Indazole Derivatives Research Articles

Synthesis of novel indazole derivatives as inhibitors of diabetics II along with molecular docking and simulation study

In the light of the pharmacological significance of the indazole and 1, 3, 4-thiadiazole scaffold, hybrid analogs of indazole and 1, 3, 4-thiadiazole (1–14) were synthesized, identified using HREI-MS, 1H, and 13CNMR, and their capability for inhibition of α-amylase and α-glucosidase enzymes was evaluated. Generally, most of the synthesized derivatives of the series exhibited good inhibition activity in comparison to the reference drug acarbose with IC50 value of 10.30 ± 0.20 for α-amylase, and 9.80 ± 0.20 for α-glucosidase. Amongst the synthesized derivatives, fluoro substituted analog 10 appeared to be the most potent inhibitor having IC50 value of 9.90 ± 0.30 for α-amylase and 9.20 ± 0.30 for α-glucosidase. A structure activity relationship (SAR) for the series was established based on electronic effects and the positions of various groups on the phenyl ring. To comprehend the chemicals' binding interactions, molecular docking along with simulation study were also carried out. Compound 10 was ranked top in the series based on docking score and interactions with receptors. Compound 10 establish more H-bond contacts with the active site's residue of alpha-amylase and α-glucosidase as compared to all other compounds. Furthermore, 10 was found to be highly stable throughout 50 ns MD simulation. As compared to the control drug, 10 revealed high stability with both α-amylase and α-glucosidase enzymes during molecular dynamics simulation.

3-Alkoxy-1-Benzyl-5-Nitroindazole Derivatives Are Potent Antileishmanial Compounds.

Indazoles have previously been identified as molecules with antiprotozoal activity. In this study, we evaluate the in vitro activity of thirteen 3-alkoxy-1-benzyl-5-nitroindazole derivatives (series D) against L. amazonensis, L. infantum, and L. mexicana. In vitro, cytotoxicity against mouse peritoneal macrophages and growth inhibitory activity in promastigotes were evaluated for all compounds, and those showing adequate activity and selectivity were tested against intracellular amastigotes. Transmission and scanning electron microscopy were employed to study the effects of 3-alkoxy-1-benzyl-5-nitroindazole and 2-benzyl-5-nitroindazolin-3-one derivatives on promastigotes of L. amazonensis. Compounds NV6 and NV8 were active in the two life stages of the three species, with the latter showing the best indicators of activity and selectivity. 3-alkoxy-1-benzyl-5-nitroindazole derivatives (series D) showed in vitro activity comparable to that of amphotericin B against the promastigote stage of Leishmania spp. Two compounds were also found to be active the amastigote stage. Electron microscopy studies confirmed the antileishmanial activity of the indazole derivatives studied and support future research on this family of compounds as antileishmanial agents.

Skeletal Editing through Single-Atom Insertion and Transmutation: An Insight into a New Era of Synthetic Organic Chemistry

AbstractConsidering the importance of heterocycles, significantly represented in medicinal chemistry and drug development, the single-atom insertion technique and transmutation strategy provide productive approaches towards complicated molecular structures through heterocycle diversification. It shows a potentially powerful approach for modifying complex substrates concisely and chemospecifically. Although skeletal editing applies to cyclic and acyclic compounds, this review focuses on the diversification of carbo- and heterocyclic compounds for synthesizing various medicinally important molecules via the single-atom insertion technique. The classification system is based on recent and critical historical methods of single-atom insertion as applied to the transmutation of aromatic rings.1 Introduction2 Skeletal Editing through Carbon-Atom Insertion2.1 Skeletal Editing of Indoles and Pyrroles Derivatives: Carbon-Atom Insertion into a C=C Bond2.2 Skeletal Editing of Pyrazole and Indazole Derivatives: Carbon-Atom Insertion into an N–N Bond2.3 Skeletal Editing of Pyrazole and Indazole Derivatives: Insertion of CF3 Group into Heteroarenes2.4 Skeletal Editing of Imidazole Derivatives: Carbon-Atom Insertion into C–N Bond2.5 Skeletal Editing through Atom-to-Atom Transmutation3 Skeletal Editing through N-Atom Insertion3.1 Nitrogen-Atom Insertion into Carbocycles3.2 Nitrogen-Atom Insertion into Heterocycles3.3 Carbon to Nitrogen Transmutation3.3 Molecular Editing through Isotopic Transmutation4 Conclusion

