CYP3A4-IN-2 is a specific inhibitor of cytochrome P450 3A4 ( CYP3A4 ) with the IC 50 value of 0.055 μM. CYP3A4-IN-2 is a ritonavir analogue with increased hydrophobicity of the R2 side group and stronger inhibitory effect compared to ritonavir. CYP3A4-IN-2 can be used as an antiviral agent and immunosuppressants.