Research And Application On Evaluating The Hydrophobicity Of Pharmaceuticals Using Capillary Electrophoresis

The hydrophobicity of pharmaceutical is an important physicochemical property, and is of great significance in the biopharmaceutical-related fields, particularly in the processes of the design and development of pharmaceuticals. To find some better methods and better models to evaluate the hydrophobicity of pharmaceuticals is a target which has been always aimed at by scientists. Microemulsion capillary electrophoresis (MCE) and liposome capillary electrophoresis (LCE), which are both belonged to capillary electrophoresis (CE), have been used as powerful methods to indirect measure the hydrophobic parameters (logP_ow) of various kinds of compounds. In order to obtain a correct logP_ow value, the migration parameters in both MCE and LCE must be accurately required, because the migration parameters are highly related with the accuracy of logP_ow measurement in CE. However, in conventional MCE, the shortage of obtaining the electrophoretic mobilities of the microemulsion phase (μ_me) with tracing method was discovered, and the influences of concentration, injection volume of analyte and high electric-field on measuring the electrophoretic mobilities of analyte (μ_eff) were found, too. In addition, the same problem in obtaining the electrophoretic mobilities of liposome (μl) is also existed in LCE. Therefore, an improved MCE and LCE are expected to be established to ensure the accuracy ofμ_me,μ_eff andμl, which would obtain much more accurate logP_ow values.In this thesis, two improved capillary electrophoresis methods, including MCE and LCE were investigated to evaluate the hydrophobicity of pharmaceuticals. The preparation process and the reliability of them were studied in detail and several applications with satisfactory results were performed. The main contents and results are listed as follows:1. The compositions of microemulsion were investigated systematically. Five alkyl-benzenes were used to study the effects of types and concentrations of surfactant, oil phase, and co-surfactant, pH values and ion strengths of buffer on the retention time and resolution in MCE. The results showed: the better surfactant is SDS and its suitable range of concentration is 45¹00 mM; the better oil phase is 1-heptane and its suitable range is 80¹00 mM; the better co-surfactant is 1-butanol and its suitable range is 800⁹00 mM, which would offer some valuable information and directions to select the proper composition of microemulsion for MCE measuring logP_ow. 2. In MCE, a mathematical model of the accuracy of logP_ow (ΔlogP_ow) as a function of the deviation of migration time (Δtm) was presented for the first time. Our model shows that for a given microemulsion system, there is an interval of migration times, where a high accuracy in the determination of logP_ow can be obtained. However, when the migration time approaches either the migration time of the electroosmotic flow or that of the microemulsion phase, the accuracy of logP_ow deteriorates rapidly. The model was experimentally verified by three different microemulsion systems. The model could give some directions for the measurement of logP_ow by MCE.3. A novel improved method of MCE (I-MCE) to evaluate the hydrophobicity of pharmaceuticals was established by improving two aspects of conventional MCE. On the one hand, non-linearity fitting program was used to obtainμ_me to avoid the error from tracingμ_me, which was called I-μ_me-MCE. The logP_ow values of five uncharged pharmaceuticals were obtained by I-μ_me-MCE, and the average error and average relative error between logP_ow values by I-μ_me-MCE and the ones from literature was 0.08 logarithm units and 3.73%, better than the ones by conventional MCE. On the other hand, extrapolating method was used to eliminate the effects of concentrations and injection volumes of analytes, and stable enough microemulsion was selected to eliminate the effect of high electric-field onμ_eff measurement, which was called I-μ_eff-MCE. Applying the I-μ_eff-MCE method to determine the logP_ow values of six uncharged alkyl-benzenes, and the average error and avererage relative error between logP_ow values by I-μ_eff-MCE and the ones from literature was 0.15 logarithm units and 5.35% relatively, better than the ones by conventional MCE. Combined both of I-μ_me-MCE and I-μ_eff-MCE methods, an improved MCE (I-MCE) was developed.4. I-MCE method was applied to estimate logP_ow values of uncharged compounds, charged pharmaceuticals, and the components in herb medicine extracts compared to the conventional MCE. The logP_ow of all pharmaceuticals obtained by I-MCE agreed with those obtained by classical shake flask or literature, the errors between them were within 0.1 logarithm units, much better than the ones by conventional MCE. 5. The LCE method to evaluate the hydrophobicity of pharmaceuticals was established. The electrophoretic mobility of liposomeμl was also obtained by non-linearity fitting method. The logP_ow values of eight pharmaceuticals measured by this iteration LCE method were compared to those determined by non-iteration method and by shake-flask or literatues. In addition, the correlation between logP_ow in LCE and the logarithm of penetration parameter (logPm), and the ones between logP_ow literatures and logPm were studied. It was told that the relativity of logP_ow obtained by LCE and logPm was better. It also proved that as a biomembrane model, liposome is more similar to biomembrane than octanol-water system. The LCE method has the potential to be an screening model in vitro at the early stage of the drug discovery process.Two improved CE methods, I-MCE and new LCE, would be alternative techniques to evaluate the hydrophobicity of pharmaceuticals.