Neolignans and Diarylheptanoids with Anti-Inflammatory Activity from the Rhizomes of Alpinia zerumbet

The dried leaves and rhizomes of Alpinia zerumbet have been traditionally used as food and medicine. Anti-inflammatory activity-guided phytochemical investigation into the rhizomes of A. zerumbet led to the isolation of 17 compounds including 10 neolignans (1-10, 1a, 1b, 2a, 2b, 3a, 3b, 4, and 5 are new compounds) and seven diarylheptanoids (11-17) in which 1-3 were three pairs of enantiomers. 4 was only one enantiomer and 5 was a racemic mixture. Compounds 1a, 1b, 2a, and 2b incorporated an 8′,9′-dinorneolignan skeleton, which was rare in the lignan family. The planar structures of these compounds were elucidated by extensive analyses of spectroscopic data. The relative and absolute configurations were determined by the time-dependent density functional theory (TDDFT)-based electronic circular dichroism (ECD) calculation method. The 95% ethanol extract and ethyl acetate extract of A. zerumbet were found to show anti-inflammatory activity against croton oil-induced ear edema in mice with inhibition rates of 20.0 and 47.6% at a dose of 80 mg/kg, respectively. Bioassays showed that compounds 1a, 1b, 2a, 2b, and 12 moderately inhibited nitric oxide (NO) production in lipopolysaccharide (LPS)-induced RAW264.7 cells with IC50 values of 3.62, 7.63, 6.51, 5.60, and 8.33 μM, respectively.