A new vinyl selenone-based domino approach to spirocyclopropyl oxindoles endowed with anti-HIV RT activity

Self-Supported Chiral Dirhodium Organic Frameworks Enables Efficient Asymmetric Cyclopropanation

The development of heterogeneous chiral dirhodium catalysts for fabricating important bioactive substances and reducing the loss of noble metals has long been of significant interest. However, there still remains formidable synthetic challenges since it requires multiple steps of the synthetic process, and rhodium is easily leached from solid materials during the reaction. Here, we demonstrated a self-supported strategy based on the Suzuki-Miyaura coupling reaction to construct two chiral dirhodium organic frameworks for heterogeneous asymmetric catalysis. The synthetic approach is simple and efficient since it requires only a small number of preparation steps and does not require any catalyst supporting materials. The obtained chiral dirhodium materials can be highly efficient and recyclable heterogeneous catalysts for asymmetric cyclopropanation between diazooxindole and alkenes. Importantly, Rh2-MOCP-2 exhibited almost similar catalytic performance compared to homogeneous catalyst Rh2(S-Br-NTTL)4. The afforded catalytic performance (93.9% yield with 80.9% ee) highly surpasses previous heterogeneous dirhodium catalysts reported to date.

Design, synthesis and biological evaluation of indole-2-carboxylic acid derivatives as novel HIV-1 integrase strand transfer inhibitors

Integrase plays an important role in the life cycle of HIV-1, and integrase strand transfer inhibitors (INSTIs) can effectively impair the viral replication. However, drug resistance mutations have been confirmed to decrease the efficacy of INSTI during the antiviral therapy. Herein, indole-2-carboxylic acid (1) was found to inhibit the strand transfer of integrase, and the indole nucleus of compound 1 was observed to chelate with two Mg2+ ions within the active site of integrase. Through optimization of compound 1, a series of indole-2-carboxylic acid derivatives were designed and synthesized, and compound 17a was proved to markedly inhibit the effect of integrase, with IC50 value of 3.11 μM. Binding mode analysis of 17a demonstrated that the introduced C6 halogenated benzene ring could effectively bind with the viral DNA (dC20) through π-π stacking interaction. These results indicated that indole-2-carboxylic acid is a promising scaffold for the development of integrase inhibitors.

B(C6F5)3-catalyzed cyclopropanation of 3-alkenyl-oxindoles with diazomethanes

Spirocyclopropane-oxindoles are key motifs in biologically active compounds and are versatile synthetic intermediates. Herein, we report a metal-free, B(C₆F₅)₃ catalyzed cyclopropanation of 3-alkenyl-oxindoles with diazomethanes. This provides 25 variants of spirocyclopropane-oxindole derivatives. These spirocyclopropane-oxindole products were obtained in good to excellent yields (up to 99%) and high diastereoselectivities (up to 20 : 1 d.r.) under mild reaction conditions and could be performed on a gram scale.

The Solubility Studies and the Complexation Mechanism Investigations of Biologically Active Spiro[cyclopropane-1,3'-oxindoles] with β-Cyclodextrins

In this work, we first improved the aqueous solubility of biologically active spiro[cyclopropane-1,3′-oxindoles] (SCOs) via their complexation with different β-cyclodextrins (β-CDs) and proposed a possible mechanism of the complex formation. β-CDs significantly increased the water solubility of SCOs (up to fourfold). Moreover, the nature of the substituents in the β-CDs influenced the solubility of the guest molecule (MβCD > SBEβCD > HPβCD). Complexation preferably occurred via the inclusion of aromatic moieties of SCOs into the hydrophobic cavity of β-CDs by the numerous van der Waals contacts and formed stable supramolecular systems. The phase solubility technique and optical microscopy were used to determine the dissociation constants of the complexes (Kc~102 M−1) and reveal a significant decrease in the size of the formed crystals. FTIR-ATR microscopy, PXRD, and 1H-1H ROESY NMR measurements, as well as molecular modeling studies, were carried out to elucidate the host−guest interaction mechanism of the complexation. Additionally, in vitro experiments were carried out and revealed enhancements in the antibacterial activity of SCOs due to their complexation with β-CDs.

