantiomeric analysis of D- and L-pipecolic acid in plasma using a chiral capillary gas chromatography column and mass fragmentography.

Chiral Mn(III) Schiff base complex catalyzed aerobic enantioselective epoxidation of prochiral non-functionalized olefins

Dissymmetric Mn(III) chiral Schiff base complexes derived from 1 R,2 R(−)-1,2 diaminocyclohexane with 3-acetyl 4-hydroxy 6-methyl 2-pyrone and 2-hydroxy benzaldehyde, 5-chloro-, 5-methoxy-, 5-nitro-, 3-tertiary butyl- and 3,5 ditertiary butyl 2-hydroxy benzaldehyde have been prepared. Microanalysis, IR, UV/Vis spectroscopy, conductance measurement, optical rotation, CD spectroscopy and cyclic voltammetry accomplished the characterization of the complexes. These complexes were used for aerobic enantioselective epoxidation of 1-hexene, 1-octene, and 1,2-dihydronaphthalene using molecular oxygen in the presence of 2-methylpropanal as sacrificial reductant. Reaction progress was monitored on gas chromatography (GC) and the enantiomeric excess of the resulting epoxide was evaluated by chiral capillary column on GC and 1H NMR using Eu (hfc) 3 as chiral shift reagent. Good to excellent conversions and epoxide selectivity for all the substrates were obtained with all the catalysts while enantiomeric excess was relatively better in the case of 1,2-dihydronaphthalene. The extent of enantioselectivity with respect to the substrates and catalysts is shown by 3-D view presentation.

Selenomethionine chiral speciation in yeast and parenteral solutions by chiral phase capillary gas chromatography-ICP-MS

Chiral resolution and speciation of DL-selenomethionine enantiomers by capillary gas chromatography (GC) as N-trifluoroacetyl (TFA)-O-isopropyl derivatives using an l-valine-tert-butylamide modified polydimethylsiloxane chiral stationary phase (Chirasil-L-Val) were investigated. Good resolution was achieved using a temperature program from 100 °C (held for 3 min) to 160 °C at 1.5 °C min –1 and He as carrier gas. Very good selectivity and excellent detection limits of 0.25 µg L –1 (0.1 µg L –1 as Se) for each enantiomer were obtained by on-line coupling of the chiral capillary column with selenium-specific detection by inductively coupled plasma mass spectrometry (ICP-MS). Experimental parameter optimization is described in detail. This optimised GC-ICP-MS method was successfully applied to the determination of the optical purity of l-selenomethionine in commercial samples, to the determination of the enantiomeric ratio of selenomethionine in parenteral solutions used for human use and also to chiral Se speciation in selenized yeast.

Absolute chemical structure of the myxobacterial pheromone of Stigmatella aurantiaca that induces the formation of its fruiting body

Stigmatella aurantiaca, a species of myxobacteria, produces a novel extracellular signaling molecule, 8-hydroxy-2,5,8-trimethyl-4-nonanone, which promotes its developmental cycle. To determine the absolute configuration of this pheromone, which contains one asymmetric carbon, we prepared the R- and S-enantiomers by stereoselective synthesis. The synthesized R- and S-enantiomers each showed nearly the same fruiting body-inducing activities as the natural pheromone. Gas chromatography-mass spectrometry (GC-MS) analysis using a chiral capillary column revealed that the naturally-produced pheromone is a mixture of both enantiomers.

Absolute chemical structure of the myxobacterial pheromone ofStigmatella aurantiacathat induces the formation of its fruiting body

Stigmatella aurantiaca, a species of myxobacteria, produces a novel extracellular signaling molecule, 8-hydroxy-2,5,8-trimethyl-4-nonanone, which promotes its developmental cycle. To determine the absolute configuration of this pheromone, which contains one asymmetric carbon, we prepared the R- and S-enantiomers by stereoselective synthesis. The synthesized R- and S-enantiomers each showed nearly the same fruiting body-inducing activities as the natural pheromone. Gas chromatography-mass spectrometry (GC-MS) analysis using a chiral capillary column revealed that the naturally-produced pheromone is a mixture of both enantiomers.

