Synthesis and structure-activity relationship studies in serotonin 5-HT4 receptor ligands based on a benzo[de][2,6]naphthridine scaffold

Discovery and Preclinical Characterization of Usmarapride (SUVN-D4010): A Potent, Selective 5-HT4 Receptor Partial Agonist for the Treatment of Cognitive Deficits Associated with Alzheimer's Disease

A series of oxadiazole derivatives were synthesized and evaluated as 5-hydroxytryptamine-4 receptor (5-HT₄R) partial agonists for the treatment of cognitive deficits associated with Alzheimer's disease. Starting from a reported 5-HT₄R antagonist, a systematic structure-activity relationship was conducted, which led to the discovery of potent and selective 5-HT₄R partial agonist 1-isopropyl-3-{5-[1-(3-methoxypropyl) piperidin-4-yl]-[1,3,4]oxadiazol-2-yl}-1H-indazole oxalate (Usmarapride, 12l). It showed balanced physicochemical-pharmacokinetic properties with robust nonclinical efficacy in cognition models. It also showed disease-modifying potential, as it increased neuroprotective soluble amyloid precursor protein alpha levels, and dose-dependent target engagement and correlation of efficacy with oral exposures. Phase 1 clinical studies have been completed and projected efficacious concentration was achieved without any major safety concerns. Phase 2 enabling long-term safety studies have been completed with no concerns for further development.

Understanding the Molecular Basis of 5-HT4 Receptor Partial Agonists through 3D-QSAR Studies

Alzheimer's disease (AD) is a neurodegenerative disorder whose prevalence has an incidence in senior citizens. Unfortunately, current pharmacotherapy only offers symptom relief for patients with side effects such as bradycardia, nausea, and vomiting. Therefore, there is a present need to provide other therapeutic alternatives for treatments for these disorders. The 5-HT₄ receptor is an attractive therapeutic target since it has a potential role in central and peripheral nervous system disorders such as AD, irritable bowel syndrome, and gastroparesis. Quantitative structure-activity relationship analysis of a series of 62 active compounds in the 5-HT₄ receptor was carried out in the present work. The structure-activity relationship was estimated using three-dimensional quantitative structure-activity relationship (3D-QSAR) techniques based on these structures' field molecular (force and Gaussian field). The best force-field QSAR models achieve a value for the coefficient of determination of the training set of R²_training = 0.821, and for the test set R²_test = 0.667, while for Gaussian-field QSAR the training and the test were R²_training = 0.898 and R²_test = 0.695, respectively. The obtained results were validated using a coefficient of correlation of the leave-one-out cross-validation of Q²_LOO = 0.804 and Q²_LOO = 0.886 for force- and Gaussian-field QSAR, respectively. Based on these results, novel 5-HT₄ partial agonists with potential biological activity (pEC₅₀ 8.209-9.417 for force-field QSAR and 9.111-9.856 for Gaussian-field QSAR) were designed. In addition, for the new analogues, their absorption, distribution, metabolism, excretion, and toxicity properties were also analyzed. The results show that these new derivatives also have reasonable pharmacokinetics and drug-like properties. Our findings suggest novel routes for the design and development of new 5-HT₄ partial agonists.

A 4,5-quinolimide-based fluorescent sensor for sequential detection of Cu2+ and cysteine in water and living cells with application in a memorized device

In this study, a new 4,5-quinolimide-based fluorescent sensor BNC was synthesized and characterized. BNC showed single selectivity for Cu²⁺via the "turn-off" fluorescence among various common metal ions. After forming a 1:1 stoichiometric complex with Cu²⁺, the detection limit (LOD) of BNC for Cu²⁺ was measured to be 0.44 μM. Subsequently, the in situ generated BNC-Cu²⁺ complex had been used for sensing Cys with the LOD of 1.5 μM through the displacement strategy, resulting in the revivable emission of BNC. According to the "off-on-off" fluorescence cycle of BNC generated by the alternate addition of Cu²⁺ and Cys, a reversible memorized device with "read-write-read-erase" behavior was constructed at the molecular level. Furthermore, the recoveries of Cu²⁺ in lake water with BNC were in the range of 95.0-105%. And sequential fluorescence imagings of BNC for Cu²⁺ and Cys were successfully applied in living yeast cells.

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.

Development of subnanomolar-affinity serotonin 5-HT4 receptor ligands based on quinoline structures

A structure–affinity relationship study led to the discovery of 7h–j as novel 5-HT₄ receptor ligands showing K_i values in the subnanomolar range.

Multivalent ligands for the serotonin 5-HT4 receptor

5-HT₄ receptors are known to form constitutive dimers in membranes. To explore whether multivalency can enhance ligand interactions and/or efficacy in 5-HT₄ receptors, the structure of the partial agonist ML10302 was modified with oligo(ethylene glycol) chains, thus generating, by a gradual approach, short and long tethered bivalent or tetravalent ligands and the corresponding spanner-linked monovalent controls. Both bivalent and tetravalent ligands displayed a 10-20-fold increase in binding affinity compared to appropriate controls, but no multivalent ligand showed greater binding energy than ML10302 itself. Furthermore, the direct assessment of receptor-Gs interaction and studies of cAMP signalling indicated that multivalency does not enhance the efficacy of ML10302.

A 4,5-quinolimide-based fluorescent sensor for the turn-on detection of Cd2+ with live-cell imaging

The first 4,5-quinolimide sensor, BNA, bearing the amide-DPA receptor, was reported for sensing Cd²⁺ with live-cell imaging.

Highly solvatochromic and tunable fluorophores based on a 4,5-quinolimide scaffold: novel CDK5 probes

Novel 4,5-quinolimide-based fluorophores are more solvatochromic and red-shifted than known naphthalimide analogues. Conjugation of one of these fluorophores to a peptide derived from CDK5 kinase demonstrated its sensitivity for monitoring the interaction with its regulatory partner p25. Introduction of the quinolimide-labelled peptide into living glioblastoma cells probed the interaction with endogenous p25.

Discovery and SAR of N-(1-((substituted piperidin-4-yl)methyl)-3-methoxypiperidin-4-yl)-2-methoxybenzamide derivatives: 5-Hydroxytryptamine receptor 4 agonist as a potent prokinetic agent

A series of novel benzamide derivatives, altering the 4-fluorophenylalkyl moiety in cisapride, were synthesized as 5-HT4 receptor agonists, and SAR of these analogs was examined on in vitro and in vivo prokinetic activities. These compounds were synthesized for high 5-HT4 receptor binding affinities and low hERG affinities. Several types of analogs were obtained and screened for 5-HT4 binding, hERG blocking, agonism, and gastric emptying assessment. Among the analogues, compound 23g showed promising results compared with the other analogs with respect to gastric emptying rates in rats. Therefore, we suggest that it may be a clinical candidate for the development of a potent prokinetic agent to treat GI disorders.

Synthesis and SAR of Imidazo[1,5-a]pyridine derivatives as 5-HT4 receptor partial agonists for the treatment of cognitive disorders associated with Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease which has a higher prevalence and incidence in older people. The need for improved AD therapies is unmet. The 5-hydroxytryptamine4 receptor (5-HT4R) partial agonists may be of benefit for both the symptomatic and disease-modifying treatment of cognitive disorders associated with AD. Herein, we report the design, synthesis and SAR of imidazo[1,5-a] pyridine derivatives as 5-HT4R partial agonists. The focused SAR, optimization of ADME properties resulted the discovery of compound 5a as potent, selective, brain penetrant 5-HT4 partial agonist as a lead compound with good ADME properties and efficacy in both symptomatic and disease modifying animal models of cognition.