Review of Synthesis of Multispiro Heterocyclic Compounds from Isatin

Recent updates on vinyl cyclopropanes, aziridines and oxiranes: access to heterocyclic scaffolds

This present review delineates the repertoire of vinyl cyclopropanes and their stuctural analogues to accomplish a wide array of oxa-cycles, aza-cycles, and thia-cycles under transition metal catalysis and metal-free approaches from early 2019 to the present date. The generation of electrophilic π-allyl intermediates and 1-3/1-5-dipolarophile chemistry originating from VCPs are always green, step- and atom-economical and sustainable strategies in comparsion with prefunctionalized and/or C-H activation protocols. Here, the strained ring-system extends its applicability by relieving the strain to undergo a ring-expansion reaction to accomplish 5-9 membered carbo- and heterocyclic systems. The availability of chiral ligands in the ring-expansion reaction of VCPs and their analogues has paved the way to realizing asymmetric synthetic transformations.

Dual activity of indolin-2-ones containing an arylidene motif: DNA and BSA interaction

Applying a multistep approach, novel indolin-2-ones (IND) that possess an arylidene motif have been synthesized. Eight compounds were chosen for different biological tests (antimicrobial and cytotoxicity). IND containing 2-thienyl (4h) fragment have been found to exhibit good antimicrobial activity against B. cereus. Molecules that have 3-aminophenyl (4d) or 2-pyridyl (4g) groups have shown the best antifungal activities against all tested fungi. These compounds have also been noticed as promising pharmaceuticals against MCF-7 cancer cell lines. Experimental outcomes from the investigation of the interaction of 4d with DNA implied its moderate binding to DNA (KSV = 1.35 × 104 and 3.05 × 104 M-1 for EB and Hoechst binder, respectively). However, considerably stronger binding of 4d to BSA has been evidenced (Ka = 6.1 × 106 M-1). In summary, IND that contains m-aminobenzylidene fragment (4d) exhibits a good dual biological activity making it a promising candidate for further investigation in the drug discovery sector.

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.

Graphene Oxide Catalyzed Synthesis of Fused Chromeno Spiro Pyrrolidine Oxindoles via Tandem Decarboxylation and 1,3-Dipolar Cycloaddition

A short and efficient multicomponent sequence for synthesizing fused novel polyheterocyclic chromeno spiro-pyrrolidine oxindoles via 1,3-dipolar cycloaddition reaction mediated by reactive azomethine ylides catalyzed by the Graphene Oxide (GO) is reported herein. This approach was utilized for synthesizing fused polyheterocyclic spiro-pyrrolothiazole and spiro-pyrrole oxindoles with yields ranging from good to excellent. A heterogeneous GO catalyst with an ultra-low catalytic loading of 0.05 wt% could proficiently catalyze the reaction without the formation of any side products and can also be visualized by the formation of solid mass in the reaction flask. The methodology is green in nature and the products were isolated by simple filtration without the use of any chromatographic techniques.

Synthesis, spectroscopic investigation, crystal structure analysis, quantum chemical study, biological activity and molecular docking of three isatin derivatives

Three isatin derivatives, namely, 1-allyl-3-hydroxy-3-(6-oxocyclohex-1-en-1-yl)indolin-2-one, C₁₇H₁₇NO₃, 1-ethyl-3-hydroxy-3-(6-oxocyclohex-1-en-1-yl)indolin-2-one, C₁₆H₁₇NO₃, and 5-bromo-3-hydroxy-1-methyl-3-(6-oxocyclohex-1-en-1-yl)indolin-2-one, C₁₅H₁₄BrNO₃, were synthesized, crystallized by the slow-evaporation technique, characterized by ¹H and ¹³C NMR spectroscopy, and analysed by the single-crystal X-ray diffraction (XRD) method. Quantum chemical parameters, such as the energy of the highest occupied molecular orbital, energy of the lowest unoccupied molecular orbital, energy gap, electronic energy, ionization potential, chemical potential, global hardness, global softness and electrophilicity index, were calculated. The druglikeness and bioactivity scores of the compounds were calculated. The activities of these isatin derivatives against bacterial strains, such as Eschericia coli, Proteus vulgaris, Shigella flexneri, Staphylococcus aureus and Micrococcus luteus, and the fungal strain Aspergillus niger, were determined using the well-diffusion assay method. Molecular docking studies were carried out to predict the binding mode of the isatin compounds with the penicillin binding protein enzyme and to identify the interactions between the enzyme and the ligands under study.

