1,7-Disubstituted oxyindoles are potent and selective EP3 receptor antagonists

Synthetic strategies for the construction of C3-fluorinated oxindoles

C3-fluorinated oxindoles are important scaffolds known to demonstrate various biological properties. As bio-isosteres of oxindoles, these compounds have shown tremendous potential in drug research discovery programs. Besides, they also serve as starting materials for synthesizing other fluorine-containing new architectures, thus launching research for developing new methods for their synthesis. Consequently, various approaches have been developed over the years to synthesize C3-fluorinated oxindoles. This review highlights the strategies developed to date to access C3-difluoro and monofluorooxindoles via intermolecular and intramolecular approaches. The key findings of the strategies developed are discussed along with the prevailing mechanism.

Transition-Metal-Catalyzed C-H Bond Activation for the Formation of C-C Bonds in Complex Molecules

Site-predictable and chemoselective C-H bond functionalization reactions offer synthetically powerful strategies for the step-economic diversification of both feedstock and fine chemicals. Many transition-metal-catalyzed methods have emerged for the selective activation and functionalization of C-H bonds. However, challenges of regio- and chemoselectivity have emerged with application to highly complex molecules bearing significant functional group density and diversity. As molecular complexity increases within molecular structures the risks of catalyst intolerance and limited applicability grow with the number of functional groups and potentially Lewis basic heteroatoms. Given the abundance of C-H bonds within highly complex and already diversified molecules such as pharmaceuticals, natural products, and materials, design and selection of reaction conditions and tolerant catalysts has proved critical for successful direct functionalization. As such, innovations within transition-metal-catalyzed C-H bond functionalization for the direct formation of carbon-carbon bonds have been discovered and developed to overcome these challenges and limitations. This review highlights progress made for the direct metal-catalyzed C-C bond forming reactions including alkylation, methylation, arylation, and olefination of C-H bonds within complex targets.

Divergent Regioselective Csp2-H Difluoromethylation of Aromatic Amines Enabled by Nickel Catalysis

Herein, the first catalytic protocol for nickel-catalyzed ortho or para position difluoromethylation of various aromatic amines has been developed with the assistance of a bidentate phosphine ligand, offering an invaluable synthesis means to construct extensive p-difluoromethylated products and difluorooxindole derivatives with significant functional fragments. Furthermore, the gram-scale reaction, broad substrate scope, excellent functional-group compatibility, late-stage difluoromethylation of pesticides, and even formal synthesis of HDAC6 inhibitors further demonstrate the usefulness of this method.

Copper/B2pin2-catalyzed C–H difluoroacetylation–cycloamidation of anilines leading to the formation of 3,3-difluoro-2-oxindoles

An original and efficient synthesis of 3,3-difluoro-2-oxindole derivatives has been developed via copper/B₂pin₂-catalyzed difluoroacetylation of aniline via C–H activation followed by intramolecular amidation.

Mapping PTGERs to the Ovulatory Follicle: Regional Responses to the Ovulatory PGE2 Signal

Prostaglandin E2 (PGE2) is a key intrafollicular mediator of ovulation in many, if not all, mammalian species. PGE2 acts at follicular cells via four distinct PGE2 receptors (PTGERs). Within the ovulatory follicle, each cell type (e.g., oocyte, cumulus granulosa cell, mural granulosa cell, theca cell, endothelial cell) expresses a different subset of the four PTGERs. Expression of a subset of PTGERs has consequences for the generation of intracellular signals and ultimately the unique functions of follicular cells that respond to PGE2. Just as the ovulatory LH surge regulates PGE2 synthesis, the LH surge also regulates expression of the four PTGERs. The pattern of expression of the four PTGERs among follicular cells before and after the LH surge forms a spatial and temporal map of PGE2 responses. Differential PTGER expression, coupled with activation of cell-specific intracellular signals, may explain how a single paracrine mediator can have pleotropic actions within the ovulatory follicle. Understanding the role of each PTGER in ovulation may point to previously unappreciated opportunities to both promote and prevent fertility.

Transition-Metal-Free Fluoroarylation of Diazoacetamides: A Complementary Approach to 3-Fluorooxindoles

An efficient transition-metal-free fluoroarylation reaction of N-aryl diazoacetamides with NFSI (N-fluorobenzenesulfonimide) is described. This reaction directly provides 3-fluorooxindole derivatives in yields of 67-93% with high selectivity via a carbene-free process under mild reaction conditions.

