Structure and biogenesis of jolkinin, a highly oxygenated ellagitannin from Euphorbia jolkinii

A new ellagitannin, jolkinin (2), was isolated from the fresh whole plant of Euphorbia jolkinii, and its structure, including absolute configuration, was determined on the basis of spectroscopic and chemical evidence. A highly oxygenated acyl group with unique hexacyclic structure is attached to the 2,4-positions of 1-O-galloyl-3,6-(R)-hexahydroxydiphenoyl-beta-d-glucopyranose. The structural similarity to elaeocarpusin (4) suggests that jolkinin is produced by a condensation reaction between ascorbic acid and geraniin (1), the dominant ellagitannin in this plant, which contains a dehydrohexahydroxydiphenoyl group. A plausible mechanism for jolkinin formation is also proposed.