Novel GPR43 Agonists Exert an Anti-Inflammatory Effect in a Colitis Model.

GPR43 (also known as FFAR2), a metabolite-sensing G-protein-coupled receptor stimulated by short-chain fatty acid (SCFA) ligands is involved in innate immunity and metabolism. GPR43 couples with Gαi/o and Gαq/11 heterotrimeric proteins and is capable of decreasing cyclic AMP and inducing Ca2+ flux. The GPR43 receptor has additionally been shown to bind ß-arrestin 2 and inhibit inflammatory pathways, such as NF-ΚB. However, GPR43 shares the same ligands as GPR41, including acetate, propionate, and butyrate, and determination of its precise functions in association with endogenous ligands, such as SCFAs alone, therefore remains a considerable challenge. In this study, we generated novel synthetic agonists that display allosteric modulatory effects on GPR43 and downregulate NF-ΚB activity. In particular, the potency of compound 187 was significantly superior to that of preexisting compounds in vitro. However, in the colitis model in vivo, compound 110 induced more potent attenuation of inflammation. These novel allosteric agonists of GPR43 clearly display anti-inflammatory potential, supporting their clinical utility as therapeutic drugs.

Rapid Access to the Structural Core of Aflavinines via Stereoselective Tandem Intramolecular Diels-Alder Cycloaddition Controlled by the Allylic 1,3-Strain.

An expedient route to access the functionalized structural core of aflavinines has been developed starting from three readily available fragments over 12 steps in 29.1% overall yield without using any transition metal catalysis. The key feature of this approach is a tandem intramolecular Diels-Alder cycloaddition to complete the hexacyclic framework with the correct stereochemistry and all the requisite structural elements in place to achieve the total synthesis of aflavinine and its congeners.

Facile ring opening reaction of oxazolone enables efficient amidation for aminoisobutyric acid.

4,4-Dimethyloxazolones derived from N-protected aminoisobutyric acid (AIB) are particularly known as poor electrophiles due to the steric hindrance around the carbonyl and not employed as useful intermediates for amidation whereas numerous examples have been reported to support the utility of other oxazolones in amidation. AIB is an important and strategical synthon in medicinal chemistry but the peptide bond formation of the N-protected urethane derivatives of AIB is known to be often unproductive due to the rapid formation of the stable 4,4-dimethyloxazolone via an intramolecular cyclization. We discovered that the 4,4-dimethyloxazolone of an AIB urethane is in fact an excellent electrophile that enables efficient amidation even with weakly reactive nucleophiles. The 4,4-dimethyloxazolone can be stored in a pure form and used as a reagent offering an efficient and convenient synthetic tool for generating AIB-peptide analogs.

An efficient synthetic protocol for amide derivatives of Boc-2-aminoisobutyrate.

Aminoisobutyric acid (AIB) is an important building block widely incorporated by medicinal chemists in molecular design. Owing to the steric challenge, elaborating AIB's carboxylic acid using conventional amidation protocols is often problematic. We discovered that an amidation protocol utilizing methyl Boc-aminoisobutyrate and magnesium amidates of various reactivities produces the corresponding amide derivatives in good to excellent yields.

Blue light effect on retinal pigment epithelial cells by display devices.

Blue light has high photochemical energy and induces cell apoptosis in retinal pigment epithelial cells. Due to its phototoxicity, retinal hazard by blue light stimulation has been well demonstrated using high intensity light sources. However, it has not been studied whether blue light in the displays, emitting low intensity light, such as those used in today's smartphones, monitors, and TVs, also causes apoptosis in retinal pigment epithelial cells. We attempted to examine the blue light effect on human adult retinal epithelial cells using display devices with different blue light wavelength ranges, the peaks of which specifically appear at 449 nm, 458 nm, and 470 nm. When blue light was illuminated on A2E-loaded ARPE-19 cells using these displays, the display with a blue light peak at a shorter wavelength resulted in an increased production of reactive oxygen species (ROS). Moreover, the reduction of cell viability and induction of caspase-3/7 activity were more evident in A2E-loaded ARPE-19 cells after illumination by the display with a blue light peak at a shorter wavelength, especially at 449 nm. Additionally, white light was tested to examine the effect of blue light in a mixed color illumination with red and green lights. Consistent with the results obtained using only blue light, white light illuminated by display devices with a blue light peak at a shorter wavelength also triggered increased cell death and apoptosis compared to that illuminated by display devices with a blue light peak at longer wavelength. These results show that even at the low intensity utilized in the display devices, blue light can induce ROS production and apoptosis in retinal cells. Our results also suggest that the blue light hazard of display devices might be highly reduced if the display devices contain less short wavelength blue light.

