A self-included cyclomaltoheptaose derivative studied by NMR spectroscopy and molecular modelling

The 3D structure of 6-deoxy-6-L-tyrosinylamidocyclomaltoheptaose, a self-complexing beta-cyclodextrin derivative, was determined by NMR and molecular modelling. The aminoacyl side-chain is included in the cavity and induces chemical-shift variations in the CD proton signals, allowing their complete assignment. Dipolar interactions between protons of the tyrosine ring and internal protons of the cyclodextrin were used to obtain distance constraints. Then 42 structures were calculated from 32 distance constraints--21 shorter than 4 A involve the host-guest interactions--using a simulated annealing procedure. Starting from one of the resulting structures, a 250-ps molecular dynamics simulation was carried out in a waterbox without constraint. The simulation data are in agreement with NMR data such as nOe and ring-current effects. The cyclodextrin part takes an elliptical shape, which tightly fits the aromatic moiety. As a consequence, the respective motion of the host and the guest moieties have the same amplitude and time scale: the self-inclusion complex shows only little flexibility.