3, 4-dichloroisocoumarin is a compound of isocoumarin, which is an effective inhibitor of serine protease. 3, 4-dichloroisocoumarin can bind to the active site of serine protease, thereby inhibiting its enzyme activity. Serine proteases play an important role in a variety of biological processes, including digestion, immune response, and cell signaling. Therefore, 3, 4-dichloroisocoumarins are widely used in biochemical research to study the function and mechanism of these enzymes.