Papyriflavonol A, a new prenylated flavonol isolated from Broussonetia papyrifera, selectively inhibits recombinant human secretory phospholipase A(2)s (sPLA(2)s). Papyriflavonol A was found to inhibit human group IIA and V sPLA(2)s potently and irreversibly in a dose-dependent manner, with respective IC(50) values of 3.9 and 4.5 microM. The inhibitory effects of papyriflavonol A against bovine group IB (IC(50) of 76.9 microM) and the human group X (IC(50) of 225 microM) sPLA(2)s were weaker than those against human group IIA and V sPLA(2)s, and human group IIF sPLA(2) was not inhibited. In addition, papyriflavonol A potently inhibited the stimulus-induced production of leukotriene C(4) with an IC(50) value of approximately 0.64 microM in mouse bone marrow-derived mast cells. In addition, papyriflavonol A significantly reduced IgE-dependent passive cutaneous anaphylaxis in rats. These results indicate that papyriflavonol A provides a basis for novel types of antiinflammatory drugs.