Indazole derivatives and their therapeutic applications: a patent review (2013-2017)

Design of Promising Thiazoloindazole-Based Acetylcholinesterase Inhibitors Guided by Molecular Docking and Experimental Insights

Alzheimer's disease is characterized by a progressive deterioration of cognitive function and memory loss, and it is closely associated with the dysregulation of cholinergic neurotransmission. Since acetylcholinesterase (AChE) is a critical enzyme in the nervous system, responsible for breaking down the neurotransmitter acetylcholine, its inhibition holds a significant interest in the treatment of various neurological disorders. Therefore, it is crucial to develop efficient AChE inhibitors capable of increasing acetylcholine levels, ultimately leading to improved cholinergic neurotransmission. The results reported here represent a step forward in the development of novel thiazoloindazole-based compounds that have the potential to serve as effective AChE inhibitors. Molecular docking studies revealed that certain of the evaluated nitroindazole-based compounds outperformed donepezil, a well-known AChE inhibitor used in Alzheimer's disease treatment. Sustained by these findings, two series of compounds were synthesized. One series included a triazole moiety (Tl45a-c), while the other incorporated a carbazole moiety (Tl58a-c). These compounds were isolated in yields ranging from 66 to 87% through nucleophilic substitution and Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) reactions. Among the synthesized compounds, the thiazoloindazole-based 6b core derivatives emerged as selective AChE inhibitors, exhibiting remarkable IC50 values of less than 1.0 μM. Notably, derivative Tl45b displays superior performance as an AChE inhibitor, boasting the lowest IC50 (0.071 ± 0.014 μM). Structure-activity relationship (SAR) analysis indicated that derivatives containing the bis(trifluoromethyl)phenyl-triazolyl group demonstrated the most promising activity against AChE, when compared to more rigid substituents such as carbazolyl moiety. The combination of molecular docking and experimental synthesis provides a suitable and promising strategy for the development of new efficient thiazoloindazole-based AChE inhibitors.

A comprehensive review on phosphatidylinositol-3-kinase (PI3K) and its inhibitors bearing pyrazole or indazole core for cancer therapy

Cancer is a complex and multifaceted group of diseases with a high mortality rate characterized by uncontrolled proliferation of abnormal cells. Dysregulation of normal signalling pathways in cancer contributes to the different hallmarks of this disease. The signalling pathway of which phosphatidylinositol 3-kinase (PI3K) is a part is not an exception. In fact, dysregulated activation of PI3K signalling pathways can result in unbridled cellular proliferation and enhanced cell survival, thereby fostering the onset and advancement of cancer. Therefore, there is substantial interest in developing targeted therapies specifically aimed at inhibiting the PI3K enzyme and its associated pathways. Also, the therapeutic interest on pyrazoles and indazoles has been growing due to their various medicinal properties, namely, anticancer activity. Derivatives of these compounds have been studied as PI3K inhibitors, and they showed promising results. There are already some PI3K inhibitors approved by Food and Drug Administration (FDA), such as Idelalisib (Zydelig®) and Alpelisib (Piqray®). In this context, this review aims to address the importance of PI3K in cellular processes and its role in cancer. Additionally, it aims to report a comprehensive literature review of PI3K inhibitors, containing the pyrazole and indazole scaffolds, published in the last fifteen years, focusing on structure-activity relationship aspects, thus providing important insights for the design of novel and more effective PI3K inhibitors.

Catalyst-free photoarylation of 2-aryl-2H-indazoles by carbon-iodine bond activation

A photocatalyst-free visible-light induced arylation of 2-aryl-2H-indazoles with aryl iodides has been developed for the first time to produce 3,2-diaryl-2H-indazoles in good to moderate yields. In this transformation, potassium tert-butoxide acts as an activator of the C-I bond and also as a scavenger of in situ generated HI in the reaction. This method exhibits high functional group tolerance with a wide substrate scope and it has been successfully applied to the synthesis of liver X receptor agonists and also for fluorescent probes. This is the first report on the photoarylation of 2-arylindazoles at the C3-position with aryl iodides under catalyst-free conditions.

