Diastereomeric difference of inclusion modes between (−)‐epicatechin gallate, (−)‐epigallocatechin gallate and (+)‐gallocatechin gallate, with β‐cyclodextrin in aqueous solvent

Inclusion complexes of (−)‐epicatechin gallate (ECg) as well as (+)‐gallocatechin gallate (GCg) and β‐cyclodextrin (β‐CD) in an aqueous solution were investigated using several NMR techniques and a computational method. ECg and EGCg formed a 1:1 complex with β‐CD, in which the A ring and a portion of the C ring were included from the wide secondary hydroxyl group side of the β‐CD cavity, and the B and B′ rings were left outside the cavity. GCg formed a 1:2 complex with β‐CD, in which the A and B rings of GCg were included by two molecules of β‐CD. The difference between the two modes of inclusion of the 1:1 complex of ECg, EGCg·β‐CD and the 1:2 complex of GCg·β‐CD might have resulted from the size of the space between the B and B′ rings in aqueous solution. As a result of nueclear Overhauser effect (NOE) experiments, GCg was considered to have a large enough space between the B and B′ rings to include the B ring in the β‐CD cavity; on the other hand, ECg and EGCg have no such large space. Copyright © 2008 John Wiley & Sons, Ltd.