Determination Of Enantiomeric Ratios Research Articles

Pronounced Self-Induced Diastereomeric Anisochronism in Anisidine Amino Acid Diamides.

The emergent properties resulting from selective supramolecular interactions are of significant importance for materials and chemical systems. For the directed use of such properties, a fundamental understanding of the interaction mechanism and the resulting mode of function is necessary for a tailored design. The self-induced diastereomeric anisochronism effect (SIDA), which occurs in the intermolecular interaction of chiral molecules, generates unique properties such as chiral self-recognition and nonlinear effects. Here we show that anisidine amino acid diamides lead to extraordinary signal splitting in NMR spectra through supramolecular interaction and homochiral self-recognition. By systematic experiments we have investigated the underlying SIDA effect, explored its limits and finally successfully utilized it in the determination of enantiomeric ratios by NMR spectroscopy of chiral 'SIDA-inactive' compounds such as thalidomide.

Determination of Aristocularine Enantiomers by Dispersive Liquid–Liquid Microextraction and Chiral High-performance Liquid Chromatography

ABSTRACTHere is reported a novel analytical approach for the extractive separation and determination of enantiomeric ratios of aristocularine in bovine serum albumin. The results demonstrate suitable analytical performances. The separation was performed by chiral high-performance liquid chromatography with a 5-µm column using a mobile phase of 1:1 n-hexane:ethanol at a flow rate of 0.7 mL min−1 with ultraviolet–visible absorption, circular dichroism, and polarimetric detection. The enantiomers were eluted at 13.2 and 15.6 min for (+) and (−)-aristocularine, with a resolution of 1.58 and a separation factor of 1.27. The analytical parameters for the dispersive liquid–liquid microextraction were optimized; under these conditions, the extraction recoveries were from 88.6% to 93.9% for a two-step extraction. The precision, reported as the percent relative standard deviation, had values from 2.9% to 3.2% for 0.5 µg mL−1 of analyte for five replicate measurements using ultraviolet–visible absorption and circular dichroism detection. The limits of detection were between 0.05 and 0.08 µg mL−1 with enrichment ratios up to a value of 12.

Development of Electrophoretic Methods for Simultaneous Determination of Enantiomeric Ratio and Composition of Diastereomeric Salt Mixtures

Obtaining enantiomeric pure compounds is—among other techniques—possible in a resolvation experiment via diastereomeric salt formation, excellently exemplified by a modified Pope–Peachy method performed in supercritical carbon dioxide as solvent. The salt precipitation is followed by supercritical fluid extraction (SFE) to separate the diastereomeric salts and the unreacted enantiomers. To evaluate the extraction efficiency, conversion and enantioselectivity achieved, it is essential to determine the enantiomer excess and the residual resolving agent content in extracts and raffinates. Carefully chosen experimental parameters enable the simultaneous determination of certain anions and cations in capillary electrophoresis in a single run, which has not been reported for diastereomeric mixtures so far. In this paper, a partially validated chiral selective cyclodextrin enabled capillary electrophoresis method is presented for the characterization of cis-permethrinic acid samples resolved with (R)-1-phenylethylamine prepared by the SFE-based resolvation technique. To evaluate the efficiency of the resolvation, a cyclodextrin enabled chiral separation method was developed applying permethylated-β-cyclodextrin as chiral selector. The theoretical possibility of the widespread application of the developed method (with minor adjustments) is justified for other selectands and selectors. The developed methods can be thereby applied for the fast and reliable control of resolvation experiments.

Phenylselenenylmenthane derivatives and their enantiomeric discrimination by 1H and 13C NMR spectroscopy in the presence of a chiral dirhodium complex

AbstractThe phenylselenenylmenthane and ‐menthene derivatives 1–4 were studied in terms of 1H and 13C signal assignments, conformational analysis and also complexation shifts (Δδ) and dispersion effects (Δν) observed when non‐racemic (ca 2 : 1) mixtures of the chiral selenides were exposed to an equimolar amount of the chiral dirhodium complex Rh*. The complexation site is the selenium atom exclusively. Whereas Δδ values are moderate or small, dispersed signals (split into two owing to the existence of diastereomeric adducts) can be observed, many of which are large enough for a facile determination of enantiomeric ratios of the selenides irregardless of the conformational behaviour of the selenides and the adduct composition. Thus, the ‘dirhodium method’ is simple and reliable for chiral recognition in the class of organoselenium compounds which is gaining increasing importance in developing new techniques of asymmetric synthesis. Copyright © 2002 John Wiley & Sons, Ltd.