Synthesis and biological evaluation of 3-aryl-3-(4-phenoxy)-propionic acid as a novel series of G protein-coupled receptor 40 agonists

Enantioselective synthesis of 4-aryl-3,4-dihydrocoumarins via N-heterocyclic carbene catalyzed β-arylation/cyclization of α-bromoenals

4-Aryl-3,4-dihydrocoumarins are one of the most important structural motifs. Herein, we disclose an enantioselective N-heterocyclic carbene catalyzed β-arylation/cyclization of α-bromoenals with 3-aminophenols under mild conditions. The protocol allows for the rapid preparation of 4-aryl-3,4-dihydrocoumarins in acceptable yields with good enantioselectivities. The products of this reaction could be converted into chiral diarylpropanoic acid derivatives without erosion of the enantioselectivity.

Brønsted Acid-Mediated Multicomponent One-Pot Approach to Direct Construction of 4-Aryl-hydrocoumarin Derivatives

The facile and efficient synthesis of a unique class of 4-aryl-hydrocoumarins having enormous applications in medicinal chemistry and natural products is presented. We have for the first time developed a Brønsted acid-catalyzed, multicomponent, one-pot approach for producing various 4-aryl-coumarin derivatives. The feedstock availability of these precursors allowed access to a wide range of 2-chromanone derivatives in good to excellent yields under mild conditions. The practicality of this protocol was justified by the synthesis of bioactive compounds, late-stage functionalization of natural products, and gram-scale synthesis.

Palladium Catalyzed Enantioselective Hayashi-Miyaura Reaction for Pharmaceutically Important 4-Aryl-3,4-dihydrocoumarins

The first palladium-catalyzed asymmetric addition of arylboronic acids to coumarins was successfully established, providing a straightforward asymmetric approach to achieving pharmaceutically important 4-aryl-3,4-dihydrocoumarins. This methodology features easily accessible and bench-stable ligands, a wide substrate scope, mild conditions, and accommodation of electron-withdrawing arylboronic acids.

Photocatalytic Synthesis of Diarylmethyl Silanes via 1,6-Conjugate Addition of Silyl Radicals to p-Quinone Methides

A novel photocatalytic method for the preparation of diarylmethyl silanes was reported through silyl radicals addition strategy to p-QMs (p-quinone methides). This protocol could tolerate a variety of functional groups affording the corresponding silylation products with moderate to excellent yields. The resulting silylation products could be easily converted into a series of bioactive GPR40 agonists and useful p-QMs precursors for the synthesis of compounds possessing both quaternary carbon centers and silicon substituents through simple operation. A plausible mechanism of silyl radicals to p-QMs was proposed on the basis of experimental results and previous literature.

Highly enantioselective Ni-catalyzed asymmetric hydrogenation of β,β-disubstituted acrylic acids

A highly enantioselective Ni-catalyzed hydrogenation of β,β-disubstituted acrylic acids was first realized using Ph-BPE, providing straightforward access to chiral carboxylic acids in high yields with excellent enantioselectivities, up to 99% ee.

Organocatalytic Asymmetric Addition of Aromatic α-Cyanoketones to o-Quinone Methides: Synthesis of 3,4-Dihydrocoumarins and Tetrasubstituted Chromans

The first organocatalytic asymmetric addition of aromatic α-cyanoketones to in situ-generated o-quinone methides has been developed. The products 3,4-dihydrocoumarin and tetrasubstituted chroman were obtained via addition of aromatic α-cyanoketones to in situ-generated o-quinone methides followed by treatment with 0.7 N HCl. With 10 mol % catalyst, the desired products were obtained in high enantio- and diastereoselectivities.

Discovery and development of CPL207280 as new GPR40/FFA1 agonist

Due to a unique mechanism that limits the possibility of hypoglycemia, the free fatty acid receptor (FFA1) is an attractive target for the treatment of type 2 diabetes. So far, however, none of the promising agonists have been able to enter the market. The most advanced clinical candidate, TAK-875, was withdrawn from phase III clinical trials due to liver safety issues. In this article, we describe the key aspects leading to the discovery of CPL207280 (13), the design of which focused on long-term safety. The introduction of small, nature-inspired acyclic structural fragments resulted in compounds with retained high potency and a satisfactory pharmacokinetic profile. Optimized synthesis and upscaling provided a stable, solid form of CPL207280-51 (45) with the properties required for the toxicology studies and ongoing clinical trials.

