Use of RP-TLC and theoretical computational methods to compare the lipophilicity of phenolic drugs

The chromatographic behavior of the phenolic drugs niclosamide, hexachlorophene, ibuprofen, pentazoeine, ethamivan, bithionol, salicylanilide, caffeic acid, p-coumaric acid, 4-aminosalicylic acid, ferulic acid, and methyldopa has been investigated on RP8F(254s) and RP18F(254s) TLC plates with methanol-water mixtures in different volume proportions as mobile phases. Linear relationships were obtained between the R-M values of the drugs and the volume fraction of methanol in the mobile phase. Retention values, R-M were extrapolated to zero methanol content and the lipophilicity values R-MW(RP8) and R-MW(RP18) obtained were compared both with measured partition coefficients (log P-exp) and with partition coefficients (AlogPs, IAlogP, AB/logP, COSMOFFrag, miLogP, KOWWIN, and xlogP) calculated using seven different software products. Comparison of the calculated partition coefficients revealed IAlogP, KOWWIN, miLogP, and (logP) over bar (where is the average of all the theoretical partition coefficients) usually correlate best with chromatographic lipophilicity R-MW. The results indicate that chromatographic lipophilicity R-MW can be used as a measure of the lipophilicity of the phenolic drugs investigated.