Molecular Puzzle Ring: pseudo[1]Rotaxane from a Flexible Cyclodextrin Derivative

A pseudo[1]rotaxane formed by a flexible cyclodextrin (CD) derivative (1-R) with a bulky end group has been investigated on kinetic quantitation. 1-Rs have the cinnamamide moiety as a guest and a bulky end group (R) as a rate-determining moiety of the threading process. The R groups play an important role for the formation of pseudo[1]rotaxane, and kinetics of the self-inclusion process was found to be controlled by the size and shapes of the R groups. 1-Ad and 1-Me derivatives, which have an adamantyl and methyl end group, respectively, formed self-inclusion complexes by threading of the arm moiety with a conformational conversion of altrose from C-1(4) form to C-4(1), form. Flexibility of the altro-alpha-CD cavity resulted in an induced fit (from C-1(4) to C-4(1)) to the arm moiety, and introducing a bulky end group allowed the stability of this pseudo[1] rotaxane to be enhanced.