Recent Updates on Free Fatty Acid Receptor 1 (GPR-40) Agonists for the Treatment of Type 2 Diabetes Mellitus

BACKGROUND

The global incidence of type 2 diabetes mellitus (T2DM) has enthused the development of new antidiabetic targets with low toxicity and long-term stability. In this respect, free fatty acid receptor 1 (FFAR1), which is also recognized as a G protein-coupled receptor 40 (GPR40), is a novel target for the treatment of T2DM. FFAR1/GPR40 has a high level of expression in β-cells of the pancreas, and the requirement of glucose for stimulating insulin release results in immense stimulation to utilise this target in the medication of T2DM.

METHODS

The data used for this review is based on the search of several scienctific databases as well as various patent databases. The main search terms used were free fatty acid receptor 1, FFAR1, FFAR1 agonists, diabetes mellitus, G protein-coupled receptor 40 (GPR40), GPR40 agonists, GPR40 ligands, type 2 diabetes mellitus and T2DM.

RESULTS

The present review article gives a brief overview of FFAR1, its role in T2DM, recent developments in small molecule FFAR1 (GPR40) agonists reported till now, compounds of natural/plant origin, recent patents published in the last few years, mechanism of FFAR1 activation by the agonists, and clinical status of the FFAR1/GPR40 agonists.

CONCLUSION

The agonists of FFAR1/GRP40 showed considerable potential for the therapeutic control of T2DM. Most of the small molecule FFAR1/GPR40 agonists developed were aryl alkanoic acid derivatives (such as phenylpropionic acids, phenylacetic acids, phenoxyacetic acids, and benzofuran acetic acid derivatives) and thiazolidinediones. Some natural/plant-derived compounds, including fatty acids, sesquiterpenes, phenolic compounds, anthocyanins, isoquinoline, and indole alkaloids, were also reported as potent FFAR1 agonists. The clinical investigations of the FFAR1 agonists demonstrated their probable role in the improvement of glucose control. Though, there are some problems still to be resolved in this field as some FFAR1 agonists terminated in the late phase of clinical studies due to "hepatotoxicity." Currently, PBI-4050 is under clinical investigation by Prometic. Further investigation of pharmacophore scaffolds for FFAR1 full agonists as well as multitargeted modulators and corresponding clinical investigations will be anticipated, which can open up new directions in this area.

Non-hydrogen bond catalyst-mediated diastereoselective conjugate additions of 5H-oxazol-4-ones to o-hydroxyphenyl-substituted p-quinone methides

An efficient DBU-catalyzed conjugate addition of 5H-oxazol-4-ones to o-hydroxyphenyl-substituted p-quinone methides has been developed, affording the valuable diarylmethanes in high yields with excellent diastereoselectivity. This strategy demonstrates a robust access to a wide range of diarylmethane derivatives possessing biologically significant o-hydroxyphenol and p-hydroxyphenol moieties under mild reaction conditions.

Lewis acid-catalyzed annulative partial dimerization of 3-aryloxyacrylates to 4-arylchroman-2-ones: synthesis of analogues of tolterodine, RORγ inhibitors and a GPR40 agonist

A beguiling annulative partial dimerization of 3-aryloxyacrylates to 4-arylchroman-2-ones catalyzed by Lewis acid (BF3·OEt2) has been developed. The reaction involves two molecules of 3-aryloxyacrylate, resulting in the loss of one propiolate molecule to furnish 4-arylchroman-2-one, an important structural motif found in many natural products. This methodology has been elaborated to synthesize analogues of tolterodine, RORγ inhibitors and a GPR40 agonist.

Complex Pharmacology of Free Fatty Acid Receptors

G protein-coupled receptors (GPCRs) are historically the most successful family of drug targets. In recent times it has become clear that the pharmacology of these receptors is far more complex than previously imagined. Understanding of the pharmacological regulation of GPCRs now extends beyond simple competitive agonism or antagonism by ligands interacting with the orthosteric binding site of the receptor to incorporate concepts of allosteric agonism, allosteric modulation, signaling bias, constitutive activity, and inverse agonism. Herein, we consider how evolving concepts of GPCR pharmacology have shaped understanding of the complex pharmacology of receptors that recognize and are activated by nonesterified or "free" fatty acids (FFAs). The FFA family of receptors is a recently deorphanized set of GPCRs, the members of which are now receiving substantial interest as novel targets for the treatment of metabolic and inflammatory diseases. Further understanding of the complex pharmacology of these receptors will be critical to unlocking their ultimate therapeutic potential.

Transition metal-free decarboxylative alkylation reactions

This review summarizes recent advances in the transition metal-free decarboxylative alkylation of carboxylic acids and their derivatives.

