A series of 3-substituted-1 (3H)-isobenzofuranone 6a–g and 7a–g were synthesized from phthalic anhydride. The compound 6a–g was resolved. The antiplatelet activities of these compounds were evaluated using in vitro experiment of platelet aggregation. The levels of antiplatelet activity were displayed as following sequence: l-isomer> dl-isomer> d-isomer, respectively. The alkylphthalide is more active than the corresponding alkenephthalide. ...