A review of poly(ADP-ribose)polymerase-1 (PARP1) role and its inhibitors bearing pyrazole or indazole core for cancer therapy

Cancer is a disease with a high mortality rate characterized by uncontrolled proliferation of abnormal cells. The hallmarks of cancer evidence the acquired cells characteristics that promote the growth of malignant tumours, including genomic instability and mutations, the ability to evade cellular death and the capacity of sustaining proliferative signalization. Poly(ADP-ribose) polymerase-1 (PARP1) is a protein that plays key roles in cellular regulation, namely in DNA damage repair and cell survival. The inhibition of PARP1 promotes cellular death in cells with homologous recombination deficiency, and therefore, the interest in PARP protein has been rising as a target for anticancer therapies. There are already some PARP1 inhibitors approved by Food and Drug Administration (FDA), such as Olaparib and Niraparib. The last compound presents in its structure an indazole core. In fact, pyrazoles and indazoles have been raising interest due to their various medicinal properties, namely, anticancer activity. Derivatives of these compounds have been studied as inhibitors of PARP1 and presented promising results. Therefore, this review aims to address the importance of PARP1 in cell regulation and its role in cancer. Moreover, it intends to report a comprehensive literature review of PARP1 inhibitors, containing the pyrazole and indazole scaffolds, published in the last fifteen years, focusing on structure-activity relationship aspects, thus providing important insights for the design of novel and more effective PARP1 inhibitors.

Design, synthesis, and pharmacological evaluation of indazole carboxamides of N-substituted pyrrole derivatives as soybean lipoxygenase inhibitors

In this paper, we attempted to develop a novel class of compounds against lipoxygenase, a key enzyme in the biosynthesis of leukotrienes implicated in a series of inflammatory diseases. Given the absence of appropriate human 5-lipoxygenase crystallographic data, solved soybean lipoxygenase-1 and -3 structures were used as a template to generate an accurate pharmacophore model which was further used for virtual screening purposes. Eight compounds (1-8) have been derived from the in-house library consisting of N-substituted pyrroles conjugated with 5- or 6-indazole moieties through a carboxamide linker. This study led to the discovery of hit molecule 8 bearing a naphthyl group with the IC50 value of 22 μM according to soybean lipoxygenase in vitro assay. Isosteric replacement of naphthyl ring with quinoline moieties and reduction of carbonyl carboxamide group resulted in compounds 9-12 and 13, respectively. Compound 12 demonstrated the most promising enzyme inhibition. In addition, compounds 8 and 12 were found to reduce the carrageenan-induced paw edema in vivo by 52.6 and 49.8%, respectively. In view of the encouraging outcomes concerning their notable in vitro and in vivo anti-inflammatory activities, compounds 8 and 12 could be further optimized for the discovery of novel 5-lipoxygenase inhibitors in future. A structure-based 3D pharmacophore model was used in the virtual screening of in-house library to discover novel potential 5-lipoxygenase inhibitors.

LiOtBu-Promoted Intramolecular 1,3-Dipolar Cycloaddition of the 2'-Alkynyl-biaryl-2-aldehyde N-Tosylhydrazones Approach to 3-Substituted 1H-Dibenzo[e,g]indazoles

A two-step, one-pot synthesis of 3-substituted 1H-dibenzo[e,g]indazoles in good to high yields via a LiOtBu-promoted intramolecular 1,3-dipolar cyclization of 2'-alkynyl-biaryl-2-aldehyde N-tosylhydrazones was developed. The N-Ts-hydrazones used were prepared in situ via the reactions of 2'-alkynyl-biaryl-2-aldehydes and TsNHNH2(p-methylbenzenesulfonohydrazide). Two types of signals related to the hydrogen bonds, forming in several products, were observed in the 1H NMR spectra recorded in DMSO-d6, assigned to N-H bonds in their dimeric species of product and tautomer.

Research and development of N,N'-diarylureas as anti-tumor agents

Tumor neovascularization provides abundant nutrients for the occurrence and development of tumors, and is also an important factor in tumor invasion and metastasis, which has attracted extensive attention in anti-tumor therapy. Sorafenib is a clinically approved multi-targeted anti-tumor drug that targets vascular endothelial growth factor receptor (VEGFR) and inhibits the formation of tumor angiogenesis, thereby achieving the purpose of suppressing tumor growth. Since the approval of sorafenib, N,N'-diarylureas have received extensive attention as the key pharmacophore in its chemical structure. And a series of N,N'-diarylureas were designed and synthesized to screen a new generation of anti-tumor drug candidates through chemical modification and structural optimization. Moreover, the rational design of targeted drugs is beneficial to reduce toxic side effects and drug resistance and improve the curative effect. Here, this article reviews the research progress in the design, classification, structure-activity relationship (SAR) and biological activity of N,N'-diarylureas, in order to provide some prospective routes for the development of clinically effective anti-tumor drugs.

Copper-Catalyzed Hydroamination: Enantioselective Addition of Pyrazoles to Cyclopropenes

Chiral N-cyclopropyl pyrazoles and structurally related heterocycles are prepared using an earth-abundant copper catalyst under mild reaction conditions with high regio-, diastereo-, and enantiocontrol. The observed N2:N1 regioselectivity favors the more hindered nitrogen of the pyrazole. Experimental and DFT studies support a unique mechanism that features a five-centered aminocupration.

