New 6′-Amino-5′-cyano-2-oxo-1,2-dihydro-1′H-spiro[indole-3,4′-pyridine]-3′-carboxamides: Synthesis, Reactions, Molecular Docking Studies and Biological Activity

The purpose of this work was to prepare new isatin- and monothiomalondiamide-based indole derivatives, as well as to study the properties of the new compounds. The four-component reaction of 5-R-isatins (R = H, CH3), malononitrile, monothiomalonamide (3-amino-3-thioxo- propanamide) and triethylamine in hot EtOH yields a mixture of isomeric triethylammonium 6′-amino-3′-(aminocarbonyl)-5′-cyano-2-oxo-1,2-dihydro-1′H- and 6′-amino-3′-(aminocarbonyl)- 5′-cyano-2-oxo-1,2-dihydro-3′H-spiro[indole-3,4′-pyridine]-2′-thiolates. The reactivity and structure of the products was studied. We found that oxidation of spiro[indole-3,4′-pyridine]-2′-thiolates with DMSO-HCl system produced only acidification products, diastereomeric 6′-amino-5′-cyano-5-methyl-2-oxo-2′-thioxo-1,2,2′,3′-tetrahydro-1′H-spiro-[indole-3,4′-pyridine]- 3′-carboxamides, instead of the expected isothiazolopyridines. The alkylation of the prepared spiro[indole-3,4′-pyridine]-2′-thiolates upon treatment with N-aryl α-chloroacetamides and α-bromoacetophenones proceeds in a regioselective way at the sulfur atom. In the case of α-bromoacetophenones, ring-chain tautomerism was observed for the S-alkylation products. According to NMR data, the compounds consist of a mixture of stereoisomers of 2′-amino-6′-[(2-aryl-2-oxoethyl)thio]-3′-cyano-2-oxo-1′H-spiro[indoline-3,4′-pyridine]-5′-carboxamides and 5′-amino-3′-aryl-6′-cyano-3′-hydroxy-2-oxo-2′,3′-dihydrospiro[indoline-3,7′-thiazolo[3,2-a]pyridine]-8′-carboxamides in various ratios. The structure of the synthesized compounds was confirmed by IR spectroscopy, HRMS, 1H and 13C DEPTQ NMR studies and the results of 2D NMR experiments (1H-13C HSQC, 1H-13C HMBC). Molecular docking studies were performed to investigate suitable binding modes of some new compounds with respect to the transcriptional regulator protein PqsR of Pseudomonas aeruginosa. The docking studies revealed that the compounds have affinity for the bacterial regulator protein PqsR of Pseudomonas aeruginosa with a binding energy in the range of −5.8 to −8.2 kcal/mol. In addition, one of the new compounds, 2′-amino-3′-cyano-5-methyl-2-oxo-6′-{[2-oxo-2-(p-tolylamino)ethyl]thio}-1′H-spiro-[indoline-3,4′-pyridine]-5′-carboxamide, showed in vitro moderate antibacterial effect against Pseudomonas aeruginosa and good antioxidant properties in a test with 1,1-diphenyl-2-picrylhydrazyl radical. Finally, three of the new compounds were recognized as moderately active herbicide safeners with respect to herbicide 2,4-D in the laboratory experiments on sunflower seedlings.

A facile approach to spiro[dihydrofuran-2,3'-oxindoles] via formal [4 + 1] annulation reaction of fused 1H-pyrrole-2,3-diones with diazooxindoles

There has been developed an easy synthetic approach to spiro[dihydrofuran-2,3'-oxindoles] via a highly diastereoselective formal [4 + 1] cycloaddition reaction of [e]-fused 1H-pyrrole-2,3-diones with diazooxindoles. The described novel heterocyclic systems are heteroanalogues of antimicrobial and antibiofilm fungal metabolites. The developed reaction represents the first example of involving 1H-pyrrole-2,3-diones fused at the [e]-side in a [4 + 1] annulation reaction.

