Synthesis and pharmacological evaluation of carboxamide derivatives as selective serotoninergic 5-HT4 receptor agonists

Novel gut-restricted bivalent agonists targeting mucosal 5-HT4R: Design, synthesis, and biological evaluation

Chronic idiopathic constipation (CIC) is a prevalent gastrointestinal disorder with limited therapeutic options that balance efficacy and safety. Current therapies, such as the 5-HT4 receptor (5-HT4R) agonist prucalopride, demonstrate efficacy but are often associated with systemic side effects, highlighting the need for gut-restricted alternatives. Herein, we report for the first time the rational design and synthesis of gut-restricted bivalent agonists targeting mucosal 5-HT4R by integrating pharmacophores of prucalopride and tenapanor. Structural optimization, particularly of linker length and properties, led to the discovery of compound 4, which exhibited potent 5-HT4R agonistic activity, high selectivity, and favorable physicochemical properties. Preclinical studies demonstrated that compound 4 significantly enhanced whole-gut and colonic transit, increased fecal output and water content, while maintaining minimal systemic absorption, confirming its gut-restricted nature. These findings underscore the feasibility of gut-restricted 5-HT4R agonists as a novel therapeutic strategy for CIC and provide valuable insights into the development of safer, more effective treatments for gastrointestinal disorders.

Synthesis and preliminary pharmacological results on new naphthalene derivatives as 5-HT(4) receptor ligands

The indole derivative GR 113808 is currently used as the reference ligand for labelling the 5-HT(4) serotoninergic receptors. Previous works in our laboratories established the bioisosteric equivalency of the indole heterocycle and naphthalene in a series of melatonin receptor ligands. Based on this knowledge we designed new analogues of GR 113808 by introducing two bioisosteric modifications: firstly, the indole ring was replaced by a naphthalene one and secondly, the ester linkage was replaced by an amide group. Compound 8 emerged within this novel series as it displayed high and selective affinity at 5-HT(4) receptors (Ki 5-HT(4) = 6 nM, Ki 5-HT(3) = 100 nM, Ki values at other 5-HT receptors were higher than 1000 nM). Compound 8 is currently undergoing further pharmacological evaluation.