Solvation chiral solvating agents

Kagan and coworkers determined and studied in detail the crystal structure of a 1 1 molecular complex between (i )-methyl p-tolyl sulfoxide (10) and S)-N-(3,5-dinitrobenzoyl)-l-phenylethylamine (11). They suggested that amide 11, which had been used as a chiral solvating agent for sulfoxides, might find use as a resolving agent for these compounds. ... 

Nuclear Magnetic Resonance Spectroscopy Measured in a Chiral Solvent or with a Chiral Solvating Agent. One method of NMR analysis for enantiomer composition is to record the spectra in a chiral environment, such as a chiral solvent or a chiral solvating agent. This method is based on the diastereomeric interaction between the substrate and the chiral environment applied in the analysis. 

There are three types of chiral auxiliary that are used chiral derivatizing agents (CDAs), chiral lanthanide shift reagents (CLSRs) and chiral solvating agents (CSAs)75. Chiral derivatizing agents (CDAs), such as the enantiomers of o -methoxy-o -(trifluoromethyl)phenylacetic acid (MTPA, 83)76, require the separate formation of discrete... 

Related to the NMR use of CLSRs is the application of chiral solvating agents (CSAs), so-called because the first report of the determination of enantiomeric excess by NMR was that of a partially racemic sample of 2,2,2-trifluro-l-phenylethanol (98),... 

S )-Ar- -Butyl-2-(phenylcarbamoyloxy)propionamide (193) was used as chiral solvating agent in the NMR determination of the enantiomer composition of the N-(3,4-dinitrobenzoyl) derivative of amino acid ethyl esters400. 

In conclusion, the most important result is that the use of permethylated cyclodextrin as chiral solvating agent for NMR spectroscopy not only affords a simple and practical way for the determination of the stereochemical purities of trisubstituted allenes, but also allows one to simultaneously determine their absolute configuration. Indeed, TRIMEB induced only positive complexation shifts of all the allene protons, which are greater for the (S )-enantiomer than for the (R)-enantiomer, independent of the structure of the allene. This empirical correlation seems to be reliable since it has been satisfied by a large number of trisubstituted allenes. 

Barretta and coworkers63 reported a direct determination of the enantiomeric purity of chiral trisubstituted allenes by using permethylated cyclodextrin as a chiral solvating agent. They found that the heptakis ft-cyclodextrin TRIMEB discussed above can be successfully used as a chiral solvating agent (CSA) for the NMR determination of the enantiomeric purity of trisubstituted allenes llOa-f. An accurate analysis of the experimental conditions (molar ratio aliene/TRIMEB, temperature and solvent) required to optimize the enantioseparation has been carried out. The XH NMR spectra of TRIMEB, allenes llOa-f, and the mixtures TRIMEB/allene have been recorded at 300 MHz in CD3OD as solvent. 

Consequently, the splitting observed is due to the fact that TRIMEB induces nonequivalence in the proton nuclei of the two enantiomers of the allenes, thus enabling one to determine the enantiomeric purities by using a chiral solvating agent. In all cases examined the extent of the nonequivalence, i.e. the difference of the proton chemical shifts of the two enantiomers in the presence of TRIMEB, can be increased by increasing the... 

The detailed structure of the small bacteriocin (isolated from the culture broth of the Gram-negative bacterium Rhizobium leguminosarum) as N-[(3R)-hydroxy-7-ns-tetradecenoyl]-L-HSL 14 was elucidated largely by the 1-D and 2-D and 13C spectroscopy. The absolute configuration of both asymmetric carbon atoms in the molecule was determined by the use of chiral solvating agents (S)-(+)- and (R)-(-)-2,2,2-trifhioro-l-(9-anthryl)ethanol [11]. 

Equations [1] and [2] describe the interaction of enantiomeric solutes A and A with chiral solvating agent S. Solvates (or association complexes) are formed that are diastereomeric and thus can, in principle, have different properties. Relevant differences are those in... 

Magnitudes and Senses of Nonequivalence Observed for (/ )-(-)-Enriched TFPE (la) in Some Chiral Amine Solvating Agents ... 

Chiral solvating agent each agent was determined to be more than 90% enan-tiomerically pure, except for Id and le whose purity was found to be ca. 80% hence data obtained by these two fluoroalcohols has been corrected to 100%. Unless otherwise noted, the molar ratio of CSA to solute is between 2.4 and 3.3. From ref. 21. 

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