Oligocholate foldamer with ‘prefolded’ macrocycles for enhanced folding in solution and surfactant micelles

A cholate oligomer was synthesized with six linear cholate groups sandwiched by two tricholate macrocycles at the two termini. Two pyrenyl labels on the compound allowed its conformation to be studied by fluorescence spectroscopy. The linear/macrocyclic hybrid oligomer was found to fold consistently better than a linear analogue in mixed organic solvents and surfactant micelles. The enhanced folding was hypothesized to occur as the tricholate macrocycles, by their prefolded configuration, facilitate the preferential solvation of the facially amphiphilic cholate groups. In general, the folding-enhancing effect was stronger as the environment became more challenging for the oligocholate to fold. Most unusually, the hybrid oligocholate folded better in a more challenging binary methanol/ethyl acetate mixture than in the methanol/hexane/ethyl acetate ternary solvents that have been considered the most ‘folding-friendly’ to all other cholate foldamers.