High-throughput determination of octanol/water partition coefficients using a shake-flask method and novel two-phase solvent system

Abstract

A high-throughput method for determining the octanol/water partition coefficient (Po/w) of a large variety of compounds exhibiting a wide range in hydrophobicity was established. The method combines a simple shake-flask method with a novel two-phase solvent system comprising an acetonitrile–phosphate buffer (0.1M, pH 7.4)—1-octanol (25:25:4, v/v/v; AN system). The AN system partition coefficients (KAN) of 51 standard compounds for which logPo/w (at pH 7.4; logD) values had been reported were determined by single two-phase partitioning in test tubes, followed by measurement of the solute concentration in both phases using an automatic flow injection-ultraviolet detection system. The logKAN values were closely related to reported logD values, and the relationship could be expressed by the following linear regression equation: logD=2.8630 logKAN –0.1497(n=51). The relationship reveals that logD values (+8 to –8) for a large variety of highly hydrophobic and/or hydrophilic compounds can be estimated indirectly from the narrow range of logKAN values (+3 to –3) determined using the present method. Furthermore, logKAN values for highly polar compounds for which no logD values have been reported, such as amino acids, peptides, proteins, nucleosides, and nucleotides, can be estimated using the present method. The wide-ranging logD values (+5.9 to –7.5) of these molecules were estimated for the first time from their logKAN values and the above regression equation.