(-)-Xanthienopyran, a new inhibitor of superoxide anion generation by activated neutrophils, and further constituents of the seeds of Xanthium strumarium

The dried seeds of Xanthium strumarium (Asteraceae) are used after thorough stir-frying as an ingredient in traditional Chinese medicines for relieving allergy. Two new compounds, xanthialdehyde (2) and (-)-xanthienopyran (7), as well as 26 known compounds were isolated in the present study. The structures of the isolates were elucidated by spectroscopic methods. Among them, compound 7 exhibited significant selective inhibition of superoxide anion generation by human neutrophils induced by formyl-L-methionyl-L-leucyl-L-phenylalanine, with an IC₅₀ value of 1.72 μg/mL.