molecules Review Structural Revisions in Natural Ellagitannins Hidetoshi Yamada 1,* ID , Shinnosuke Wakamori 1 ID , Tsukasa Hirokane 2 ID , Kazutada Ikeuchi 3 ID and Shintaro Matsumoto 1 1 School of Science and Technology, Kwansei Gakuin University, Sanda 669-1337, Japan;
[email protected] (S.W.);
[email protected] (S.M.) 2 Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Tokushima 770-8514, Japan;
[email protected] 3 Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan;
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[email protected]; Tel.: +81-795-65-8342 Received: 18 June 2018; Accepted: 17 July 2018; Published: 30 July 2018 Abstract: Ellagitannins are literally a class of tannins. Triggered by the oxidation of the phenolic parts on β-pentagalloyl-D-glucose, ellagitannins are generated through various structural conversions, such as the coupling of the phenolic parts, oxidation to highly complex structures, and the formation of dimer and lager analogs, which expand the structural diversity. To date, more than 1000 natural ellagitannins have been identified. Since these phenolic compounds exhibit a variety of biological activities, ellagitannins have potential applications in medicine and health enhancement. Within the context of identifying suitable applications, considerations need to be based on correct structural features. This review describes the structural revisions of 32 natural ellagitannins, namely alnusiin; alnusnin A and B; castalagin; castalin; casuarinin; cercidinin A and B; chebulagic acid; chebulinic acid; corilagin; geraniin; isoterchebin; nobotanin B, C, E, G, H, I, J, and K; punicalagin; punicalin; punigluconin; roxbin B; sanguiin H-2, H-3, and H-6; stachyurin; terchebin; vescalagin; and vescalin.