Phenanthrenoid monomers and dimers from Juncus alatus: Isolation, structural characterization, and anti-inflammatory...

A systematic investigation of the whole plant of Juncus alatus Franch. et Sav. resulted in the identification of seven novel phenanthrene dimers named alatusins A-G (1-7) and 11 undescribed monomers (8-9, 11-14 and 18-22), in addition to six known analogues (10, 15-17 and 23-24). The structures of new compounds were fully characterized through comprehensive analysis of HRESIMS, 1D and 2D NMR spectroscopic data, single-crystal X-ray diffraction experiment, and time-dependent density functional theory (TDDFT) electronic circular dichroism (ECD) calculation. Compounds 1-4 feature a methylene tethering two phenanthrene/9,10-dihydrophenanthrene monomers, while 5 possesses an undescribed linkage of C-5/C-5'. Compound 6 was constructed by forming a six-membered ring spiroed at C-5'. Compound 7 possesses a furan ring to connect two monomeric halves. All the connection patterns have never or rarely been reported before. The racemates of compounds 5, 6, 7, and 14 were separated via chiral HPLC, and their stereochemistry was characterized on-line by circular dichroism (CD) spectroscopy (LC-CD coupling) and comparison of the calculated and experimental ECD spectra. Most compounds were tested for their inhibition of NO on LPS stimulated murine RAW 264.7 cells. Compounds 13 and 18-21 exhibited potent inhibitory activity, with IC₅₀ values of 4.11 ± 0.59, 2.89 ± 0.90, 5.98 ± 1.86, 5.77 ± 1.36, and 5.68 ± 0.14 μM, respectively. In the ELISA assays, compound 18 significantly redused the production of pro-inflammatory cytokines, including TNF-α, IL-6, and MCP-1, in LPS-stimulated macrophages. Possible biosynthetic pathways of new dimeric compounds 1-7 were proposed.