Site‐Selective Rhodium(III)‐Catalyzed C−H Amination of 7‐Azaindoles with Anthranils: Synthesis and Anticancer Evaluation

Advances in transition metal-catalyzed C-H amination strategies using anthranils

Modern times have witnessed an uprise in the synthesis and derivatization of nitrogen-containing fused heterocycles. Amination reactions involving nitrene chemistry have always been the most convenient choice for the incorporation of a nitrogen atom in a molecule. The utilization of an open nitrene species harnesses harsh conditions. Hence, transition metal-catalyzed C-H amination reactions using aminating agents have been an attractive choice. Electrophilic aminating agents for C-H amination reactions are well exploited due to their desirable reaction conditions. Out of all, anthranils have paved the way forward due to their utility in simultaneously forming two new functional groups (amine and carbonyl). Amination using anthranils follows a metal-nitrenoid pathway. Often, the amination has been followed by a Lewis acid or transition metal-mediated intramolecular cyclization to directly produce fused heterocycles. This review broadly demonstrates the utilization of anthranils as an aminating agent for transition metal-catalyzed C-H amination reactions. The focus has been given to the scope, limitations, and mechanistic understanding of using such an electrophilic aminating agent, anthranil, with transition metals.

TBAI-Catalysed Formal [4+4]-Cycloaddition: Easy Access to Oxa-Bridged Eight-Membered Heterocycles

TBAI-catalysed [4+4]-cyclization reaction of anthranils with hydrazones to deliver oxa-bridged eight-membered heterocycles in accepted yields was developed. Preliminary mechanistic studies indicated that the reaction involved the in situ generation of vinyldiazenes from readily available hydrazones followed by an aza-Michael addition of the anthranil substrates onto the vinyldiazenes and subsequent annulation. This transformation involved the formation of two new C-N bonds and C-O bond in one pot, overcoming the synthetic limitations of anthranils in organic chemistry. This strategy benefits from high efficiency and atomic economy with mild reaction conditions.

Synthesis of Succinimide-Linked Indazol-3-ols Derived from Maleimides under Rh(III) Catalysis

The structural modification of N-aryl indazolols as tautomers of N-aryl indazolones has been established as a hot topic in pharmaceutics and medicinal chemistry. We herein disclose the rhodium(III)-catalyzed 1,4-addition reaction of maleimides with N-aryl indazol-3-ols, which provides the succinimide-bearing indazol-3-ol scaffolds with complete regioselectivity and a good functional group tolerance. Notably, the versatility of this protocol is demonstrated by the use of drug-molecule-linked and fluorescence-probe-linked maleimides.

N-Aroyloxycarbamates as switchable nitrogen and oxygen precursor: Ir/Cu controlled divergent C–H functionalization of heteroarenes

Chemodivergent control in the functionalization of nitrogen-directed aromatic C–H bonds has been achieved by a switchable catalyst.

Cu(II)-Catalyzed C-N, C-O, C-Cl, C-S, and C-Se Bond Formation via C(sp2)-H Activation Using 7-Azaindole as an Intrinsic Directing Group

A general protocol has been developed for the construction of carbon-heteroatom (C-N, C-Cl, C-O, C-S, and C-Se) bonds using the bench stable, earth-abundant, and environmentally benign copper catalyst. Only oxygen is sufficient to regenerate the copper catalyst. Control experiments suggested that the proto-demetalation step is reversible. Depending on the coupling partner, the reaction follows either disproportionation or radical pathways to complete the catalytic cycle. The synthetic utility of the developed protocol has been demonstrated via various functional group transformations.

Cp*Co(III)-catalyzed C-H amination/annulation cascade of sulfoxonium ylides with anthranils for the synthesis of indoloindolones

Cp*Co(iii)-catalyzed [4+1] annulation of sulfoxonium ylides with anthranils has been developed for the synthesis of indole-indolone scaffolds. The dual functionality of anthranils was exploited, wherein the nitrogen has been used for C-H amination and the aldehyde group was utilized in the subsequent intramolecular aldol condensation to furnish the corresponding annulated products.