Selective novel inverse agonists for human GPR43 augment GLP-1 secretion.

GPR43/Free Fatty Acid Receptor 2 (FFAR2) is known to be activated by short-chain fatty acids and be coupled to Gi and Gq family of heterotrimeric G proteins. GPR43 is mainly expressed in neutrophils, adipocytes and enteroendocrine cells, implicated to be involved in inflammation, obesity and type 2 diabetes. However, several groups have reported the contradictory data about the physiological functions of GPR43, so that its roles in vivo remain unclear. Here, we demonstrate that a novel compound of pyrimidinecarboxamide class named as BTI-A-404 is a selective and potent competitive inverse agonist of human GPR43, but not the murine ortholog. Through structure-activity relationship (SAR), we also found active compound named as BTI-A-292. These regulators increased the cyclic AMP level and reduced acetate-induced cytoplasmic Ca(2+) level. Furthermore, we show that they modulated the downstream signaling pathways of GPR43, such as ERK, p38 MAPK, and NF-κB. It was surprising that two compounds augmented the secretion of glucagon-like peptide 1 (GLP-1) in NCI-H716 cell line. Collectively, these novel and specific competitive inhibitors regulate all aspects of GPR43 signaling and the results underscore the therapeutic potential of them.

Concise Synthesis of Broussonone A.

A concise and expeditious approach to the total synthesis of broussonone A, a p-quinol natural compound, has been developed. The key features of the synthesis include the Grubbs II catalyst mediated cross metathesis of two aromatic subunits, and a chemoselective oxidative dearomatizationin the presence of two phenol moieties. Especially, optimization associated with the CM reaction of ortho-alkoxystyrenes was also studied, which are known to be ineffective for Ru-catalyzed metathesis reactions under conventional reaction conditions because ortho-alkoxy group could coordinate to the ruthenium center, resulting in the potential complication of catalyst inhibition.

Validation of cyclooxygenase-2 as a direct anti-inflammatory target of 4-O-methylhonokiol in zymosan-induced animal models.

4-O-methylhonokiol (MH) is known to inhibit inflammation by partially understood mechanisms. Here, the anti-inflammatory mechanisms of MH were examined using enzymatic, cellular, and animal assays. In enzymatic assays, MH inhibited COX-2 activity with an IC50 of 0.062 µM, and also COX-1 with an IC50 of 2.4 µM. In cellular assays, MH was immunotoxic above 10 µM. At non-toxic concentrations (below 3 µM), MH strongly inhibited COX-2-mediated prostaglandin production with an IC50 of 0.1 µM, whereas did not or slightly affect other functions of B cells, T cells, dendritic cells, and macrophages. In an animal model, MH inhibited the increase in footpad thickness and popliteal lymph node weight in zymosan-injected mice. When analyzed the draining pLNs of zymosan-injected mice on day 5, MH inhibited the overall inflammatory responses. However, MH inhibited cyclooxygenase (COX)-2-mediated prostaglandin production without affecting tumor necrosis factor-α production in inflamed tissues within 6 h after zymosan injection. In summary, our data suggest that COX-2 may be a direct anti-inflammatory target of MH in vitro and in vivo.

Discovery of a novel class of diacylglycerol acyltransferase 2 inhibitors with a 1H-pyrrolo[2,3-b]pyridine core.

