Comparative RP-HPTLC Lipophilicity Analysis of Bioactive 1,3,4-Thiadiazole-Resorcinol Conjugates

The behavior of bioactive 1,3,4-thiadiazoles of anticancer potency and cholinesterases (ChEs) inhibitors was examined by high-performance thin-layer chromatography (HPTLC) in a reversed phase (RP) system. The chromatographic systems consisted of C-18 or C-8-bonded silica as the stationary phase and binary mixtures of water with methanol, acetonitrile, acetone, or dioxane as the mobile phase. The lipophilicity parameters R_Mw (the R_M value of a solute extrapolated to pure water as the mobile phase) were determined based on the linear relationship between compound retention and water content in the mobile phase. R_Mw parameters obtained from various chromatographic systems were analyzed both in relation to each other and compared with other lipophilicity parameters, including log k_w values obtained by RP-18 HPLC and computationally calculated log P. Descriptive, correlation and principal component analyses were applied. The applicability of the HPTLC method for assessing the lipophilicity of 1,3,4-thiadiazole-resorcinol conjugates was demonstrated based on the log k_w values determined by HPLC according to the OECD-recommended procedure and described previously. The correlation coefficients (r) between the R_Mw parameters for these systems and log k_w (C-18) is ≥0.81, whereas for the C-8 stationary phases R_Mw versus log k_w is ≥0.95. Taking into account the results of descriptive and correlation analysis, the C18 stationary phase with methanol as the organic modifier and the C8 stationary phase with methanol or dioxan as the organic modifier were found to be the most suitable chromatographic systems for lipophilicity determination of bioactive compounds.