4 years ago

Non-enzymatic Oxidation of a Pentagalloylglucose Analog to Ellagitannins

Hidetoshi Yamada, Seiya Ashibe, Yuri Ueno, Yuji Kume, Takashi Iwashita, Shinnosuke Wakamori, Kazutada Ikeuchi
The occurrence of more than 1,000 structural diversity in ellagitannins has been hypothesized to begin with oxidation of penta-O-galloyl--D-glucose (-PGG) to couple the galloyl groups. However, the non-enzymatic behavior of -PGG in the oxidation is unknown. Here, we disclose which galloyl groups on glucose tended to couple and which axial chirality was predominant in the derived hexahydroxydiphenoyl groups, when an analog of -PGG was subjected to oxidation. The study revealed that the galloyl groups coupled, in the following order of production ratio: at the 4,6-, 1,6-, 1,2-, 2,3-, and 3,6-positions with respective S, S, R, S, and R-axial chirality. Among them, the most preferred 4,6-coupling reflected the tendency observed in natural ellagitannins. An astonishing fact was that the second best was the 1,6-coupling. With the detection of a 3,6-coupled product, this work demonstrated that even ellagitannin skeletons with an axial-rich glucose core may generate non-enzymatically.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201708703

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