Discovery of XEN907, a spirooxindole blocker of NaV1.7 for the treatment of pain

A structural atlas of druggable sites on Nav channels

Voltage-gated sodium (Nav) channels govern membrane excitability by initiating and propagating action potentials. Consistent with their physiological significance, dysfunction, or mutations in these channels are associated with various channelopathies. Nav channels are thereby major targets for various clinical and investigational drugs. In addition, a large number of natural toxins, both small molecules and peptides, can bind to Nav channels and modulate their functions. Technological breakthrough in cryo-electron microscopy (cryo-EM) has enabled the determination of high-resolution structures of eukaryotic and eventually human Nav channels, alone or in complex with auxiliary subunits, toxins, and drugs. These studies have not only advanced our comprehension of channel architecture and working mechanisms but also afforded unprecedented clarity to the molecular basis for the binding and mechanism of action (MOA) of prototypical drugs and toxins. In this review, we will provide an overview of the recent advances in structural pharmacology of Nav channels, encompassing the structural map for ligand binding on Nav channels. These findings have established a vital groundwork for future drug development.

Metal-Free Regioselective Oxa-Michael Approach to Access Spirooxindole-Fused Tetrahydrofuran/Tetrahydropyran through [3 + 2]/ [4 + 2] Spirocyclization of Methyleneindolinones with Haloalcohols

An efficient one-pot metal-free, base-catalyzed method has been developed for the regioselective [3 + 2]/[4 + 2] annulation reactions of electrophilic methyleneindolinones with haloalcohols to furnish spirooxindole derivatives under mild reaction conditions. This reaction afforded the corresponding products with two contiguous stereocenters including a quaternary center in good to excellent yield (up to 95%) with moderate to good diastereoselectivities (up to 12.5:1 dr) with complete regioselectivity.

Enantioselective organocatalytic Friedel-Crafts reaction of electron-rich phenols and isatins by Takemoto's thiourea catalyst

Takemoto's catalysts were used to organocatalyze the enantioselective Friedel-Crafts reaction with different electron-rich phenols and substituted isatins. The resulting 3-aryl-3-hydroxyl-2-oxindoles were obtained in good yields (85-96%) with up to 99% ee. The substrate scope was broadened with this methodology compared to reported examples catalyzed by cinchonidine thiourea.

Entry to new spiroheterocycles via tandem Rh(II)-catalyzed O-H insertion/base-promoted cyclization involving diazoarylidene succinimides

A facile approach to novel medicinally relevant spiro heterocyclic scaffolds (namely furan-2(5H)-ones, tetrahydrofurans and pyrans spiro-conjugated with the succinimide ring) has been developed. The protocol consists of Rh(II)-catalyzed insertion of heterocyclic carbenes derived from diazoarylidene succinimides (DAS) into the O-H bond of propiolic/allenic acids or brominated alcohols, followed by base-promoted cyclization to afford the target spirocyclic compounds in good to high yields.

Base controlled rongalite-mediated reductive aldol/cyclization and dimerization of isatylidene malononitriles/cyanoacetates

In this study, we developed a novel methodology involving a base-controlled, rongalite-mediated reductive/aldol reaction, followed by cyclization of isatylidene malononitriles/cyanoacetates, resulting in the synthesis of spiro[2,3-dihydrofuran-3,3'-oxindole]. Additionally, we have disclosed a rongalite-mediated dimerization process for isatylidene malononitriles, yielding dispiro[cyclopent-3'-ene]bisoxindole. The utilization of rongalite in this reaction serves a dual purpose, acting both as a reducing agent and a C1 synthon. The developed approach has several advantages like a simple reaction setup, a wide substrate scope, requiring less time, using water as a green solvent, no metal or catalyst is required and products can be easily isolated via filtration with excellent yields under mild reaction conditions.

