Synthesis of New Substituted 5 H-Benzo[ e]imidazo[1,2- a][1,4]diazepines via Pictet-Spengler Reaction and Their Neuroprotective and Anticonvulsant Evaluation

We herein report the design, Pictet-Spengler reaction-mediated synthesis, and neuroprotective evaluation of new 10,11-dihydro-5H-benzo[e]imidazo[1,2-a][1,4]diazepines without (7a) or with iminic anchor (8a-8f), along with representative 5H-benzo[e]imidazo[1,2-a][1,4]diazepines (oxidized compounds; 7ao and 8co), and some nonrigid benzodiazepine analogues (4, 5a-5c, and 6a-6c). Compounds 8b, 8c, and 8e did not show any neurotoxic effects in the Neuro2a and SHSY-5Y cell lines up to 10 μM concentration and increased the number of neurite-bearing cells and neurite length, suggesting the protective abilities of compounds. In pentylenetetrazole (PTZ)-treated cells, 8b, 8c, and 8e exerted neuroprotective effects by increasing cell viability and reducing ROS levels. Notably, 8b at 10 μM reduced ROS formation more than diazepam and Other compounds. Further, protein expression studies indicated that compounds at 10 μM concentration upregulated the GABA_Aα1 expression compared to PTZ alone-treated cells. The binding analysis at the GABA_A site, using molecular docking and MD simulations, suggested a neuroprotective effect of these compounds via GABA_A targeting. In vivo, compound 8b demonstrated a dose-dependent anticonvulsant effect in the PTZ-induced kindling mouse model, significantly delaying seizure onset while reducing the seizure duration, frequency, and severity with efficacy comparable to that of diazepam.

GABAA; MD simulation; Pictet−Spengler reaction; antiepileptic compounds; benzodiazepine; neuroprotection.