Green Synthesis of Aromatic Nitrogen-Containing Heterocycles by Catalytic and Non-Traditional Activation Methods

Recent advances in the environmentally benign synthesis of aromatic N-heterocycles are reviewed, focusing primarily on the application of catalytic methods and non-traditional activation. This account features two main parts: the preparation of single ring N-heterocycles, and their condensed analogs. Both groups include compounds with one, two and more N-atoms. Due to the large number of protocols, this account focuses on providing representative examples to feature the available methods.

Design, Synthesis and Antitumor Activity of 1H-indazole-3-amine Derivatives

A series of indazole derivatives were designed and synthesized by molecular hybridization strategy, and these compounds were evaluated the inhibitory activities against human cancer cell lines of lung (A549), chronic myeloid leukemia (K562), prostate (PC-3), and hepatoma (Hep-G2) by methyl thiazolyl tetrazolium (MTT) colorimetric assay. Among these, compound 6o exhibited a promising inhibitory effect against the K562 cell line with the IC₅₀ (50% inhibition concentration) value of 5.15 µM, and this compound showed great selectivity for normal cell (HEK-293, IC₅₀ = 33.2 µM). Moreover, compound 6o was confirmed to affect apoptosis and cell cycle possibly by inhibiting Bcl2 family members and the p53/MDM2 pathway in a concentration-dependent manner. Overall, this study indicates that compound 6o could be a promising scaffold to develop an effective and low-toxic anticancer agent.

New Indazol-Pyrimidine-Based Derivatives as Selective Anticancer Agents: Design, Synthesis, and In Silico Studies

In this research study, the authors successfully synthesized potent new anticancer agents derived from indazol-pyrimidine. All the prepared compounds were tested for in vitro cell line inhibitory activity against three different cancerous cell lines. Results demonstrated that five of the novel compounds-4f, 4i, 4a, 4g, and 4d-possessed significant cytotoxic inhibitory activity against the MCF-7 cell line, with IC₅₀ values of 1.629, 1.841, 2.958, 4.680, and 4.798 μM, respectively, compared to the reference drug with an IC₅₀ value of 8.029 μM, thus demonstrating promising suppression power. Compounds 4i, 4g, 4e, 4d, and 4a showed effective cytotoxic activity stronger than the standard against Caco2 cells. Moreover, compounds 4a and 4i exhibited potent antiproliferative activity against the A549 cell line that was stronger than the reference drug. The most active products, 4f and 4i, werr e further examined for their mechanism of action. It turns out that they were capable of activating caspase-3/7 and, therefore, inducing apoptosis. However, produced a higher safety profile than the reference drug, towards the normal cells (MCF10a). Furthermore, the dynamic nature, binding interaction, and protein-ligand stability were explored through a Molecular Dynamics (MD) simulation study. Various analysis parameters (RMSD, RMSF, RoG, and SASA) from the MD simulation trajectory have suggested the stability of the compounds during the 20 ns MD simulation study. In silico ADMET results revealed that the synthesized compounds had low toxicity, good solubility, and an absorption profile since they met Lipinski's rule of five and Veber's rule. The present research highlights the potential of derivatives with indazole scaffolds bearing pyrimidine as a lead compound for designing anticancer agents.

Rh(III)-Catalyzed C-H Functionalization/Annulation of 1-Arylindazolones: Divergent Synthesis of Fused Indazolones and Allyl Indazolones

Rh(III)-catalyzed C-H/N-H annulation and C-H allylation of phenylindazolones have been realized by employing 5-methylene-1,3-dioxan-2-one and 4-vinyl-1,3-dioxolan-2-one as scalable cross-coupling partners, delivering functionalized indazolone fused heterocycles and branched and linear allyl indazolones respectively in moderate to high yield. These divergent synthesis protocols showcase mild conditions, broad substrate scope, and high functional-group compatibility. In addition, scale-up synthesis and preliminary mechanistic exploratory were also accomplished.

Visible-light-induced cascade reaction: a sustainable approach towards molecular complexity

Photoredox catalysis has demonstrated rapid evolution in the field of synthetic organic chemistry. On the other hand, the splendour of cascade reactions in providing complex molecular architectures renders them a cutting-edge research area. Therefore, the merging of photocatalysis with cascade synthesis brings out a synthetic paradigm with immense potential. The development of photocascade catalysis for a target molecule with a particular molecular skeleton and stereochemical framework presents certain challenges but provides a robust and environmentally benign synthetic alternative. This comprehensive review assembles all the accomplishments and highlights of visible-light-induced cascade reactions with literature coverage up to October 2022.