Synthesis of 3-substituted 2-oxindoles from secondary α-bromo-propionanilides via palladium-catalyzed intramolecular cyclization

In contrast to aromatic halides, coupling reactions involving oxidative addition of alkyl halides, especially secondary or tertiary halides, to transition metals tend to be more challenging. Herein a palladium-catalyzed intramolecular cyclization of α-bromo-propionanilides has been developed, delivering a series of 3-substituted 2-oxindoles in high yields. The method features easy to prepare starting materials, broad substrate scope and excellent functional group tolerance. A detailed mechanistic investigation has been performed.

Development of novel indolin-2-one derivative incorporating thiazole moiety as DHFR and quorum sensing inhibitors: Synthesis, antimicrobial, and antibiofilm activities with molecular modelling study

Nowadays, it's imperative to develop novel antimicrobial agents active against both drug-sensitive and drug-resistant bacterial infections with favorable profiles as high efficacy, low toxicity, and short therapy duration. Accordingly, a series of new thiazolo-indolin-2-one derivatives were synthesized based on acid and base catalyzed condensation or reaction of thiosemicarbazone 8 with different electrophilic reagents. The structure of the new compounds was confirmed based on elemental analysis and spectral data. Based on the MIC results, the most active thiazolo-indoline derivatives 2, 4, 7a, and 12 exhibited promising antibacterial activity against gram-positive and gram-negative bacteria with weak to moderate antifungal activities. Surprisingly, the N-(thiazol-2-yl)benzenesulfonamide derivative 4 was found to be most active on antibiofilm activity against both S. aureus (ATCC 29213) with BIC₅₀ (1.95 ± 0.01 µg/mL), while 5-(2-oxoindolin-3-ylidene)-thiazol-4(5H)-one derivative 7a exhibited the strongest antibiofilm activity against P. aeruginosa pathogens with BIC₅₀ (3.9 ± 0.16 µg/mL). Further, the thiazole derivatives 2, 4 and 12 exhibited a significant inhibition activity against the fsr system in a dose-dependent manner without affecting bacterial growth. The target derivatives behaved synergistic and additively effect against MDR p. aeruginosa, and thiazole derivative 12 exhibited a high synergistic effect with most tested antibiotics except Cefepime with FIC value ranging between 0.249 and 1.0, reducing their MICs. Interestingly, the 3-(2-(4-thiazol-2-yl)hydrazono)indolin-2-one derivative 12 displayed the highest selectivity to DHFR inhibitory with IC₅₀ value 40.71 ± 1.86 nM superior to those of the reference Methotrexate. Finally, in silico molecular modeling simulation, some physicochemical properties and toxicity predictions were performed for the most active derivatives.

Enantioselective Construction of Spirooxindole-Fused Cyclopentanes

The present study reports an asymmetric organocatalytic cascade reaction of oxindole derivates with α,β-unsaturated aldehydes efficiently catalyzed by simple chiral secondary amine. Spirooxindole-fused cyclopentanes were produced in excellent isolated yields (up to 98%) with excellent enantiopurities (up to 99% ee) and moderate to high diastereoselectivities. The synthetic utility of the protocol was exemplified on a set of additional transformations of the corresponding spiro compounds. In addition, a study showing the promising biological activity of selected enantioenriched products was accomplished.

A one-pot synthesis of piperidinium spirooxindoline-pyridineolates and indole-substituted pyridones in aqueous or ethanol medium

Piperidinium spirooxindoline-pyridineolate has been prepared via one-pot multicomponent reaction of isatin, malononitrile, cyanoacetohydrazide, and piperidine in water or ethanol medium at room temperature. In addition, the synthesis of two indole-substituted 2-pyridones from indole-3-carbaldehyde, malononitrile, and cyanoacetohydrazide in the presence of piperidine is described.