Dinuclear Zn-Catalytic System as Brønsted Base and Lewis Acid for Enantioselectivity in Same Chiral Environment

Zinc (Zn) is a crucial element with remarkable significance in organic transformations. The profusion of harmless zinc salts in the Earth's outer layer qualifies zinc as a noteworthy contender for inexpensive and eco-friendly reagents and catalysts. Recently, widely recognized uses of organo-Zn compounds in the field of organic synthesis have undergone extensive expansion toward asymmetric transformations. The ProPhenol ligand, a member of the chiral nitrogenous-crown family, exhibits the spontaneous formation of a dual-metal complex when reacted with alkyl metal (R-M) reagents, e.g., ZnEt2. The afforded Zn complex possesses two active sites, one Lewis acid and the other Brønsted base, thereby facilitating the activation of nucleophiles and electrophiles simultaneously within the same chiral pocket. In this comprehensive analysis, we provide a thorough account of the advancement and synthetic potential of these diverse catalysts in organic synthesis, while emphasizing the reactivity and selectivities, i.e., dr and ee due to the design/structure of the ligands employed.

Oxindole and Benzoxazinone Alkaloids from the Seeds of Persea americana (Avocado) and Their SIRT1 Stimulatory Activity

Persea americana Mill. (Lauraceae), commonly known as avocado, is a well-known food because of its nutrition and health benefits. The seeds of avocado are major byproducts, and thus their phytochemicals and bioactivities have been of interest for study. The chemical components of avocado seeds were investigated by using UPLC-qTOF-MS/MS-based molecular networking, resulting in the isolation of seven new oxindole alkaloids (1-7) and two new benzoxazinone alkaloids (8 and 9). The chemical structures of the isolated compounds were identified by the analysis of NMR data in combination with computational approaches, including NMR and ECD calculations. Bioactivities of the isolated compounds toward silent information regulation 2 homologue-1 (SIRT1) in HEK293 cells were assessed. The results showed that compound 1 had the most potent effect on SIRT1 activation with an elevated NAD+/NADH ratio with potential for further investigation as an anti-aging agent.

Diversified Stitching of Ynones with Oxindole-3-oxy acrylates: One-Flask Spiro-annulation Protocol toward Assorted 3H/5H-Spiro[furan-2,3'-indolin]-2'-ones

Spiroannulation of oxindole-3-oxy acrylates with ynones involving two overlapping, base differentiated cascades has been observed. Initial exposure of ynones and oxindole 3-oxy acrylates to K2CO3 triggered a tandem Michael-Michael cascade to deliver a pair of spiroannulated diastereomers. Further exposure to LiHMDS led to deep restructuring through a second multistep cascade involving stereoselective recreation of the C3 quaternary center to furnish 3H-spiro[furan-2,3'-indolin]-2'-ones with functional amplification and scrambling. This new scaffold can be directly accessed in a one-flask operation from ynones and oxindole-3-oxy acrylates.

Medicinal chemistry approaches to target the MNK-eIF4E axis in cancer

Aberrant translation of proteins that promote cell proliferation is an essential factor that defines oncogenic processes and cancer. The process for ribosomal translation of proteins from mRNA requires an essential initiation step which is controlled by the protein eIF4E, which binds the RNA 5'-cap and forms the eIF4F complex that subsequently translates protein. Typically, eIF4E is activated by phosphorylation on Ser209 by MNK1 and MNK2 kinases. Substantial work has shown that eIF4E and MNK1/2 are dysregulated in many cancers and this axis has therefore become an active area of interest for developing new cancer therapeutics. This review summarizes and discusses recent work to develop small molecules that target different steps in the MNK-eIF4E axis as potential cancer therapeutics. The aim of this review is to cover the breadth of different molecular approaches being taken and the medicinal chemistry basis for their optimization and testing as new cancer therapeutics.