Diacylglycerol acyltransferase 2 (DGAT2), which catalyzes the final step in triacylglycerol (TG) synthesis, is a key enzyme associated with hepatic steatosis and insulin resistance. Here, using an in vitro screen of 20000 molecules, we identified a class of compounds with a substituted 1H-pyrrolo[2,3-b]pyridine core which proved to be potent and selective inhibitors of human DGAT2. Of these compounds, H2-003 and -005 exhibited a considerable reduction in TG biosynthesis in HepG2 hepatic cells and 3T3-L1 preadipose cells. These compounds exert DGAT2-specific-inhibitory activity, which was further confirmed in DGAT2- or DGAT1-overexpressing HEK293 cells. In addition, these compounds almost completely abolished lipid droplet formation in 3T3-L1 cells when co-treated with a DGAT1 inhibitor, which was not attained using either a DGAT2 or DGAT1 inhibitor alone. Collectively, we identified two DGAT2 inhibitors, H2-003 and -005. These compounds will aid in DGAT2-related lipid metabolism research as well as in therapeutic development for the treatment of metabolic diseases associated with excessive TG.

Synthesis of xanthone derivatives based on α-mangostin and their biological evaluation for anti-cancer agents.

A xanthone-derived natural product, α-mangostin is isolated from various parts of the mangosteen, Garcinia mangostana L. (Clusiaceae), a well-known tropical fruit. Novel xanthone derivatives based on α-mangostin were synthesized and evaluated as anti-cancer agents by cytotoxicity activity screening using 5 human cancer cell lines. Some of these analogs had potent to moderate inhibitory activities. The structure-activity relationship studies revealed that phenol groups on C3 and C6 are critical to anti-proliferative activity and C4 modification is capable to improve both anti-cancer activity and drug-like properties. Our findings provide new possibilities for further explorations to improve potency.

Perspectives on the therapeutic potential of short-chain fatty acid receptors.

There is rapidly growing interest in the human microbiome because of its implication in metabolic disorders and inflammatory diseases. Consequently, understanding the biology of short chain fatty acids and their receptors has become very important for identifying novel therapeutic avenues. GPR41 and GPR43 have been recognized as the cognate receptors for SCFAs and their roles in metabolism and inflammation have drawn much attention in recent years. GPR43 is highly expressed on immune cells and has been suggested to play a role in inflammatory diseases such as inflammatory bowel disease. Both GPR41 and GPR43 have been implicated in diabetes and obesity via the regulation of adipose tissue and gastrointestinal hormones. So far, many studies have provided contradictory results, and therefore further research is required to validate these receptors as drug targets. We will also discuss the synthetic modulators of GPR41 and GPR43 that are critical to understanding the functions of these receptors.

ß-Arrestin 2 mediates G protein-coupled receptor 43 signals to nuclear factor-κB.

G-protein coupled receptor 43 (GPR43) serves as a receptor for short-chain fatty acids (SCFAs), implicated in neutrophil migration and inflammatory cytokine production. However, the intracellular signaling pathway mediating GPR43 signaling remains unclear. Here, we show that ß-arrestin 2 mediates the internalization of GPR43 by agonist. Agonism of GPR43 reduced the phosphorylation and nuclear translocation of nuclear factor-κB (NF-κB), which was relieved by short interfering RNA (siRNA) of ß-arrestin 2. Subsequently, mRNA expression of proinflammatory cytokines, interleukin (IL)-6 and IL-1ß, was downregulated by activation of GPR43 and knockdown of ß-arrestin 2 recovered the expression of the cytokines. Taken together, these results suggest that GPR43 may be a plausible target for a variety of inflammatory diseases.

Identification and validation of a selective small molecule inhibitor targeting the diacylglycerol acyltransferase 2 activity.