Enantioselective Synthesis of Bispiro[indanedione-oxindole-cyclopropane]s through Organocatalytic [2+1] Cycloaddition

A series of compounds featuring a novel bispiro[indanedione-oxindole-cyclopropane] moiety have been synthesized through a squaramide-catalyzed [2+1] cycloaddition reaction. The tandem Michael-alkylation reaction of 2-arylidene-1,3-indanediones with 3-bromooxindoles furnished the cycloadducts in high yields with excellent diastereo- and enantioselectivities. The ammonium ylide in the catalytic process, as a key intermediate, was revealed by the high-resolution mass spectrometry study.

Stereoselective Domino Reactions in the Synthesis of Spiro Compounds

This review summarizes the latest developments in asymmetric domino reactions, with the emphasis on the preparation of spiro compounds. Discussions on the stereoselectivity of the transformations, the reaction mechanisms, the rationalization of the stereochemical outcome, and the applications of domino reactions to the synthesis of biologically active molecules and natural products are included when appropriate.

1 Introduction

2 Asymmetric Domino Reactions

2.1 Domino Reactions Initiated by Michael Reactions

2.2 Domino Reactions Initiated by Mannich Reactions

2.3 Domino Reactions Initiated by Knoevenagel Reactions

2.4 Domino Reactions Initiated by Cycloaddition Reactions

2.5 Domino Reactions Initiated by Metal Insertion

2.6 Other Mechanisms

3 Conclusion

"Green Is the Color": An Update on Ecofriendly Aspects of Organoselenium Chemistry

Organoselenium compounds have been successfully applied in biological, medicinal and material sciences, as well as a powerful tool for modern organic synthesis, attracting the attention of the scientific community. This great success is mainly due to the breaking of paradigm demonstrated by innumerous works, that the selenium compounds were toxic and would have a potential impact on the environment. In this update review, we highlight the relevance of these compounds in several fields of research as well as the possibility to synthesize them through more environmentally sustainable methodologies, involving catalytic processes, flow chemistry, electrosynthesis, as well as by the use of alternative energy sources, including mechanochemical, photochemistry, sonochemical and microwave irradiation.

Green Protocol for the Novel Synthesis of Thiochromeno[4,3-b]pyridine and Chromeno[4,3-b]pyridine Derivatives Utilizing a High-Pressure System

A suitable and effective Q-tube-assisted strategy for the synthesis of novel, unrivalled thiochromeno[4,3-b]pyridine and chromeno[4,3-b]pyridine derivatives has been sophisticated, which includes ammonium acetate-mediated cyclocondensation reactions between 3-oxo-2-arylhydrazonopropanals and heterobenzocyclic ketones such as thiochroman-4-one and chroman-4-one, respectively. The high-pressure Q-tube reactor was shown to be superior to conventional heating. Furthermore, this Q-tube reactor-assisted protocol is safe owing to facile pressing and sealing, a broad substrate scope, and simple work-up and purification processes, as well as being scalable and having a high atom economy. The proposed mechanistic route includes two sequential dehydrative stages. In this investigation, X-ray crystallographic analysis was performed to authenticate the targeted products.

Mechanism and Selectivity of Cyclopropanation of 3-Alkenyl-oxindoles with Sulfoxonium Ylides Catalyzed by a Chiral N,N'-Dioxide-Mg(II) Complex

