Controlling the Chair Conformation of a Mannopyranose in a Large-Amplitude [2]Rotaxane Molecular Machine

Large-amplitude mannosyl [2]rotaxane molecular machines based on an anilinium and mono- or disubstituted pyridinium amide stations were synthesized. Dibenzo[24]crown-8 (DB24C8) initially resides around the anilinium station in both the cases. The mannosyl [2]rotaxane molecular machines 3a,b were successfully obtained from the initially prepared mannoside azide 1a,b containing a pyridinium amide moiety and the alkyne ammonium 2, by using the copper(I)-catalyzed Huisgen alkyne-azide 1,3-dipolar cycloaddition, also called CuAAC click chemistry. The interlocked architecture of glycorotaxanes 3a,b and 4a,b and the localization of the macrocycle at different pH were studied by 1H NMR spectroscopy. It was observed that the DB24C8 moved toward the pyridinium amide station upon deprotonation. However, with the disubstituted amide, DB24C8 forms hydrogen bonds with the pyridinium H7 atoms, which are located near the cationic nitrogen atom, and interacts by ion dipole contacts with the cationic charge.