GLUTATHIONE-MEDIATED CONVERSION OF THE ELLAGITANNIN GERANIIN INTO CHEBULAGIC ACID

Geranlin (1), a widely distributed ellagitannin having a dehydrohexahy droxydiphenoyl (DHHDP) ester moiety, was converted into chebulagic aci d (2), an ellagitannin having a chebuloyl ester moiety, which was repo rted to be a potent inhibitor of DNA topoisomerases. This was achieved by addition of the thiol group of glutathione to the six-membered ace tal ring form of the DNHDP moiety (1a) with concomitant hydrolytic rin g cleavage and subsequent reductive desulfurization with Raney nickel. The concurrent addition of the thiol to the five-membered acetal ring form of the DHHDP group (1b) generated the product 14 and its precurs or 13, which are structurally related to naturally occurring ellagitan nins isolated from Euphorhiaceous plants, Thus, the rearrangements obs erved in these reactions may be relevant to the metabolism of DHHDP es ters in plants.