Application of thin-layer chromatography to investigate oscillatory instability of the selected profen enantiomers in dichloromethane

The usefulness of thin-layer chromatography (TLC) as an efficient measuring technique in the studies of oscillatory trans-enantiomerization of profens from the S to the R configuration (and vice versa) during their storage as 70% ethanol solutions is demonstrated in the literature. S-(+)-ibuprofen, S-(+)-naproxen, and S,R-(+/-)-2-phenylpropionic acid are utilized as the test profens. It is proven possible to show oscillatory instability with the racemic S,R-(+/-)-2-phenylpropionic acid also. Correctness of the TLC assessment is successfully confirmed by means of polarimetry. Upon these preliminary results, it is concluded that the most probable mechanism might embrace the keto-enol tautomerism because of a convenient migration of the proton from one moiety of the profen molecule to another in an aqueous medium. To indirectly verify this hypothesis, profens are stored in dichloromethane, deliberately hampering their ability to dissociate and to re-structure. It is obvious though that the (much less pronounced) electrolytic dissociation can occur in the non-aqueous media as well. It is shown that the non-aqueous solvent considerably suppresses, although they do not completely eradicate, the oscillatory trans-enantiomerization of profens. In view of these findings, the reports which claim a predominant therapeutic potential of the respective S-profens become less convincing and certainly need reconsideration.