24312-00-3Relevant articles and documents
Identification and sensory evaluation of dehydro- and deoxy-ellagitannins formed upon toasting of oak wood (Quercus alba L.)
Glabasnia, Arne,Hofmann, Thomas
, p. 4109 - 4118 (2007)
Traditionally, spirits such as whiskey are matured in toasted wood barrels to improve the sensory quality of the final beverage. In order to gain first insight into the puzzling road map of thermal ellagitannin transformation chemistry and provide evidence for the changes in sensory active nonvolatiles in oak wood during toasting, the purified oak ellagitannins castalagin and vescalagin, their corresponding dimers roburin A and roburin D, and 33-carboxy-33-deoxyvescalagin were thermally treated in model experiments. Besides mouth-coating and golden-brown colored melanoidin-type polymers, individual major reaction products were produced as transient intermediates which were identified for the first time by means of LC-MS/MS and 1D/2D-NMR spectroscopy. Depending strongly on the stereochemistry, castalagin is oxidized to the previously unreported dehydrocastalagin, whereas its diastereomer vescalagin, differing only in the stereochemistry at carbon C-1, is most surprisingly converted into deoxyvescalagin. Comparative model experiments with 33-carboxy-33-deoxyvescalagin revealed castalagin, vescalagin, dehydrocastalagin, and deoxyvescalagin as typical reaction products, thus indicating decarboxylation as a key step in the thermal degradation of that ellagitannin. Similar to the ellagitannin monomers, LC-MS/MS analyses gave strong evidence that the corresponding dimer roburin A, containing the vescalagin configuration at C-1, was converted into the deoxyroburin A, whereas roburin D, exhibiting the castalagin configuration at C-1, was oxidized to give the dehydroroburin D. Human sensory experiments revealed that the ellagitannin derivatives imparted an astringent mouth-coating sensation with threshold concentrations ranging from 1.1 to 126.0 μmol/L, depending strongly on their chemical structure.
Tannins and Related Compounds. LI. Elucidation of the Stereochemistry of the Triphenoyl Moiety in Castalagin and Vescalagin, and Isolation of 1-O-Galloyl Castalagin from Eugenia grandis
Nonaka,Gen-Ichiro,Ishimaru, Kanji,Watanabe, Michiyo,Nishioka, Itsuo,Yamauchi, Tatsuo,Wan, Alfred S. C.
, p. 217 - 220 (2007/10/02)
The chirality of the nonahydroxytriphenoyl group in castalagin (1) and vescalagin (2) was determined to be in the S,S-series on the basis of circular dichroism analysis.In addition, a new ellagitannin (4) has been isolated from the leaves of Eugenia grandis (Myrtaceae), and the structure was established to be 1-O-galloyl castalagin on the basis of chemical and spectroscopic evidence. Keywords --- castalagin; vescalagin; C-glycosidic ellagitannin; atropisomerism; absolute stereochemistry; nonahydroxytriphenoyl group; flavogallonic acid; Eugenia grandis; 1-O-galloyl castalagin
