Anti-inflammatory octahydroindolizine alkaloid enantiomers from Dendrobium crepidatum.

Six pairs of octahydroindolizine-type alkaloid enantiomers (1-6) including three new compounds [(-)-1/(+)-1, 2] were isolated from the stems of Dendrobium crepidatum. Their structures including the absolute configurations were elucidated by extensive spectroscopic analyses and comparison between the experimental and calculated electronic circular dichroism (ECD). All compounds were examined for their inhibitory effects on nitric oxide (NO) production induced by lipopolysaccharide (LPS) in RAW264.7 cells. It was found that compounds (+)-1, 2 and (+)-6 exhibited pronounced inhibition on NO production with IC₅₀ values in the range of 3.62-16.11 µM, being more active than the positive control, dexamethasone (IC₅₀ = 47.04 µM). In vivo, compound 6 (100, 50 and 10 mg/kg) showed protective effects against LPS-induced acute lung injury (ALI) in mice.