Synthesis of 3-fluoroalkenyl-3-trifluoromethyl-2-oxindoles by the reaction of indoline-2,3-diones with difluoromethylene phosphabetaine

An unprecedent reaction of indoline-2,3-diones and (triphenylphosphonio)difluoroacetate (PDFA) afforded novel 3-fluoroalkenyl-3-trifluoromethyl-2-oxindoles in moderate to excellent yields. These products could be transformed into other trifluoromethylated oxindole derivatives.

Visible-light photoredox intramolecular difluoroacetamidation: facile synthesis of 3,3-difluoro-2-oxindoles from bromodifluoroacetamides

We report an operationally simple, visible-light-driven protocol for intramolecular C-H difluoroacetamidation of arenes for the synthesis of biologically relevant 3,3-difluoro-2-oxindoles at room temperature. Using fac-Ir(ppy)3 as a photocatalyst and a 3 W blue LED as a light source, an array of difluoroxindoles was prepared from rapidly available tertiary aryl bromodifluoroacetamides in moderate to excellent yields.

Palladium-catalyzed C-7 alkenylation of indolines using molecular oxygen as the sole oxidant

A general and efficient palladium-catalyzed C-7 alkenylation of indolines using molecular oxygen as the sole oxidant has been described.

Palladium-catalyzed intramolecular C-H difluoroalkylation: synthesis of substituted 3,3-difluoro-2-oxindoles

The synthesis of 3,3-difluoro-2-oxindoles through a robust and efficient palladium-catalyzed CH difluoroalkylation is described. This process generates a broad range of difluorooxindoles from readily prepared starting materials. The use of BrettPhos as the ligand was crucial for high efficiency. Preliminary mechanistic studies suggest that oxidative addition is the rate-determining step for this process.

Direct conversion of indoles to 3,3-difluoro-2-oxindoles via electrophilic fluorination

3,3-Difluoro-2-oxindoles can be obtained directly from indoles in moderate yields via electrophilic fluorination using N-fluorobenzenesulfonimide as a mild fluorinating reagent. The presence of tert-butyl hydroperoxide during the reaction, together with additional heating after quenching the reaction with triethylamine, is beneficial to the formation of the desired product.

Synthesis and stereochemical determination of complestatin A and B (neuroprotectin A and B)

Recently, we reported the first total synthesis of chloropeptin II (1, complestatin), the more strained and challenging of the two naturally occurring chloropeptins. Central to the design of the approach and by virtue of a single-step, acid-catalyzed ring expansion rearrangement of chloropeptin II to chloropeptin I, the route also provided a total synthesis of chloropeptin I. Herein, we report a complementary and divergent oxidation of chloropeptin II (1, complestatin) to either complestatin A (2, neuroprotectin A) or complestatin B (3, neuroprotectin B), providing the first synthesis of the natural products and establishing their remaining stereochemical assignments. Key to the approach to complestatin A (2, neuroprotectin A) was the development of two different single-step indole oxidations (HCl-DMSO and NBS, THF-H(2)O) that avoid the rearrangement of chloropeptin II (1) to chloropeptin I (4), providing the 2-oxindole 2 in superb yields (93% and 82%). With a mechanistic understanding of features that impact the latter oxidation and an appreciation of the intrinsic reactivity of the chloropeptin II indole, its modification (NCS, THF-H(2)O; Cs(2)CO(3), DMF-H(2)O) provided a two-step, single-pot oxidation of chloropeptin II (1) to afford directly the 3-hydroxy-2-oxindole complestatin B (3, neuroprotectin B). Extensive studies conducted on the fully functionalized synthetic DEF ring system of chloropeptin II were key to the unambiguous assignment of the stereochemistry as well as the exploration and subsequent development of the mild oxidation conditions used in the synthesis of complestatin A and B.

Structure-activity relationship studies of novel 3-oxazolidinedione-6-naphthyl-2-pyridinones as potent and orally bioavailable EP3 receptor antagonists

Multiple regions of the 3-oxazolidinedione-6-naphthyl-pyridinone series identified via high throughput screening were explored. SAR studies of these regions including the left-hand side oxazolidinedione moiety, α-substituent on the oxazolidinedione ring, central pyridinone core, and substituents on the central pyridinone core led to the discovery of potent EP(3) receptor antagonists such as compound 29 which possesses outstanding rat pharmacokinetic properties. Synthesis and SAR of these novel compounds and DMPK properties of representative compounds are discussed.