In a search for new inhibitors of platelet aggregation, certain coumarin-bearing α-methylene- γ-butyrolactones were synthesized and evaluated for inhibitory activity against thrombin (Thr)-, arachidonic acid (AA)-, collagen (Col)-, and platelet-activating factor (PAF)-induced aggregation in washed rabbit platelets. These compounds were efficiently synthesized from commercially available 7-hydroxycoumarin or its derivative. Among them, 7-[(2, 3, 4, 5- ...