Chiroptical Sensing of Amino Acid Derivatives by Host-Guest Complexation with Cyclo[6]aramide.

A hydrogen-bonded (H-bonded) amide macrocycle was found to serve as an effective component in the host-guest assembly for a supramolecular chirality transfer process. Circular dichroism (CD) spectroscopy studies showed that the near-planar macrocycle could produce a CD response when combined with three of the twelve L-α-amino acid esters (all cryptochiral molecules) tested as possible guests. The host-guest complexation between the macrocycle and cationic guests was explored using NMR, revealing the presence of a strong affinity involving the multi-point recognition of guests. This was further corroborated by density functional theory (DFT) calculations. The present work proposes a new strategy for amplifying the CD signals of cryptochiral molecules by means of H-bonded macrocycle-based host-guest association, and is expected to be useful in designing supramolecular chiroptical sensing materials.