Recent Strategies in the Synthesis of Spiroindole and Spirooxindole Scaffolds

Spiroindole and spirooxindole scaffolds are very important spiro-heterocyclic compounds in drug design processes. Significant attention has been directed at obtaining molecules based on spiroindole and spirooxindole derivatives that have bioactivity against cancer cells, microbes, and different types of disease affecting the human body. Due to their inherent three-dimensional nature and ability to project functionalities in all three dimensions, they have become biological targets. Considering reports on spiroindole and spirooxindole-containing scaffolds in the past decades, introducing novel synthetic procedures has been an active research field of organic chemistry for well over a century and will be useful in creating new therapeutic agents. This review summarizes the pharmacological significance of spiroindole and spirooxindole scaffolds and highlights the latest strategies for their synthesis, focusing particularly on the past 2 years with typical examples. The spiroindole and spirooxindoles in this review are divided by the type and ring size of the spirocycle that is fused to indole or oxindole. Summarizing these procedures will be very beneficial for discovering novel therapeutic candidate molecules.

Diversified strategy for the synthesis of DNA-encoded oxindole libraries

DNA-encoded library technology (DELT) employs DNA as a barcode to track the sequence of chemical reactions and enables the design and synthesis of libraries with billions of small molecules through combinatorial expansion. This powerful technology platform has been successfully demonstrated for hit identification and target validation for many types of diseases. As a highly integrated technology platform, DEL is capable of accelerating the translation of synthetic chemistry by using on-DNA compatible reactions or off-DNA scaffold synthesis. Herein, we report the development of a series of novel on-DNA transformations based on oxindole scaffolds for the design and synthesis of diversity-oriented DNA-encoded libraries for screening. Specifically, we have developed 1,3-dipolar cyclizations, cyclopropanations, ring-opening of reactions of aziridines and Claisen–Schmidt condensations to construct diverse oxindole derivatives. The majority of these transformations enable a diversity-oriented synthesis of DNA-encoded oxindole libraries which have been used in the successful hit identification for three protein targets. We have demonstrated that a diversified strategy for DEL synthesis could accelerate the application of synthetic chemistry for drug discovery.

Constructing DNA-encoded oxindole libraries by a diversified strategy.

Stereoselective synthesis and applications of spirocyclic oxindoles

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

Advances of α-activated cyclic isothiocyanate for the enantioselective construction of spirocycles

The efficient and enantioselective synthesis of pharmaceutically important spirocycles has attracted the focus of organic and medicinal chemists. In this context, with the excellent reactivity of α-activated isothiocyanate as formal 1,3-dipoles in the (3 + 2) cyclization process, the cyclic isothiocyanates featuring important pharmacophores, such as oxindole, pyrazolone, and indanone moieties, have emerged as powerful precursors to access a variety of spirocycles with highly structural diversities. In addition, the facile transformations of these spirocycles have shown potential applications in drug design. This review will cover the recent advances of α-activated cyclic isothiocyanates in the enantioselective construction of spirocycles since 2015, and the applications of corresponding products in organic and medicinal chemistry.

Diastereodivergent synthesis of dispiroheterocyclic structures comprising pyrrolidinyloxindole and imidazothiazolotriazine moieties

Highly diastereoselective methods for the synthesis of two different diastereomers of polynuclear dispiroheterocyclic compounds with five chiral centers comprising pyrrolidinyloxindole and imidazothiazolotriazine moieties (dispiro[imidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazine-7,3'-pyrrolidine-2',3''-indoles]) have been developed on the basis of a dipolar cycloaddition of azomethine ylides to benzylidene derivatives of imidazothiazolotriazines and an alkali-induced rearrangement of the thiazolotriazine fragment. The different sequence of the cycloaddition and rearrangement stages allows us to perform the targeted synthesis of two diastereomerically pure products from the same starting compounds.

Synthesis, Characterization, and Reactivity of a Hypervalent-Iodine-Based Nitrooxylating Reagent

Herein, the synthesis and characterization of a hypervalent-iodine-based reagent that enables a direct and selective nitrooxylation of enolizable C-H bonds to access a broad array of organic nitrate esters is reported. This compound is bench stable, easy-to-handle, and delivers the nitrooxy (-ONO₂ ) group under mild reaction conditions. Activation of the reagent by Brønsted and Lewis acids was demonstrated in the synthesis of nitrooxylated β-keto esters, 1,3-diketones, and malonates, while its activity under photoredox catalysis was shown in the synthesis of nitrooxylated oxindoles. Detailed mechanistic studies including pulse radiolysis, Stern-Volmer quenching studies, and UV/Vis spectroelectrochemistry reveal a unique single-electron-transfer (SET)-induced concerted mechanistic pathway not reliant upon generation of the nitrate radical.