Metal-free synthesis of dihydrofuran derivatives as anti-vicinal amino alcohol isosteres

Dihydrofuran cores are commonly incorporated into synthetically and pharmacologically significant scaffolds in natural product and drug discovery chemistry. Herein, we report a concise and practical strategy to construct spiro-dihydrofuran and amino dihydrofuran scaffolds as anti-vicinal amino alcohol isosteres. Hypervalent iodine (PhI(OAc)(NTs₂))-mediated C-H activation of alkynes resulted in two-bond formations with one pi bond cleavage: (i) C(sp²)-N(sp³) and O(sp³)-C(sp²); (ii) C(sp²)-N(sp³) and C(sp³)-C(sp²). The metal-free 5-endo-dig oxidative cyclization provided versatile amino 2,3- and 2,5-dihydrofurans bearing the C₅ quaternary carbon. The non-toxicity of all synthesised dihydrofurans was verified via in vitro cell viability assay.

Structural basis for NaV1.7 inhibition by pore blockers

Voltage-gated sodium channel Na_V1.7 plays essential roles in pain and odor perception. Na_V1.7 variants cause pain disorders. Accordingly, Na_V1.7 has elicited extensive attention in developing new analgesics. Here we present cryo-EM structures of human Na_V1.7/β1/β2 complexed with inhibitors XEN907, TC-N1752 and Na_V1.7-IN2, explaining specific binding sites and modulation mechanism for the pore blockers. These inhibitors bind in the central cavity blocking ion permeation, but engage different parts of the cavity wall. XEN907 directly causes α- to π-helix transition of DIV-S6 helix, which tightens the fast inactivation gate. TC-N1752 induces π-helix transition of DII-S6 helix mediated by a conserved asparagine on DIII-S6, which closes the activation gate. Na_V1.7-IN2 serves as a pore blocker without causing conformational change. Electrophysiological results demonstrate that XEN907 and TC-N1752 stabilize Na_V1.7 in inactivated state and delay the recovery from inactivation. Our results provide structural framework for Na_V1.7 modulation by pore blockers, and important implications for developing subtype-selective analgesics.

Synthesis, Characterization, and Cytotoxicity of New Spirooxindoles Engrafted Furan Structural Motif as a Potential Anticancer Agent

A new series of spirooxindoles based on ethylene derivatives having furan aryl moiety are reported. The new hybrids were achieved via [3 + 2] cycloaddition reaction as an economic one-step efficient approach. The final constructed spirooxindoles have four contiguous asymmetric carbon centers. The structure of 3a is exclusively confirmed using X-ray single crystal diffraction. The supramolecular structure of 3a is controlled by O···H, H···H, and C···C intermolecular contacts. It includes layered molecules interconnected weak C-H···O (2.675 Å), H···H (2.269 Å), and relatively short Cl···Br interhalogen interactions [3.4500(11)Å]. Using Hirshfeld analysis, the percentages of these intermolecular contacts are 10.6, 25.7, 6.4, and 6.2%, respectively. The spirooxindoles along with ethylene derivatives having furan aryl moiety were assessed against breast (MCF7) and liver (HepG2) cancer cell lines. The results indicated that the new chalcone 3b showed excellent activity in both cell lines (MCF7 and HepG2) with IC₅₀ = 4.1 ± 0.10 μM/mL (MCF7) and 3.5 ± 0.07 μM/mL (HepG2) compared to staurosporine with 4.3 and 2.92 folds. Spirooxindoles 6d (IC₅₀ = 4.3 ± 0.18 μM/mL), 6f (IC₅₀ = 10.3 ± 0.40 μM/mL), 6i (IC₅₀ = 10.7 ± 0.38 μM/mL), and 6j (IC₅₀ = 4.7 ± 0.18 μM/mL) exhibited potential activity against breast adenocarcinoma, while compounds 6d (IC₅₀ = 6.9 ± 0.23 μM/mL) and 6f (IC₅₀ = 3.5 ± 0.11 μM/mL) were the most active hybrids against human liver cancer cell line (HepG2) compared to staurosporine [IC₅₀ = 17.8 ± 0.50 μM/mL (MCF7) and 10.3 ± 0.23 μM/mL (HepG2)]. Molecular docking study exhibited the virtual mechanism of binding of compound 3b as a dual inhibitor of EGFR/CDK-2 proteins, and this may highlight the molecular targets for its cytotoxic activity.