Quantitative Analysis of Menthol Isomer Distributions in Selected Samples

Menthol occurs naturally in oils of the Mentha species in the (1 R, 3R, 4S)-(–) form (l-menthol), whereas synthetic menthol is available either in the same form or as a racemic mixture (d- and l-menthol). Quantitative analysis of the presence of the (1S, 3S, 4R)-(+)- form (d-menthol) is achieved by using gas chromatographic analysis on a chiral capillary column with selective ion monitoring detection. Detection of the presence of as little as 0.01 % (d-menthol in the total menthol concentration is possible with relative standard deviation values averaging around 7%. Minimal sample preparation with short sample analysis times of 30 min provide for a rapid sample turn around. This method should be applicable to the speciation of menthol in a wide variety of menthol-containing products, including cigarettes.

Three dehydrobutyrine-containing microcystins from Nostoc

Three cyclic heptapeptide hepatotoxins, [Asp 3, ADMAdda 5, Dhb 7] microcystin RR, [Asp 3, ADMAdda 5, Dhb 7] microcystin HtyR and [Asp 3, ADMAdda 5, Dhb 7] microcystin LR, were isolated from a Nostoc species. Their structures were assigned on the basis of 1H and 13C NMR, HR FAB mass spectrometry and amino acid analysis using GC-mass spectrometry on a chiral capillary column. All three microcystins contained dehydrobutyrine (Dhb), instead of dehydroalanine (Dha), d-aspartic acid, instead of d- erythro- β-methylaspartic acid ( d-MeAsp), and 9-acetoxy-3-amino-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (ADMAdda), instead of the corresponding 9-methoxyl derivative (Adda). This is the first report on the identification of Dhb-containing microcystins from Nostoc.

Aerobic, enantioselective epoxidation of non-functionalized olefins catalyzed by Ni(II) chiral Schiff base complexes

Some symmetrical and non symmetrical square planar Ni(II) chiral Schiff base complexes derived from 1 S,2 S(+)diaminocyclohexane, S(+)1,2-diaminopropane and 1 R,2 R(-)diphenyldiamino ethane with 3-acetyl-4-hydroxy-6-methyl-2-pyrone have been prepared. The characterization of the complexes was done by physico–chemical methods viz. microanalysis, conductance measurement, IR-, UV/visible-, 1 H -, 13 C { 1 H }NMR, CD spectral studies, optical rotation and cyclic voltammetry. These complexes catalyses the epoxidation of non-functionalized olefins viz. 1-hexene, 1-octene, trans-4-octene and indene with molecular oxygen as terminal oxidant in presence of the sacrificial reductant. Excellent chemical yield was obtained by GC with middle and terminal long chain alkenes than indene although the enantiomeric excess is good for indene with catalyst 3 and evaluated by 1 H NMR using chiral shift reagent Eu(hfc) 3 or by chiral capillary column on GC.

Characterization of Seven New Hydrocarbon Compounds Present in the Aroma of Virgin Olive Oils.

Seven isomeric hydrocarbons were detected in the volatile fraction of three samples of virgin olive oil. Chemical ionization mass spectrometry was used to assign the molecular formulas. Their structures were confirmed by comparison of retention time and mass spectral data with those of a synthetic sample obtained by pentene radical coupling. A final characterization of each chromatographic peak was done by means of a chiral capillary column to distinguish the optically active compounds from the isomers without chiral centers. For the quantitation the recovery factor in the oily matrix during the extraction of the volatile fraction was obtained using a related chemical, the commercially available beta-citronellene. On the basis of the previous literature and the present experiments a tentative rationalization of the involved biochemical pathway is proposed.

