Four pairs of new enantiomeric guaiane sesquiterpenoids from the rhizomes of Alisma plantago-aquatica.

Four pairs of undescribed enantiomeric guaiane sesquiterpenoids, (±)-alismaenols A-D (1a/1b, 3a/3b-5a/5b), together with a pair of known ones (2a/2b) were isolated from the rhizomes of Alisma plantago-aquatica. The structures and relative configurations of the isolates were established by analysis of their 1D, 2D-NMR and HRESIMS data. Their absolute configurations were determined by comparison of their experimental CD spectra and calculated electronic circular dichroism (ECD) spectra or by single-crystal X-ray diffraction analysis. All compounds (1a/1b-5a/5b) were evaluated for their inhibitory effects on nitric oxide (NO) production in LPS-induced RAW 264.7 cells, and compound 1a exhibited stronger activity (IC50 = 12.89 μM) than indomethacin (IC50 = 14.03 μM).