The mechanism and stereoselectivity of an asymmetric cyclopropanation reaction between 3-alkenyl-oxindole and sulfoxonium ylide catalyzed by a chiral N,N'-dioxide-Mg(II) complex were explored using the B3LYP-D3(BJ) functional and the def2-TZVP basis set. The noncatalytic reaction occurred via a stepwise mechanism, with activation barriers of 21.6-23.5 kcal mol^-1. The C₂-C_α bond formed followed by the carbanion S_N2 substitution, constructing a three-membered ring in spiro-cyclopropyl oxindoles, accompanied by the release of dimethylsulfoxide. The electron-withdrawing N-protecting t-butyloxy carbonyl (Boc) and acetyl (Ac) groups in isatin enhanced the local electrophilicity of the C2 atom and the repulsion between the two COPh groups in the reactants, contributing to high reactivity as well as good diastereoselectivity results. The N-Boc-3-phenacylideneoxindole coordinated to the chiral ligand (L-PiPr₂) in a bidentate fashion, forming a hexacoordinate-Mg(II) complex as the reactive species. The origin of enantioselectivity was from the shielding effect of 2,6-diisopropylphenyl groups in the ligand toward the si-face of oxindole. The repulsion between the SO(CH₃)₂ and COPh groups in 3-alkenyl-oxindole and the neighboring ortho-iPr group in the ligand directed the re-face of ylide to attack the re-face of oxindole preferably, contributing to the high diastereoselectivity of the product. A metal-ion-ligand matching relationship was important for a good asymmetric induction effect of the chiral N,N'-dioxide-metal catalyst. A large chiral cavity in the Zn(II) catalyst weakened the shielding effect of 2,6-diisopropylphenyl groups in the ligand toward the prochiral face of oxindole, leading to inferior enantioselectivity observed in the experiment.

TFA-catalyzed Q-Tube Reactor-Assisted Strategy for the Synthesis of Pyrido[1,2-b][1,2,4]triazine and Pyrido[1',2':2,3][1,2,4]triazino[5,6-b]indole Derivatives

An efficient high-pressure-assisted trifluoroacetic acid-catalyzed protocol for synthesizing unreported novel pyrido[1,2-b][1,2,4]triazine and pyrido[1',2':2,3][1,2,4]triazino[5,6-b]indole derivatives has been established. This strategy includes the condensation reactions of various 1-amino-2-imino-4-arylpyridine-3-carbonitrile derivatives with indoline-2,3-dione (isatin) derivatives and α-keto acids such as pyruvic acid and phenylglyoxylic acid. This strategy includes utilizing the Q-tube reactor as an efficient and safe tool to conduct these reactions under high-pressure conditions. In addition, trifluoroacetic acid was used to induce this transformation. In this research, conducting the targeted reactions under high pressure using the Q-tube reactor was found to be superb in comparison to that under the traditional refluxing conditions. X-ray single-crystal analysis was utilized in this study to authenticate the structure of the synthesized products.

Modern Synthetic Strategies with Organoselenium Reagents: A Focus on Vinyl Selenones

In recent years, vinyl selenones were rediscovered as useful building blocks for new synthetic transformations. This review will highlight these advances in the field of multiple-bond-forming reactions, one-pot synthesis of carbo- and heterocycles, enantioselective construction of densely functionalized molecules, and total synthesis of natural products.

Visible-Light-Mediated Cyclopropanation Reactions of 3-Diazooxindoles with Arenes

The cyclopropanation reaction of 3-diazooxindoles with arenes was first accomplished using visible-light irradiation. A series of spiro[norcaradiene-7,3'-indolin]-2'-ones were synthesized for the first time in high yields and with excellent diastereoselectivities. The synthetic usefulness of this catalyst-free photochemical methodology is illustrated by the further controllable rearrangement and epoxidation reactions.

A three-component [3 + 2]-cycloaddition/elimination cascade for the synthesis of spirooxindole-pyrrolizines

A three-component synthesis of novel spirooxindole-tetrahydropyrrolizines from secondary α-aminoacids, isatins and vinyl selenones has been disclosed. Products were formed in good yields and high diastereoselectivity by 1,3-dipolar cycloaddition of in situ generated azomethine ylides followed by spontaneous elimination of benzeneseleninic acid. Good regioselectivities with aryl substituted vinyl selenones were observed. The method showed good functional group tolerance, providing a direct approach to biologically relevant spirooxindoles under mild reaction conditions.

Diastereoselective trans Cyclopropanation of 3-Alkylidene Oxindoles with In Situ Generated α-Diazo Carbonyls or α,β-Unsaturated Diazo Compounds

An efficient diastereoselective trans cyclopropanation of 3-alkylidene oxindoles with in situ generated α-diazo carbonyl compounds or α,β-unsaturated diazo compounds under metal-free conditions has been developed to synthesize 3-spirocyclopropyl-2-oxindole derivatives. The procedure is based on the 1,3-dipolar character of the corresponding diazo compounds under base-catalyzed conditions. The method has a wide substrate scope and uses easily available starting materials.