Synthesis of catalytically active polymer-bound Mn(III) salen complexes for enantioselective epoxidation of styrene derivatives

Catalytically active metal-complexing polymer-containing chiral Mn(III) salen moieties derived from (1 R, 2 R)-(−)-diphenylethylenediamine, (1 S, 2 S)-(+)-cyclohexanediamine, and ( S)-(+)-diaminopropane with α-naphthyl salicylaldehyde anchored to the polymeric matrix obtained from styrene-4-vinyl pyridine-divinyl benzene (PVPD) have been synthesised. These catalysts were used for enantioselective epoxidation of styrene and substituted styrenes, viz. 4-chloro-, 4-methyl and4-nitrostyrene using iodosyl benzene as terminal oxidant by GLC. The enantiomeric excess of the resulting epoxide was determined by GLC using chiral capillary column or by 1H-NMR using chiral-shift reagent Eu(hfc) 3. Each catalyst/substrate combination was examined under epoxidation condition and the results for catalysts 1–3 are presented as Hammet plots. A mechanism involving formation of an Mn-oxo complex and oxygen transfer from a reactive Mn-oxo intermediate to styrene was also proposed for the reaction. These catalysts can be recycled at least ten times without loss of its activity.

Chiral Ru(III) metal complex-catalyzed aerobic enantioselective epoxidation of styrene derivatives with co-oxidation of aldehyde

Ru(III) chiral Schiff base complexes 1–3 derived from dehydroacetic acid with 1 S,2 S-(+) diaminocyclohexane, 1 R,2 R-(−)1,2 diphenyl ethylenediamine and S-(+)1,2 diaminopropane have been prepared. The characterization of the complexes was done by microanalysis, magnetic moment, IR-, UV/Vis-, CD spectral studies, optical rotation, conductance measurements and cyclic voltammetry. The enantioselective epoxidation of styrene and substituted styrenes viz., 4-chloro-, 4-nitro- and 4-methyl styrene was achieved by the combined use of molecular oxygen and sacrificial reductant isobutyraldehyde catalyzed by the above synthesized Ru(III) chiral Schiff base complexes. Good yields of the desired epoxides were obtained with styrene and 4-chlorostyrene by GLC. Enantiomeric excess of the epoxide was evaluated by 1H-NMR using chiral shift reagent Eu(hfc) 3 and by chiral capillary column. The extent of enantioselectivity is shown on Hammet plots.

Synthesis, physicochemical studies and aerobic enantioselective epoxidation of non functionalized olefins catalyzed by new Co(II) chiral salen complexes

Co(II) chiral salen complexes 1– 3 derived from α-naphthyl salicylaldehyde with 1 S,2 S (+) diaminocyclohexane, 1 R,2 R (−) diaminodiphenylethane and S(+) 1,2-diaminopropane have been prepared. The characterization of the complexes was done by microanalysis, magnetic moment, IR-, UV/Vis-, CD spectral studies, optical rotation, conductance measurements and cyclic voltammetry. Epoxidation of non-functionalized prochiral olefins viz. styrene, trans 3-nonene and trans 4-octene was achieved by the combined use of an atmospheric pressure of molecular oxygen and sacrificial reductant isobutyraldehyde catalyzed by the above synthesized Co(II) chiral salen complexes with and without pyridine N-oxide as cooxidant. Good yields of the desired epoxide were obtained with the substrate trans 3-nonene and trans 4-octene by GLC. Enantiomeric excess of the epoxide were evaluated by 1 H NMR using chiral shift reagent Eu(hfc) 3 and by chiral capillary column.

Enantioselective gas chromatographic assay of 2-alkylamines using N-(trifluoroacetyl)prolyl derivatives and a chiral capillary column

The chromatographic properties of (R)-(+)-N-(trifluoroacetyl)prolyl and (S)-(-)-N-(trifluoroacetyl)prolyl derivatives on a chiral gas chromatography capillary column were assessed for the measurement of enantiomeric purities of 2-butylamine, 2-pentylamine, 2-hexylamine, 2-heptylamine and 2-octylamine and their N-methyl analogues, which are used as precursors in the synthesis of some selective, specific, irreversible monoamine oxidase-B inhibitors. Using a Chirasil-Val column it was possible to separate all four diastereomers of the primary amines, and three of the four isomers of the secondary amines. Quantitation of the enantiomers is facilitated even with enantiomerically impure reagent when compared to the use of an achiral phase.

