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The chemical constituents of two root samples of Eupatorium heterophyllum DC. collected in Yunnan Province, China, were investigated. Five new oligomeric benzofurans (1–5), nine new benzofuran/dihydrobenzofuran derivatives, and a new thymol analog were isolated, and their structures were determined using extensive spectroscopic techniques, such as 1D and 2D NMR spectroscopy and DFT calculations of the CD spectra. Most of the new compounds, including oligomeric benzofurans (1–5), were obtained from only one of the root samples. Furthermore, this is the first example that produces oligomeric benzofurans in this plant. These results imply that diversification of secondary metabolites in E. heterophyllum is ongoing. Plausible biosynthetic pathways for 1–5 are also proposed., Molecules, 27(24), art. no. 8856; 2022

Amariin is an ellagitannin with two dehydrohexahydroxydiphenoyl (DHHDP) moieties connecting glucose 2,4- and 3,6-hydroxy groups. This tannin is predominant in the young leaves of Triadica sebifera and Carpinus japonica. However, as the leaves grow, the 3,6-DHHDP is converted to its reduced form, the hexahydroxydiphenoyl (HHDP) group, to generate geraniin, a predominant ellagitannin of the matured leaves. The purified amariin is unstable in aqueous solution, and the 3,6-(R)-DHHDP is spontaneously degraded to give HHDP, whereas 2,4-(R)-DHHDP is stable. The driving force of the selective reduction of the 3,6-DHHDP of amariin is shown to be the conformational change of glucose from O,3B to 1C4. Heating geraniin with pyridine affords 2,4-(R)-DHHDP reduction products. Furthermore, the acid hydrolysis of geraniin yields two equivalents of ellagic acid. Although the reaction mechanism is still ambiguous, these results propose an alternative biosynthetic route of the ellagitannin HHDP groups., Molecules, 25(5), art.no.1051; 2020

The leaves of Castanopsis sieboldii (Fagaceae) contain characteristic hexahydroxydiphenoyl (HHDP) esters of 28-O-glucosyl 2&alpha, 3&beta, 23,24-tetrahydroxyolean- and urs-12-en-28-oic acids. In this study, uncharacterized substances were detected in the young leaves, which are not observed in the mature leaves. Preliminary HPLC analyses indicated that the substances had dehydro-HHDP (DHHDP) ester groups, however, the esters were unstable and decomposed during extraction. Therefore, the compounds were isolated as their stable phenazine derivatives by extracting the young leaves with acidic aqueous EtOH containing o-phenylenediamine. The structures of the phenazine derivatives indicated that the unstable metabolites of the young leaves were 3,24-DHHDP esters of the abovementioned triterpenes. Extraction of the young leaves with 80% acetonitrile containing reducing agents, ascorbic acid or dithiothreitol afforded the corresponding HHDP esters. Furthermore, heating of the young leaves in 80% acetonitrile also yielded the same HHDP esters as the reduction products. The results suggested that the HHDP esters are reductively produced from DHHDP esters in the young leaves. In addition, the structures of five previously reported triterpene HHDP esters were revised.