Discovery of a New Class of Potent, Selective, and Orally Bioavailable CRTH2 (DP2) Receptor Antagonists for the Treatment of Allergic Inflammatory Diseases

1,3-Dipolar cycloaddition reactions of isatin-derived azomethine ylides for the synthesis of spirooxindole and indole-derived scaffolds: recent developments

The unique therapeutic and biological characteristics of spirooxindole have led to the presentation of numerous reactions for the synthesis of spirooxindoles through 1,3-Dipolar cycloaddition of highly reactive isatin-derived azomethine ylides with activated olefins as the main tool for the formation of spirocyclic oxindoles during the last 4 years. Therefore, there is a need to highlight the recent developments in this area, along with the representative synthetic methods and relevant reaction mechanisms from 2018 to 2021. The representative synthetic methodologies were listed in four sections based on the procedure to form the azomethine ylide species including isatins and amino acids, isatin-derived α-(trifluoromethyl)imine, isatins and benzylamines, and from isatin-derived cyclic imine 1,3-dipoles.

Verification of preparations of (1H-indol-3-yl)methyl electrophiles and development of their microflow rapid generation and substitution

Although highly reactive (1H-indol-3-yl)methyl electrophiles such as (1H-indol-3-yl)methyl halides are potential precursors for the synthesis of various indole derivatives, some researchers have reported difficulties in their preparation due to concomitant undesired dimerization/oligomerization. Nevertheless, there have been some reports on the preparation of (1H-indol-3-yl)methyl halides. To resolve this contradiction, all the previously reported preparations of (1H-indol-3-yl)methyl halides were examined. However, we could not reproduce any of these preparations, and we revised several structures of indole derivatives. Here we show the rapid (0.02 s) and mild (25 °C) generation of an (1H-indol-3-yl)methyl electrophile that enables the rapid (0.1 s) and mild (25 °C) nucleophilic substitution in a microflow reactor. Eighteen unprotected indole analogues can be successfully synthesized using the developed microflow nucleophilic substitution with various nucleophiles.

Nickel-catalyzed asymmetric reductive arylcyanation of alkenes with acetonitrile as the cyano source

Chiral 3-cyanomethyl oxindoles were synthesized in high enantioselectivities and yields. The employment of acetonitrile as a cyano source via Zn(OTf)2-assisted β-carbon elimination is distinct from the common cyanation reaction modes.

Base-free enantioselective SN2 alkylation of 2-oxindoles via bifunctional phase-transfer catalysis

N-Protected oxindole derivatives of unprecedented malleability bearing ester moieties at C-3 have been shown to participate in enantioselective phase-transfer-catalysed alkylations promoted by ad-hoc designed quaternary ammonium salts derived from quinine bearing hydrogen-bond donating substituents. For the first time in such phase-transfer-catalysed enolate alkylations, the reactions were carried out under base-free conditions. It was found that urea-based catalysts outperformed squaramide derivatives, and that the installation of a chlorine atom adjacent to the catalyst’s quinoline moiety aided in avoiding selectivity-reducing complications related to the production of HBr in these processes. The influence of steric and electronic factors from both the perspective of the nucleophile and electrophile were investigated and levels of enantiocontrol up to 90% ee obtained. The synthetic utility of the methodology was demonstrated via the concise enantioselective synthesis of a potent CRTH2 receptor antagonist.

Stereoselective synthesis of trifluoroethyl 3,2'-spirooxindole γ-lactam through the organocatalytic cascade reaction of 3-((2,2,2-trifluoroethyl)amino)indolin-2-one

Newly designed 3-((2,2,2-trifluoroethyl)amino)indolin-2-ones were used for the facile synthesis of chiral fluoroalkyl-containing 3,2'-spirooxindole γ-lactam products. The secondary amine-catalysed Michael/hemiaminalization cascade reaction of 3-((2,2,2-trifluoroethyl)amino)indolin-2-one with α,β-unsaturated aldehydes followed by oxidation can easily produce the desired products in high yields (up to 86%) with excellent enantioselectivities (up to 99% ee) and diastereoselectivities (up to >95 : 5 dr).

Enantioselective organocatalytic formal [3+2]-cycloaddition of isatin-derived ketimines with benzylidenemalononitriles and benzylidineindanones

Electron-deficient alkenes undergo organocatalysed formal [3+2]-cycloaddition with isatin-derived imines, generating complex spirocyclic products with high yield and stereoselectivity.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

Double Spirocyclization of Arylidene-Δ2-Pyrrolin-4-Ones with 3-Isothiocyanato Oxindoles

Arylidene-Δ2-pyrrolin-4-ones undergo organocatalyzed double spirocyclization with 3-isothiocianato oxindoles in a domino 1,4/1,2-addition sequence. The products contain three contiguous stereocenters (ee up to 98%, dr up to 99:1, 12 examples). The absolute configuration of the major diastereomer was determined by single crystal X-ray analysis. Along with heterocyclic Michael acceptors based on oxazolone, isoxazolone, thiazolidinone, pyrazolone, and pyrimidinedione, the reported results display the applicability of unsaturated Δ2-pyrrolin-4-ones (pyrrolones) for the organocatalyzed construction of 3D-rich pyrrolone-containing heterocycles.

