Thin-layer chromatographic detection of new azaphenothiazines

Many new phenothiazines exhibit promising anticancer and antibacterial activities, reversal of multidrug resistance and potential treatment in Alzheimer's, Creutzfeldt-Jakob and AIDS diseases. Their synthesis may proceed through a stage of the Smiles rearrangement and may lead to different products: cyclic phenothiazines (rearranged or not), cyclic side-products of isosteric structures and non-cyclic products when the ring-closure processes did not occur. The TLC method was found suitable for detection of new modified phenothiazines (being tri-, tetra- and pentacyclic azaphenothiazines with hydrogen, alkyl, dialkylaminoalkyl, aryl and heteroaryl substituents at the thiazine nitrogen atom and in a few cases additional substituents in the benzene ring) during their synthesis. The natural fluorescence of phenothiazines and azaphenothiazines under irradiation of UV light of 365 nm is very characteristic and becomes useful additional analytical information of these compounds. The spots of azaphenothiazines were also distinguished from the spots of substrates and side-products by giving color reactions with the visualizing reagents: sulfuric acid in ethanol, concentrated nitric acid and citric acid in acetic anhydride. The combination of the separation (the RF values) and the spot color detection (as the native fluorescence and the results of the usage of visualizing reagents) facilitated the identifications of new azaphenothiazines in the reaction mixtures containing also other compounds. This paper is the first attempt of the determination of new azaphenothiazines by TLC method preceding the identification by spectroscopic methods. It facilitates the separation of the proper fraction in column chromatography and preparative TLC.