Influence of organic modifier and separation modes for lipophilicity assessment of drugs using thin layer chromatography indices

Lipophilicity constitutes one of the most important physicochemical properties in the design and development of drug molecules. In the present work thin layer chromatography (TLC) has been utilized to evaluate lipophilicity of 11 representative drugs, which included six proton pump inhibitors (omeprazole, pantoprazole, rabeprazole, lansoprazole, ilaprazole, and tenatoprazole), an anti-vertigo drug, betahistine, nonsteroidal anti-inflammatory drug, ibuprofen, anti-malarial drug, atovaquone, an anti-HIV agent, atazanavir and a hormonal drug, calcitriol. Normal as well as reversed-phase separation modes were evaluated to study the effect of different organic modifiers for the estimation of lipophilicity. The quantitative descriptor of lipophilicity, the partition coefficient (logP) was estimated by suitably optimizing the solvent systems for both the modes. The best mobile phase pairs for NPTLC and RPTLC were toluene-acetonitrile and water-methanol respectively. Principal component analysis, hierarchical cluster analysis, as well as non-parametric methods like sum of ranking differences and generalized pair wise correlation revealed the dominant pattern in the data. The results obtained from both the separation modes were comparable and were in good agreement with the computational data for all the drugs.