Figure 3.

Carboxy-functionalized P1 residues intended as occluding loop-targeting moieties in the dipeptide-derived cathepsin B inhibitor. Structure of the P1 residue described by Greenspan et al. (left; X = N) and Schmitz et al. (middle; X = N) and derived alternative P1 residue (right) for the design of cathepsin B-directed dipeptide alkynes (X = CH).