A derivatization-directed three-component synthesis of fluorescent spiro [dihydropyridine-4,3ʹ-indoline]s

The synthesis of spiro[chromeno[4,3- b]pyrazolo[4,3- e]pyridine-7,3ʹ-indoline]s is achieved via three-component reactions of 5-amino-3-methylpyrazole, 4-aminocoumarin, and isatin derivatives. This protocol provides expedient synthesis of 10-unsubstituted derivatives of the parent heterocyclic spiro framework and does not lead to coumarin ring opening. The synthesis is highly convergent as no by-products are present in the reaction mixtures. The spiro products show violet fluorescence emissions depending on the nature of their substituents.

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.

Highly regio- and diastereoselective [3 + 2]-cycloadditions involving indolediones and α,β-disubstituted nitroethylenes

A highly diastereoselective [3 + 2]-cycloaddition strategy involving multiple oxindoles and several α,β-disubstituted nitroethylenes is developed to access tetra-substituted α-spiropyrrolidine frameworks. A variety of α-amino acids were employed for the first time in order to generate azomethine ylides under thermal conditions, affording regioisomers 13 and 14 merely by changing the α-substituents (R = H and substituted carbons) of the α-amino acids. The reaction tolerates various sterically demanding, electron-rich and electron-deficient aryl and nitrogen substituents on glycines, oxindoles and nitroethylenes. The operational simplicity, such as the use of a metal-free and non-inert environment, the utilization of non-halogenated solvents and the ease of isolation, adhering to the principles of green chemistry, makes this process attractive for scale-up opportunities. The reaction delivers good yields (80-94%) and diastereoselectivities (up to 98 : 2) in favor of (cis,cis)-spirooxindoles, with opposite regioselectivity compared to β-nitrostyrenes under identical conditions. Two spiropyrrolidine cycloadducts with unprotected amides exhibited significant activity against Gram-positive MRSA.

Combined Scaffold Evaluation and Systems-Level Transcriptome-Based Analysis for Accelerated Lead Optimization Reveals Ribosomal Targeting Spirooxindole Cyclopropanes

With evolutionary drug resistance impacting efforts to treat disease, the need for small molecules that exhibit novel molecular mechanisms of action is paramount. In this study, we combined scaffold-directed synthesis with a hybrid experimental and transcriptome analysis to identify bis-spirooxindole cyclopropanes that inhibit cancer cell proliferation through disruption of ribosomal function. These findings demonstrate the value of an integrated, biologically inspired synthesis and assay strategy for the accelerated identification of first-in-class cancer therapeutic candidates.

Diastereoselective ABB' Three-Component Synthesis of Highly Functionalized Spirooxindoles Bearing Five Consecutive Asymmetric Carbons

The synthesis of spirooxindoles bearing tetrahydro-4 H-cyclopenta[ b]furan framework was established starting from isatin-derived aldehydes and 2 equiv of 1,3-dicarbonyl compounds involving a piperidine-catalyzed ABB' three-component domino process. This reaction was highly diastereoselective affording a single diastereomer of spirooxindoles with five consecutive asymmetric carbons including spiro and tetrasubstituted carbon centers. In addition, this waste-free (-2H₂O) reaction showed high atom economy and step economy by creating four new bonds, including three C-C bonds and one C-O bond, and two rings (one carbo- and one heterocyclic) in a single operation. The mechanism of this three-component domino process involved sequential Knoevenagel condensation-Michael addition-intramolecular oxa-Michael addition-intramolecular aldol reactions.