Asymmetric catalytic epoxidation of styrene by dissymmetric Mn(III) and Ru(III) chiral Schiff base complexes synthesis and physicochemical studies

Some dissymmetric Mn(III) and Ru(III) chiral Schiff base complexes derived from 1 R,2 R(−)1,2-diaminocyclohexane with 3-acetyl-4-hydroxy-6-methyl-2-pyrone and salicylaldehyde, 5-chloro-5-methoxy-and 5-nitrosalicylaldehyde have been synthesized. The characterization of the complexes was accomplished by microanalysis, IR, UV-Vis, CD spectroscopy, conductance measurements, magnetic susceptibility, optical rotation and electrochemical studies. The asymmetric epoxidations catalyzed by the complexes were examined with styrene using the terminal oxidant, iodosylbenzene to assess the stereoselectivity in the epoxidation of styrene by changing substituents on the catalyst. In all cases the R form of the catalyst resulted in S(−) form of the product as a dominant enantiomer. Optical yield of the resulting epoxide was determined by GLC using chiral capillary column/ 1H NMR using Eu(hfc) 3 as a chiral shift reagent.

Determination of the enantiomeric composition of α‐terpineol in essential oils

AbstractNatural enantiomerically pure (4R) (+)‐α‐terpineol was detected, for the first time, in the essential oil of Micromeria fruticosa (L.) Druce. High enantiomeric purities of the (+)‐enantiomer (78‐88%) were detected in seven other oils. Relatively high enantiomeric purities of (4S) (−)‐α‐terpineol (80%) were detected in the oils of cinnamon and Laurus nobilis L. Lower enantiomeric purities of the (−)‐enantiomer (64‐69%) were detected in another four oils, using a permethylated β‐cyclodextrin chiral capillary GC column.

Biosynthesis of (+)-cubenene and (+)-epicubenol by cell-free extracts of cultured cells of Heteroscyphus planus and cyclization of [2H]farnesyl diphosphates

The absolute stereochemistry of cubenene and epicubenol from cultured cells of Heteroscyphus planus was determined as both (+)-isomers by 1H and 13C NMR spectroscopy, GLC using a chiral capillary column, and optical rotations. Incubation of two geometrical isomers of deuteriated farnesyl diphosphate (FPP) with a cell-free extract from cultured cells indicated that both compounds were specifically formed from (2E,6E)-FPP. Gas–liquid chromatography–mass spectrometry (GLC–MS) and 2H NMR analyses of (+)-cubenene and (+)-epicubenol generated from [1,1-2H2]- and [6-2H]-FPP confirmed the presence of 1,2- and 1,3-hydride shifts in their formation.

Chiral gc analysis of enantiomerically pure (r)(—)‐linalyl acetate in some lamiaceae, myrtle and petitgrain essential oils

AbstractEnantiomerically pure (R)(—)‐linalyl acetate was detected in the essential oils of Salvia sclarea L. (clary sage), Salvia dominica L., Mentha citrata Ehrh., Myrtus communis L. (myrtle) and Citrus aurantium L. (petitgrain) using Lipodex E as a chiral capillary column.

Chiral GC analysis of (1R)(+)‐pulegone with high enantiomeric purity in essential oils of some lamiaceae aromatic plants

Abstract(1R)(+)‐Pulegone with high enantiomeric purity (95–100%) was detected in the essential oils from fresh leaves of Mentha piperita L., M. longifolia (L.) Huds., M. pulegium L., M. sylvestris L., Calamintha incána (Sm.) Heldr. and Micromeria fruticosa. L. High enantiomeric purities were found in samples of commercial (+)‐ and (—)‐pulegone. Direct enantiomeric separation was performed using a Cyclodex B chiral capillary column.