A new synthesis is proposed for cordiachromene A (CCA), a bioactive component of the ascidianAplidium antillenseGravier, using a method producing a racemic mixture. The anti‐inflammatory activities of a natural extract and a chemically synthetic form of CCA were assessed in vivo by carrageenan‐induced rat‐paw edema. The activity of synthetic CCA was confirmed by a test on kaolin‐induced granuloma in the rat. Strong activities were measured for both CCA, but comparison of results of the first test suggests that only the natural optically active isomer has an anti‐inflammatory effect. CCA is similar to indomethacin in its effect on carrageenan‐induced rat‐paw edema and ten times as active as p