Development of promising acetylcholinesterase and butyrylcholinesterase inhibitors: Synthesis, in vitro and in silico approaches of pyridine derived fused bis-oxadiazole and bis-thiadiazole derivatives

The present study aims to synthesize new thiadiazole/oxadiazole fused thiadiazole derivatives, incorporating pyridine moiety as effective inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) to treat Alzheimer disease. Initially, pyridine based thiosemicarbazone was synthesized by treating pyridine 2,6-dicarboxaldehyde with thiosemicarbazide. Thiosemicarbazone was cyclized into bis-thiadiazole, which further react with different isothiocyanates to give pyridine-based bis-(thiadiazole-fused-thiadiazole) derivatives (4a-h). Next pyridine based semicarbazone was synthesized by treating pyridine 2,6-dicarboxaldehyde with semicarbazide. Then semicarbazone was cyclized into bis-oxadiazole which further react with different isothiocyanates to give pyridine-based bis-(oxadiazole-fused-thiadiazole) derivatives (7a-h).The synthetic analogs were structurally elucidated through H-1 NMR,C-13 NMR and HRMS (EI) analysis and assessed for acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitory potential. All synthetic analogues showed varying degrees of inhibitory effects on AChE and BuChE, with IC50 value ranging from 12.89 +/- 1.10 mu M - 61.76 +/- 2.40 mu M for AChE and 14.79 +/- 1.20 mu M - 56.87 +/- 2.50 mu M for BuChE in comparison of standard inhibitor Galantamine (IC50= 37.40 +/- 1.20 mu M for AChE and IC50 = 41.20 +/- 1.90 mu M for BuChE). Among the series, analogues 4c IC50 = 13.32 +/- 1.30 mu M (against AChE), and 15.17 +/- 1.40 mu M (against BuChE), and 7c IC50 = 12.89 +/- 1.10 mu M (against AChE) and 14.79 +/- 1.20 mu M (against BuChE) exhibited notable inhibitory activity against AChE and BuChE enzymes, Moreover, molecular docking studies were conducted on potential analogues to investigate their binding interactions with the targeted enzyme's active sites.