Sphingosine Kinase 2 Inhibitors: Rigid Aliphatic Tail Derivatives Deliver Potent and Selective Analogues

Sphingosine 1-phosphate (S1P) is a pleiotropic signaling molecule that interacts with five native G-protein coupled receptors (S1P1–5) to regulate cell growth, survival, and proliferation. S1P has been implicated in a variety of pathologies including cancer, kidney fibrosis, and multiple sclerosis. As key mediators in the synthesis of S1P, sphingosine kinase (SphK) isoforms 1 and 2 have attracted attention as viable targets for pharmacologic intervention. In this report, we describe the design, synthesis, and biological evaluation of sphingosine kinase 2 (SphK2) inhibitors with a focus on systematically introducing rigid structures in the aliphatic lipid tail present in existing SphK2 inhibitors. Experimental as well as molecular modeling studies suggest that conformationally restricted “lipophilic tail” analogues bearing a bulky terminal moiety or an internal phenyl ring are useful to complement the “J”-shaped sphingosine binding pocket of SphK2. We identified 14c (SLP9101555) as a potent SphK2 inhibitor (K_i = 90 nM) with 200-fold selectivity over SphK1. Molecular docking studies indicated key interactions: the cyclohexyl ring binding in the cleft deep in the pocket, a trifluoromethyl group fitting in a small side cavity, and a hydrogen bond between the guanidino group and Asp308 (amino acid numbering refers to human SphK2 (isoform c) orthologue). In vitro studies using U937 human histiocytic lymphoma cells showed marked decreases in extracellular S1P levels in response to our SphK2 inhibitors. Administration of 14c (dose: 5 mg/kg) to mice resulted in a sustained increase of circulating S1P levels, suggesting target engagement.

Enantioselective synthesis of tetrahydrofuran spirooxindoles via domino oxa-Michael/Michael addition reaction using a bifunctional squaramide catalyst

An enantioselective approach for the synthesis of tetrahydrofuran spirooxindoles via domino oxa-Michael/Michael addition reaction of γ-hydroxyenones to isatylidene malononitriles, using a cinchona derived bifunctional squaramide catalyst has been developed. The methodology is the first success of enantioselective oxa-Michael addition to isatylidene malononitriles. The spiro products were obtained in excellent yields with moderate to good enantio- and diastereoselectivities. Scale-up of the reaction and synthetic transformation of the spiro product into structurally complex molecules have been performed.

Urea derivative organocatalyzed enantioselective Friedel-Crafts alkylation of α-naphthols with isatins

An organocatalytic enantioselective Friedel-Crafts alkylation of α-naphthols with isatin derivatives was catalyzed by Takemoto-type urea catalyst to give optical active 3-(naphthalen-2-yl)-3-hydroxy-2-oxindoles in 75%-92% yields with up to 95% enantiomeric excess (ee) value. The catalyst type and the substrate scope were broadened in this methodology.

BF3·OEt2 catalyzed decarbonylative arylation/C-H functionalization of diazoamides with arylaldehydes: synthesis of substituted 3-aryloxindoles

A metal-free BF₃·OEt₂ catalyzed direct decarbonylative arylation of diazoamides with readily accessible aryl aldehydes under an open-air atmosphere was developed to afford 3-aryloxindoles via 1,2-aryl migration with high selectivity. The reaction offers an efficient pathway for 3-arylation of diazoamides under relatively mild conditions, which shows a high level of functional group tolerance of both electron-donating and electron-withdrawing groups with a broad substrate scope. 3-Aryloxindoles were also obtained by a substituent-controlled chemo- and site-selective C-H bond functionalization of unprotected salicylaldehyde derivatives.

