NMR Study of the Solution Structures of the Inclusion Complexes of β-Cyclodextrin with (+)-Catechin and (−)-Epicatechin

The probable structures of the inclusion complexes of β-cyclodextrin (β-CD) with (+)-catechin (CA) and (−)-epicatechin (EC) in D 2 O at 35 °C were investigated using NMR. In the β-CD·CA inclusion complex, a large portion of the flavonoid skeleton was included in the β-CD cavity and the axis of C 1 ‘ −C 4 ‘ of the B ring inclined to the molecular axis of β-CD, and the CA molecule fitted tightly with β-CD. In the β-CD·EC inclusion complex, the B ring was included deeply in the β-CD cavity from the secondary hydroxyl group side and the A ring was left outside the cavity near the secondary hydroxyl group side and EC molecule fitted loosely.