Optical activity chromatographic studies

Some optically active cationic and racemic anionic complexes were examined to elucidate the mechanism of chiral recognition of cations and anions capable of forming hydrogen bonds [313]. The chromatographic study showed that enantiomers of some anionic complexes form favourable ion pairs with cationic A-complexes (Table 31). 

Allenmark, S., Techniques used for studies of optically active compounds, in Chromatographic Enantiosep-aration Methods and Application, 2nd ed., Ellis Horwood Ltd., London, 1991. 

One of the most studied polymerization systems employs alkyllithium initiators that are modified by chiral amine ligands for the polymerization of sterically bulky methacrylates [8,38,39,40,41], acrylates [42],crotonates [43], and acrylamides [44]. A primary example is the reaction of triphenylmethyl methacrylate with an initiator derived from 9-fluorenyllithium and (-)-sparteine (3) at -78 °C (Scheme 4). The resultant isotactic polymer is optically active, and is postulated to adopt a right-handed helix as it departs from the polymerization site. This polymer has been particularly successful as a chiral stationary phase for the chromatographic resolution of atropisomers [8]. Many modifications of the or-ganolithium initiator/chiral ligand system have been explored. Recently, Okamo-to has applied enantiopure radical initiators for the enantioselective polymerization of bulky methacrylate monomers [45]. 

AUenmark, S. Techniques Used for Studies of Optically Active Compounds, in Chromatographic Enantioseparation Methods and Application, 2nd Ed. Ellis Horwood Ltd London, 1991. 

The separation of amino acids into particular enantiomers was the subject of mass spectrometric studies but also ESI MS was applied to determine by kinetic resolution the enantiomeric excess of optically active alcohols and amines in nanoscale by diastereoselective derivatization with optically active acids [38], This method has several distinctive features among others, easily available chiral acids can be used (the authors used A -benzoyl proline derivatives), no chromatographic separations are required, it is insensitive to certain impurities, it is fast and requires only small amount of substrate (10 nmol or less). The method can take an advantage when accuracy of enantiomeric excess measurement is sufficient within 10% limits. 

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