Journal
CHEMISTRY-AN ASIAN JOURNAL
Volume 16, Issue 13, Pages 1735-1740Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/asia.202100380
Keywords
biomimetic synthesis; biosynthesis; ellagitannins; natural products; oxidation
Categories
Funding
- JSPS KAKENHI [JP20K07102, JP17K08338, JP16K07741]
- MEXT [JPMXS0422500320]
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Through investigation of CuCl2-mediated oxidation reactions in an aqueous medium, it was found that in the biosynthesis of ellagitannins, DHHDP is the initial product of the oxidative coupling of two galloyl groups, and subsequent reductive metabolism forms HHDP esters.
Hexahydroxydiphenoyl (HHDP) and dehydrohexahydroxydiphenoyl (DHHDP) groups are the major acyl components of ellagitannins, which are polyphenols whose biosynthesis have attracted considerable attention; however, the mechanisms of the production of HHDP and DHHDP in the ellagitannin biosynthesis have not been clarified. With the aim of elucidating such a mechanism, this study investigates the CuCl2-mediated oxidation of simple galloyl derivatives in an aqueous medium. It is shown that the oxidation of methyl gallate affords a DHHDP-type dimer, whose reduction with Na2S2O4 yields an HHDP-type dimer. However, the oxidation of the HHDP-type product over CuCl2 does not afford the parent DHHDP ester. The oxidation of 1,4-butanediol digallate under the same conditions produces a DHHDP-type product via the intramolecular coupling of galloyl groups. These results strongly suggest that the DHHDP group is the initial product of the oxidative coupling of two galloyl groups in the ellagitannin biosynthesis, and subsequent reductive metabolism affords HHDP esters.
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