Following Nature's Footprint: Mimicking the High-Valent Heme-Oxo Mediated Indole Monooxygenation Reaction Landscape of Heme Enzymes

Pathways for direct conversion of indoles to oxindoles have accumulated considerable interest in recent years due to their significance in the clear comprehension of various pathogenic processes in humans and the multipotent therapeutic value of oxindole pharmacophores. Heme enzymes are predominantly responsible for this conversion in biology and are thought to proceed with a compound-I active oxidant. These heme-enzyme-mediated indole monooxygenation pathways are rapidly emerging therapeutic targets; however, a clear mechanistic understanding is still lacking. Additionally, such knowledge holds promise in the rational design of highly specific indole monooxygenation synthetic protocols that are also cost-effective and environmentally benign. We herein report the first examples of synthetic compound-I and activated compound-II species that can effectively monooxygenate a diverse array of indoles with varied electronic and steric properties to exclusively produce the corresponding 2-oxindole products in good to excellent yields. Rigorous kinetic, thermodynamic, and mechanistic interrogations clearly illustrate an initial rate-limiting epoxidation step that takes place between the heme oxidant and indole substrate, and the resulting indole epoxide intermediate undergoes rearrangement driven by a 2,3-hydride shift on indole ring to ultimately produce 2-oxindole. The complete elucidation of the indole monooxygenation mechanism of these synthetic heme models will help reveal crucial insights into analogous biological systems, directly reinforcing drug design attempts targeting those heme enzymes. Moreover, these bioinspired model compounds are promising candidates for the future development of better synthetic protocols for the selective, efficient, and sustainable generation of 2-oxindole motifs, which are already known for a plethora of pharmacological benefits.

Cinchona Alkaloid Derived Iodide Catalyzed Enantioselective Oxidative α-Amination of Carbonyl Compounds toward the Construction of Spiroindolyloxindole

Novel cinchona alkaloid derived iodide catalysts were developed for the enantioselective oxidative α-amination of 2-oxindoles, providing various functionalized spiropyrrolidine oxindoles in high yields and with good enantioselectivities. This iodide/ROOH catalytic system features a one-step synthesis of a catalyst with multiple functionalities, ease of operation, and good scalability, thereby enriching the repertoire of iodide catalysis for enantioselective oxidative coupling reactions.

endo-5-Norbornene-2,3-dimethanol-promoted asymmetric Heck/Suzuki cascade reaction of N-(2-bromophenyl)acrylamides

An endo-5-norbornene-2,3-dimethanol-promoted highly enantioselective palladium-catalyzed Heck/Suzuki cascade reaction of N-(2-bromophenyl)acrylamides has been developed.

Efficient synthesis of spiro diheterocycles via multi-component dicyclization reaction

Spiro diheterocycles with one valuable quaternary carbon were constructed in one pot via an in situ cyclization–respiroannulation strategy.

Diastereoselective Synthesis of Tetrabenzohydrofuran Spirooxindoles via Diethyl Phosphite-Mediated Coupling of Isatins with o-Quinone Methides

Diethyl phosphite-initiated coupling of isatins with o-quinone methides (o-QMs) is reported. This reaction involves a cascade transformation initiated by base-promoted addition of phosphite to isatins, followed by [1,2]-phospha-Brook rearrangement. This generates α-phosphonyloxy enolates that are subsequently intercepted by o-QMs and finally intramolecular ring closure. This protocol was used to diastereoselectively synthesize a range of trans-tetrabenzohydrofuran spirooxindoles in moderate to good yields with moderate to excellent diastereoselectivities.