Regiodivergent Cu-Promoted, AcOH-Switchable Distal Versus Proximal Direct Cyanation of 1-Aryl-1H-indazoles and 2-Aryl-2H-indazoles via Aerobic Oxidative C-H Bond Activation

A copper-promoted regiodivergent, AcOH-switchable, distal and proximal direct cyanation of N-aryl-(1H/2H)-indazoles via aerobic oxidative C(sp²)-H bond activation has been developed. The inclusion or exclusion of AcOH as an additive is the foremost cause for the positional switch in the C-CN bond formation method that results in (C-2')-cyanated 2-aryl-2H-indazoles 3a-j, (C-2')-cyanated 1-aryl-1H-indazoles 4a-j [distal], or C-3 cyanated 2-aryl-2H-indazoles 5a-i [proximal] products in good to excellent yields and showed various functional group tolerance. The cyanide (CN^-) ion surrogate was generated via the unification of dimethylformamide and ammonium iodide (NH₄I). The utilization of molecular oxygen (aerobic oxidative strategy) as a clean and safe oxidant is liable for generous value addition. The further pertinence of the developed protocol has been demonstrated by transforming the synthesized cyanated product into numerous other functional groups, which will, undoubtedly, accomplish utilization in the synthetic area of biologically important compounds and medicinal chemistry.

Ultrasound-promoted convenient and ionic liquid [BMIM]BF4 assisted green synthesis of diversely functionalized pyrazolo quinoline core via one-pot multicomponent reaction, DFT study and pharmacological evaluation

An ultrasound-assisted green protocol for one-pot synthesis of a new series of pharmaceutically relevant pyrazolo quinoline derivatives (4a-t) were synthesized, characterized, and evaluated using DFT and biological activities. Pyrazolo quinoline derivatives (4a-t) were synthesized via a three-component tandem reaction of 1,3-dicarbonyl compound (1a-b), substituted aromatic aldehyde (2a-o), and 5-amino indazole (3a) in the presence of 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM]BF₄ ionic liquid in ethanol at ambient conditions. The main purpose of the present work is selective functionalization of pyrazolo quinoline (4a-t) core excluding another potential parallel reaction under environmentally benign reaction conditions. The present protocol shows features such as amphiphilic behavior of ionic liquid during reaction transformation, and reusability of the [BMIM]BF₄ ionic liquid under mild reaction condition. All newly derived compounds were evaluated for their in vitro anti-inflammatory and antioxidant activity. Among them, compound 4c showed encouraging antioxidant activity compared with standard antioxidant ascorbic acid, and compounds 4n and 4r displayed very good anti-inflammatory activity compared with a standard drug. In this study, a theoretical computational density functional study was also executed to perform the geometry optimizations, frontier molecular orbital approach, and molecular electrostatic potential (MESP). The DFT study was carried out with the basis set DFT/B3LYP/6-31+G (d, p) level of theory. The quantum chemical descriptors (QCDS) and MESP diagrams were plotted to examine the biological reactivities of representative pyrazolo quinolines (4a-t).

Ortho C-H Functionalizations of 2-Aryl-2H-Indazoles

C-H Functionalization is ubiquitously considered as a powerful, efficient and handy tool for installing various functional groups in complex organic heterocycles in an easier and step-economic way. Similarly, indazole is endowed as a potent heterocycle and is eminent for its profound impact in biological, medicinal and industrial chemistry. In this scenario, C-H functionalization at the selective ortho position of 2-arylindazole in assistance of a metal catalyst is also becoming an appealing approach in synthetic organic chemistry. This review addressed the recent findings and developments on ortho C-H functionalization of 2-aryl-2H-indazazoles with literature coverage extending from 2018 to May 2022.

Novel indazole skeleton derivatives containing 1,2,3-triazole as potential anti-prostate cancer drugs

In this study, a novel batch of indazole containing 1,2,3-triazole agents were designed and synthesized. The antiproliferative activity of target compounds in four human cancer cells, PC-3 (human prostate cancer cell), MCF-7 (human breast cancer cell), HepG-2 (human hepatoma cell) and MGC-803 (human gastric cancer cell), was evaluated by thiazole blue (MTT). In the antiproliferative activity screening, we were surprised to find that most compounds have specific cytotoxicity to PC-3 cancer cells. In particular, 9a has an IC₅₀ value of 4.42 ± 0.06 μmol/L against PC-3 cell. Cloning experiments showed that 9a could inhibit the formation of PC-3 cancer cell clone in a dose-dependent manner. Through cell cycle arrest experiment, we found that compound 9a can block the cell cycle in G2/M phase and inhibit cell proliferation. Finally, by evaluating the safety of compound 9a, we noticed that it showed fairly good safety both in vivo and in vitro. Overall, based on the biological activity evaluation and safety, analogue 9a can be viewed as a potential lead compound for further development of novel anti-prostate cancer drug.

