Determination of partition coefficients using 1 H NMR spectroscopy and time domain complete reduction to amplitude-frequency table (CRAFT) analysis

NMR spectroscopy in drug discovery and development: Evaluation of physico-chemical properties

Determination of physico-chemical properties of compounds is one of the corner-stones in selection of hit molecules for further progression into lead development in the modern drug discovery process. The speed of traditional analyses and limited quantities of hit molecules are obstacles for efficient acquisition of experimental data. Herein, the range of applications of quantitative nuclear magnetic resonance (NMR) spectroscopy as a fast technique used to evaluate solubility, log P and pKa are discussed.

Band-selective excitation NMR spectroscopy and quantitative time-domain analysis using Complete Reduction to Amplitude-Frequency Table (CRAFT) to determine distribution coefficients during drug development

A sensitive quantitative ¹ H NMR method for determining distribution or partition coefficients has been developed that is applicable to early drug discovery. After partitioning and equilibration, aliquots from each layer are analyzed using band-selective excitation ¹ H NMR spectroscopy in regions that are free of 1-octanol and water solvent signals. Signals are quantitated directly using CRAFT software, and their amplitudes are adjusted to correct for nonuniformity within the excitation band. Using this approach, the distribution coefficients for 20 drugs present at low concentrations were determined giving values that were in excellent agreement with literature values.

Exploring hydrophobicity limits of polyproline helix with oligomeric octahydroindole-2-carboxylic acid

The polyproline-II helix is the most extended naturally occurring helical structure and is widely present in polar, exposed stretches and "unstructured" denatured regions of polypeptides. Can it be hydrophobic? In this study, we address this question using oligomeric peptides formed by a hydrophobic proline analogue, (2S,3aS,7aS)-octahydroindole-2-carboxylic acid (Oic). Previously, we found the molecular principles underlying the structural stability of the polyproline-II conformation in these oligomers, whereas the hydrophobicity of the peptide constructs remains to be examined. Therefore, we investigated the octan-1-ol/water partitioning and inclusion in detergent micelles of the oligo-Oic peptides. The results showed that the hydrophobicity is remarkably enhanced in longer oligomeric sequences, and the oligo-Oic peptides with 3 to 4 residues and higher are specific towards hydrophobic environments. This contrasts significantly to the parent oligoproline peptides, which were moderately hydrophilic. With these findings, we have demonstrated that the polyproline-II structure is compatible with nonpolar media, whereas additional manipulations of the terminal functionalities feature solubility in extremely nonpolar solvents such as hexane.