Silyl Cyanopalladate-Catalyzed Friedel–Crafts-Type Cyclization Affording 3-Aryloxindole Derivatives

3-Aryloxindole derivatives were synthesized through a Friedel–Crafts-type cyclization. The reaction was catalyzed by a trimethylsilyl tricyanopalladate complex generated in situ from trimethylsilyl cyanide and Pd(OAc)2. Wide varieties of diethyl phosphates derived from N-arylmandelamides were converted almost quantitatively into oxindoles. When N,N-dibenzylamide was used instead of an anilide substrate, a benzo-fused δ-lactam was obtained. An oxindole product was subjected to substitution reactions to afford 3,3-diaryloxindoles with two different aryl groups.

Stereoselective synthesis and applications of spirocyclic oxindoles

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

Ir(III)-Catalyzed C-H Functionalization of Triphenylphosphine Oxide toward 3-Aryl Oxindoles

With triphenylphosphine oxide serving as both the directing group and the reagent, we have developed a Cp*Ir(III)-catalyzed direct C-H functionalization of triphenylphosphine oxide with 3-diazooxindoles to afford a range of 3-(2-(diphenylphosphoryl)phenyl)indolin-2-one derivatives in moderate to excellent yields. The title products are potentially important building blocks for organic synthesis through various chemical transformations. This protocol is simple and efficient and offers high atom economy with only N₂ as the byproduct.

Asymmetric Dearomatization of Indole by Palladium/PC-Phos-Catalyzed Dynamic Kinetic Transformation

A palladium-catalyzed intermolecular dynamic kinetic asymmetric dearomatization of 3-arylindoles with internal alkynes was developed with the use of achiral Xantphos and chiral sulfinamide phosphine ligand (PC-Phos) as the co-ligands. This method could deliver various spiro[indene-1,3'-indole] compounds in good yields (up to 95 % yield) with up to 98 % ee. The salient features of the transformation include the use of readily available substrates, ease of scale-up and the versatile functionalization of the products. The mechanistic experiments gave some insights on active intermediates.

Dearomative 1,4-difunctionalization of naphthalenes via palladium-catalyzed tandem Heck/Suzuki coupling reaction

Dearomative functionalization reactions represent an important strategy for the synthesis of valuable three-dimensional molecules from simple planar aromatics. Naphthalene is a challenging arene towards transition-metal-catalyzed dearomative difunctionalization reactions. Reported herein is an application of naphthalene as a masked conjugated diene in a palladium-catalyzed dearomative 1,4-diarylation or 1,4-vinylarylation reaction via tandem Heck/Suzuki sequence. Three types of 1,4-dihydronaphthalene-based spirocyclic compounds are achieved in excellent regio- and diastereoselectivities. Key to this transformation is the inhibition of a few competitive side reactions, including intramolecular naphthalenyl C-H arylation, intermolecular Suzuki cross-coupling, dearomative 1,2-difunctionalization, and dearomative reductive-Heck reaction. Density functional theory (DFT) calculations imply that the facile exergonic dearomative insertion of a naphthalene double bond disrupts the sequence of direct Suzuki coupling, leading to the tandem Heck/Suzuki coupling reaction. The observed regioselectivity towards 1,4-difunctionalization is due to the steric repulsions between the introduced aryl group and the spiro-scaffold in 1,2-difunctionalization.

Naphthalene is a challenging arene towards transition-metal-catalyzed dearomative difunctionalization. Here, the authors show that naphthalene may act as a masked conjugated diene in palladium-catalyzed dearomative 1,4-diarylation or 1,4-vinylarylation via a tandem Heck/Suzuki sequence.

Palladium-catalysed 5-endo-trig allylic (hetero)arylation

A palladium-catalysed intramolecular allylic (hetero)arylation strategy for the synthesis of fused cyclopentenes incorporated with all-carbon quaternary and spiro centres is described. The method is straightforward, shows broad scope, proceeds in synthetically useful yields, and provides a rare means to construct complex cyclopentanoids. The reaction is believed to involve a kinetically unfavourable 5-endo-trig carbocyclisation of the tethered (π-allyl)palladium system. Further, this method was successfully applied as the key step in the total synthesis of diterpene natural products taiwaniaquinone H and dichroanone.

