When it comes to logP vs. logD, the difference is in pH dependency. Whereas logP is pH independent, logD changes depending on pH levels.

• Lipophilicity, commonly expressed as octanol/water distribution coefficient (LogP), is an important physicochemical parameter in the drug discovery process which can be used to predict the pharmacokinetic properties and intestinal absorption of a drug.¹

• The partition coefficient LogP is a constant for the molecule in its neutral form. The distribution coefficient LogD takes into account all neutral and charged forms of the molecule, and varies with pH due to poor solubility of charged forms in octanol.

• LogP or LogD is used to calculate Lipophilic Efficiency (LipE) or Lipophilic Ligand Efficiency (LLE) of research compounds, where the efficiency of a compound is defined as its potency, via measured values of pIC50 or pEC50, minus its LogP or LogD (LLE = pIC50 – LogP/D).²⁻⁴

• BioDuro’s LogD assay uses the octanol / buffer shake flask method for determining lipophilicity. LC-MS/MS is used to quantify the samples.

Readout: logD(pH)

Controls: Testosterone; others available on request

Assay Description:

1 mL of 1-octanol and 1 mL of buffer are added to a glass vial. Compound stock solution (10 mM in DMSO) is added and the vial is rotated for one hour using a shaker at room temperature. The layers are allowed to separate and aliquots of each layer are taken.

Aliquots of the 1-octanol and aqueous solutions are serially diluted using DMSO to give the final samples for LC-MS/MS analysis. Three sequential dilutions are made of each 1-octanol phase, covering a 2500-fold range in concentration. Two sequential dilutions are made of each final aqueous phase, covering a 100-fold concentration range. The MS peak areas from these solutions are used to generate a log(peak area) against log(relative concentration) calibration line. LogD is calculated from the ratio of the 1-octanol relative concentrations to the interpolated aqueous relative concentrations.

The MS detection is performed by using a SCIEX API 4000 Q trap instrument. Each compound is analyzed by reversed phase HPLC using a Kinetex 2.6u C18 100 Å column (3.0 mm X 30 mm, Phenomenex). Mobile phase – solvent A: water with 0.1% formic acid,  solvent B: acetonitrile with 0.1% formic acid.

Data Analysis:

LogD is calculated using the following formula:

logD = log {(compound concentration in octanol) / (compound concentration in aqueous phase)}

Abbreviations:

DMSO                     Dimethylsulfoxide

HPLC                       High-performance liquid chromatography

LC                             Liquid chromatography

MS                           Mass spectrometry

Literature:

1. Lipinski C. A.; “Drug-like properties and the causes of poor solubility and poor permeability”; J. Pharmacol. Toxicol. Methods. 44, 235, (2000).

2. Leeson, P. D.; Springthorpe, B.; “The influence of drug-like concepts on decision-making in medicinal chemistry“, Nature Rev. Drug Discov.6, 881, (2007).

3. Edwards, M. P.; Price, D.A.; “Role of Physicochemical Properties and Ligand Lipophilicity Efficiency in Addressing Drug Safety Risks“, Ann. Rep. Med. Chem. 45, 381, (2010).

4. Shultz, M. D.; “Setting expectations in molecular optimizations: Strengths and limitations of commonly used composite parameters”, Bioorg. Med. Chem. Lett. 23, 5980, (2013).

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