Twelve guaiane-type sesquiterpenoids, including four new ones, 10-O-methyl-orientalol A (1), 10-Oethyl-alismoxide (2), 3β,4β-expoxy-chrysothol (3), orientalol G (4), and a new norsesquiterpenoid, orientalol H (5), were isolated from Chinese Alismatis Rhizoma, the dried rhizome of Alisma orientale. The structures of new compounds were elucidated on the basis of spectroscopic data. Moreover, the inhibition of lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW264.7 cells of all compounds was tested.Key words Alismatis Rhizoma; Alisma orientale; guaiane-type sesquiterpenoid; anti-inflammatory Alismatis Rhizoma ("Zexie" in Chinese), a Chinese crude drug prepared from dried rhizome of the aquatic plant Alisma orientale (SAM.) JUZEP. (Alismataceae) widely cultivated in China and Japan, has been used as a diuretic agent used to "remove dampness and promote water metabolism" in the body according to Chinese medicinal principles.1-5) Previous phytochemical and pharmacological study on Alismatis Rhizoma reported the isolation of prostane-type triterpenes and guaiane-type sesquiterpenes, which exhibited a series of bioactivities, such as diuretic, anti-hepatitis B virus (HBV), antibacterial, anti-hypertentive, hypolipidemic, anti-inflammatory, positive hypocholesterolemic activity, and repairing action to cholinergic acetyltransferase, etc.1-3,6-10) With the aim of discovering more structurally unique and bioactive terpenoids from natural resource, five new guaiane-type sesquiterpenes (1-5) along with seven known ones (6-12) (Fig. 1) were isolated from Alismatis Rhizoma. Furthermore, all compounds were examined for their anti-inflammatory potential and compounds 6 and 12 showed moderate inhibition of nitric oxide (NO) production with IC 50 values of 36.997 and 48.602 µM, respectively. Herein, we report the isolation, structural elucidation and biological evaluation of the isolated compounds.
Results and DiscussionThe powdered Alismatis Rhizoma was extracted with 95% EtOH, and the concentrated extract was suspended in H 2 O followed by partition with EtOAc. The EtOAc fraction was purified using various column chromatographies to yield twelve guaiane-type sesquiterpenoids (1-12).Compound 1, colorless oil, gave rise to a quasi-molecular ion peak at m/z 291.1935 ([M+Na] + ) in the positive high resolution-electrospray ionization (HR-ESI)-MS, which corresponded to the molecular formula C 16 H 28 O 3 , in combination with its 13 C-NMR and distortionless enhancement by polarization transfer (DEPT) analysis. The IR spectrum exhibited a broad absorption at 3420 cm −1 due to hydroxyl group. The 1 H-NMR spectrum (Table 1) showed the presence of a tertiary methyl [δ H 1.09 (3H, s)], a hydroxymethyl [δ H 3.80 (1H, dd,