APPLICATION OF THIN-LAYER CHROMATOGRAPHY (TLC) TO INVESTIGATING OSCILLATORY INSTABILITY OF THE SELECTED PROFEN ENANTIOMERS

Abstract

SUMMARY In our earlier studies we intended to evaluate the performance of thin-layer chromatography (TLC) as an analytical tool applied to separation of the selected profen (i.e. 2-arylpropionic acid) enantiomers and we selected ibuprofen as a model analyte for this purpose. Surprisingly enough, TLC is relatively seldom used for separation of enantiomers, even though – despite the low number of theoretical plates (N) in this particular technique in comparison with fully automated column chromatographic techniques (basically GC and HPLC) – it seems very well suited for complete separation of two analytes only (i.e. a pair of enantiomers). Separation of profens can be regarded as a particularly urgent analytical task, because they are among the most widely prescribed synthetic non-steroidal anti-inflammatory drugs and in medicinal chemistry we must be vigilantly aware of possible unpredictable consequences of dispensing medicines as racemic mixtures. In earlier and in more recent studies we have provided enough evidence not only to prove that the analytical performance of TLC is sufficient for separation of the enantiomers of ibuprofen, but also – even more important – to demonstrate the usefulness of this simple yet very efficient separation technique in physicochemical studies of the oscillatory instability of profens when stored for long periods of time in aqueous media. By use of TLC it was possible to show the oscillatory transenantiomerization of the profens from the S to the R form, and vice versa, during storage. The correctness of our TLC assessment with regard to structural oscillation of enantiomeric profens was later successfully confirmed by means of polariemetry.