Ellagitannins and Related Compounds from Penthorum chinense

Four new ellagitannin metabolites, penthorumnins A-D (1-3 and 5), were isolated from the dried stem of Penthorum chinense. The structures were determined using spectroscopic and chemical analysis as well as using computations that revealed the following: (1) the acyl group of penthorumnin A (1) has a unique cyclopentane carboxylic acid structure that is derived from a hexahydroxydiphenoyl (HHDP) group; (2) penthorumnin B (2) has a 2-carboxymethyl-2,3-dihydro-3-oxo-1 H-indene-1-carboxylic acid structure that originates from the acyl group of penthorumnin A; (3) penthorumnin C (3) is a glucoside of trihydroxyacetophenone with an acyl group that is oxidatively derived from the HHDP group. This acyl group is closely related to that of balanophotannin F (4), which has been previously isolated from Balanophora japonica and whose absolute configuration has been revised using the DFT method; and (4) penthorumnin D (5) is defined as 2',4',6'-trihydroxyacetophenone 4'- O-[4,6-( S)-dehydrohexahydroxydiphenoyl]-β-glucoside. The variety of acyl groups in these ellagitannins is indicative of the occurrence of a unique metabolism in this plant involving the HHDP ester.