Design and characterization of novel dirhodium coordination polymers – the impact of ligand size on selectivity in asymmetric cyclopropanation

Novel dirhodium coordination polymers are synthesized and characterized by various spectroscopic techniques. The catalysts exhibit good stability and excellent catalytic performance and selectivity in the cyclopropanation of diazooxindoles.

Stereoselective synthesis and applications of spirocyclic oxindoles

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

Synthesis of Spiro 3,3'-Cyclopropyl Oxindoles Via N-Bromosuccinimide-Mediated Ring-Closing and Contraction Cascade

An N-bromosuccinimide-mediated cascade reaction involving the cyclization/oxygen-migration/ring-contraction process of 3-(β, β-diaryl) indolylethanol was disclosed. A variety of spiro 3,3'-cyclopropyl oxindole derivatives were efficiently synthesized in good yields under mild reaction conditions. A possible mechanism was suggested based on intermediate isolation and computational studies.

High pressure assisted synthetic approach for novel 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine and 5,6-dihydrobenzo[h]quinoline derivatives and their assessment as anticancer agents

A novel, expedient and effective methodology for the synthesis of distinctly substituted 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine and 5,6-dihydrobenzo[h]quinoline systems has been developed with a new synthetic platform. This process includes ammonium acetate-mediated cyclocondensation reactions of 3-oxo-2-arylhydrazonopropanals with benzosuberone and tetralone precursors, respectively, using the high-pressure Q-tube reactor, which has been found to be superior to both conventional heating and microwave irradiation. The novel protocol benefits from its high atom efficiency, economy, ease of workup, broad substrate scope and is also applicable to gram-scale synthesis. To identify and confirm the newly synthesized targeted compounds, the X-ray single-crystal as well as all possible spectroscopic methods were utilized. The cytotoxicity of the newly synthesized 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine 4a-j and 5,6-dihydrobenzo-[h]quinolines derivatives 6a-e were preliminary examined toward three cell lines of human cancer; lung cancer (A549), breast cancer (MCF-7) and colon cancer (HCT-116), by applying the MTT colorimetric assay. The achieved results reflected the promising profile of the prepared compounds in this study against cancer cells and have shown that members from the synthesized 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine 4a-j exhibited promising cytotoxicity's against MCF-7, and A549 cancer cells respectively, while the HCT-116 (colon) cancer cells were inhibited by certain examples of 5,6-dihydrobenzo[h]quinoline derivatives 6c,d. These promising results could serve as a good primary base for further research into the design of anticancer drugs.

Dirhodium Coordination Polymers for Asymmetric Cyclopropanation of Diazooxindoles with Olefins: Synthesis and Spectroscopic Analysis

A facile approach is reported for the preparation of dirhodium coordination polymers [Rh₂ (L1)₂ ]_n (Rh₂ -L1) and [Rh₂ (L2)₂ ]_n (Rh₂ -L2; L1=N,N'-(pyromellitoyl)-bis-L-phenylalanine diacid anion, L2=bis-N,N'-(L-phenylalanyl) naphthalene-1,4,5,8-tetracarboxylate diimide) from chiral dicarboxylic acids by ligand exchange. Multiple techniques including FTIR, XPS, and ¹ H→¹³ C CP MAS NMR spectroscopy reveal the formation of the coordination polymers. ¹⁹ F MAS NMR was utilized to investigate the remaining TFA groups in the obtained coordination polymers, and demonstrated near-quantitative ligand exchange. DR-UV-vis and XPS confirm the oxidation state of the Rh center and that the Rh-single bond in the dirhodium node is maintained in the synthesis of Rh₂ -L1 and Rh₂ -L2. Both coordination polymers exhibit excellent catalytic performance in the asymmetric cyclopropanation reaction between styrene and diazooxindole. The catalysts can be easily recycled and reused without significant reduction in their catalytic efficiency.