TfOH-Promoted Decyanative Cyclization toward the Synthesis of 2,1-Benzisoxazoles

A novel solvent-free, TfOH-promoted decyanative cyclization approach for the synthesis of 2,1-benzisoxazoles has been developed. The reactions are complete instantly at room temperature and result in the formation of the desired 2,1-benzisoxazoles in a 34-97% isolated yield.

Straightforward Construction and Functionalizations of Nitrogen-Containing Heterocycles Through Migratory Insertion of Metal-Carbenes/Nitrenes

Nitrogen-containing heterocycles are widely found in various biologically active substrates, pharmaceuticals, natural products and organic materials. Consequently, the continuous effort has been devoted towards the development of straightforward, economical, environmentally acceptable, efficient and ingenious methods for the synthesis of various N-containing heterocycles and their functionalizations. Arguably, one of the most prominent direct strategy is regioselective C-H bond functionalizations which provide the step and atom economical approaches in the presence of suitable coupling partners. In this context, site-selective migratory insertion of metal carbenes/nitrenes to the desired C-H bonds has proven as a useful tool to access various functionalized nitrogen heterocycles. In this personal account, we highlight some of our contemporary development toward constructing N-containing heterocycles and their direct functionalizations via transition metal catalysed C-H bond functionalizations based on migratory insertion of metal-carbenes and nitrenes.

Copper-catalyzed ortho-selective direct sulfenylation of N-aryl-7-azaindoles with disulfides

A copper-catalyzed direct C-H chalcogenation of N-aryl-azaindoles with disulfides is described. This transformation was performed using Earth abundant Cu(OAc)₂ as a catalyst, benzoic acid as an additive, air as a terminal oxidant, and readily available diaryl and dialkyldisulfides (or diselenide) as chalcogenation reagents. High functional group tolerance and excellent regioselectivity are demonstrated by the efficient preparation of a wide range of ortho-sulfenylation-7-azaindoles.

Preparation of anthranils via chemoselective oxidative radical cyclization of 3-(2-azidoaryl) substituted propargyl alcohols

In the presence of K₂S₂O₈ and HOAc, 3-(2-azidoaryl) substituted propargyl alcohols can go through chemoselective oxidative radical cyclizations to give a pool of anthranils based on Meyer-Schuster rearrangement. It's proposed that the cyclizations were triggered exclusively by the direct attack of oxygen radicals on the azides. The weak N-O bonds in anthranils could be easily cleaved in the presence of transition metal catalysts and went through aminations with 2-oxo-2-phenylacetic acid and iodobenzene.

Biological Evaluation of Oxindole Derivative as a Novel Anticancer Agent against Human Kidney Carcinoma Cells

Renal cell carcinoma has emerged as one of the leading causes of cancer-related deaths in the USA. Here, we examined the anticancer profile of oxindole derivatives (SH-859) in human renal cancer cells. Targeting 786-O cells by SH-859 inhibited cell growth and affected the protein kinase B/mechanistic target of rapamycin 1 pathway, which in turn downregulated the expression of glycolytic enzymes, including lactate dehydrogenase A and glucose transporter-1, as well as other signaling proteins. Treatment with SH-859 altered glycolysis, mitochondrial function, and levels of adenosine triphosphate and cellular metabolites. Flow cytometry revealed the induction of apoptosis and G0/G1 cell cycle arrest in renal cancer cells following SH-859 treatment. Induction of autophagy was also confirmed after SH-859 treatment by acridine orange and monodansylcadaverine staining, immunocytochemistry, and Western blot analyses. Finally, SH-859 also inhibited the tumor development in a xenograft model. Thus, SH-859 can serve as a potential molecule for the treatment of human renal carcinoma.

Pd-Catalyzed C-H Halogenation of Indolines and Tetrahydroquinolines with Removable Directing Group

Pd-catalyzed directing-group-assisted regioselective halogenations to C7 of indolines and C8 of tetrahydroquinolines were achieved in good to excellent yields. The practicality and utility of the developed method have been illustrated by various functional group transformations such as arylation, alkenylation, cyanation, and silylation utilizing the installed synthetic handle. The concise synthesis of primaquine, an antimalarial drug, and formal syntheses of two bioactive natural products, hippadine and pratosine, have also been demonstrated.

