A Recent Appraisal of Small-Organic Molecules as Anti-Alzheimer’s Agents

Background: Alzheimer’s disease (AD) is an irreversible, progressive and very complex brain disorder. There is still uncertainty about the etiology of AD; however, a few hallmarks like an aggregation of tau proteins, amyloid-β plaques, oxidative stress, low level of choline in the brain etc., play significant roles. Objective: In the present work, we aim to evaluate the recent progress in the development of small organic molecules containing heterocycles like thiazole, pyridines, dihydropyridines, piperidines, pyrrolidines, pyrazoles, quinolines etc. as anti-Alzheimer’s agents. Method: Several databases, including SciFinder, ScienceDirect, Bentham Science, and PubMed, were searched for relevant articles and reviewed for the present work. Results: Several research groups are actively working on these heterocycle-based compounds as potent single-target inhibitors. Most of the analogues have been evaluated for their cholinesterase (acetylcholinesterase and butyrylcholinesterase) inhibition potential. Several studies have also reported the inhibitory potential of the analogues against MAO-A, MAO-B, and BACE-1 enzymes. However, instead of targeting one enzyme or protein, more than one heterocycle ring is being joined to develop MTDLs (multi-target-directed ligands). Donepezil has become the focal point of anti-AD drug discovery projects. Several research groups have reported various donepezil-based analogues by replacing/ modifying its various ring systems like indanone, piperidine or the methylene linker. Conclusion: Small molecules with nitrogen-containing heterocycles have become the core of drug discovery efforts for AD. With the increasing prominence of the MTDL approach, several new ligands are being discovered as potent anti-AD agents.