A 5,7-Dimethoxyflavone/Hydroxypropyl-β-Cyclodextrin Inclusion Complex with Anti-Butyrylcholinesterase Activity

This study aimed to improve the water solubility of 5,7-dimethoxyflavone (5,7-DMF) isolated from Kaempferia parviflora by complexation with 2-hydroxypropyl-beta-cyclodextrin (HP beta-CD). The phase solubility profile of 5,7-DMF in the presence of HP beta-CD was classified as A(L)-type and indicated a 1:1 mole ratio. Differential scanning colorimetry, X-ray diffraction, NMR and SEM analyses supported the formation of a 5,7-DMF/HP beta-CD inclusion complex involving the A ring of 5,7-DMF inside the HP beta-CD cavity. This is the first example of CD inclusion with the A ring of non-hydroxyl flavones. The stability and binding constants of the complexes were determined using the phase solubility and UV-vis absorption spectroscopy, respectively. The water solubility of 5,7-DMF was increased 361.8-fold by complexation with HP beta-CD and overcame the precipitation problem observed in aqueous buffers, such as during in vitro anti-butyrylcholinesterase activity assays. The 1:1 mole ratio of the 5,7-DMF/HP beta-CD complex showed a 2.7-fold higher butyrylcholinesterase inhibitory activity (in terms of the IC50 value) compared to the non-complexed compound.