Study of the Addition Mechanism of 1H-Indazole and Its 4-, 5-, 6-, and 7-Nitro Derivatives to Formaldehyde in Aqueous Hydrochloric Acid Solutions

The reaction of NH-indazoles with formaldehyde in aqueous hydrochloric acid has been experimentally studied by solution and solid-state nuclear magnetic resonance (NMR) and crystallography. The mechanism of the formation of N₁-CH₂OH derivatives was determined. For the first time, 2-substituted derivatives have been characterized by multinuclear NMR. Theoretically, calculations with gauge-invariant atomic orbitals (GIAOs) at the Becke three-parameter (exchange) Lee–Yang–Parr B3LYP/6-311++G(d,p) level have provided a sound basis for the experimental observations. The first X-ray structures of four (1H-indazol-1-yl)methanol derivatives are reported.

Indazole-based microtubule-targeting agents as potential candidates for anticancer drugs discovery

Tremendous research is focused on developing novel drug candidates targeting microtubules to inhibit their function in several cellular processes, including cell division. In this regard, several indazole derivatives were sought to target the colchicine binding site on the β-tubulin, a crucial protein required to form microtubules, to develop microtubule targeting agents. Even though there are several reviews on the indazole-based compounds, none of them focused on using indazole scaffold to develop microtubule targeting agents. Therefore, this review aims to present the advances in research on compounds containing indazole scaffolds as microtubule targeting agents based on the articles published in the last two decades. Among the articles reviewed, we found that compounds 6 and 7 showed the lowest IC₅₀ values of 0.6 ∼ 0.9 nM in the cell line studies, making them the strongest indazole derivatives that target microtubules. The compounds 30, 31, 37 (IC₅₀ = ∼ 1 nM) and compounds 8, 38 (IC₅₀ = ∼ 2 nM) have proved to be potent microtubule inhibitors. The compounds 18, 31, 44, 45 also showed strong anticancer activity (IC₅₀ = ∼ 8 nM). It is important to notice that except for compounds 9, 12, 13, 15, and SRF, the top activity compounds including 6, 7, 8, 10, 11, 30, 31, 37, 44, and 45 contain 3,4,5‑trimethoxyphenyl substitution similar to that of colchicine. Therefore, it appears that the 3,4,5‑trimethoxyphenyl substituent on the indazole scaffold is crucial for targeting CBS.

Drug Investigation to Dampen the Comorbidity of Rheumatoid Arthritis and Osteoporosis via Molecular Docking Test

At present, most rheumatoid arthritis (RA) patients are at risk of osteoporosis (OP), which is increased by 1.5 times compared to non-RA individuals. Hence, we investigated overlapping targets related directly to the occurrence and development of RA and OP through public databases (DisGeNET, and OMIM) and literature. A total of 678 overlapping targets were considered as comorbid factors, and 604 out of 678 were correlated with one another. Interleukin 6 (IL-6), with the highest degree of value in terms of protein−protein interaction (PPI), was considered to be a core target against comorbidity. We identified 31 existing small molecules (< 1000 g/mol) as IL-6 inhibitors, and 19 ligands were selected by the 3 primary criteria (Lipinski’s rule, TPSA, and binding energy). We postulated that MD2-TLR4-IN-1 (PubChem ID: 138454798), as confirmed by the three criteria, was the key ligand to alleviate comorbidity between RA and OP. In conclusion, we described a promising active ligand (MD2-TLR4-IN-1), and a potential target (IL-6) against comorbidity of RA and OP, providing scientific evidence for a further clinical trial.

Unorthodox cascade reaction of arynes and N-nitrosamides leading to indazole scaffolds

An unusual cascade annulation of arynes with N-alkyl-N-nitrosamides is developed by leveraging aryne σ-insertion and C(sp³)-H bond functionalization strategies under transition-metal-free conditions at ambient temperature, offering functionalized indazoles in high yields and regioselectivity. The protocol is scalable and exhibits a broad substrate scope. The reaction mechanism is also studied with DFT calculations.

Synthesis of 3C-alkylated active methylene substituted 2H-indazole derivatives via sequential ring opening of donor–acceptor cyclopropanes and reductive cyclization reaction

A facile synthesis of 3C-alkylated active methylene substituted 2H-indazoles from o-nitrocyclopropanes and primary arylamines catalyzed by Ni(ClO4)2.6H2O/SnCl2.2H2O is reported.