Down-regulation of G protein-coupled receptor 137 by RNA interference inhibits cell growth of two hepatoma cell lines

G protein-coupled receptors (GPCRs) are important signal transduction mediators and pharmacological therapeutic targets. G protein-coupled receptor 137 (GPR137) was initially reported as a novel orphan GPCR around 10 years ago. Some orphan GPCRs have been implicated in cancer cell proliferation and migration. The aim of this study is to investigate the role of GPR137 in hepatocellular carcinoma (HCC). GPR137 is widely expressed in several human HCC cell lines, as determined by real-time PCR. We then applied lentivirus mediated RNA interference (RNAi) to knock down GPR137 expression in two HCC cell lines HepG2 and Bel7404. Depletion of GPR137 remarkably inhibited cell proliferation and colony formation capacity. Knockdown of GPR137 in HepG2 cells led to cell cycle arrest at G0/G1 phase and G2/M phase, and induced cell apoptosis, as determined by flow cytometry analysis, which contributed to cell growth inhibition. Our findings suggested that GPR137 could facilitate HCC cell proliferation and thus promote hepatocarcinogenesis.

Discovery of 3-aryl-3-ethoxypropanoic acids as orally active GPR40 agonists

The G protein-coupled receptor 40 (GPR40) mediates enhancement of glucose-stimulated insulin secretion in pancreatic β cells. The GPR40 agonist has been attracting attention as a novel insulin secretagogue with glucose dependency for the treatment of type 2 diabetes. The optimization study of compound 1 led to a potent and bioavailable GPR40 agonist 24, which showed insulin secretion and glucose lowering effects in rat OGTT. Compound 24 is a potential lead compound for a novel insulin secretagogue with a low risk of hypoglycemia.

An efficient multistep ligand-based virtual screening approach for GPR40 agonists

G protein-coupled receptor 40/free fatty acid receptor 1 (GPR40/FFAR1) is a member of the GPCR superfamily, and GPR40 agonists have therapeutic potential for type 2 diabetes. With the crystal structure of GPR40 currently unavailable, various ligand-based virtual screening approaches can be applied to identify novel agonists of GPR40. It is known that each ligand-based method has its own advantages and limitations. To improve the efficiency of individual ligand-based methods, an efficient multistep ligand-based virtual screening approach is presented in this study, including the pharmacophore-based screening, physicochemical property filtering, protein-ligand interaction fingerprint similarity analysis, and 2D-fingerprint structural similarity search. A focused decoy library was generated and used to evaluate the efficiency of this virtual screening protocol. This multistep workflow not only significantly improved the hit rate compared with each individual ligand-based method, but also identified diverse known actives from decoys. This protocol may serve as an efficient virtual screening tool for the targets without crystal structures available to discover novel active compounds.

Free fatty acid (FFA) and hydroxy carboxylic acid (HCA) receptors

Saturated and unsaturated free fatty acids (FFAs), as well as hydroxy carboxylic acids (HCAs) such as lactate and ketone bodies, are carriers of metabolic energy, precursors of biological mediators, and components of biological structures. However, they are also able to exert cellular effects through G protein-coupled receptors named FFA1-FFA4 and HCA1-HCA3. Work during the past decade has shown that these receptors are widely expressed in the human body and regulate the metabolic, endocrine, immune and other systems to maintain homeostasis under changing dietary conditions. The development of genetic mouse models and the generation of synthetic ligands of individual FFA and HCA receptors have been instrumental in identifying cellular and biological functions of these receptors. These studies have produced strong evidence that several FFA and HCA receptors can be targets for the prevention and treatment of various diseases, including type 2 diabetes mellitus, obesity, and inflammation.

Activation of GPR40 as a therapeutic target for the treatment of type 2 diabetes

The stimulation of insulin secretion by glucose can be modulated by multiple nutritive, hormonal, and pharmacological inputs. Fatty acids potentiate insulin secretion through the generation of intracellular signaling molecules and through the activation of cell surface receptors. The G-protein-coupled receptor 40 (GPR40), also known as free fatty acid receptor 1 (we will use GPR40 in this review), has emerged as an important component in the fatty acid augmentation of insulin secretion. By signaling predominantly through Gαq/11, GPR40 increases intracellular calcium and activates phospholipases to generate diacylglycerols resulting in increased insulin secretion. Synthetic small-molecule agonists of GPR40 enhance insulin secretion in a glucose-dependent manner in vitro and in vivo with a mechanism similar to that found with fatty acids. GPR40 agonists have shown efficacy in increasing insulin secretion and lowering blood glucose in rodent models of type 2 diabetes. Recent phase I and phase II clinical trials in humans have shown that the GPR40 agonist TAK-875 reduces fasting and postprandial blood glucose and lowers HbA1c with efficacy equal to that of the sulfonylurea glimepiride without inducing hypoglycemia or evidence of tachyphylaxis. These data suggest that targeting the GPR40 receptor can be a viable therapeutic option for the treatment of type 2 diabetes.

