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

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.

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.

Several databases, including SciFinder, ScienceDirect, Bentham Science, and PubMed, were searched for relevant articles and reviewed for the present work.

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.

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.