Bioactive Heterocyclic Compounds as Potential Therapeutics in the Treatment of Gliomas: A Review

Cancer is one of the most alarming diseases, with an estimation of 9.6 million deaths in 2018. Glioma occurs in glial cells surrounding nerve cells. The majority of the patients with gliomas have a terminal prognosis, and the ailment has significant sway on patients and their families, be it physical, psychological, or economic wellbeing. As Glioma exhibits, both intra and inter tumour heterogeneity with multidrug resistance and current therapies are ineffective. So the development of safer anti gliomas agents is the need of hour. Bioactive heterocyclic compounds, eithernatural or synthetic,are of potential interest since they have been active against different targets with a wide range of biological activities, including anticancer activities. In addition, they can cross the biological barriers and thus interfere with various signalling pathways to induce cancer cell death. All these advantages make bioactive natural compounds prospective candidates in the management of glioma. In this review, we assessed various bioactive heterocyclic compounds, such as jaceosidin, hispudlin, luteolin, silibinin, cannabidiol, tetrahydrocannabinol, didemnin B, thymoquinone, paclitaxel, doxorubicin, and cucurbitacins for their potential anti-glioma activity. Also, different kinds of chemical reactions to obtain various heterocyclic derivatives, e.g. indole, indazole, benzimidazole, benzoquinone, quinoline, quinazoline, pyrimidine, and triazine, are listed.

Regioselective N-alkylation of the 1H-indazole scaffold; ring substituent and N-alkylating reagent effects on regioisomeric distribution

The indazole scaffold represents a promising pharmacophore, commonly incorporated in a variety of therapeutic drugs. Although indazole-containing drugs are frequently marketed as the corresponding N-alkyl 1H- or 2H-indazole derivative, the efficient synthesis and isolation of the desired N-1 or N-2 alkylindazole regioisomer can often be challenging and adversely affect product yield. Thus, as part of a broader study focusing on the synthesis of bioactive indazole derivatives, we aimed to develop a regioselective protocol for the synthesis of N-1 alkylindazoles. Initial screening of various conditions revealed that the combination of sodium hydride (NaH) in tetrahydrofuran (THF) (in the presence of an alkyl bromide), represented a promising system for N-1 selective indazole alkylation. For example, among fourteen C-3 substituted indazoles examined, we observed > 99% N-1 regioselectivity for 3-carboxymethyl, 3-tert-butyl, 3-COMe, and 3-carboxamide indazoles. Further extension of this optimized (NaH in THF) protocol to various C-3, -4, -5, -6, and -7 substituted indazoles has highlighted the impact of steric and electronic effects on N-1/N-2 regioisomeric distribution. For example, employing C-7 NO2 or CO2Me substituted indazoles conferred excellent N-2 regioselectivity (≥ 96%). Importantly, we show that this optimized N-alkylation procedure tolerates a wide structural variety of alkylating reagents, including primary alkyl halide and secondary alkyl tosylate electrophiles, while maintaining a high degree of N-1 regioselectivity.

Exploration of chalcones and related heterocycle compounds as ligands of adenosine receptors: therapeutics development

Adenosine receptors (ARs) are ubiquitously distributed throughout the mammalian body where they are involved in an extensive list of physiological and pathological processes that scientists have only begun to decipher. Resultantly, AR agonists and antagonists have been the focus of multiple drug design and development programmes within the past few decades. Considered to be a privileged scaffold in medicinal chemistry, the chalcone framework has attracted a substantial amount of interest in this regard. Due to the potential liabilities associated with its structure, however, it has become necessary to explore other potentially promising compounds, such as heterocycles, which have successfully been obtained from chalcone precursors in the past. This review aims to summarise the emerging therapeutic importance of adenosine receptors and their ligands, especially in the central nervous system (CNS), while highlighting chalcone and heterocyclic derivatives as promising AR ligand lead compounds.

Synthesis and biological evaluation of indazole derivatives as anti-cancer agents

Several FDA approved small molecule anti-cancer drugs contain indazole scaffolds. Here, we report the design, synthesis and biological evaluation of a series of indazole derivatives. In vitro antiproliferative activity screening showed that compound 2f had potent growth inhibitory activity against several cancer cell lines (IC₅₀ = 0.23–1.15 μM). Treatment of the breast cancer cell line 4T1 with 2f inhibited cell proliferation and colony formation. 2f dose-dependently promoted the apoptosis of 4T1 cells, which was connected with the upregulation of cleaved caspase-3 and Bax, and downregulation of Bcl-2. 2f also decreased the mitochondrial membrane potential and increased the levels of reactive oxygen species (ROS) in 4T1 cells. Additionally, treatment with 2f disrupted 4T1 cells migration and invasion, and the reduction of matrix metalloproteinase metalloproteinase-9 (MMP9) and increase of tissue inhibitor matrix metalloproteinase 2 (TIMP2) were also observed. Moreover, 2f could suppress the growth of the 4T1 tumor model without obvious side effects in vivo. Taken together, these results identified 2f as a potential small molecule anti-cancer agent.

One of the synthesized indazole derivatives, 2f, displayed inhibitory activities against proliferation, migration and invasion of breast cancer cell line 4T1, with the potential of inducing cell apoptosis, and suppressing tumor growth in vivo.

