Crystal Structures of Flavone C-Glycosides from Oolong Tea Leaves: Chafuroside A Dihydrate and Chafuroside B Monohydrate.

Chafuroside A and chafuroside B are flavone C-glycosides isolated from oolong tea leaves. They have a number of beneficial pharmacological activities related to antiinflammation at various concentrations. However, no crystallographic study of chafurosides has yet been reported. In the present study, the crystal structures of chafuroside A and chafuroside B were investigated using single-crystal X-ray diffraction. The asymmetric unit of the chafuroside A crystal consists of one chafuroside A and two water molecules, and that of chafuroside B contains one chafuroside B and one water molecule. The flavone moiety of chafuroside A is curved, i.e., the angle between the best-fit planes of the chromene and phenyl rings is 18.9°, whereas the chafuroside B flavone moiety is relatively flat. A comparison of the curvatures of the flavone moieties of various C-glycosides showed that the curvature of chafuroside A is significantly larger than those of the others. This structural feature might contribute to the differences between the strengths of the pharmacological activities of chafurosides A and B.