Engaging Isatins in Multicomponent Reactions (MCRs) - Easy Access to Structural Diversity

Multicomponent reactions (MCRs) are a valuable tool in diversity-oriented synthesis. Its application to privileged structures is gaining relevance in the fields of organic and medicinal chemistry. Isatin, due to its unique reactivity, can undergo different MCRs, affording multiple interesting scaffolds, namely oxindole-derivatives (including spirooxindoles, bis-oxindoles and 3,3-disubstituted oxindoles) and even, under certain conditions, ring-opening reactions occur that leads to other heterocyclic compounds. Over the past few years, new methodologies have been described for the application of this important and easily available starting material in MCRs. In this review, we explore these novelties, displaying them according to the structure of the final products obtained.

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.

Green synthesis of spiro[indoline-3,4'-pyrano[2,3-c]pyrazoles] using Fe3O4@l-arginine as a robust and reusable catalyst

The synthesized Fe3O4@l-arginine showed strong catalytic performance in the one-pot synthesis of spiropyranopyrazoles via the reactions of hydrazines, β-keto esters, isatins, and malononitrile or ethyl cyanoacetate under solvent-free conditions. The biologically active heterocyclic compounds including spiropyranopyrazole derivatives were efficiently synthesized in short reaction times and excellent yields in the presence of Fe3O4/l-arginine at room temperature. The highlighted features of the Fe3O4@l-arginine nanocomposite are highly stable, easy to separate, low loading, cost-effective with easy preparation and reusability of the catalyst. The heterogeneous nanocomposite was fully characterized by SEM, EDX, FT-IR, XRD and TEM analysis.

Pseudo five component reaction towards densely functionalized spiro[indole-3,2'-pyrrole] by picric acid, an efficient syn-diastereoselective catalyst: insight into the diastereoselection on C(sp3)-C(sp3) axial conformation

A new series of highly-functionalized spiro compounds of pyrrole were synthesized by a one pot, step-economic condensation of isatin, arylamine and β-keto ester catalyzed by wet picric acid. Initially, the reaction was proposed with an expectation of the formation of a multi-spiro heterocyclic framework of highly-substituted piperidine. However, the isomeric compound was characterized to be a five-membered pyrrole derivative with a diverse scope of variations having different types of substituents in the three components respectively. The possibility of formation of various diastereomers around the hindered single bond and the spiro carbon was limited, as only syn products syn-60 and syn-60' were isolated in all the reactions performed under the standard conditions. Probably the reactions were mediated by the si-facial formation of the bonds in a picric acid stabilized charge transfer complex transition state. Also, the manner a molecule achieves the most stabilized energy minimized arrangement with all its substituents in space was studied by DFT calculations where syn-60 was more stable than syn-60'. The studies on the formation of syn-60 and syn-60' were carried out by variation of electronic and steric factors in each of the components of the reactions.

Ball Milling Promoted N-Heterocycles Synthesis

In the last years, numerous protocols have been published using ball milling for organic synthesis. Compared to other methods such as microwave or ultrasound irradiation and ionic liquids, ball mill chemistry is an economical, and ecofriendly method in organic synthesis that is rather underrepresented in the knowledge of organic chemists. The aim of this review is to explore the advantages of the application of ball milling in synthesis of N-heterocyclic compounds.

