Structure-Activity Relationship Studies of Tetrahydroquinolone Free Fatty Acid Receptor 3 Modulators

Structure-activity relationship studies of tetrahydroquinolone derivatives as GPR41 modulators

GPR41, a G protein-coupled receptor, serves as a sensor for short-chain fatty acids and plays a crucial role in regulating multiple physiological processes such as the maintenance of metabolic and immune homeostasis. Therefore, the modulation of GPR41 has garnered attention as a potential strategy for the treatment of various disorders. We conducted a structure-activity relationship study on a lead tetrahydroquinolone derivative bearing a 2-(trifluoromethoxy)benzene group that displayed antagonistic activity toward GPR41. Modification of the aryl group attached to the furan moiety revealed that derivatives containing di- or trifluorobenzene, instead of 2-(trifluoromethoxy)benzene, exhibited agonistic activity toward GPR41, comparable with the reported agonistic modulator AR420626. These results suggest that the aryl group plays a pivotal role in regulating the activity of compounds toward GPR41, providing valuable insights for the design of GPR41 modulators.

Discovery of Potent Tetrazole Free Fatty Acid Receptor 2 Antagonists

The free fatty acid receptor 2 (FFA2), also known as GPR43, mediates effects of short-chain fatty acids and has attracted interest as a potential target for treatment of various metabolic and inflammatory diseases. Herein, we report the results from bioisosteric replacement of the carboxylic acid group of the established FFA2 antagonist CATPB and SAR investigations around these compounds, leading to the discovery of the first high-potency FFA2 antagonists, with the preferred compound TUG-2304 (16l) featuring IC50 values of 3-4 nM in both cAMP and GTPγS assays, favorable physicochemical and pharmacokinetic properties, and the ability to completely inhibit propionate-induced neutrophil migration and respiratory burst.

Chemoselective Condensation of 3-Amino-2-cyclohexenones with Cinnamaldehydes: Switchable Synthesis of Dihydroquinolinones and Hexahydroacridinediones

Herein, a chemoselective condensation of 3-amino-2-cyclohexenones and cinnamaldehydes for switchable synthesis of dihydroquinolinones and hexahydroacridinediones was developed. Mechanism analysis showed that the formation of dihydroquinolinones involved trimolecular condensation and oxidative aromatization, while the formation of hexahydroacridinediones involved acid hydrolysis of enaminone and dehydration-aromatization. This strategy provides a convenient way to switch from the same substrates to produce two different quinolinone derivatives.

Chemogenetics defines a short-chain fatty acid receptor gut-brain axis

Volatile small molecules, including the short-chain fatty acids (SCFAs), acetate and propionate, released by the gut microbiota from the catabolism of nondigestible starches, can act in a hormone-like fashion via specific G-protein-coupled receptors (GPCRs). The primary GPCR targets for these SCFAs are FFA2 and FFA3. Using transgenic mice in which FFA2 was replaced by an altered form called a Designer Receptor Exclusively Activated by Designer Drugs (FFA2-DREADD), but in which FFA3 is unaltered, and a newly identified FFA2-DREADD agonist 4-methoxy-3-methyl-benzoic acid (MOMBA), we demonstrate how specific functions of FFA2 and FFA3 define a SCFA-gut-brain axis. Activation of both FFA2/3 in the lumen of the gut stimulates spinal cord activity and activation of gut FFA3 directly regulates sensory afferent neuronal firing. Moreover, we demonstrate that FFA2 and FFA3 are both functionally expressed in dorsal root- and nodose ganglia where they signal through different G proteins and mechanisms to regulate cellular calcium levels. We conclude that FFA2 and FFA3, acting at distinct levels, provide an axis by which SCFAs originating from the gut microbiota can regulate central activity.

The Specificity and Broad Multitarget Properties of Ligands for the Free Fatty Acid Receptors FFA3/GPR41 and FFA2/GPR43 and the Related Hydroxycarboxylic Acid Receptor HCA2/GPR109A

The paradigm of ligand-receptor interactions postulated as "one compound-one target" has been evolving; a multi-target, pleiotropic approach is now considered to be realistic. Novel series of 1,4,5,6,7,8-hexahydro-5-oxoquinolines, pyranopyrimidines and S-alkyl derivatives of pyranopyrimidines have been synthesized in order to characterise their pleiotropic, multitarget activity on the FFA3/GPR41, FFA2/GPR43, and HCA2/GPR109A receptors. Hexahydroquinoline derivatives have been known to exhibit characteristic activity as FFA3/GPR41 ligands, but during this study we observed their impact on FFA2/GPR43 and HCA2/GPR109A receptors as well as their electron-donating activity. Oxopyranopyrimidine and thioxopyranopyrimidine type compounds have been studied as ligands of the HCA2/GPR109A receptor; nevertheless, they exhibited equal or higher activity towards FFA3/GPR41 and FFA2/GPR43 receptors. S-Alkyl derivatives of pyranopyrimidines that have not yet been studied as ligands of GPCRs were more active towards HCA2/GPR109A and FFA3/GPR41 receptors than towards FFA2/GPR43. Representative compounds from each synthesized series were able to decrease the lipopolysaccharide-induced gene expression and secretion of proinflammatory cytokines (IL-6, TNF-α) and of a chemokine (MCP-1) in THP-1 macrophages, resembling the effect of HCA2/GPR109A ligand niacin and the endogenous ligand propionate. This study revealed groups of compounds possessing multitarget activity towards several receptors. The obtained data could be useful for further development of multitarget ligands.

Structure-Activity Relationship Explorations and Discovery of a Potent Antagonist for the Free Fatty Acid Receptor 2

Free fatty acid receptor 2 (FFA2) is a sensor for short-chain fatty acids that has been identified as an interesting potential drug target for treatment of metabolic and inflammatory diseases. Although several ligand series are known for the receptor, there is still a need for improved compounds. One of the most potent and frequently used antagonists is the amide-substituted phenylbutanoic acid known as CATPB ( 1 ). We here report the structure-activity relationship exploration of this compound, leading to the identification of homologues with increased potency. The preferred compound 37 (TUG-1958) was found, besides improved potency, to have high solubility and favorable pharmacokinetic properties.

Targeting lipid GPCRs to treat type 2 diabetes mellitus - progress and challenges

Therapeutic approaches to the treatment of type 2 diabetes mellitus that are designed to increase insulin secretion either directly target β-cells or indirectly target gastrointestinal enteroendocrine cells (EECs), which release hormones that modulate insulin secretion (for example, incretins). Given that β-cells and EECs both express a large array of G protein-coupled receptors (GPCRs) that modulate insulin secretion, considerable research and development efforts have been undertaken to design therapeutic drugs targeting these GPCRs. Among them are GPCRs specific for free fatty acid ligands (lipid GPCRs), including free fatty acid receptor 1 (FFA1, otherwise known as GPR40), FFA2 (GPR43), FFA3 (GPR41) and FFA4 (GPR120), as well as the lipid metabolite binding glucose-dependent insulinotropic receptor (GPR119). These lipid GPCRs have demonstrated important roles in the control of islet and gut hormone secretion. Advances in lipid GPCR pharmacology have led to the identification of a number of synthetic agonists that exert beneficial effects on glucose homeostasis in preclinical studies. Yet, translation of these promising results to the clinic has so far been disappointing. In this Review, we present the physiological roles, pharmacology and clinical studies of these lipid receptors and discuss the challenges associated with their clinical development for the treatment of type 2 diabetes mellitus.