Metal-free, regioselective, visible light activation of 4CzIPN for the arylation of 2H-indazole derivatives

Highly regioselective organo photocatalysis of 4CzIPN (1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene) for the arylation of 2H-indazole is demonstrated. The present synthetic route provides a highly safe and easily accessible aniline precursor as an arylation reagent. The photoactivated 4CzIPN organocatalyst is found to be more efficient for single electron transfer without any organic base for the radical reaction. The carbazole-based photocatalyst (4CzIPN) with wide redox potential is stable and recyclable for further reaction transformations. Many indazole and aniline derivatives were used in the reaction and provided the arylated indazole derivatives in good to excellent yield.

Highly regioselective organo photocatalysis of 4CzIPN (1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene) for the arylation of 2H-indazole is demonstrated.

Oxidative cross-dehydrogenative coupling (CDC) via C(sp2)-H bond functionalization: tert-butyl peroxybenzoate (TBPB)-promoted regioselective direct C-3 acylation/benzoylation of 2H-indazoles with aldehydes/benzyl alcohols/styrenes

An efficient, cost-effective, transition-metal-free, oxidative C_(sp²)–H/C_(sp²)–H cross-dehydrogenative coupling via a C_(sp²)–H bond functionalization protocol for the regioselective direct C-3 acylation/benzoylation of substituted 2H-Indazoles 1a–m with substituted aldehydes 2a–q/benzyl alcohols 5a–e/styrenes 6a–e is reported. The operationally simple protocol proceeds in the presence of tert-butyl peroxybenzoate (TBPB) as an oxidant in chlorobenzene (PhCl) as a solvent at 110 °C for 24 h under an inert atmosphere, which furnished a diverse variety of substituted 3-(acyl/benzoyl)-2H-indazoles 3a–q/4a–l in up to 87% yields. The reaction involves a free-radical mechanism and proceeds via the addition of an in situ generated acyl radical (from aldehydes/benzyl alcohols/styrenes) on 2H-indazoles. The functional group tolerance, broad substrate scope, control/competitive experiments and gram-scale synthesis and its application to the synthesis of anti-inflammatory agent 11 and novel indazole-fused diazepine 13 further signify the versatile nature of the developed methodology.

An efficient transition-metal-free oxidative C_(sp²)–H/C_(sp²)–H cross-dehydrogenative coupling via C_(sp²)–H bond functionalization for regioselective C-3 acylation/benzoylation of 2H-indazoles with aldehydes/benzyl alcohols/styrenes is reported.

Synthesis, Antiprotozoal Activity, and Cheminformatic Analysis of 2-Phenyl-2H-Indazole Derivatives

Indazole is an important scaffold in medicinal chemistry. At present, the progress on synthetic methodologies has allowed the preparation of several new indazole derivatives with interesting pharmacological properties. Particularly, the antiprotozoal activity of indazole derivatives have been recently reported. Herein, a series of 22 indazole derivatives was synthesized and studied as antiprotozoals. The 2-phenyl-2H-indazole scaffold was accessed by a one-pot procedure, which includes a combination of ultrasound synthesis under neat conditions as well as Cadogan's cyclization. Moreover, some compounds were derivatized to have an appropriate set to provide structure-activity relationships (SAR) information. Whereas the antiprotozoal activity of six of these compounds against E. histolytica, G. intestinalis, and T. vaginalis had been previously reported, the activity of the additional 16 compounds was evaluated against these same protozoa. The biological assays revealed structural features that favor the antiprotozoal activity against the three protozoans tested, e.g., electron withdrawing groups at the 2-phenyl ring. It is important to mention that the indazole derivatives possess strong antiprotozoal activity and are also characterized by a continuous SAR.

Indazole as a Privileged Scaffold: The Derivatives and their Therapeutic Applications

BACKGROUND

Heterocyclic compounds, also called heterocycles, are a major class of organic chemical compound that plays a vital role in the metabolism of all living cells. The heterocyclic compound, indazole, has attracted more attention in recent years and is widely present in numerous commercially available drugs. Indazole-containing derivatives, representing one of the most important heterocycles in drug molecules, are endowed with a broad range of biological properties.

METHODS

A literature search was conducted in PubMed, Google Scholar and Web of Science regarding articles related to indazole and its therapeutic application.

RESULTS

The mechanism and structure-activity relationship of indazole and its derivatives were described. Based on their versatile biological activities, the compounds were divided into six groups: anti-inflammatory, antibacterial, anti-HIV, antiarrhythmic, antifungal and antitumour. At least 43 indazole-based therapeutic agents were found to be used in clinical application or clinical trials.

CONCLUSION

This review is a guide for pharmacologists who are in search of valid preclinical/clinical drug compounds where the progress of approved marketed drugs containing indazole scaffold is examined from 1966 to the present day. Future direction involves more diverse bioactive moieties with indazole scaffold and greater insights into its mechanism.

