Prediction of bioavailability of phenolic acids by potentiometric titration method and chromatographic techniques

Early screening of physico-chemical and ADME (Absorption, Distribution, Metabolism and Elimination) properties has become the key interest in drug discovery. Molecular lipophilicity is a major physico-chemical property, which describes oral absorption, cell uptake, protein binding, blood-brain penetration and metabolism of the bioactive substances. Phenolic acids (a group of molecules present in majority of plants) exhibit protective effects against many diseases, but whether they can reach their sites of action, particularly in humans, is largely unknown. The aim of our work was to investigate several ADME parameters of 8 phenolic acids by chromatographic techniques (RP-TLC and RP-HPLC) and potentiometric titration method. Nowadays chromatography has a tendency to replace tedious „shake-flask“ method for measuring lipophilicity. The TLC measurements were performed on 10×20cm glass plates precoated with RP-18F_254s. The HPLC measurements were performed using Agilent 1100 LC System, with ZORBAX SB-C18, 4.6×150mm, 3.5µm particle size column. The binary solvent system, methanol–phosphate buffer (pH=2.5), was used as a mobile phase in both techniques with a varying content of organic modifier (80–5%). The potentiometric titration method was chosen to get detailed information on the partitioning characteristics of target compounds at all pH values. pK _a values and lipophilic pH-profiles were determined using Sirius instrument GLpKa. Linear regression has shown good correlation between R _M(TLC) and logk _w(HPLC) values (r=0.96). The correlation between experimental data and ADME parameters predicted by different computer programs was considered in order to evaluate the predictive power of the theoretical approaches applied to predict the lipophilicity of phenolic acids. Moderate correlations (r <0.90) between experimental and theoretical values demand constant evaluation of calculated data validity.