Stereocontrolled [3+2] Cycloaddition of Donor-Acceptor Cyclopropanes to Iminooxindoles: Access to Spiro[oxindole-3,2'-pyrrolidines]

A novel stereocontrolled assembly of spiro[oxindole-3,2'-pyrrolidines] via [3+2]-cycloaddition of donor-acceptor cyclopropanes to electron-poor ketimines, iminooxindoles, was developed. The method allows for efficient employment of common readily available donor-acceptor cyclopropanes, functionalized with ester, keto, nitro, cyano etc. groups, and N-unprotected iminooxindoles. The stereospecificity of the initial S_N2-like imine attack on a cyclopropane molecule together with a high diastereoselectivity of further C-C bond formation facilitate a rapid access to spiro[oxindole-3,2'-pyrrolidines] in their optically active forms. Preliminary in vitro testing of the synthesized compounds against LNCaP (p53+) and PC-3 (p53-) cells revealed good antiproliferative activities and p53-selectivity indices for several compounds that are intriguing in terms of their further investigation as inhibitors of MDM2-p53 interaction.

Asymmetric Synthesis of Spirocyclopentane Oxindoles Containing Four Consecutive Stereocenters and Quaternary α-Nitro Esters via Organocatalytic Enantioselective Michael-Michael Cascade Reactions

An enantioselective domino Michael-Michael reaction of nitroolefins and 2-nitro-3-arylacrylates has been established, which provided a series of spirocyclopentane oxindoles with four consecutive stereocenters including quaternary α-nitro esters with good yields (up to 73%) and excellent enantioselectivities (up to 97% ee). The reaction was realized and optimized with the aid of a chiral squaramide-amine catalyst. The structures of 11 products were confirmed by single-crystal X-ray diffraction analysis.

Construction of Bispirooxindole Heterocycles via Palladium-Catalyzed Ring-Opening Formal [3 + 2]-Cycloaddition of Spirovinylcyclopropyl Oxindole and 3-Oxindole Derivatives

A palladium-catalyzed ring-opening oxo-formal [3 + 2]-cycloaddition reaction of novel donor-acceptor spirovinylcyclopropyl oxindole with 3-oxindole is described. The developed protocol provides facile access to oxo-bispirooxindole derivatives in good yields (up to 82% yield) with excellent diastereoselectivities (up to 20:1 dr).

Protecting group-directed annulations of tetra-substituted oxindole olefins and sulfur ylides: regio- and chemoselective synthesis of cyclopropane- and dihydrofuran-fused spirooxindoles

Protecting group-controlled regio- and chemoselective synthesis of cyclopropane- and dihydrofuran-fused spirooxindoles containing vicinal quaternary carbon centers.

Ppm Cu Catalyst Enables tert-Alkylation Followed by C-H Cyclization To Synthesize Substituted Oxindoles

In this paper, we established highly efficient Cu-catalyzed tandem tert-alkylation C-H cyclization of α-bromocarbonyls and methacrylamides to produce substituted oxindoles. The maximum turnover number was up to 48 000 with reasonable yield. Although the catalyst loadings were very low, the reaction was not involving radical chain reaction. The resulting oxindoles were able to transform into aza-multicyclic compound via a reduction.

Transition-Metal-Free Synthesis of N-Hydroxy Oxindoles by an Aza-Nazarov-Type Reaction Involving Azaoxyallyl Cations

A novel transition-metal-free method to construct N-hydroxy oxindoles by an aza-Nazarov-type reaction involving azaoxyallyl cation intermediates is described. A variety of functional groups were tolerated under the weak basic reaction conditions and at room temperature. A one-pot process was also developed to make the reaction even more practical. This method provides alternative access to oxindoles and their biologically active derivatives.

Catalytic asymmetric synthesis of spirooxindoles: recent developments

The past four years have witnessed significant developments in the field of the catalytic asymmetric synthesis of spirooxindoles, and this feature article outlines the recent progress in this area, including the contributions of our group. This article is divided into sections according to the size and type of the generated spiro-ring fused at the C3-position of the oxindole core.