Oligomerization mechanism of epigallocatechin-3-O-gallate during autoxidation
Yosuke Matsuo1, Kohei Katayama2, Takako Yamashita1
1Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
Abstract:
The autoxidation of tea catechins by dissolved oxygen proceeds in pH-neutral aqueous solutions, and the major products are oligomers. However, the reaction mechanisms have not been clarified. In this study, the autoxidation of (-)-epigallocatechin-3-O-gallate (1) was examined. The autoxidation with β-cyclodextrin, which includes the A-ring of 1, significantly suppressed oligomer production and increased the formation of products generated by the oxidative cleavage of the B-ring, indicating the participation of the A-ring in the oligomerization. Further, the autoxidation of 1 in the presence of phloroglucinol, a mimic of the catechin A-ring, yielded products via the nucleophilic addition of phloroglucinol to the B-ring quinone of 1. These results indicated that the oxidative A-B ring couplings accounted for the major oligomerization mechanism.
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