Enantiomer最新文献

New chirally modified p-tert-butylthiacalix[4]arenes were synthesized via conformation- and/or regioselective etherification with ethyl bromoacetate followed by hydrolysis of the ester moiety and then subsequent amidation with (S)-1-phenyl-ethylamine or (S)-1-(1-naphthyl)ethylamine. These chiral selectors were coated with OV-17 on capillary columns to examine their ability as chiral stationary phases (CSPs) for discrimination of enantiomeric amino acid, amine and alcohol derivatives. It was found that CSP-(S)-4 prepared from cone-shaped tetra-(S)-1-phenylethylamide (S)-4 showed good to fair separations for all the samples examined. On the contrary, the corresponding CSP-(S)-14 prepared from the cone-shaped tetraamide (S)-14 of the parent p-tert-butylcalix[4]arene did not indicate any enantioseparation at all for the same samples, showing that the bridging group of the calix[4]arene ring is critical for the advent of enantioselectivity. The effect of the types and the numbers of the chiral amide groups in the chiral selectors on enantioselectivity was also discussed.

The pH-dependent and temperature-controlled enantiomerization of oxazepam has been studied by dynamic micellar electrokinetic chromatography in an aqueous buffer system with sodium cholate as the chiral surfactant. Experimental interconversion profiles featuring plateau formation were simulated by the new program ChromWin 99. Peak form analysis yielded rate constants and kinetic activation parameters of the enantiomerization of oxazepam between 5 degrees C and 25 degrees C.

Several 1-(o-aryl)barbituric and -2-thiobarbituric acid derivatives were proven to be chiral in their conformational ground states due to the hindered rotation about the C(aryl)-N(1) bond, by observation of diastereotopic groups (H or CH3) at 5-position of the heteroring by 1H and 13C NMR. Some of the enantiomers were semipreparatively enriched by liquid chromatography on triacetylcellulose or on cellulose tris-(3,5-dimethyl)-phenylcarbamate (chiralcel OD-H). Circular dichroism spectra of the enriched enantiomers have been examined with reference to their stereostructures.

Several alkyl aryl and aryl benzyl sulfoxides have been prepared in optically active form via enantioselective Ti-catalyzed oxidation of the corresponding sulfides. The absolute configuration was assigned on the basis of optical rotation while in the case of some new sulfoxides it was determined by the analysis of their circular dichroism spectra. The alkyl aryl sulfoxides have been efficiently resolved by CHIRALCEL OB chiral stationary phase (CSP) while the aryl benzyl sulfoxides were better separated on CHIRALCEL OJ CSP. In both cases the S enantiomer was always eluted first. This finding can then allow to determine the absolute configuration of alkyl aryl and aryl benzyl sulfoxides on the basis of their elution order on these CSPs.

The first two examples of the successful application of chiral salen ligands for diastereoselective syntheses of dinuclear Ti(IV), (L1Ti)2O2 and (PdI2L2Ti)2O2 species with defined chirality and geometry at the metal centre are presented. The structure of the complexes was established by X-ray structural analysis. Both complexes have similar structural features: (1) chiral salen ligands have cis-beta configuration around Ti centres, (2) (R,R) chirality of ligands induces delta helicity of ligand, and (3) syn arrangement of ligand donor atoms in relation to the TiO2Ti plane. Stereoselective effects of the dimers are discussed engaging available literature data. A model has been proposed to rationalise high syn selectivity in the formation of dimers.

A convenient method is described for the resolution of racemic Albuterol by selective crystallization of its di-p-toluoyl-D-tartrate salt. The separation resulted in a 38% yield of the (R)-enantiomer. Racemization of the (S)-enantiomer occurs in diluted H2SO4 at 100 degrees C in 80% yield. This racemic mixture was recycled to the diastereomer salt, in order to improve the overall yield. The (R)-Albuterol tartrate salt was decomposed in a sulfuric acid solution, and the (R)-Albuterol was isolated as its sulfate salt with 67% overall yield with 99.5% optical purity.

Achiral lanthanide tris beta-diketonate complexes are added to the acid and ester derivatives of the chiral NMR solvating agents dinitrobenzoyl-L-leucine and N-1-(1-naphthyl)ethylaminocarbonyl-L-valine to enhance enantiomeric discrimination. With the acid derivative, the solvating agent bonds directly to the lanthanide(III) complex to create an anionic species, and larger shifts are usually observed for the resonances of the enantiomer that associates more strongly with the solvating agent. With the ester derivative, the solvating agent generally does not bind to the lanthanide, whereas the substrate does. In this situation, the enantiomer that associates less strongly with the solvating agent exhibits the larger lanthanide-induced shifts. The effectiveness of adding neutral lanthanide complexes containing two beta-diketonate ligands and one chiral carboxylate ligand is compared to the anionic species with three beta-diketonate ligands and a chiral carboxylate ligand.

Amination of aryl trifluoromethyl ketones with ammonium formate readily gave racemic 2,2,2-trifluoro-1-arylethylamines in good yields. Resolution of 2,2,2-trifluoro-1-phenylethylamine was carried out with the Pseudomonas fluorescens lipase via enantioselective alcoholysis of its chloroacetamide.

Kinetic resolution of racemic beta-halohydrins has been achieved by reaction with benzoyl chloride in the presence of a catalytic amount (0.3 mol%) of a chiral diamine combined with diisopropylethylamine to afford the corresponding benzoates and unreacted beta-halohydrins in good to excellent enantioselectivities. The benzoate can be converted to the corresponding allylic benzoate without loss of optical purity by treatment with (1,5-diazabicyclo[4.3.0]non-5-ene).

Using normal-phase HPLC, the enantiomers of 4-(2',4'-difluorobiphenyl-4-yl)-4-oxo-2-methylbutanoic acid (flobufen) could be separated on Whelk-O1 (alpha = 1.34), ULMO (alpha = 1.08) and Chiralcel ODH (alpha = 1.33) chiral stationary phases. (R,R/S,S)- and (R,S/S,R)-5-(2',4'-difluorobiphenyl-4-yl)-3-methylfuran-2-one, the lactone of the 4-hydroxy metabolite could be completely separated on ULMO only. On the same CSP this 4-(2',4'-difluorobiphenyl-4-yl)-4-hydroxy-2-methylbutanoic acid could be separated in part (alpha = 1.06 and 1.12). Absolute configuration of the metabolites was established by NOE experiments.