Cascade reaction of isatins with nitro-substituted enamines: highly selective synthesis of functionalized (Z)-3-(1-(arylamino)-2-oxoarylidene)indolin-2-ones

A novel protocol for the construction of functionalized (Z)-3-(1(-arylamino)-2-oxoarylidene)indolin-2-ones (AOIDOs) from isatins 1 with nitro-substituted enamines 2via an unprecedented cascade reaction catalyzed by sulfamic acid is developed.

Rapid abnormal [3+2]-cycloaddition of isatin N,N′-cyclic azomethine imine 1,3-dipoles with chalcones

More than 35 new compounds were prepared rapidly in moderate to excellent yields with high diastereoselectivities by K₂CO₃-promoted abnormal 1,3-diploar cycloaddition of isatin N, N′-cyclic azomethine imines with chalcones.

Application of isatin-derived saturated esters in the synthesis of 3,3'-spirooxindole γ-butyrolactams

Stable while reactive isatin-derived saturated esters have been utilized as 3-carbon synthons in a base-promoted formal [3 + 2] annulation with N-Boc imines. The developed protocol offers a direct pathway for the rapid and divergent construction of two classes of 3,3'-spirooxindole γ-butyrolactam skeletons that are recognized as the privileged structures of various bioactive compounds. This protocol also has the advantages of mild reaction conditions, scalability and wide reaction scope.

The one pot asymmetric synthesis of 3,3'-pyrrolidonyl spiroxindoles via a regio- and stereoselective domino reaction

A highly efficient regio- and stereoselective domino aziridine ring opening and lactamization reaction between aziridines and 3-carboxy oxindole esters has been developed for the one pot asymmetric synthesis of 4-aryl-3,3'-spiropyrrolidonyl oxindoles with excellent selectivity (dr >99 : 1 and ee up to >99%). It was further extended to a sequential one pot protocol for the asymmetric synthesis of NH-free 3,3'-pyrrolidonyl spiroxindole, maintaining the same selectivity.

Enantioselective Synthesis of 2-Oxindole Spirofused Lactones and Lactams by Heck/Carbonylative Cylization Sequences: Method Development and Applications

An efficient one-pot assembly of all-carbon spiro-oxindole compounds from non-oxindole-based materials has been developed through a palladium-catalyzed asymmetric Heck/carbonylative lactonization and lactamization sequence. Diversified spirooxindole γ-and δ-lactones/lactams were accessed in high yields with good to excellent enantioselectivities (up to 99 % ee) under mild reaction conditions. The natural product coixspirolactam A was conveniently synthesized by applying the current methodology, and thus its absolute configuration was elucidated for the first time. Asymmetric synthesis of an effective CRTH2 receptor antagonist has also been demonstrated utilizing this method in the key step.

Discovery of 3,3'-Spiro[Azetidine]-2-oxo-indoline Derivatives as Fusion Inhibitors for Treatment of RSV Infection

A new series of 3,3'-spirocyclic-2-oxo-indoline derivatives was synthesized and evaluated against respiratory syncytial virus (RSV) in a cell-based assay and animal model. Extensive structure-activity relationship study led to a lead compound 14h, which exhibited excellent in vitro potency with an EC₅₀ value of 0.8 nM and demonstrated 71% oral bioavailability in mice. In a mouse challenge model of RVS infection, 14h demonstrated superior efficacy with a 3.9log RSV virus load reduction in the lung following an oral dose of 50 mg/kg.

Synthesis of spiropyrrolidine oxindolesviaAg-catalyzed stereo- and regioselective 1,3-dipolar cycloaddition of indole-based azomethine ylides with chalcones

In excess of 100 new compounds were prepared in moderate to high yields (50–95%) with good to excellent diastereoselectivity (11 : 1 → 20 : 1 dr) by Ag-catalyzed 1,3-dipolar cycloaddition.

Organocatalytic Michael/cyclization cascade reactions of 3-isothiocyanato oxindoles with 3-trifluoroethylidene oxindoles: an approach for the synthesis of 3′-trifluoromethyl substituted 3,2′-pyrrolidinyl-bispirooxindoles

A series of 3′-trifluoromethyl substituted 3,2′-pyrrolidinyl-bispirooxindoles were constructed via an asymmetric Michael/cyclization cascade reaction.

