Lateral Interactions in the Racemic Mixtures

Among the difficult (and sometimes referred to as sensitive ) chromatographic separations, those of enantiomeric antipodes and racemic mixtures are of particularly great importance and of the highest interest. This is because many compounds with a therapeutic effect (and incomparably more often the synthetic species than the natural ones) appear in a clearly defined enantiomeric form and for reasons of safety, need to be isolated from their opposite counterparts. Most phar-macodynamically active compounds are equipped with polar functionalities that make them interact with biological receptors and with the other constituents of a biological environment, and it often happens that these functionahties are of the AB type. In such cases, it can be justly concluded that an almost proverbial difficulty 

FIGURE 2.20 Schematic presentation of the hydrogen-bonded cyclic dimers of enantiomeric antipodes of 2-phenylpropionic acid, Ibuprofen, and Naproxen (the latter two compounds are drugs from the group of profens). 

Needless to add, lateral interactions among the enantiomeric antipodes can very strongly (and, of course, negatively) affect their preparative thin-layer (and also technological column) separation, carried out in the range of the nonlinear isotherm of adsorption. 

The traditional method of determination of the numerical values of the retardation factor, Rjn quasi-automatically assumes the following preconditions  

Circular (or symmetrically ellipsoidal) chromatographic band shape 

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