Synthesis, Structure–Activity
Relationships,
and Preclinical Evaluation of Heteroaromatic Amides and 1,3,4-Oxadiazole
Derivatives as 5‑HT4 Receptor Partial Agonists
Alzheimer’s
disease (AD) is a neurodegenerative disorder
that has a higher prevalence and incidence in people older than 60
years. The need for improved AD therapies is unmet as the current
therapies are symptomatic with modest efficacy. Partial agonists of
the 5-HT4 receptor (5-HT4R) offer both symptomatic
and disease-modifying treatments as they shift amyloid-precursor-protein
(APP) processing from the amyloidogenic pathway to the nonamyloidogenic
pathway by activating the α-secretase enzyme. In addition, they
also offer symptomatic treatment by increasing levels of the neurotransmitter
acetylcholine in the brain. Because of this fascinating dual mechanism
of action, several chemical scaffolds having 5-HT4R pharmacophores
were designed and evaluated. Most of the synthesized compounds showed
potent in vitro affinities and in vivo efficacies. Upon analysis of
focused structure–activity relationships, compound 4o was identified as a potent 5-HT4R partial agonist with
favorable ADME properties and good in vivo efficacy. GR-125487, a
selective 5-HT4R antagonist, attenuated the activity of
compound 4o in the novel-object-recognition-test cognition
model.