Discovery of novel H3R antagonists with potent antiseizure activity and favorable pharmacokinetics via scaffold-hopping from pitolisant to rigid 4-phenylindoles.

In the present work, scaffold hopping starting from pitolisant furnished a novel class of 4-phenylindole histamine H₃ receptor antagonists. All twenty designed analogues were synthesized and comprehensively profiled in biological assays. Compounds 3a, 3b, 3g, 3m, and 3n showed potent H3R antagonism with IC50 values of 2.82, 3.15, 1.32, 3.37, and 1.49 μM respectively, among which 3g and 3n were the most active. In subtype selectivity assays, compounds 3g and 3m exhibited potent H2R antagonistic effects (with IC50 of 0.6970 and 0.4844 μM, respectively), and this activity was stronger than their H3R activity. Compound 3n also showed considerable H2R antagonism with IC50 values of 1.317 μM. In the mouse maximal electroshock model, compound 3n demonstrated an ED50 of 16.44 mg/kg, comparable to pitolisant (16.34 mg/kg). In the zebrafish pentylenetetrazol model, compound 3n reduced locomotor activity by 98.66% at 10 μM, superior to pitolisant (97.49%) and the classic antiseizure drug carbamazepine (58.47%). The antiseizure effect of compound 3n was confirmed to be H3R-mediated using the selective agonist RAMH, while the H2R agonist dimaprit dihydrochloride failed to reverse its activity, ruling out H2R involvement. Safety profiling revealed no neurotoxicity at therapeutic doses, a favorable hERG safety margin (IC50 = 0.9377 μM), and low cytotoxicity. Pharmacokinetic evaluation showed oral bioavailability of 60.73% for compound 3n, which was higher than that of pitolisant (31.9%), and effective blood-brain barrier penetration with brain-to-plasma ratios exceeding unity. Molecular docking revealed that compound 3n engaged H3R through a distinct hydrogen bond and π-interaction network. These results support compound 3n as a promising antiseizure candidate.