Design, synthesis and biological evaluation of indazole derivatives as VEGFR-2 kinase inhibitors with anti-angiogenic properties

The strategy of inhibiting angiogenesis, specifically by targeting vascular endothelial growth factor receptor 2 (VEGFR-2), has been proven effective in tumor treatment. In this study, we designed several VEGFR-2 kinase inhibitors based on an indazole scaffold. Among them, the most potent compound, 30, inhibits VEGFR-2 (IC50 = 1.24 nM) with subtle selectivity over other kinases. It demonstrates significant inhibitory activity against HUVEC angiogenesis and inhibits cell migration in a dose-dependent manner. Additionally, it exhibits low acute toxicity in mice. In vivo studies, compound 30 demonstrates favorable pharmacokinetic profiles. It suppresses tumor angiogenesis in the zebrafish subintestinal vessel model, indicating that it may be a potential angiogenesis inhibitor for further development.

Advancements in Combating Fungal Infections: A Comprehensive Review on the Development of Azole Hybrid Antifungals.

In this review, we have summarized antifungal agents containing potent azole analogues. The provided literature is related to the development and application of azole derivatives and has been accessed from electronic data bases such as Science direct, Google Scholar, and Pubmed using keywords such as "design, synthesis and evaluation", "azole hybrids", "diazole hybrids", "indazole derivatives", "imidazole derivatives", "triazole derivatives", "tetrazole derivatives" and related combinations. From this review, it was identified that azole derivatives with promising antifungal activity play a vital role in drug discovery and development. The literature revealed that azole derivatives can effectively fight several types of microorganisms, such as Candida albicans, Aspergillus niger, and others. The rational design and structure‒activity relationship of these compounds are discussed in this paper, highlighting their potential as effective therapeutic options against various fungal pathogens. Moreover, this work addresses the challenges and future directions in the development of azole hybrids. The results of docking studies of several of the hybrids that the researchers provided are also summarized. The current work attempts to review such innovations, which may lead to the preparation of novel therapeutics. More research is required to confirm their safety and effectiveness in clinical practices.

An efficient and simple approach for synthesizing indazole compounds using palladium-catalyzed Suzuki-Miyaura cross-coupling.

A series of indazole derivatives (6a-6i and 7a-7i) has been synthesized using Suzuki Miyaura cross-coupling with a palladium catalyst from readily available starting materials. An efficient and reliable methodology was employed for the synthesis, and the compounds were thoroughly characterized using 1H NMR, 13C NMR, FT-IR, and HRMS analysis to confirm their structural integrity and purity. Density function theory (DFT) computation identified four compounds (6g, 6h, 7g, and 7h) with significant energy band gaps. Additionally, the molecular electrostatic potential study highlighted the distinct electrical characteristics of these indazole molecules. Subsequent molecular docking investigations were carried out using the AUTODOCK method with two separate protein data bank (PDB) structures (6FEW, 4WA9) involved in renal cancer pathways. The results showed that eight substances PDB: 6FEW (6g, 6h, 7g, and 7h) and PDB: 4WA9 (6a, 6c, and 7c, 7g) had the highest binding energies, indicating their potential as therapeutic agents for treating kidney cancer.

Cyy-272, an indazole derivative, effectively mitigates obese cardiomyopathy as a JNK inhibitor

Obesity has shown a global epidemic trend. The high-lipid state caused by obesity can maintain the heart in a prolonged low-grade inflammatory state and cause ventricular remodeling, leading to a series of pathologies, such as hypertrophy, fibrosis, and apoptosis, which eventually develop into obese cardiomyopathy. Therefore, prolonged low-grade inflammation plays a crucial role in the progression of obese cardiomyopathy, making inflammation regulation an essential strategy for treating this disease. Cyy-272, an indazole derivative, is an anti-inflammatory compound independently synthesized by our laboratory. Our previous studies revealed that Cyy-272 can exert anti-inflammatory effects by inhibiting the phosphorylation and activation of C-Jun N-terminal kinase (JNK), thereby alleviating lipopolysaccharide (LPS)-induced acute lung injury (ALI). The current study aimed to evaluate the potential of Cyy-272 to mitigate the occurrence and progression of obese cardiomyopathy through the inhibition of the JNK signaling pathway. Our results indicate that the compound Cyy-272 has encouraging therapeutic effects on obesity-induced cardiac injury. It significantly inhibits inflammation in cardiomyocytes and heart tissues induced by high lipid concentrations, further alleviating the resulting hypertrophy, fibrosis, and apoptosis. Mechanistically, the protective effect of Cyy-272 on obese cardiomyopathy can be attributed to its direct inhibition of JNK protein phosphorylation. In conclusion, we identified a novel compound, Cyy-272, capable of alleviating obese cardiomyopathy and confirmed that its effect is achieved through direct inhibition of JNK.

