(-)-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 (Astera- ceae) are used after thorough stir-frying as an in- gredient in traditional Chinese medicines for re- lieving allergy. Two new compounds, xanthialde- hyde (2) and (-)-xanthienopyran (7), as well as 26 known compounds were isolated in the pres- ent study. The structures of the isolates were elu- cidated by spectroscopic methods. Among them, compound 7 exhibited significant selective in- hibition of superoxide anion generation by hu- man neutrophils induced by formyl-L-methion- yl-L-leucyl-L-phenylalanine, with an IC50 value of 1.72 μg/mL.