Geraniin is a dehydroellagitannin found in geraniums. It is found for instance in Geranium thunbergii, which is one of the most popular folk medicines and also an official antidiarrheic drug in Japan. It can also be found in the rind of Nephelium lappaceum (rambutan). It mediates apoptosis by cleavage of focal adhesion kinase through up-regulation of Fas ligand expression in human melanoma cells. It is formed with one hexahydroxydiphenic acid unit, one modified hexahydroxydiphenic acid unit (dehydrohexahydroxydiphenic acid or DHHDP) and one gallic acid unit linked to a glucose molecule. It is forming an equilibrium mixture of six-membered hemi-ketal and five-membered hemi-ketal forms. Chebulagic acid is formed from geraniin through a glutathione-mediated conversion.
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