Dimeric 9,10-dihydrophenanthrene derivatives from Bletilla striata and their atropisomeric nature

Four pairs of undescribed racemic bi(9,10-dihydro) phenanthrene and phenanthrene/bibenzyl atropisomers, bletistriatins A-D (1–4), along with 22 known compounds were isolated from the rhizomes of Bletilla striata. These dimeric derivatives were constructed through direct C–C connection or an oxygen bridge. The structures of new compounds were fully established by extensive analysis of MS, and 1D and 2D NMR spectroscopic data. Owing to sterically...