Reinvestigation of the Stereochemistry of the <i>C</i>‑Glycosidic Ellagitannins, Vescalagin and Castalagin

The stereochemistry of the <i>C</i>-glycosidic ellagitannins, vescalagin and castalagin, has been reinvestigated using computational methods. DFT calculations of their ¹H and ¹³C NMR spectra, as well as TDDFT calculations of the ECD spectra of their des-hexahydroxydiphenoyl analogues, revealed that the structure of the triphenoyl moiety of vescalagin and castalagin should be revised

New Metabolites of <i>C</i>‑Glycosidic Ellagitannin from Japanese Oak Sapwood

Two unusual ellagitannin metabolites, quercusnins A (<b>3</b>) and B (<b>4</b>), have been isolated from the sapwood of <i>Quercus crispula</i>, and their structures determined by spectroscopic methods, as well as DFT calculations of ¹H and ¹³C NMR chemical shifts of the possible four diastereomers. Treatment of the major ellagitannin species, vescalagin, with Shiitake mushroom (<i>Lentinula edodes</i>) gave <b>3</b>, which indicated that these unique ellagitannins were the fungal metabolites of ellagitannins

Three new flavans in dragon's blood from <i>Daemonorops draco</i>

<div><p>Three new flavans were isolated from chloroform extracts of dragon's blood from <i>Daemonorops draco</i>, together with eight known compounds. The structures of the new flavans were determined by 1D and 2D NMR spectroscopic analysis. These compounds are the first examples of 2-methoxyflavans from <i>D. draco</i> and regarded as derivatives of biogenetic intermediates from flavans to chalcones, which are characteristic of the dragon's blood.</p></div

Flavonoid compounds related to seed coat color of wheat

<p>In red wheat, reddish-brown pigments accumulate in testa of mature seeds. Half-cut wheat seeds were immersed in <i>p</i>-dimethylaminocinnamaldehyde (DMACA) reagent that stains flavanol structures blue. Testa of 10–40 days after flowering (DAF) in red wheat (“Norin 61” and “Satonosora”) seeds were stained blue and the reagent color changed to blue with 10–25 DAF seeds. No blue staining was observed in white wheat (“Tamaizumi”) seeds during maturation. “Norin 61” seed coats at 10 DAF contained dihydroquercetin, dihydromyricetin, (+)-catechin, procyanidin B3, and prodelphinidin B3, which were identified by HPLC-diode array detector and LC-MS/MS analyses. These five components began accumulating 7 DAF, reached maxima at 10 or 15 DAF, and then decreased in red wheat seeds, but were not detected in white wheat seeds. These results suggest that flavanol and proanthocyanidins are possible precursors of the reddish-brown pigments of red wheat seeds, and are converted to insoluble compounds as the seeds mature.</p> <p>Dihydroflavonols, flavanol, and proanthocyanidin dimers accumulated in immature red wheat seeds, whose mature seed coat has reddish-brown pigments, but not in white wheat seeds.</p

Stereochemistry of the Black Tea Pigments Theacitrins A and C

Theacitrins A–C are yellow pigments of black tea that are produced by oxidative coupling of gallocatechins, i.e., flavan-3-ols with pyrogallol-type B-rings. However, their stereostructures have not yet been determined. In this study, DFT calculations of NMR chemical shifts of theacitrin C (<b>1</b>) and TDDFT calculations of the ECD spectra of theacitrinin A (<b>5</b>), a degradation product of theacitrin C (<b>1</b>), were used to determine the stereostructure of the theacitrins. Furthermore, the preparation of theacitrins A (<b>4</b>) and C (<b>1</b>) by enzymatic oxidation of an epigallocatechin (<b>7</b>) and epigallocatechin-3-<i>O</i>-gallate (<b>2</b>) mixture confirmed their structural relationship

Diastereomeric Ellagitannin Isomers from Penthorum chinense

From the dried stem of Penthorum chinense (Penthoraceae), 1-<i>O</i>-galloyl-4,6-(<i>R</i>)-hexahydroxydiphenoyl (HHDP)-β-d-glucose and 2′,4′,6′-trihydroxyacetophenone 4′-<i>O-</i>[4,6-(<i>R</i>)-HHDP]-β-d-glucoside were isolated together with their (<i>S</i>)-HHDP isomers. Ellagitannins with a 4,6-(<i>S</i>)-HHDP-glucose moiety are widely distributed in the plant kingdom; however, 4,6-(<i>R</i>)-HHDP glucoses are extremely rare. Lowest-energy conformers of 1-<i>O</i>-galloyl-(<i>S</i>)- and (<i>R</i>)-HHDP-glucopyranoses were derived by density functional theory calculations, and the calculated ¹H and ¹³C NMR chemical shifts and the ¹H–¹H coupling constants were in agreement with the experimental values. The results revealed a conformational difference of the diastereomeric macrocyclic ester rings. In addition, a new compound, 1′,3′,5′-trihydroxybenzene 1′-<i>O</i>-[4,6-(<i>S</i>)-HHDP]-β-d-glucoside, was also isolated