Synthesis of Functionalized 3-Spiro[cyclopropa[a]pyrrolizine]- and 3-Spiro[3-azabicyclo[3.1.0]hexane]oxindoles from Cyclopropenes and Azomethine Ylides via [3 + 2]-Cycloaddition

3-Spiro[cyclopropa[a]pyrrolizine]- and 3-spiro[3-azabicyclo[3.1.0]hexane]oxindoles were prepared in moderate to high yields via one-pot three-component reactions using substituted isatins, α-amino acids, and cyclopropenes. The key step is an intramolecular [3 + 2]-cycloaddition reaction of an in situ generated azomethine ylide onto a cyclopropene. Both N-substituted and N-unsubstituted α-amino acids, dipeptide Gly-Gly, and also benzylamine were used as the amine component for the azomethine ylide generation. The anticancer activity of some of the obtained compounds against human leukemia K562 cell line was evaluated by flow cytometry in vitro.

Squaramide-catalyzed asymmetric Michael/cyclization cascade reaction of 3-isothiocyanato oxindoles with chalcones for synthesis of pyrrolidinyl spirooxindoles

An efficient method for the construction of pyrrolidinyl spirooxindoles with 3-isothiocyanato oxindoles and chalcones via a Michael/cyclization cascade reaction has been developed using squaramide. The products were obtained in high yields with excellent stereo selectivities.

An enantioselective synthesis of spiro-oxindole-based 3,4-dihydropyrroles via a Michael/cyclization cascade of 3-aminooxindoles with 2-enoylpyridines

This work provides a highly stereoselective route to access spiro[pyrrolidin-3,2′-oxindoles] and represents a new perspective for the synthesis of spirocyclic oxindoles.

Prostaglandin D2 receptor antagonists in early development as potential therapeutic options for asthma

INTRODUCTION

Asthma is a chronic inflammatory disease characterized by bronchial hyper-reactivity. Although many currently available treatment regimens are effective, poor symptom control and refractory severe disease still represent major unmet needs. In the last years, numerous molecular therapeutic targets that interfere with the innate inflammatory response in asthma have been identified. Promising preliminary results concern the signaling cascade promoted by prostaglandin D2 (PGD2) and its receptor antagonists.

AREAS COVERED

The aim of this review is to provide the most recent clinical and preclinical data on the efficacy and safety of newly developed compounds for the treatment of allergic asthma. The authors will present an overview of the pathogenetic molecular mechanisms sustaining the chronic inflammatory response in asthma; the focus will be then directed on the mediators of the PGD2 pathway, the chemoattractant receptor-homologous molecule expressed on TH2 cells, and their latest antagonists developed.

EXPERT OPINION

Bronchodilators and corticosteroids are not sufficient to achieve a satisfactory management of all asthmatic patients; the development of new specific treatments appears therefore essential. The good results in terms of cellular, functional and clinical outcomes, together with an acceptable safety of the CRTh2 antagonists represent a promising start for a tailored management of allergic asthma.

Synthesis of isatins by the palladium-catalyzed intramolecular acylation of unactivated aryl C(sp2)–H bonds

Synthesis of isatins from formyl-N-arylformamides is achieved via PdCl₂-catalyzed intramolecular acylation.

Expression of DP2 (CRTh2), a prostaglandin D₂ receptor, in human mast cells

PGD₂ has long been implicated in allergic diseases. Recent cloning of a second PGD₂ receptor, DP2 (also known as CRTh2), led to a greater understanding of the physiological and pathophysiological implications of PGD₂. PGD₂ signaling through DP1 and DP2 mediates different and often opposite effects in many cell types of the immune system. Although mast cells (MC) are the largest source of PGD₂ in the body, there is little information about their potential expression of DP2 and its functional significance. In this study, we show that tissue MC in human nasal polyps express DP2 protein, and that human MC lines and primary cultured human MC express mRNA as well as protein of DP2. By immunohistochemistry, we detected that 34% of MC in human nasal polyps expressed DP2. In addition, flow cytometry showed that 87% of the LAD2 human MC line and 98% of primary cultured human MC contained intracellular DP2. However, we could not detect surface expression of DP2 on human MC by single cell analysis using imaging flow cytometry. Blocking of endogenous PGD2 production with aspirin did not induce surface expression of DP2 in human MC. Two DP2 selective agonists, DK-PGD₂ and 15R-15-methyl PGD₂ induced dose-dependent intracellular calcium mobilization that was abrogated by pertussis toxin, but not by three DP2 selective antagonists. MC mediator release including degranulation was not affected by DP2 selective agonists. Thus, human MC express DP2 intracellularly rather than on their surface, and the function of DP2 in human MC is different than in other immune cells such as Th2 cells, eosinophils and basophils where it is expressed on the cell surface and induces Th2 cytokine and/or granule associated mediator release. Further studies to elucidate the role of intracellular DP2 in human MC may expand our understanding of this molecule and provide novel therapeutic opportunities.