Folded-to-unfolded structural switching of a macrocyclic aromatic hexaamide based on conformation changes in the amide groups induced by N-alkylation and dealkylation reactions

• A cyclic hexaamide containing three 4-methoxybenzyl and three butyl groups was synthesized.
• The hexaamide containing six tertiary amides with cis conformation formed a “fold” structure.
• The hexaamide containing alternate tertiary and secondary amide formed an “unfold” structure.
• The conformational change of the hexaamide displays reversible switching.

A macrocyclic compound has been designed and synthesized containing six para-phenylene groups and six alternate N-butyl and N-4-methoxybenzyl substituted amides. The three N-4-methoxybenzyl groups could be removed by N-dealkylation under acidic conditions to give the corresponding secondary amides, which underwent a switch in their conformation from cis to trans. Single crystal X-ray crystallographic analysis revealed that the macrocyclic compound containing six alternate N-butyl and N-4-methoxybenzyl substituted tertiary amide groups existed as the “folded” structure, whereas the macrocyclic compound with six alternate tertiary and secondary amide groups existed as the “unfolded” structure. Furthermore, these changes in the conformation of the hexaamide displayed reversible switching between the “folded” and “unfolded” states.