An overview of spirooxindole as a promising scaffold for novel drug discovery

Introduction: Spirooxindole, a unique and versatile scaffold, has been widely studied in some fields such as pharmaceutical chemistry and synthetic chemistry. Especially in the application of medicine, quite a few compounds featuring spirooxindole motif have displayed excellent and broad pharmacological activities. Many identified candidate molecules have been used in clinical trials, showing promising prospects.Areas covered: This article offers an overview of different applications and developments of spirooxindoles (including the related natural products and their derivatives) in the process of drug innovation, including such as in anticancer, antimicrobial, anti-inflammatory, analgesic, antioxidant, antimalarial, and antiviral activities. Furthermore, the crucial structure-activity relationships, molecular mechanisms, pharmacokinetic properties, and main synthetic methods of spirooxindoles-based derivatives are also reviewed.Expert opinion: Recent progress in the biological activity profiles of spirooxindole derivatives have demonstrated their significant position in present-day drug discovery. Furthermore, we believe that the multidirectional development of novel drugs containing this core scaffold will continue to be the research hotspot in medicinal chemistry in the future.

Divergent syntheses of spirooxindoles from oxindole-embedded four-membered synthon via cycloaddition reactions

The construction of five and six membered heterocycle fused spirooxindoles was achieved via the [4 + 1] and formal [4 + 2] cycloadditions between our rationally designed four-membered synthons and pyridinium methylides and α-bromoacetophenones, respectively.

Green oxidation of indoles using halide catalysis

Oxidation of indoles is a fundamental organic transformation to deliver a variety of synthetically and pharmaceutically valuable nitrogen-containing compounds. Prior methods require the use of either organic oxidants (meta-chloroperoxybenzoic acid, N-bromosuccinimide, t-BuOCl) or stoichiometric toxic transition metals [Pb(OAc)₄, OsO₄, CrO₃], which produced oxidant-derived by-products that are harmful to human health, pollute the environment and entail immediate purification. A general catalysis protocol using safer oxidants (H₂O₂, oxone, O₂) is highly desirable. Herein, we report a unified, efficient halide catalysis for three oxidation reactions of indoles using oxone as the terminal oxidant, namely oxidative rearrangement of tetrahydro-β-carbolines, indole oxidation to 2-oxindoles, and Witkop oxidation. This halide catalysis protocol represents a general, green oxidation method and is expected to be used widely due to several advantageous aspects including waste prevention, less hazardous chemical synthesis, and sustainable halide catalysis.

Indole oxidation represents a fundamental organic transformation delivering valuable nitrogen compounds. Here, the authors report a general halide catalysis protocol applied to three classes of oxidation reactions of indoles with oxone as a sustainable terminal oxidant.

µ-TRTX-Ca1a: a novel neurotoxin from Cyriopagopus albostriatus with analgesic effects

Human genetic and pharmacological studies have demonstrated that voltage-gated sodium channels (VGSCs) are promising therapeutic targets for the treatment of pain. Spider venom contains many toxins that modulate the activity of VGSCs. To date, only 0.01% of such spider toxins has been explored, and thus there is a great potential for discovery of novel VGSC modulators as useful pharmacological tools or potential therapeutics. In the current study, we identified a novel peptide, µ-TRTX-Ca1a (Ca1a), in the venom of the tarantula Cyriopagopus albostriatus. This peptide consisted of 38 residues, including 6 cysteines, i.e. IFECSISCEIEKEGNGKKCKPKKCKGGWKCKFNICVKV. In HEK293T or ND7/23 cells expressing mammalian VGSCs, this peptide exhibited the strongest inhibitory activity on Na_v1.7 (IC₅₀ 378 nM), followed by Na_v1.6 (IC₅₀ 547 nM), Na_v1.2 (IC₅₀ 728 nM), Na_v1.3 (IC₅₀ 2.2 µM) and Na_v1.4 (IC₅₀ 3.2 µM), and produced negligible inhibitory effect on Na_v1.5, Na_v1.8, and Na_v1.9, even at high concentrations of up to 10 µM. Furthermore, this peptide did not significantly affect the activation and inactivation of Na_v1.7. Using site-directed mutagenesis of Na_v1.7 and Na_v1.4, we revealed that its binding site was localized to the DIIS3-S4 linker region involving the D816 and E818 residues. In three different mouse models of pain, pretreatment with Cala (100, 200, 500 µg/kg) dose-dependently suppressed the nociceptive responses induced by formalin, acetic acid or heat. These results suggest that Ca1a is a novel neurotoxin against VGSCs and has a potential to be developed as a novel analgesic.

