Pirkle-concept

CSPs based on chiral selectors related to the Pirkle concept... 

All the CSPs related to the Pirkle concept have the following features in common. 

Most Pirkle-concept CSPs had either a K-accepior or a K-donor moiety. However, the commercialized Whelk-O 1 CSP is a hybrid of rr-acceptor and rr-donor CSPs tsee Fig. 9.25). It has been designed to have a cleft-like binding site formed by orthogonally arranged 3,5-dinitrobenzoyl and tetrahydrophenanthrene moieties aromatic groups are... 

A CSP based on the analogues 3,5-dinitrobenzoylated 1,2-diphenylethane-1,2-diamine (DNB-DPEDA) (see Fig. 9.26a) [349-353] has been commercialized by Regis under the tradename Ulmo. This CSP has proven to be excellent for the direct separation of aryl alcohol enantiomers without derivatization (see Fig. 9.26b) [349,351]. This improved Pirkle-concept CSP, that contains also ir-acidic as well as moderate n-basic aromatic binding sites, nicely resolved a wide variety of chiral drugs [350] and compounds of pharmaceutical interest [352]. 

ENANTIOSEPARATION OF PHARMACEUTICALLY RELEVANT CHIRAL COMPOUNDS USING PIRKLE-CONCEPT CSPs... 

For example, polymer-supported CSPs with Pirkle-concept SOs (e.g. (S)-valine-3,5-dimethylaniIide) attached to monodisperse macroporous polymethaciylate beads gave reasonable enantioselectivity and efficiency for 3,5-dinitrobenzamido derivatives of a-amino acids under normal-phase conditions [368.370], It could be demonstrated that such a CSP based on polymeric particles provided enhanced enantioselectivities... 

Recent strategies in CSP development and optimization related to the Pirkle concept and to low molecular weight synthetic chiral selectors. In the attempt to proceed more effectively with the development of new tailor-made CSPs, solid-phase syntheses and combinatorial chemistry approaches involving SO and/or CSP libraries have been tested. 

An interesting feature of the terguride-based CSP is its self-recognition ability, i.e. the terguride-based CSP can be used to separate the enantiomers of terguride [392]. This self-recognition phenomenon is often observed also for Pirkle-concept CSPs. 

Enantioseparations in SEC have been reported for several CSPs. including native and derivatized cyclodextrin-based CSPs [427-432. Pirkle-concept CSPs [77,336-338,347,348,363,365,433,434], polysaccharide type CSPs [137.435-438], macrocyclic antibiotic type CSPs [436], and others. 

Cleveland, T. Pirkle-concept chiral stationary phases for the HPLC separation of pharmaceutical race-mates. J.Liq.Chromatogr, 1995, 18, 649—671... 

In order to broaden the capabilities of the Pirkle concept, both polar and polarizable groups were introduced into the molecule. The most popular of this type of chiral stationary phase are the (R,R) Whelk-01 and the (S,S)Whelk-01 phases, the structures of which are shown below. These phases are more versatile and have a wider field of application than the phases previously described. The phases are covalently bonded to the silica and so they can be used with almost any type of solvent. However, they have been found to operate most effectively in the normal phase mode. It should be noted that the polarizable character of the aromatic ring is essential for the stationary phase to function well. As the Pirkle phases are generally available in both the (R) and (S) configurations, the reversal of the elution order of a pair of enantiomers is possible. This stationary phase was originally designed for the separation of the Naproxen enantiomers but has found a wide application to the separation of epoxides, alcohols, diols, amides, imides and carbamates. 

Baeyens, W.R.G. Van Der Weken, G. Aboul-Enein, H.Y. Reygaerts, S. Smet, E. Comparison of the enantiomeric separation of some 2-arylpropionic acids on a novel Pirkle-concept stationary packing by narrow-bore and conventional liquid chromatography, Biomed.Chromatogr., 2000,14, 58 60. 

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