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The identification of unstable metabolites of ellagitannins having ortho-quinone structures or reactive carbonyl groups is important to clarify the biosynthesis and degradation of ellagitannins. Our previous studies on the degradation of vescalagin, a major ellagitannin of oak young leaves, suggested that the initial step of the degradation is regioselective oxidation to generate a putative quinone intermediate. However, this intermediate has not been identified yet. In this study, young leaves of Quercus dentata were extracted with 80% acetonitrile containing 1,2-phenylenediamine to trap unstable ortho-quinone metabolites, and subsequent chromatographic separation afforded a phenazine derivative of the elusive quinone intermediate of vescalagin. In addition, phenylenediamine adducts of liquidambin and dehydroascorbic acid were obtained, which is significant because liquidambin is a possible biogenetic precursor of C-glycosidic ellagitannins and ascorbic acid participates in the production of another C-glycosidic ellagitannin in matured oak leaves., Molecules, 28(3), art. no. 1246; 2023

Eight samples of Eupatorium heterophyllum leaves were collected at different locations in Yunnan and Sichuan provinces in China, and their chemical constituents were investigated. Thirteen previously undescribed sesquiterpene lactones—seven germacranolides, three eudesmanolides, two guaianolides, and a 2-norelemanolide—were isolated, and their structures were elucidated based on extensive spectroscopic analyses. The major constituents in the six samples from northwestern Yunnan and Sichuan are hiyodorilactones A and B, whereas that in the two samples from the region near Kunming, Yunnan is eupatoriopicrin. These results and previously reported results suggest the presence of locality-dependent intra-specific diversity in the chemical constituents of E. heterophyllum leaves., Molecules, 28(13), art. no. 5107; 2023

Thearubigins (TRs) are chemically ill-defined black tea pigments composed of numerous catechin oxidation products. TRs contain oligomeric components; however, the oligomerization mechanisms are poorly understood. The comparison of the 13C nuclear magnetic resonance (NMR) spectra of TRs with different molecular sizes suggested the participation of A-ring methine carbons in the oligomerization. Crushing fresh tea leaves with phloroglucinol, a mimic of the catechin A-rings, yielded the phloroglucinol adducts of the B-ring quinones of pyrogallol-type catechins and dehydrotheasinensins, indicating that intermolecular oxidative couplings between pyrogallol-type B-rings and A-rings are involved in the oligomerization. This is supported by the comparison of the 13C NMR spectra of the oligomers generated from the dehydrotheasinensins and epicatechin. Furthermore, the presence of the quinones or related structures in the catechin oligomers is shown by condensation with 1,2-phenylenediamine. The pyrogallol-type catechins account for approximately 70% of tea catechins; therefore, the B–A ring couplings of the pyrogallol-type catechins are important in the catechin oligomerization involved in TR production., Journal of agricultural and food chemistry, 71(41), pp.15319-15330; 2023

Seven new dihydrobenzofurans and 2 new propynyl thiophenes were isolated from the roots of Eupatorium heterophyllum together with 13 known compounds. The compounds were characterized using spectroscopic methods including 2D NMR, infrared, and mass spectrometric techniques. Aerial parts of this plant have been known to contain various sesquiterpenoids and displayed high chemical diversity (several compounds isolated and/or identified) among their chemical constituents depending on the collection site. Nevertheless, we found that the chemical diversity in the roots was lower than in the aerial parts., Natural Product Communications, 17(1), doi: 10.1177/1934578X211072331; 2022

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