Discovery and Optimization of Potent GPR40 Full Agonists Containing Tricyclic Spirocycles

GPR40 (FFAR1 or FFA1) is a target of high interest being pursued to treat type II diabetes due to its unique mechanism leading to little risk of hypoglycemia. We recently reported the discovery of AM-1638 (2), a potent full agonist of GPR40. In this report, we present the discovery of GPR40 full agonists containing conformationally constrained tricyclic spirocycles and their structure-activity relationships leading to more potent agonists such as AM-5262 (26) with improved rat PK profile and general selectivity profile. AM-5262 enhanced glucose stimulated insulin secretion (mouse and human islets) and improved glucose homeostasis in vivo (OGTT in HF/STZ mice) when compared to AM-1638.

Lack of GPR40/FFAR1 does not induce diabetes even under insulin resistance condition

AIMS

G protein-coupled receptor/free fatty acid receptor 1 (GPR40/FFAR1 ) regulates free fatty acid-induced insulin secretion. This study has been performed to clarify whether or not loss of GPR40/FFAR1 function exacerbates diabetes, that is, whether GPR40 has an essential physiological role in the development of diabetes or not.

METHODS

We generated GPR40/FFAR1 knockout (KO) mice and analysed their phenotypes in vitro and in vivo under the condition of dietary or genetically induced insulin resistance.

RESULTS

GPR40/FFAR1 KO mice kept on a high-fat diet became obese, developed glucose intolerance to a similar degree as GPR40/FFAR1 wild-type (WT) mice. In addition, the phenotype of KO mice harbouring diabetogenic KK background genes showed glucose intolerance at a level similar to level for control KK mice. In both mouse models with insulin resistance, insulin secretion after oral glucose load and homeostasis model assessment-insulin resistance (HOMA-IR) did not change between GPR40/FFAR1 KO and WT mice. Although glucose-induced insulin secretion under high palmitate concentration was significantly lower in KO than in WT islets, pancreatic insulin content and insulin secretion stimulated with glucose alone were not different between KO and WT mice.

CONCLUSIONS

GPR40/FFAR1 has a major role in regulating fatty-acid-mediated insulin secretion, but the lack of GPR40/FFAR1 does not exacerbate glucose intolerance and insulin resistance induced by high-fat diet or diabetogenic KK gene. Our findings indicate that loss of GPR40/FFAR1 function does not play an important role in inducing or exacerbating diabetes.

Discovery of a potent and selective free fatty acid receptor 1 agonist with low lipophilicity and high oral bioavailability

The free fatty acid receptor 1 (FFA1, also known as GPR40) mediates enhancement of glucose-stimulated insulin secretion and is emerging as a new target for the treatment of type 2 diabetes. Several FFA1 agonists are known, but the majority of these suffer from high lipophilicity. We have previously reported the FFA1 agonist 3 (TUG-424). We here describe the continued structure-activity exploration and optimization of this compound series, leading to the discovery of the more potent agonist 40, a compound with low lipophilicity, excellent in vitro metabolic stability and permeability, complete oral bioavailability, and appreciable efficacy on glucose tolerance in mice.

G protein-coupled receptors for energy metabolites as new therapeutic targets

Several G protein-coupled receptors (GPCRs) that are activated by intermediates of energy metabolism - such as fatty acids, saccharides, lactate and ketone bodies - have recently been discovered. These receptors are able to sense metabolic activity or levels of energy substrates and use this information to control the secretion of metabolic hormones or to regulate the metabolic activity of particular cells. Moreover, most of these receptors appear to be involved in the pathophysiology of metabolic diseases such as diabetes, dyslipidaemia and obesity. This Review summarizes the functions of these metabolite-sensing GPCRs in physiology and disease, and discusses the emerging pharmacological agents that are being developed to target these GPCRs for the treatment of metabolic disorders.

