New phenylpropanoids from the fruits of Xanthium sibiricum and their anti-inflammatory activity

Seven new phenylpropanoids, including two pairs of enantiomers of 8-O-4'-type neolignans, named (±)-xanthiifructins A-B (1a/1b-2a/2b), a pair of simple phenylpropanoid derivatives (±)-xanthiifructins C (3a/3b), and a racemic phenylpropanoid derivative xanthiifructin D (4), together with four known analogues (5-8) were isolated from the fruits of Xanthium sibiricum. Racemic xanthiifructins A-C were separated on chiral HPLC columns. Their structures were elucidated by comprehensive spectroscopic data analysis and comparison with the literatures. The anti-inflammatory and cytotoxic activities were evaluated for all isolates. Among them, (-)-xanthiifructin C (3b) exhibited potent inhibitory effect against nitric oxide production in lipopolysaccharide-activated RAW 264.7 mouse macrophage cells with an IC₅₀ value of 9.94 ± 0.57 μM. All compounds obviously were inactive for three human tumor cell lines (MCF-7, HepG2, and A549) with IC₅₀ values much more than 10 μM.

Keywords: Xanthium sibiricum; anti-inflammatory; cytotoxicity; enantiomer; phenylpropanoid.