Phenanthrene, 9,10-dihydrophenanthrene and bibenzyl enantiomers from Bletilla striata with their antineuroinflammatory and cytotoxic activities.

Thirteen undescribed phenanthrene and bibenzyl derivatives, named blestanols A-M, including one pair of biphenanthrene enantiomers, two bis 9,10-dihydrophenanthrene ethers, five pairs of 9,10-dihydrophenanthrene/bibenzyl atropisomers, one racemic 9,10-dihydrophenanthrene/bibenzyl dimer, one 9,10-dihydrophenanthrenebibenzyl ether, two pairs of bibenzyl derivatives, and one stilbene, together with 12 known analogues were isolated from the tubers of Bletilla striata. The structures were elucidated via spectroscopic data analysis. 15 compounds were purified to yield enantiomers (a, b) via chiral-phase HPLC, and their configurations were determined by optical rotation values and the comparison of the experimental and calculated electronic circular dichroism (ECD) curves. Blestanols K-L possessed a cycloheptene moiety, which is rarely observed in bibenzyl derivatives. A putative biosynthetic pathway for the identified components is deduced. Among these compounds, 14 compounds showed inhibition of NO production, with IC ₅₀ values ranging from 5.0 to 19.0 μM. Eight compounds displayed selective cytotoxic activities against HCT-116, HepG2, BGC-823, A549 or U251 cancer cell lines, with IC ₅₀ values ranging from 1.4 to 8.3 μM. In addition, their structure-activity relationships are discussed briefly.
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