eIF4A3-IN-1 (compound 53a) is a selective eukaryotic initiation factor 4A3 (eIF4A3) inhibitor ( IC 50 =0.26 μM; K d =0.043 μM), which binds to a non-ATP binding site of eIF4A3 and shows significant cellular nonsense-mediated RNA decay (NMD) inhibition at 10 and 3 μM and can be as a probe for further study of eIF4A3, the exon junction complex (EJC), and NMD Form:Solid IC50& Target:IC50: 0.2 μM (eIF4A3), Kd: 0.043 μM (eIF4A3)