To learn more about the structural features driving affinity to VCB and to verify the binding mode of this class of ligands, X-ray crystallographic analyses were performed. We selected with 30 and 33 two of the most potent compounds, along with 37, a bicyclic derivative which showed a drastic decrease in affinity. The compounds were soaked into crystals of VCB protein and ligand-bound structures were successfully solved to 2.6 Å (30, PDB code: 8CQK), 2.4 Å (33, PDB code: 8CQL), and 2.9 Å (37, PDB code: 8CQE) resolutions (Figure ). In general, these ligands adopted the typical binding mode expected for hydroxyproline-based VHL ligands, maintaining the key interaction network between the protein and the LHS of the ligand.