Antimicrobial Stilbenoids from Bletilla yunnanensis

new bisphenanthrene, 2,2′,4,4′,7,7′-hexamethoxy-9,9′,10,10′-tetrahydro-1,1′-biphenanthrene ( 1 ), was isolated with five known phenanthrenes ( 2–6 ) from the tubers of Bletilla yunnanensis Schltr. Their structures were elucidated by detailed spectroscopic analyses. Compounds 4 and 5 exhibited potential antibacterial activity against two Gram positive strains, Staphylococcus aureus and S. epidermidis, with the MIC values of 6.25–25 μg/mL.