The first Q-Tube based high-pressure synthesis of anti-cancer active thiazolo[4,5-c]pyridazines via the [4 + 2] cyclocondensation of 3-oxo-2-arylhydrazonopropanals with 4-thiazolidinones

A novel and efficient protocol for the synthesis of thiazolo[4,5-c]pyridazine derivatives was developed. The approach utilizes a high pressure Q-Tube reactor to promote cyclocondensation reactions between 3-oxo-2-arylhydrazonopropanals and 4-thiazolidinones. The process has a significantly high atom economy and a broad substrate scope, as well as being applicable to gram scale syntheses. The in vitro cytotoxic activities of the synthesized thiazolo[4,5-c]pyridazine derivatives were examined utilizing a MTT colorimetric assay with doxorubicin as a reference anti-cancer drug and three human cancer cell lines including HCT-116 (colon), MCF-7 (breast) and A549 (lung). The results show that thiazolopyridazines 7c, h, k and p have high cytotoxic activity against the MCF-7 cell line with respective IC50 values of 14.34, 10.39, 15.43 and 13.60 μM. Moreover, the thiazolopyridazine derivative 7s also show promising cytotoxic activity against the HCT-116 cell line with IC50 = 6.90 μM . Observations made in this effort serve as a basis for further investigations into the design and preparation of new anti-cancer drugs.

Organoselenium and organotellurium compounds containing chalcogen-oxygen bonds in organic synthesis or related processes

This chapter emphasizes aspects related to the role of organochalcogen (Se, Te) compounds with single E‒O and/or double E=O (E=Se, Te) bonds in organic synthesis, as reagents, intermediates, or catalysts, and it gives a larger extent mainly to data reported in the field during the last ten years. For each of these two heavier chalcogens the material is structured according to the oxidation state of the chalcogen and, for the same oxidation state, in sections dedicated to a particular type of compounds. Functionalization or cyclization reactions in which the organochalcogen compounds take part as nucleophiles, electrophiles or radicals, employed in various synthetic transformations, are discussed and, where available, the mechanistic aspects are outlined. New chiral species and new strategies were developed during last years in order to increase the yield, the reaction rate and the stereoselectivity in specific organic transformations, i.e. addition, oxidation, elimination, cyclization or rearrangement reactions. A notably attention was devoted to easily accessible and environmental friendly catalysts, re-usable and “green” solvents, as well as waste-free procedures.

Novel natural non-nucleoside inhibitors of HIV-1 reverse transcriptase identified by shape- and structure-based virtual screening techniques

In this work we report a parallel application of both docking- and shape-based virtual screening (VS) methods, followed by Molecular Dynamics simulations (MDs), for discovering new compounds able to inhibit the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) RNA-dependent DNA polymerase activity. Specifically, we screened more than 143000 natural compounds commercially available in the ZINC database against the best five RT crystallographic models, taking into account the five approved NNRTIs as query compounds. As a result, 20 hit molecules were selected and tested on biochemical assays for the inhibition of the RNA dependent DNA polymerase RT function and, among them, an indoline pyrrolidine (hit1), an indonyl piperazine (hit2) and an indolyl indolinone (hit3) derivatives were identified as novel non-nucleoside RT inhibitors in the low micromolar range.

Highly stereoselective spirocyclopropanation of various diazooxindoles with olefins catalyzed using Ru(ii)-complex

Optically active spirocyclopropyloxindole derivatives were efficiently synthesized from diazooxindoles and olefins in the presence of a Ru(ii)-Pheox catalyst. Among a series of Ru(ii)-Pheox catalysts, Ru(ii)-Pheox 6e was determined to be the best catalyst for spirocyclopropanation reactions of diazooxindoles with various olefins in high yields (up to 98%) with high diastereoselectivities (up to trans:cis = >99:1<) and enantioselectivities (up to 99% ee). Furthermore, as the first catalytic asymmetric synthesis, anti-HIV active candidate 4a and a bioactive compound of AMPK modulator 4c were easily synthesized from the corresponding diazooxindoles 1i and 1b, respectively, in high yields with high enantioselectivities (4a: 82% yield, 95% ee, 4b: 99% yield, 93% ee).

Optically active spirocyclopropyloxindole derivatives were efficiently synthesized from diazooxindoles and olefins in the presence of a Ru(ii)-Pheox catalyst.