Diacylglycerol acyltransferase 2 (DGAT2) is one of two distinct DGAT enzymes that catalyze the last step in triacylglycerol (TG) synthesis. Findings from previous studies suggest that inhibition of DGAT2 is a promising strategy for the treatment of hepatic steatosis and insulin resistance. Here, we identified compound 122 as a potent and selective inhibitor of human DGAT2, which appeared to act competitively against oleoyl-CoA in vitro. The selective inhibition of DGAT2 was also confirmed by the reductions in enzymatic activity and de novo TG synthesis in DGAT2-overexpressing HEK293 cells and hepatic cells HepG2. Compound 122, as a newly identified inhibitor of DGAT2, will be useful for the research on DGAT2-related lipid metabolism as well as the development of therapeutic drug for several metabolic diseases.

A novel therapeutic target, GPR43; where it stands in drug discovery.

With growing interest in human microbiome for its implication in metabolic disorders, inflammatory diseases, immune disorders and so forth, understanding the biology at the interface of the gut flora and the host becomes very important for identifying novel therapeutic avenues. GPR43 has been deorphanized and the metabolites of microbiome, such as short-chain fatty acids, serve as its natural ligands. There are numerous reports that GPR43 might be a crucial link to the novel therapies for the unmet medical needs and many drug discovery organizations are making their moves in response.

Design and synthesis of 4-O-methylhonokiol analogs as inhibitors of cyclooxygenase-2 (COX-2) and PGF1 production.

A series of novel 4-O-methylhonokiol analogs were synthesized in light of revealing structure-activity relationship for inhibitory effect of COX-2 enzyme. The key strategy of the molecular design was oriented towards modification of the potential metabolic soft spots (e.g., phenol and olefin) or by altering the polar surface area via incorporating heterocycles such as isoxazole and triazole. Most of all exhibited the inhibitory effects on COX-2 and PGF(1) production but not macrophage NO production. Especially, aryl carbamates 10 and 11 exhibited more potent inhibitory activity against COX-2 and PGF(1) production.

Synthesis of grandisol, the sexual attracting insect pheromone.

In this issue, Suh's group reported a new formal total synthesis of (±)-grandisol featuring a palladium-catalyzed 4-exo-trig cyclization. Grandisol's interesting cyclobutane structure has been a popular test model for various cyclization methods over the years. This report summarizes Suh's formal synthesis of grandisol along with a concise review of the four-membered ring cyclization strategies employed in the synthesis of grandisol.

Syntheses of sulfur and selenium analogues of pachastrissamine via double displacements of cyclic sulfate.

Bioisosteric analogues of pachastrissamine that contain sulfur and selenium atoms replacing the oxygen in the ring system, were efficiently prepared from a cyclic sulfate intermediate by sequential intermolecular and intramolecular S(N)2 displacement reactions of the dianions. The analogues exhibited cytotoxicities comparable to that of pachastrissamine.

Synthesis and anti-platelet activity of obovatol derivatives.

Obovatol derivatives were synthesized and evaluated for anti-platelet activity. Three derivatives (1, 2, 4i) displayed equipotent activity to obovatol in arachidonic acid-induced platelet aggregation. An initial SAR study revealed that the introduction of alkoxy group in B ring could enhance inhibitory activity.

Efficient and convenient preparation of 3-aryl-2,2-dimethylpropanoates via Negishi coupling.

An efficient and convenient Negishi coupling protocol was developed for the preparation of 3-aryl-2,2-dimethylpropanoates providing easy access to key pharmaceutical intermediates that often require multi-step synthesis using conventional enolate chemistry.

Synthesis of pachastrissamine from phytosphingosine: a comparison of cyclic sulfate vs an epoxide intermediate in cyclization.

[reaction: see text] The syntheses of the cytotoxic natural product pachastrissamine and its unnatural 4-epi-congener were accomplished starting from a natural phytosphingosine. The relatively unstrained cyclic sulfate intermediate smoothly underwent the 5-endo cyclization to yield the 2,3,4-trisubstituted tetrahydrofuran ring system of pachastrissamine. The corresponding epoxy alcohol afforded the 4-epi-congener via a tosylate-mediated double inversion process.