Antifibrotic Phenanthrenes of Dendrobium nobile Stems

Two new phenanthrenes (1 and 6) and four new dihydrophenanthrenes (2–5) were isolated from a methanolic extract of Dendrobium nobile stems, along with 13 known phenanthrenes and dihydrophenanthrenes (7–19). By spectroscopic analysis, the structures of compounds 1–6 were determined as 2,8-dihydroxy-3,4,7-trimethoxyphenanthrene (1), 3-hydroxy-2,4,7-trimethoxy-9,10-dihydrophenanthrene (2), 2,8-dihydroxy-3,4,7-trimethoxy-9,10-dihydrophenanthrene (3), 2-hydroxy-4,7-dimethoxy-9,10-dihydrophenanthrene (4), 2,2′-dihydroxy-3,3′,4,4′,7,7′-hexamethoxy-9,9′,10,10′-tetrahydro-1,1′-biphenanthrene (5), and 2,3,5-trihydroxy-4,9-dimethoxyphenanthrene (6), respectively. Antifibrotic activity of compounds 1–19 was evaluated employing HSC-T6, an immortalized rat hepatic stellate cell line, as an in vitro assay system by assessing cell proliferation.