Probing Mercaptobenzamides as HIV Inactivators via Nucleocapsid Protein 7

Human immunodeficiency virus type 1 (HIV-1) nucleocapsid protein 7 (NCp7), a zinc finger protein, plays critical roles in viral replication and maturation and is an attractive target for drug development. However, the development of drug-like molecules that inhibit NCp7 has been a significant challenge. In this study, a series of novel 2-mercaptobenzamide prodrugs were investigated for anti-HIV activity in the context of NCp7 inactivation. The molecules were synthesized from the corresponding thiosalicylic acids, and they are all crystalline solids and stable at room temperature. Derivatives with a range of amide side chains and aromatic substituents were synthesized and screened for anti-HIV activity. Wide ranges of antiviral activity were observed, with IC₅₀ values ranging from 1 to 100 μm depending on subtle changes to the substituents on the aromatic ring and side chain. Results from these structure-activity relationships were fit to a probable mode of intracellular activation and interaction with NCp7 to explain variations in antiviral activity. Our strategy to make a series of mercaptobenzamide prodrugs represents a general new direction to make libraries that can be screened for anti-HIV activity.

Direct Construction of 2,3-Dihydroxy-2,3-diaryltetrahydrofurans via N-Heterocyclic Carbene/Base-Mediated Domino Reactions of Aromatic Aldehydes and Vinyl Selenone

A one-pot, stereoselective construction of 2,3-dihydroxy-2,3-diaryltetrahydrofurans has been achieved via N-heterocyclic carbene (NHC)/base-mediated domino reactions of aldehydes and vinyl selenone. The products containing two contiguous quaternary hydroxyl functionalities among the three stereocenters are obtained advantageously as either acetals or ketals through the formation of five new chemical bonds in a single operation. This report constitutes an altogether different reactivity of vinyl selenone in comparison with the corresponding sulfones and phosphonates under NHC/base-mediated reactions.

Organoiodine reagent-promoted intermolecular oxidative amination: synthesis of cyclopropyl spirooxindoles

An organoiodine-promoted intramolecular direct oxidative C(sp²)–N cross-coupling reaction was developed for the preparation of cyclopropyl spirooxindoles from readily available secondary cyclopropyl carboxamides.

Zinc triflate-mediated cyclopropanation of oxindoles with vinyl diphenyl sulfonium triflate: a mild reaction with broad functional group compatibility

The first use of Zn(OTf)₂ for the cyclopropanation of unprotected oxindoles with vinyl diphenyl sulfonium triflate to show high regioselectivity.

Enantioselective Synthesis of Quaternary α-Amino Acids Enabled by the Versatility of the Phenylselenonyl Group

A novel Cinchona alkaloid-catalyzed enantioselective conjugate addition of α-alkyl substituted α-nitroacetates to phenyl vinyl selenone was developed. The resulting enantio-enriched α,α-dialkyl substituted α-nitroacetates were subsequently converted to various cyclic and acyclic quaternary α-amino acids, taking advantage of the rich functionalities of the resulting Michael adducts. Novel protocols allowing chemoselective reduction of phenyl selenone to phenyl selenide and reduction of alkyl phenyl selenones to alkanes are also reported.

Water and Aqueous Mixtures as Convenient Alternative Media for Organoselenium Chemistry

Even if water is the natural environment for bioorganic reactions, its use in organic chemistry is often severely limited by the high insolubility of the organic derivatives. In this review, we introduce some examples of the use of water to perform organoselenium chemistry. We mainly discuss the advantages of this medium when the recyclability is demonstrated and when the water can control the selectivity of a reaction or enhance the reaction rate.

Highly enantioselective synthesis of spirocyclopropyloxindoles via a Rh(ii)-catalyzed asymmetric cyclopropanation reaction

An asymmetric cyclopropanation reaction of N-Boc diazooxindoles is described with good to excellent enantioselectivities, especially with alkyl alkenes (>90% ee).

A catalyst-free, one-pot multicomponent synthesis of spiro-benzimidazoquinazolinones via a Knoevenagel–Michael-imine pathway: a microwave assisted approach

A multi-component route for the synthesis of spiro-benzimidazoquinazolinones was developed and its mechanism was studied.