Copper-catalyzed ortho-C(sp2)-H amination of benzamides and picolinamides with alkylamines using oxygen as a green oxidant

A versatile Cu-catalyzed direct ortho-C(sp2)-H amination of benzamides and picolinamides with alkylamines has been achieved. This method employs cheap and eco-friendly copper as a catalyst and oxygen as an oxidant, and also has the advantages of straightforward steps and excellent functional group compatibility. Further application of our approach was demonstrated by the synthesis of TCMDC-125116, SPHINX, and SRPIN340.

Phthalazinone-Assisted C-H Amidation Using Dioxazolones Under Rh(III) Catalysis

The preparation of phthalazinone derivatives is pivotal for their utilization as pharmaceutical agents and other entities. Herein, we report the phthalazinone-assisted carbon-nitrogen bond forming reaction using dioxazolones as robust amidation sources under Rh(III) catalysis. The broad functional group tolerance and complete site-selectivity are observed. Notably, a series of transformations of synthesized compounds into biologically relevant N-heterocycles demonstrates the applicability of the developed methodology.

Rh(iii)-Catalyzed tandem indole C4-arylamination/annulation with anthranils: access to indoloquinolines and their application in photophysical studies

An efficient Rh(iii)-catalyzed straightforward strategy was developed for the site-selective tandem C4 arylamination/annulation of indole derivatives with anthranil to provide indoloquinoline moieties.

Anthranils: versatile building blocks in the construction of C–N bonds and N-heterocycles

This review article provides an overview of the recent progress in the transformations of anthranils, which have emerged as versatile building blocks in the assembly of various C–N bonds and medicinally active heterocyclic systems.

Rhodium-Catalyzed Annulative Coupling of Isothiazoles with Alkynes through N-S Bond Cleavage

A Rh(III)-catalyzed annulative coupling of 3,5-diarylisothiazoles and alkynes is reported. The N-S bond in the isothiazole ring acts as an internal oxidant to regenerate the Rh(III) species in combination with an external Cu(II) oxidant, and the corresponding 1:2 coupling products are obtained. The remarkable difference in the reaction outcome between isothiazoles and the relevant isoxazoles has been investigated by DFT calculations, revealing that the relative stability of the enolate intermediates dictates the product selectivity.

Practical Synthesis of Benzimidazo[1,2-a]quinolines via Rh(III)-Catalyzed C-H Activation Cascade Reaction from Imidamides and Anthranils

We report a novel and practical one-pot Rh(III)-catalyzed strategy to construct benzimidazo[1,2-a]quinolines from readily available imidamides and anthranils. The cascade reaction proceeds via a C-H amination-cyclization-cyclization process in ionic liquid without any additives and possesses simple operation, moderate-to-high yield, and broad substrate scope features, which will provide the reference for the construction of biologically active fused benzimidazoles.

Cu(II)-Mediated Cross-Dehydrogenative Coupling of Indolines with Sulfonamides, Carboxamides, and Amines

A facile and efficient Cu-mediated protocol for the cross-dehydrogenative coupling of indoline with sulfonamides, carboxamides, and anilines is reported. The reaction takes place through Cu-mediated C7-H activation via a 6-membered metallacycle to afford the amide and amine derivatives in good yields with a wide range of functional group tolerance. The importance of the protocol has been demonstrated by synthesizing the antiproliferative agent, ER-67836.

