Cap-dependent endonuclease-IN-21 is a potent inhibitor of cap-dependent endonuclease ( CEN ). Cap-dependent endonuclease-IN-21 inhibits the replication of influenza virus. ap-dependent endonuclease-IN-21 has the potential for the research of influenza virus infection (influenza A) (extracted from patent WO2021233302A1, compound 8B or 8A).