Phenanthrenes from Bletilla formosana and their anti-neuroinflammatory activity.

A phytochemical investigation of the rhizomes of Bletilla formosana resulted in the isolation of four new phenanthrene dimers, bletiformosins A-D (1-3 and 6), together with four known analogues. The structures of new compounds were determined by comprehensive spectroscopic analyses, including HRESIMS and 1D and 2D NMR data. Compounds 1 and 2 represent the first phenanthrene dimers possessing a 3-3' linkage reported from the genus Bletilla. The axial chirality of phenanthrene dimers 3 and 6 was characterized by chiral HPLC coupled with on-line LC-CD analysis. The isolated compounds were preliminarily evaluated for their anti-neuroinflammatory activity in lipopolysaccharide (LPS)-stimulated BV-2 microglial cells. Compound 6 exhibited inhibitory effect on nitric oxide production, indicating potential anti-neuroinflammatory property.