An unexpected cascade reaction of 3-hydroxyoxindoles with coumarin-3-carboxylates to construct 2,3-dihydrobenzofuran spirooxindoles

An unexpected Michael addition-inspired ring-opening/closure cascade reaction of 3-hydroxyoxindoles with coumarin-3-carboxylates was developed.

Inhibition of the Ubc9 E2 SUMO-conjugating enzyme-CRMP2 interaction decreases NaV1.7 currents and reverses experimental neuropathic pain

We previously reported that destruction of the small ubiquitin-like modifier (SUMO) modification site in the axonal collapsin response mediator protein 2 (CRMP2) was sufficient to selectively decrease trafficking of the voltage-gated sodium channel NaV1.7 and reverse neuropathic pain. Here, we further interrogate the biophysical nature of the interaction between CRMP2 and the SUMOylation machinery, and test the hypothesis that a rationally designed CRMP2 SUMOylation motif (CSM) peptide can interrupt E2 SUMO-conjugating enzyme Ubc9-dependent modification of CRMP2 leading to a similar suppression of NaV1.7 currents. Microscale thermophoresis and amplified luminescent proximity homogeneous alpha assay revealed a low micromolar binding affinity between CRMP2 and Ubc9. A heptamer peptide harboring CRMP2's SUMO motif, also bound with similar affinity to Ubc9, disrupted the CRMP2-Ubc9 interaction in a concentration-dependent manner. Importantly, incubation of a tat-conjugated cell-penetrating peptide (t-CSM) decreased sodium currents, predominantly NaV1.7, in a model neuronal cell line. Dialysis of t-CSM peptide reduced CRMP2 SUMOylation and blocked surface trafficking of NaV1.7 in rat sensory neurons. Fluorescence dye-based imaging in rat sensory neurons demonstrated inhibition of sodium influx in the presence of t-CSM peptide; by contrast, calcium influx was unaffected. Finally, t-CSM effectively reversed persistent mechanical and thermal hypersensitivity induced by a spinal nerve injury, a model of neuropathic pain. Structural modeling has now identified a pocket-harboring CRMP2's SUMOylation motif that, when targeted through computational screening of ligands/molecules, is expected to identify small molecules that will biochemically and functionally target CRMP2's SUMOylation to reduce NaV1.7 currents and reverse neuropathic pain.

Transition-Metal-Free Cyclization of Propargylic Alcohols with Aryne: Synthesis of 3-Benzofuranyl-2-oxindole and 3-Spirooxindole Benzofuran Derivatives ⊥

An unprecedented base-mediated cyclization of propargylic alcohols with aryne is reported, providing a novel method for the synthesis of 3-benzofuranyl-2-oxindole and 3-spirooxindole benzofuran scaffolds via a propargyl Claisen rearrangement/cycloaddition pathway. The nature of the substituent on acetylene group of propargylic alcohol influences the outcome of the reaction. The protocol offers a transition-metal-free and operationally simple methodology with broad substrate scope as a ready access to complex oxindole-linked heterocyclic compounds.