Design, synthesis, and optimization of novel PD-L1 inhibitors and the identification of a highly potent and orally bioavailable PD-L1 inhibitor

In this paper we report the discovery of structurally novel and highly potent programmed cell death-ligand 1 (PD-L1) inhibitors targeting surface and intracellular PD-L1. A ring fusion design utilizing dimethoxyphenyl indazole derivatives was used, followed by structural extension, which further improved potency by inducing the formation of additional symmetrical interactions within the PD-L1 binding site, leading to the discovery of novel and highly active tetra-aryl-scaffold inhibitors. Key optimizations involved polar tail chain modifications that improve potency and minimize cell cytotoxicity. In addition, druggability issues that exist outside the rule-of-five chemical space were addressed. CB31, a representative compound, was found to exhibit outstanding activity in blocking programmed cell death-1 (PD-1)/PD-L1 interactions (IC50 = 0.2 nM) and enhancing T-cell functions, with minimal cell cytotoxicity. CB31 also displayed favorable oral pharmacokinetic properties, consistent with its high passive permeability and insusceptibility to efflux transporters, as well as its high metabolic stability. Additionally, CB31 demonstrated mechanistically differentiated features from monoclonal antibodies by inducing PD-L1 internalization, intracellular retention of PD-L1 with altered glycosylation pattern, and PD-L1 degradation. It also demonstrated greater effects on tumor size reduction and tumor cell killing, with enhanced T-cell infiltration, in a 3D tumor spheroid model. Overall, results show that CB31 is a promising small-molecule PD-L1 inhibitor that can inhibit PD-1/PD-L1 interactions and promote PD-L1 degradation.

Discovery of novel indazole derivatives as second-generation TRK inhibitors

NTRK gene fusion leads to the activation of downstream signaling pathways, which is a oncogenic driver in various cancers. NTRK fusion-positive cancers can be treated with the first-generation TRK inhibitors, larotrectinib and entrectinib. Unfortunately, the patients eventually face the dilemma of no drugs available as the emergence of certain resistance mutations. The development of efficient and broad-spectrum second-generation TRK inhibitors is still of great significance. Here, we analyzed the binding modes of compounds 6, 10 with TRKA protein, respectively, a series of novel indazole TRK inhibitors were designed and synthesized using molecular hybridization strategy. Among them, the optimal compound B31 showed strong antiproliferative activities against Km-12, Ba/F3-TRKAG595R, and Ba/F3-TRKAG667C cell lines with IC50 values of 0.3, 4.7, and 9.9 nM, respectively. And the inhibitory effect against TRKAG667C (IC50 = 9.9 nM) was better than that of selitrectinib (IC50 = 113.1 nM). Further, compound B31 exhibited moderate kinase selectivity and excellent plasma stability (t1/2 > 480 min). In vivo pharmacokinetic studies in Sprague-Dawley rats showed that B31 had acceptable pharmacokinetic properties.

Synthesis of 2-Aryl Indazole: Synthesis, Biological Evaluationand In-Silico Studies.

In this work, a highly effective synthesis technique for obtaining aryl indazole under mild circumstances is provided, using trimethyl phosphine as a powerful reagent. The procedure shows that a wide range of substrates can be investigated, yielding various 2-aryl indazole derivatives with acceptable to exceptional yields and a wide range of functional group tolerance. Additionally, based on In Silico studies tests were conducted to determine the anticancer activity In Vitro for all produced compounds (3 a-3 j) against A549, HT-29 and HepG2 cell lines. Compounds 3 c and 3 d, with IC50 values of 15, 53.55, 7.34, 7.10, 56.28, and 17.87 (μM) against A549, HT-29 and HepG2 respectively, showed significant anticancer activity.

