Aromatase is a well-established target for the chemoprevention of breast cancer. The dihydroisocoumarin (3 R,4 R)-(-)-6-methoxy-1-oxo-3-pentyl-3,4-dihydro-1 H-isochromen-4-yl acetate (1) (IC 50 = 1.6 +/- 0.1 microM), isolated from aerial parts of Xyris pterygoblephara, showed aromatase inhibitory