Fig. 5

Chemical structures of the highlighted molecules from library A: Chemical structures of fentanyl (A), NFEPP (B), \(\beta\)-fluorofentanyls (C), morphine (D), \(\beta\)-fluoromorphines (E) and CHEMBL3139481 (F). Docking scores in kcal/mol of neutral or acidic MOR docking scenarios are indicated below the structures, respectively. For the \(\beta\)-fluorofentanyls and -morphines the different screened derivatives are indicated by numbers 1–6 or 1–5, respectively. The docking scores of the derivative with the strongest pH specificity are shown. The potentially differently protonated nitrogen atoms in the compound structures are marked with [+]. The \(\hbox {p}K_{\hbox {a}}\) values of fentanyl, morphine and its fluorinated derivatives are indicated as previously described [47, 50] and the experimentally determined value is shown, if available. For CHEMBL3139481, the calculated estimate of its \(\hbox {p}K_{\hbox {a}}\) value is shown