New Benzofuran Oligomers from the Roots of Eupatorium heterophyllum Collected in China

Abstract

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.

Chemical Compositions of Eupatorium heterophyllum Leaf Samples from Yunnan and Sichuan Provinces of China—Isolation of 13 New Sesquiterpene Lactones

“…It is widely distributed in grasslands and forest areas at altitudes of 1700–3000 m in Southwest China (Sichuan, Yunnan, and Guizhou provinces and Xizang Autonomous Region) and has not been artificially cultivated [ 1 ]. We have been studying the intra-specific diversity in leaf and root chemicals of E. heterophyllum native to Yunnan and Sichuan provinces [ 2 , 3 , 4 , 5 , 6 ] as part of our continuing research on the chemical diversity of Asteraceae plants for obtaining unique secondary metabolites produced by limited populations within a species and for getting an insight into a chemical aspect of adaptation/differentiation. To date, diversity was observed in the minor constituents of the root chemicals of E. heterophyllum samples taken from different locations, affording various heterocyclic aromatic compounds, such as benzofuran/dihydrobenzofuran derivatives and propynyl thiophenes, in addition to some common major constituents [ 2 , 3 , 4 ].…”

“…We have been studying the intra-specific diversity in leaf and root chemicals of E. heterophyllum native to Yunnan and Sichuan provinces [ 2 , 3 , 4 , 5 , 6 ] as part of our continuing research on the chemical diversity of Asteraceae plants for obtaining unique secondary metabolites produced by limited populations within a species and for getting an insight into a chemical aspect of adaptation/differentiation. To date, diversity was observed in the minor constituents of the root chemicals of E. heterophyllum samples taken from different locations, affording various heterocyclic aromatic compounds, such as benzofuran/dihydrobenzofuran derivatives and propynyl thiophenes, in addition to some common major constituents [ 2 , 3 , 4 ]. In particular, seven oligomeric benzofurans were recently isolated for the first time from the sample collected in Lijiang City of Yunnan Province, which suggest an ongoing diversification of secondary metabolites in this species [ 4 , 5 ].…”

“…To date, diversity was observed in the minor constituents of the root chemicals of E. heterophyllum samples taken from different locations, affording various heterocyclic aromatic compounds, such as benzofuran/dihydrobenzofuran derivatives and propynyl thiophenes, in addition to some common major constituents [ 2 , 3 , 4 ]. In particular, seven oligomeric benzofurans were recently isolated for the first time from the sample collected in Lijiang City of Yunnan Province, which suggest an ongoing diversification of secondary metabolites in this species [ 4 , 5 ]. The chemical composition of the leaves, which is mainly composed of sesquiterpene lactones, is significantly different from that of the roots.…”