## 3 Results and Discussion
### Docking-Based Interaction Simulations
Among the 100\(\times\) dockings performed, the conformation of the best cluster and the lowest bind energy was selected. Molecular docking results showed that all PBD compounds can interact with the ER\(\alpha\) receptor. The binding energy (\(\Delta\)G) values obtained range from \(-11.21\) to \(-8.67\) kcal/mol, and inhibition constant (Ki) values range from 6.08 to 440.16 nM (Table 4). The binding energy indicates the stability of the ligand binding to the receptor. The more minus (more negative) the binding energy, the more stable the resulting bond in the protein-ligand complex. The inhibition constant can indicate the inhibition between the ligand and the target protein. The smaller the inhibition constant value, the smaller the inhibition in the ligand-receptor bond [78]. The amino acid residues and interaction of the ligands with ER\(\alpha\) are shown in Table 5. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Legend**} & **Inhibition** & **Binding** & **Intermolecular** & **Torsional** & **Inhibition** & **Binding** & **Intermolecular** & **Torsional** \\  & **Constant** & **Energy** & **Energy** & **Energy** & **Constant** & **Energy** & **Energy** & **Energy** & **Energy** \\  & **(nM)** & **(kcal/mol)** & **(kcal/mol)** & **(kcal/mol)** & & & **(mM)** & **(kcal/mol)** & **(kcal/mol)** & **(kcal/mol)** \\ \hline
4-OHT & 4.26 & \(-11.42\) & \(-13.81\) & 2.39 & 22 & 16.77 & \(-10.61\) & \(-12.99\) & 2.39 \\ \hline \multicolumn{1}{c}{Raloxifene} & 2.94 & \(-11.63\) & \(-14.32\) & 2.68 & 23 & 54.89 & \(-9.91\) & \(-12.29\) & 2.39 \\ \hline Lasofoxifene & 2.71 & \(-11.69\) & \(-13.78\) & 2.09 & 24 & 217.41 & \(-9.09\) & \(-11.48\) & 2.39 \\ \hline
1 & 56.27 & \(-9.89\) & \(-12.28\) & 2.39 & 25 & 16.58 & \(-10.61\) & \(-13.00\) & 2.39 \\ \hline
2 & 37.36 & \(-10.13\) & \(-12.52\) & 2.39 & 26 & 9.43 & \(-10.95\) & \(-13.33\) & 2.39 \\ \hline
3 & 127.39 & \(-9.41\) & \(-11.79\) & 2.39 & 27 & 53.23 & \(-9.92\) & \(-12.31\) & 2.39 \\ \hline
4 & 72.62 & \(-9.74\) & \(-12.72\) & 2.98 & 28 & 18.53 & \(-10.55\) & \(-12.64\) & 2.09 \\ \hline
5 & 27.07 & \(-10.32\) & \(-13.31\) & 2.98 & 29 & 39.41 & \(-10.10\) & \(-12.19\) & 2.09 \\ \hline
6 & 129.33 & \(-9.40\) & \(-12.38\) & 2.98 & 30 & 187.65 & \(-9.18\) & \(-11.26\) & 2.09 \\ \hline
7 & 10.38 & \(-10.89\) & \(-13.28\) & 2.39 & 31 & 17.47 & \(-10.58\) & \(-12.67\) & 2.09 \\ \hline
8 & 25.47 & \(-10.36\) & \(-12.75\) & 2.39 & 32 & 25.73 & \(-10.35\) & \(-12.44\) & 2.09 \\ \hline
9 & 126.50 & \(-9.41\) & \(-11.80\) & 2.39 & 33 & 204.73 & \(-9.13\) & \(-11.21\) & 2.09 \\ \hline
10 & 12.01 & \(-10.81\) & \(-12.89\) & 2.09 & 34 & 11.17 & \(-10.85\) & \(-12.94\) & 2.09 \\ \hline
11 & 14.89 & \(-10.68\) & \(-12.77\) & 2.09 & 35 & 20.31 & \(-10.49\) & \(-12.58\) & 2.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The inhibition constant and different energy values of PBD compounds and reference ligands to ER\(\alpha\) were generated from molecular docking using AutoDock4. Figure 3: Superimposition of the co-crystallized pose (orange) and the re-docking pose (blue) of 4-OHT in the active site of the ER\(\alpha\) (RMSD = 1.17 Å).