Synthesis and biological evaluation of novel N-substituted benzamides as anti-migration agents for treatment of osteosarcoma

A novel series of novel N-substituted (indole or indazole) benzamides were synthesized, and their anti-tumor properties were evaluated. The majority of tested compounds possessed moderate cytotoxicity, but inspiringly, we verified that active compound 5d presents an astonishing advantage by inhibiting the adhesion, migration, and invasion of osteosarcoma (OS) cells in vitro. Mechanistically, we confirmed 5d inhibited the migration ability of OS cells via the expression of genes related to adhesion, migration, and invasion. This effects of 5d suggest that it can be used as a potential chemotherapeutic drug to some aggressive and/or metastatic cancers, as well as in combination with other clinical anti-cancer drugs. In turn, this could enhance the therapeutic effect or reduce the risk of cell migration.

AMI, an Indazole Derivative, Improves Parkinson's Disease by Inhibiting Tau Phosphorylation

Dopaminergic neuronal loss is the main pathological character of Parkinson’s disease (PD). Abnormal tau hyperphosphorylation will lead to dopaminergic neuronal loss. An indazole derivative 6-amino-1-methyl-indazole (AMI) successfully synthesized to inhibit tau hyperphosphorylation may exert a neuroprotective effect. The in vitro study showed that AMI effectively increased cell viability and alleviated the apoptosis induced by MPP⁺ in SH-SY5Y cells. In addition, AMI treatment significantly decreased the expression of p-tau and upstream kinases GSK-3β. In the MPTP-induced PD mice models, we found AMI apparently preserved dopaminergic neurons in the substantia nigra and improved the PD behavioral symptoms. Our results demonstrate that AMI exerts a neuroprotective effect by inhibiting tau hyperphosphorylation, representing a promising new candidate for PD treatment.

Development of a Late-Stage Diversification Strategy for the 4- and 5-Positions of 4,5,6-Trisubstituted Indazoles

Indazoles represent a privileged motif in drug discovery. However, the formation of highly substituted indazoles can require the execution of lengthy synthetic routes with minimal opportunities to introduce diversity. In this report, we disclose the development of a late-stage diversification strategy for the 4- and 5-positions of 4,5,6-trisubstituted indazoles. A regioselective C-H functionalization and subsequent nucleophilic aromatic substitution provide two sequential points of diversification. The synthetic sequence delivers rapid access to an array of 4,5,6-trisubstituted indazoles in only four steps from readily available starting materials.

Discovery of New N-hydrazinecarbothioamide Indazole Hybrids: As Potential Radical (ABTS and DPPH) Scavengers

Background:

Free radicals are the main cause of numerous diseases. Their overproduction needs to be controlled in order to combat several ailments. The current study deals with the discovery of new free radical scavengers.

Methods:

Substituted N-hydrazinecarbothioamide indazoles 1-18 were evaluated for DPPH and ABTS radical scavenging activities.

Results:

All synthetic compounds possess good radical DPPH and ABTS scavenging potential in the ranges of IC50 = 2.11 ± 0.17 - 5.3 ± 0.11 μM and IC50 = 2.31 ± 0.06 - 5.5 ± 0.07 μM, respectively, as compared to standard ascorbic acid having IC50 = 2.02 ± 0.11 μM for DPPH and IC50 = 2.1 ± 0.07 μM for ABTS.

Conclusion:

These compounds could serve as leads for antioxidant activity that have the ability to control free radical generation and ward off free radical-induced disorders.

Antiproliferative and apoptotic activity of new indazole derivatives as potential anticancer agents

To develop potent and selective anticancer agents, a series of novel polysubstituted indazoles was synthesized and evaluated for their in vitro antiproliferative and apoptotic activities against two selected human cancer cell lines (A2780 and A549). Several compounds showed an interesting antiproliferative activity, with IC₅₀ values ranging from 0.64 to 17 µM against both cell lines. The most active indazoles were then tested in different pharmacological dilution conditions, adding five new cell lines (A2780, A549, IMR32, MDA-MB-231, and T47D) as targets, confirming their antiproliferative activity. Furthermore, selected compounds were able to trigger apoptosis to a significant extent and to cause, in part, a block of cells in the S phase of the cell cycle, with a concomitant decrease of cells in the G2/M and/or G0/G1 phases and the generation of hypodiploid peaks. However, molecule 7d caused a great increase of cells in G2/M and the appearance of polyploid cells. Altogether, our results suggest a good pharmacological activity for our selected polysubstituted indazoles, which are suggestive of a preferential mechanism of action as cell cycle-specific antimetabolites or as an inhibitor of enzyme activities involved in DNA synthesis, except for 7d, which, on the contrary, seems to have a mechanism involving the microtubule system.