We describe herein the therapeutic targets involved in Alzheimer's disease as well as the available drugs and their synthetic routes. Bioactive compounds under development are also exploited to illustrate some recent research advances on the medicinal chemistry of Alzheimer's disease, including structure-activity relationships for some targets. The importance of multi-target approaches, including some examples from our research projects, guides new perspectives in search of more effective drug candidates. This review comprises the period between 2001 and early 2020.
A new series of sixteen multifunctional N-benzyl-piperidine-aryl-acylhydrazones hybrid derivatives was synthesized and evaluated for multi-target activities related to Alzheimer's disease (AD). The molecular hybridization approach was based on the combination, in a single molecule, of the pharmacophoric N-benzyl-piperidine subunit of donepezil, the substituted hydroxy-piperidine fragment of the AChE inhibitor LASSBio-767, and an acylhydrazone linker, a privileged structure present in a number of synthetic aryl- and aryl-acylhydrazone derivatives with significant AChE and anti-inflammatory activities. Among them, compounds 4c, 4d, 4g and 4j presented the best AChE inhibitory activities, but only compounds 4c and 4g exhibited concurrent anti-inflammatory activity in vitro and in vivo, against amyloid beta oligomer (AbetaO) induced neuroinflammation. Compound 4c also showed the best in vitro and in vivo neuroprotective effects against AbetaO-induced neurodegeneration. In addition, compound 4c showed a similar binding mode to donepezil in both acetylated and free forms of AChE enzyme in molecular docking studies and did not show relevant toxic effects on in vitro and in vivo assays, with good predicted ADME parameters in silico. Overall, all these results highlighted compound 4c as a promising and innovative multi-target drug prototype candidate for AD treatment.
Alzheimer's disease (AD) is a progressive and incurable neurodegenerative disorder, with a dramatic socioeconomic impact. The progress of AD is characterized by a severe loss in memory and cognition, leading to behavioral changing, depression and death. During the last decades, only a few anticholinergic drugs were launched in the market, mainly acetylcholinesterase inhibitors (AChEIs), with indications for the treatment of initial and moderate stages of AD. The search for new AChEIs, capable to overcome the limitations observed for rivastigmine and tacrine, led Sugimoto and co-workers to the discovery of donepezil. Besides its high potency, donepezil also exhibited high selectivity for AChE and a very low toxicity. In this review, we discuss the main structural and pharmacological attributes that have made donepezil the first choice medicine for AD, and a versatile structural model for the design of novel AChEIs, in spite of multipotent and multitarget-directed ligands. Many recent data from literature transdue great efforts worldwide to produce modifications in the donepezil structure that could result in new bioactive chemical entities with innovative structural pattern. Furthermore, multi-potent ligands have also been designed by molecular hybridization, affording rivastigmine-, tacrine- and huperzine-donepezil potent and selective AChEIs. In a more recent strategy, structural features of donepezil have been used as a model to design multitarget-directed ligands, aiming at the discovery of new effective drug candidates that could exhibit concomitant pharmacological activities as dual or multi- enzymatic inhibitors as genuine innovative therapeutic alternatives for the treatment of AD.