Therapeutic value of steroidal alkaloids in cancer: Current trends and future perspectives

Discovery and development of new potentially selective anticancer agents are necessary to prevent a global cancer health crisis. Currently, alternative medicinal agents derived from plants have been extensively investigated to develop anticancer drugs with fewer adverse effects. Among them, steroidal alkaloids are conventional secondary metabolites that comprise an important class of natural products found in plants, marine organisms and invertebrates, and constitute a judicious choice as potential anti-cancer leads. Traditional medicine and modern science have shown that representatives from this compound group possess potential antimicrobial, analgesic, anticancer and anti-inflammatory effects. Therefore, systematic and recapitulated information about the bioactivity of these compounds, with special emphasis on the molecular or cellular mechanisms, is of high interest. In this review, we methodically discuss the in vitro and in vivo potential of the anticancer activity of natural steroidal alkaloids and their synthetic and semi-synthetic derivatives. This review focuses on cumulative and comprehensive molecular mechanisms, which will help researchers understand the molecular pathways involving steroid alkaloids to generate a selective and safe new lead compound with improved therapeutic applications for cancer prevention and therapy. In vitro and in vivo studies provide evidence about the promising therapeutic potential of steroidal alkaloids in various cancer cell lines, but advanced pharmacokinetic and clinical experiments are required to develop more selective and safe drugs for cancer treatment.

Design and synthesis of new ruthenium polypyridyl complexes with potent antitumor activity in vitro

We herein report the synthesis, characterization and anticancer activity of BTPIP (2-(4-(benzo[b]thiophen-2-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline) and its four ruthenium(II) polypyridyl complexes [Ru(NN)₂(BTPIP)](ClO₄)₂ (N-N = bpy = 2,2'-bipyridine, Ru(II)-1; phen = 1,10-phenanthroline, Ru(II)-2; dmb = 4,4'-dimethyl-2,2'-bipyridine, Ru(II)-3; dmp = 2,9-dimethyl-1,10-phenanthroline, Ru(II)-4). The DNA binding behaviors reveal that the complexes bind to calf thymus DNA by intercalation. Cytotoxicity of the complexes against A549, HepG-2, SGC-7901 and Hela cells were evaluated in vitro. Complexes Ru(II)-1, Ru(II)-2, Ru(II)-3, Ru(II)-4 show moderate activity on the cell proliferation in A549 cells with IC₅₀ values of 9.3 ± 1.2, 12.1 ± 1.6, 10.3 ± 1.6, 8.9 ± 1.2 μM, respectively. Apoptosis assessment, intracellular mitochondrial membrane potential (MMP), location in mitochondria, reactive oxygen species (ROS), cell invasion assay and cell cycle arrest were also performed to explore the mechanism of this action. When the concentration of the ruthenium(II) complexes is increased, the amount of reactive oxygen species increases obviously and the mitochondrial membrane potential decreases dramatically in A549 cells. Most importantly, the ruthenium(II) polypyridyl complexes could arrive the cytoplasm through the cell membrane and accumulate in the mitochondria. These results showed that the ruthenium(II) complexes could induce apoptosis in A549 cells through an ROS-mediated mitochondrial dysfunction pathway.

Rh(III)-Catalyzed Sequential C-H Amination/Annulation Cascade Reactions: Synthesis of Multisubstituted Benzimidazoles

An efficient and practical method to construct benzimidazoles via Rh(III)-catalyzed sequential C-H amination and annulation cascade reaction has been developed. The cascade reaction displays high step, atom, and redox economy, is compatible with the air, and has good functional group tolerance and high efficiency. The titled products can be easily further converted into imidazo[4,5-c]acridines, which were observed unique fluorescent properties.

Site-selective C(sp3)–H amination of thioamide with anthranils under Cp*CoIII catalysis

Synthetically versatile anthranils as a bifunctional amino source have been employed for the first time to enable direct amination on unactivated C(sp³)–H bonds of thioamides under Cp*Co^III catalysis.

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation. In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate. Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it. Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure. The schemes feature typical substrates used, the products obtained as well as the required reaction conditions. Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness. The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them. Accordingly, this review should be of particular interest also for scientists from industrial R&D sector. Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date.

Dual Role of Anthranils as Amination and Transient Directing Group Sources: Synthesis of 2-Acyl Acridines

The transient directing group promoted C(sp2)-H functionalization of benzaldehydes with anthranils by a cationic rhodium(III) catalyst is described. Notably, anthranils have been used as both transient directing groups and amination sources to afford 2-acyl acridines through direct C-H amination followed by acid-mediated cyclization. A range of substrate scopes and functional group tolerance were observed.