Novel small molecule compounds based on various scaffolds including chalcone, flavonoid, and resorcinol dibenzylether were designed and tested for their inhibitory activity against the Programmed Cell Death-1/Programmed Cell Death-Ligand 1 (PD-1/PD-L1) pathway. Among them, compound NP19 inhibited the human PD-1/PD-L1 interaction with IC50 values of 12.5 nM in homogeneous time-resolved fluorescence