Chiral selectors anion-exchange type

Monolithic columns with the chiral anion exchange-type selectors incorporated into the polymer matrix obtained through in situ copolymerization process of a chiral monomer (in situ approach) [80-83,85] or attached to the surface of a reactive monolith in a subsequent derivatization step (postmodification strategy) [84], both turned out to be viable routes to enantioselective macroporous monolithic columns devoid of the limitations of packed columns mentioned earlier. 

New brush-type phases (donor-acceptor interactions) are appearing all the time. " Examples are stationary phases comprising quinine derivatives and trichloro-dicyanophenyl-L-a-amino acids as chiral selectors. Quinine carbamates, which are suitable for the separation of acidic molecules through an ionic interaction with the basic quinine group, are also commonly used but in general they are classified with the anion-exchange type of chiral selectors (see further) because of their interaction mechanism, even though r-donor, r-acceptor properties occur. (Some separations on Pirkle-type CSPs are shown in Table 2.)... 

Benzyloxycarbonyl, N-(3,5-dinitrobenzyloxy carbonyl), 9-fluorenylmethoxycarbonyl, benzoyl, acetyl and N-(2,4-dinitrophenyl) derivatized amino acids and profens WAX (weak anion-exchange) type CSP tert. -butylcarbamoylquinine as chiral selector on Hypersil silica gel), 3 pm Acetonitrile-methanol (80 20)+400 mM acetic acid+4 mM triethylamine 335 mm x 100 pm i.d. 250 mm effective length, chiral separation... 

M. Lammerhofer and W. Lindner, Quinince and quinidine derivatives as chiral selectors. Beush type chiral stationary phases for high performance liquid chromatography based on chincona carbamates and their applications as chiral anion exchanger, J. Chromatogr. 741 (1966), 33. 

Xiao TL, Armstrong DW (2004) Macrocyclic antibiotics. Chapter 4. In Giibitz G, Schmid MG (eds) Chiral separations, methods and protocols. Humana Press, Totowa, NJ, pp 113-171 Lammerhofer M, Lindner W (1996) Quinine and quinidine derivatives as chiral selectors. I. Brush type chiral stationary phases for high-performance Uquid chromatography based on cinchonan carbamates and their application as chiral anion exchangers. J Chromatogr A 741 33-48... 

Lammerhofer M, Lindner W (1996) Quinine and quinidine derivatives as chiral selectors. 1. Brush type chiral stationary phases for HPLC based on dnchonan carbamates and their application as chiral anion exchangers. J Chromatogr A 741 33-48... 

Lammerhofer and Lindner reported on the enantiomer separation of derivatized amino acids and profens on a weak-anion-exchange(WAX)-type stationary phase based on chiral quinine carbamate selectors by p-CEC [54,55]. The separations were performed either under aqueous or [54] non-aqueous conditions [55]. The efficiency obtained in the p-CEC mode was about two to three time higher than with LC using an acetonitrile/buffer flow system [54], Very high resolutions and efficiencies were found for non-aqueous p-CEC. For example, the enantiomer separation of Fmoc-leucine was achieved in less than 10 min with a resolution Rs of 6.9 at about 100 000... 

A special subclass of brush-type chiral stationary phases are the ion-exchange CSPs developed by Lammerhofer and Lindner (1996). By introducing an additional ionic moiety, a strong interaction between the selector and the selectand can be achieved. The first commercial available phases are based on the Cinchona alkaloids Quinine and Quinidine with an additional weak anion-exchange function offering good separation possibilities for chiral acids. A strong dependence of the capacity from the counter ion of the mobile phase could be demonstrated by Arnell (2009). 

---