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. The major focus is on the outline of the initial structural determination, on the processes to find the errors in the structure, and on the methods for the revision of the structure.
Highlights
Tannins are astringent polyphenolic compounds with high diversity in biological activities [1,2,3].Many of the compounds have antioxidative effects and affect various organisms, such as fungi, tumor cells, and viruses
Tannins are divided into multiple classes according to the source and the chemical structures; they are roughly classified into two categories: condensed and hydrolyzable tannins [4,5]
The 1 H/13 C-NMR spectrum of sanguiin H-3 indicated that a glucose derivative possessing one HHDP group had combined with sanguiin H-2
Summary
Tannins are astringent polyphenolic compounds with high diversity in biological activities [1,2,3]. All of the previously reported structures are exhibited inside a square frame this review article, the following contrivance is usedthe in order improve intelligibility. Regarding the initial structural determination, the processes to find the errors in appears first inand each forthe revised ellagitannins, which might help understanding the structure, thedescription methods for revision of the structure, glancing at in figures might not the be overall transition. Thearose methods forprocesses the revision structure,determination glancing at figures might not be enough to compounds that in the of of thethe structural are illustrated understand; so, reading the text while referring to the figures is recommended. Frames with round corners are used that arose inthe thesimplified processes expression of the structural determination are square frames to indicate of frequent components We refer to more than 100 simplified expression of frequent components (forfor example, 8) and separate figures original papers in this review article
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