Current State of the Art in HPLC Methodology for Lipophilicity Assessment of Basic Drugs. A Review

Zone fluidics for measurement of octanol-water partition coefficient of drugs

A novel zone fluidics (ZF) system for the determination of the octanol-water partition coefficient (Pow) of drugs was developed. The ZF system consisted of a syringe pump with a selection valve, a holding column, a silica capillary flow-cell and an in-line spectrophotometer. Exact microliter volumes of solvents (octanol and phosphate buffer saline) and a solution of the drug, sandwiched between air segments, were sequentially loaded into the vertically aligned holding column. Distribution of the drug between the aqueous and octanol phases occurred by the oscillation movement of the syringe pump piston. Phase separation occurred due to the difference in densities. The liquid zones were then pushed into the detection flow cell. In this method, absorbance measurements in only one of the phase (octanol or aqueous) were employed, which together with the volumes of the solvents and pure drug sample, allowed the calculation of the Pow. The developed system was applied to the determination of the Pow of some common drugs. The log (Pow) values agreed well with a batch method (R(2)=0.999) and literature (R(2)=0.997). Standard deviations for intra- and inter-day analyses were both less than 0.1log unit. This ZF system provides a robust and automated method for screening of Pow values in the drug discovery process.

Lipophilicity assessment of ruthenium(II)-arene complexes by the means of reversed-phase thin-layer chromatography and DFT calculations

The lipophilicity of ten ruthenium(II)-arene complexes was assessed by reversed-phase thin-layer chromatography (RP-TLC) on octadecyl silica stationary phase. The binary solvent systems composed of water and acetonitrile were used as mobile phase in order to determine chromatographic descriptors for lipophilicity estimation. Octanol-water partition coefficient, logK_OW, of tested complexes was experimentally determined using twenty-eight standard solutes which were analyzed under the same chromatographic conditions as target substances. In addition, ab initio density functional theory (DFT) computational approach was employed to calculate logK_OW values from the differences in Gibbs' free solvation energies of the solute transfer from n-octanol to water. A good overall agreement between DFT calculated and experimentally determined logK_OW values was established (R² = 0.8024–0.9658).

Mobile phase pH and organic modifier in reversed-phase LC–ESI-MS bioanalytical methods: assessment of sensitivity, chromatography and correlation of retention time with in silico logD predictions

Background: The aim of the work described herein was to undertake a systematic investigation of the effect of mobile phase pH and organic modifier in typical reversed-phase LC–MS methods with regard to ESI-MS response, chromatographic performance and correlation of retention time with in silico logD predictions. Results: For the test set of pharmaceutical analytes investigated, ESI-MS response was generally greater when employing methanol rather than acetonitrile as the organic modifier, and increases of up to tenfold were observed dependent on the pH-buffered mobile phase employed. Deleterious effects on chromatographic performance of protonated basic analyte were observed under conditions of neutral to weakly basic pH. A qualitative correlation between plots of predicted logD and observed retention time against pH was demonstrated. Conclusion: In the absence of a simple and/or predictive dependence of analyte ESI-MS response on the mobile phase pH, a practical evaluation should be undertaken when absolute sensitivity is paramount. The use of in silico predictions of analyte logD to direct the development of bioanalytical assays is broadly valid, but further scrutiny is recommended in predicting the retention of ionized analyte.

Extension of the liquid chromatography/quantitative structure-property relationship method to assess the lipophilicity of neutral, acidic, basic and amphotheric drugs

A reported chromatographic method to determine the 1-octanol/water partition coefficient (logP(o/w)) has been used to estimate the lipophilicity of 33 drugs with diverse structures and functionalities, including neutral, acid, basic, and amphoteric compounds. The applicability of the chromatographic method has been extended to the UHPLC technique, and the results obtained were compared to those obtained from conventional HPLC. No significant difference between the results obtained by both techniques is noticed. Thus, the suitability of UHPLC, which involves shorter run times, for lipophilicity assessment is demonstrated. In order to show the consistency of this chromatographic method, the logP(o/w) values of those drugs which have acid-base properties have been also determined by potentiometry, and the final results have been compared with both values derived from the chromatographic method and the ones from the literature.

Estimating the Lipophilicity of Natural Products using a Polymeric Reversed Phase HPLC Method

The integration of physicochemical profiling screens such as Log P into natural products drug discovery programs is emerging as an approach to front-load drug-like properties of natural product libraries for high-throughput screening. In this study a fast-gradient HPLC method using a polystyrene-divinylbenzene PRP-1 column was developed to estimate the lipophilicity of marine natural products. An excellent correlation was found between the results of the experimental determined and the literature log P values for a diverse set of commercially available drugs using the PRP-1 column. The log P of a series of 24 marine natural products were evaluated using the new method and a good correlation was observed between the experimentally determined and software calculated log P values. Some discrepancies were observed between the measured value of log P and the software calculations of the natural products containing halogens atoms. The method is rapid, insensitive to impurities, and requires very little compound and is amenable for integration into a natural products drug discovery research program.

Rapid high performance liquid chromatography method development with high prediction accuracy, using 5cm long narrow bore columns packed with sub-2microm particles and Design Space computer modeling

Many different strategies of reversed phase high performance liquid chromatographic (RP-HPLC) method development are used today. This paper describes a strategy for the systematic development of ultrahigh-pressure liquid chromatographic (UHPLC or UPLC) methods using 5cmx2.1mm columns packed with sub-2microm particles and computer simulation (DryLab((R)) package). Data for the accuracy of computer modeling in the Design Space under ultrahigh-pressure conditions are reported. An acceptable accuracy for these predictions of the computer models is presented. This work illustrates a method development strategy, focusing on time reduction up to a factor 3-5, compared to the conventional HPLC method development and exhibits parts of the Design Space elaboration as requested by the FDA and ICH Q8R1. Furthermore this paper demonstrates the accuracy of retention time prediction at elevated pressure (enhanced flow-rate) and shows that the computer-assisted simulation can be applied with sufficient precision for UHPLC applications (p>400bar). Examples of fast and effective method development in pharmaceutical analysis, both for gradient and isocratic separations are presented.