Figure 11.

Predicted binding positions of compounds 2 and 8 with the human ABCG2 transporter protein. (A) Docked position of compound 2 within the binding site of the human ABCG2 transporter protein. Compound 2 is shown as a ball and stick model, with the atoms colored as follows: carbon = cyan, hydrogen = white, nitrogen = blue and oxygen = red. The important residues are depicted as sticks with the same color scheme as above except that carbons are indicated by the grey color. Ring centroids were represented as dark-green dots. Dotted yellow lines indicate hydrogen bonds. (B) A two-dimensional ligand−receptor interaction diagram shows the important interactions of compound 2 with the binding site residues of human ABCG2. The amino acids are shown as colored bubbles, cyan indicates polar residues and green indicates hydrophobic residues. Hydrogen bonds are indicated by the purple dotted arrow, and π-π stacking aromatic interactions are indicated by the green lines. (C) Docked position of compound 8 within the binding site of the human ABCG2 transporter protein. (D) A two-dimensional ligand−receptor interaction diagram shows the important interactions of compound 8 with the binding site residues of the human ABCG2 transporter protein. (E) Docked position of Ko143 within the binding site of the human ABCG2 protein. (F) A two-dimensional diagram shows the important contacts of Ko143 with the binding site residues of the human ABCG2 transporter protein. (G) The comparison of the binding mode of 2, 8 and Ko143 with ABCG2 protein. Compounds are shown as a ball and stick model, with the atoms colored as follows: hydrogen = white, nitrogen = blue, oxygen = red. The carbon atoms are labeled in different colors: 2 (grey), 8 (cyan), Ko143 (orange).