Discovery of phenylpropanoic acid derivatives containing polar functionalities as potent and orally bioavailable G protein-coupled receptor 40 agonists for the treatment of type 2 diabetes

As part of a program to identify potent GPR40 agonists with drug-like properties suitable for clinical development, the incorporation of polar substituents was explored with the intention of decreasing the lipophilicity of our recently disclosed phenylpropanoic acid derivative 1. This incorporation would allow us to mitigate the cytotoxicity issues observed with compound 1 and enable us to move away from the multifunctional free fatty acid-like structure. Substitutions on the 2',6'-dimethylbiphenyl ring were initially undertaken, which revealed the feasibility of introducing polar functionalities at the biphenyl 4'-position. Further optimization of this position and the linker led to the discovery of several 4'-alkoxybiphenyl derivatives, which showed potent GPR40 agonist activities with the best balance in terms of improved cytotoxicity profiles and favorable pharmacokinetic properties. Among them, 3-{2-fluoro-4-[({4'-[(4-hydroxy-1,1-dioxidotetrahydro-2H-thiopyran-4-yl)methoxy]-2',6'-dimethylbiphenyl-3-yl}methyl)amino]phenyl}propanoic acid (35) exhibited a robust plasma glucose-lowering effect and insulinotropic action during an oral glucose tolerance test in rats with impaired glucose tolerance.

Facile synthesis of 4-substituted 3,4-dihydrocoumarins via an organocatalytic double decarboxylation process

3,4-Dihydrocoumarins, considered to be valuable building blocks, have attracted considerable attention due to their various biological activities. Herein, we have documented an efficient and convenient double decarboxylation process for the synthesis of 4-substituted 3,4-dihydrocoumarin in moderate to excellent yields under mild reaction conditions (up to 98%).

Identification of fused-ring alkanoic acids with improved pharmacokinetic profiles that act as G protein-coupled receptor 40/free fatty acid receptor 1 agonists

The G protein-coupled receptor 40 (GPR40)/free fatty acid receptor 1 (FFA1) has emerged as an attractive target for a novel insulin secretagogue with glucose dependency. We previously identified phenylpropanoic acid derivative 1 (3-{4-[(2',6'-dimethylbiphenyl-3-yl)methoxy]-2-fluorophenyl}propanoic acid) as a potent and orally available GPR40/FFA1 agonist; however, 1 exhibited high clearance and low oral bioavailability, which was likely due to its susceptibility to β-oxidation at the phenylpropanoic acid moiety. To identify long-acting compounds, we attempted to block the metabolically labile sites at the phenylpropanoic acid moiety by introducing a fused-ring structure. Various fused-ring alkanoic acids with potent GPR40/FFA1 activities and good PK profiles were produced. Further optimizations of the lipophilic portion and the acidic moiety led to the discovery of dihydrobenzofuran derivative 53 ((6-{[4'-(2-ethoxyethoxy)-2',6'-dimethylbiphenyl-3-yl]methoxy}-2,3-dihydro-1-benzofuran-3-yl)acetic acid), which acted as a GPR40/FFA1 agonist with in vivo efficacy during an oral glucose tolerance test (OGTT) in rats with impaired glucose tolerance.

Short-chain free fatty acid receptors FFA2/GPR43 and FFA3/GPR41 as new potential therapeutic targets

The deorphanization of the free fatty acid (FFA) receptors FFA1 (GPR40), FFA2 (GPR43), FFA3 (GPR41), GPR84, and GPR120 has made clear that the body is capable of recognizing and responding directly to nonesterified fatty acid of virtually any chain length. Colonic fermentation of dietary fiber produces high concentrations of the short-chain fatty acids (SCFAs) acetate, propionate and butyrate, a process which is important to health. The phylogenetically related 7-transmembrane (7TM) receptors free fatty acid receptor 2 (FFA2) and FFA3 are activated by these SCFAs, and several lines of evidence indicate that FFA2 and FFA3 mediate beneficial effects associated with a fiber-rich diet, and that they may be of interest as targets for treatment of inflammatory and metabolic diseases. FFA2 is highly expressed on immune cells, in particular neutrophils, and several studies suggest that the receptor plays a role in diseases involving a dysfunctional neutrophil response, such as inflammatory bowel disease (IBD). Both FFA2 and FFA3 have been implicated in metabolic diseases such as type 2 diabetes and in regulation of appetite. More research is however required to clarify the potential of the receptors as drug targets and establish if activation or inhibition would be the preferred mode of action. The availability of potent and selective receptor modulators is a prerequisite for these studies. The few modulators of FFA2 or FFA3 that have been published hitherto in the peer-reviewed literature in general have properties that make them less than ideal as such tools, but published patent applications indicate that better tool compounds might soon become available which should enable studies critical to validate the receptors as new drug targets.