Copper-catalyzed ambient-temperature decarboxylative annulation of isatins with amidine hydrochlorides: a facile access to 2-(1,3,5-triazin-2-yl)aniline derivatives

A copper-catalyzed domino protocol for the synthesis of 2-(1,3,5-triazin-2-yl)anilines has been developed from isatins and amidine hydrochlorides at ambient temperature.

A concise construction of 12H-benzo[4,5]thiazolo[2,3-b]quinazolin-12-ones via an unusual TBHP/Na2CO3 promoted cascade oxidative cyclization and interrupted Dimroth rearrangement

An interrupted Dimroth rearrangement was merged into the oxidative cyclization between isatins and 2-haloaryl isothiocyanates, giving 12H-benzo[4,5]thiazolo[2,3-b]quinazolin-12-one derivatives.

Asymmetric synthesis of δ-amino acid derivatives via diastereoselective vinylogous Mannich reactions between N-tert-butanesulfinyl imines and dioxinone-derived lithium dienolate

A diastereoselective vinylogous Mannich reaction between theN-tert-butanesulfinyl imines and dioxinone-derived lithium dienolate was developed.

An effective one-pot access to polynuclear dispiroheterocyclic structures comprising pyrrolidinyloxindole and imidazothiazolotriazine moieties via a 1,3-dipolar cycloaddition strategy

An effective and highly regio- and diastereoselective one-pot method for the synthesis of new polynuclear dispiroheterocyclic systems with five stereogenic centers (dispiro[imidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazine-6,3'-pyrrolidine-2',3''-indoles]) comprising pyrrolidinyloxindole and imidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazine moieties has been developed. The method relies on a 1,3-dipolar cycloaddition of azomethine ylides generated in situ from isatin derivatives and sarcosine to 6-benzylideneimidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazine-2,7-diones.

Highly stereoselective [4+2] and [3+2] spiroannulations of 2-(2-oxoindolin-3-ylidene)acetic esters catalyzed by bifunctional thioureas

A new Michael-Michael cascade reaction between 2-(2-oxoindolin-3-ylidene)acetic esters 1 and nitroenoates 2, catalyzed by bifunctional thioureas, is investigated. The combination of the two Michael reactions results in a novel and facile [4+2] or [3+2] spiroannulation process, which is characterized by the following features: 1) two carbon-carbon bonds and four stereocenters, including a quaternary spiro carbon, are formed under mild conditions; 2) an unprecedented and stereochemically defined substitution pattern on the spirocarbocyclic unit is obtained; 3) the double-bond configuration of the donor-acceptor nitroenoate 2 determines the absolute configuration of the spiro center, whereas the remaining stereocenters are formed under control of the catalyst. The effect on the final stereochemical outcome of structural variations of each starting material, catalyst, and experimental conditions is analyzed in detail. In particular, the use of specifically designed chiral nitroenoates enables diverse polyfunctional spirocyclohexane derivatives containing six consecutive stereogenic centers to be constructed. To our knowledge, this is the first asymmetric organocatalytic strategy enabling both five- and six-membered β-nitro spirocarbocyclic oxindoles.

Rapid and efficient one-pot synthesis of spiro[indoline-3,4'-pyrano[2, 3-c]pyrazole] derivatives catalyzed by l-proline under ultrasound irradiation

A rapid and efficient ultrasound-promoted one-pot synthesis of spiro[indoline-3,4'-pyrano[2,3-c]pyrazole] derivatives is described here. The reaction of substituted phenylhydrazine and dialkyl acetylenedicarboxylate with substituted isatin and malononitrile is catalyzed by l-proline to give good-to-excellent yields in water/ethanol (v/v, 1:1) at room temperature.

Palladium-catalyzed asymmetric allylic amination of racemic butadiene monoxide with isatin derivatives

Pd-catalyzed asymmetric aminations of butadiene monoxide with isatin derivatives using P/alkene ligands gave high yields, ees and regioselectivity ratios.