Figure 3.

(A) Binding mode of compound 4. (B) Binding mode of compound 5a. Blue lines indicate π-cation interactions and purple lines salt bridges. Residues of the receptor MOR are represented in gray, 4 in green and 5a in purple. (C) Two-dimensional diagram of the main interactions between 4 and the residues involved in ligand recognition of the MOR binding site. (D) Two-dimensional diagram of the main interactions between 5a and the residues involved in ligand recognition of the MOR binding site. Purple lines represent hydrogen bonds, blue-red represent salt bridges, red lines represent π-cation, and green lines represent π-stacking. Hydrophobic residues are represented in green, negatively charged in red, polar in light blue and positively charged in purple.