What Is in a Structure? Cell Permeability and Solubility of Series of Macrocycles and Linear Matched Pairs

Macrocycles are a highly interesting modality to modulate difficult-to-drug targets, but often reside in chemical space where obtaining sufficient cell permeability and solubility is challenging. We have determined permeability across Caco-2 cells, aqueous solubility and log D for four series of semipeptidic macrocycles and one series of linear matched molecular pairs. By using X-ray crystallography, NMR spectroscopy, and computational chemistry, unexpected permeability differences between series and matched pairs were explained by differences in conformational preferences that determine the formation of intramolecular interactions. Macrocycles that formed intramolecular NH-π interactions and hydrogen bonds were more permeable than matched pairs unable to form such interactions. The elevated permeability of linear compounds was concluded to result from their greater conformational flexibility, allowing them to shield amide bonds and expose nonpolar groups to a greater extent than their macrocyclic matched pairs. Solubility was less dependent on specific intramolecular interactions and was predominantly low at log D >2.5.