Roburin D

C-glucosidic ellagitannins and galloylated glucoses as potential functional food ingredients with anti-diabetic properties: a study of alpha-glucosidase and alpha-amylase inhibition.[Pubmed:31927321]

Food Chem. 2020 May 30;313:126099.

Diabetes mellitus is a metabolic disorder characterized by hyperglycemia, which can be counteracted by inhibition of alpha-glucosidase and alpha-amylase, both involved in the carbohydrate metabolism. Fourteen C-glucosidic ellagitannins and three galloylated glucoses were studied as potential alpha-glucosidase and alpha-amylase inhibitors. Most of the compounds were found to be moderate inhibitors of alpha-amylase, but potent inhibitors of alpha-glucosidase, showing low-micromolar IC50 values, far lower than that of the antidiabetic drug acarbose. This selectivity can be an advantage for their possible application as functional food ingredients with anti-diabetic properties because strong alpha-amylase inhibition generally causes undesired side effects. The best inhibitors were selected for further studies. Intrinsic fluorescence measurements confirmed their high affinity towards alpha-glucosidase, highlighting a static quenching mechanism. Circular dichroism measurements and kinetics of inhibition indicated that the most active C-glucosidic ellagitannin Roburin D (RobD) is a competitive inhibitor, whereas alpha-pentagalloylglucose (alpha-PGG) acts as a mixed-type inhibitor.

Identification and sensory evaluation of dehydro- and deoxy-ellagitannins formed upon toasting of oak wood (Quercus alba L.).[Pubmed:17444655]

J Agric Food Chem. 2007 May 16;55(10):4109-18.

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 micromol/L, depending strongly on their chemical structure.

Main structural and stereochemical aspects of the antiherpetic activity of nonahydroxyterphenoyl-containing C-glycosidic ellagitannins.[Pubmed:17191843]

Chem Biodivers. 2004 Feb;1(2):247-58.

Antiherpetic evaluation of five nonahydroxyterphenoyl-containing C-glycosidic ellagitannins, castalagin (1), vescalagin (2), grandinin (3), roburin B (5), and Roburin D (7), was performed in cultured cells against four HSV-1 and HSV-2 strains, two of which were resistant to Acyclovir. All five ellagitannins displayed significant anti-HSV activities against the Acyclovir-resistant mutants, but the monomeric structures 1-3 were more active than the dimers 5 and 7. Vescalagin (2) stands out among the five congeners tested as the most potent and selective inhibitor, with an IC50 value in the subfemtomolar range and a selectivity index 5x10(5) times higher than that of Acyclovir. Molecular modeling was used to provide a rationale for the surprisingly lower activity profile of its epimer castalagin (1). These ellagitannins have promising potential as novel inhibitors in the search for non-nucleoside drugs active against Acyclovir-resistant herpes viruses.