Advances in Synthesis of Indazole Variants: A Comprehensive Review of Transition Metal, Acid/Base and Green Chemistry-based Catalytic Approaches

Background:: Indazole is a heterocyclic motif widely used in medicinal chemistry due to its positive photophysical properties. The development of new methods for synthesizing the indazole scaffold is of great importance in drug discovery. Methods:: This study presents a detailed review of current advances in indazole synthesis, focusing on catalyst-based and green chemistry approaches. The analysis is classified based on acid-base and transition-metal catalysts and green chemistry methods. Catalyst-based advances have given a new impetus to the synthesis of this effective pharmacophore. Results:: The extensive literature on indazole synthesis demonstrates the notable progress achieved through catalyst-based approaches. These methods have enabled researchers to create a wide range of indazole derivatives and analogs, facilitating their application in pharmaceutical products and organic molecules. The use of acid-base and transition-metal catalysts has been particularly effective in enhancing the efficiency and selectivity of indazole synthesis. Conclusion:: Indazoles and their variants are widely used in pharmaceutical products and organic molecules. The recent literature indicates that catalyst-based approaches have resulted in significant advancements in indazole synthesis. This review may be useful for researchers in medicinal chemistry, content chemistry, and agrochemistry.

Synthesis, in vitro and in silico screening of novel ferrocenyl substituted cyclohexenone and indazole derivatives as effective antimycobacterial agents

In response to the escalating threat of mycobacterial infections, including extensively drug-resistant tuberculosis (XDR) and multidrug-resistant tuberculosis (MDR), we synthesized novel ferrocene incorporating cyclohexenone and indazole derivatives. The compounds were synthesized via multistep reaction approach starting from chalcone precursors and evaluated against Mycobacterium fortuitum. The MIC and MBC values were calculated by following CLSI guidelines, with a focus on their ability to inhibit bacterial growth and disrupt biofilm formation. All the test compounds showed potent in vitro antimycobacterial activity against M. fortuitum. The MIC values range from 3.907 µg/mL to 500 µg/mL, whereas the MBC values range from 15.625 µg/mL to >500 µg/mL. Among the synthesized compounds, compound 3b exhibited potent antimycobacterial activity compared with standard drug Amikacin used to treat multidrug-resistant tuberculosis. 3b demonstrated significant inhibition of bacterial growth and showed the capacity to effectively suppress biofilm formation and disrupt pre-existing biofilms. This molecule also displayed favourable ADMET profile and good oral bioavailability, besides showing potential interactions with the target enzyme as revealed by docking studies and validated by enzyme assay. Collectively, these studies position 3b as a potential lead molecule that could be further optimized to develop ferrocene incorporating indazole based antimycobacterial agents.

TYM-3-98, a novel selective inhibitor of PI3Kδ, demonstrates promising preclinical antitumor activity in B-cell lymphomas

AimsPI3Kδ is expressed predominately in leukocytes and is commonly found to be aberrantly activated in human B-cell lymphomas. Although PI3Kδ has been intensively targeted for discovering anti-lymphoma drugs, the application of currently approved PI3Kδ inhibitors has been limited due to unwanted systemic toxicities, thus warranting the development of novel PI3Kδ inhibitors with new scaffolds. Main methodsWe designed TYM-3-98, an indazole derivative, and evaluated its selectivity for all four PI3K isoforms, as well as its efficacy against various B-cell lymphomas both in vitro and in vivo. Key findingsWe identified TYM-3-98 as a highly selective PI3Kδ inhibitor over other PI3K isoforms at both molecular and cellular levels. It showed superior antiproliferative activity in several B-lymphoma cell lines compared with the approved first-generation PI3Kδ inhibitor idelalisib. TYM-3-98 demonstrated a concentration-dependent PI3K/AKT/mTOR signaling blockage followed by apoptosis induction. In vivo, TYM-3-98 showed good pharmaceutical properties and remarkably reduced tumor growth in a human lymphoma xenograft model and a mouse lymphoma model. SignificanceOur findings establish TYM-3-98 as a promising PI3Kδ inhibitor for the treatment of B-cell lymphoma.

Exploring novel indazole derivatives as ASK1 inhibitors: Design, synthesis, biological evaluation and docking studies

Apoptosis signal regulated kinase 1 (ASK1, MAP3K5) is a member of the mitogen activated protein kinase (MAPK) signaling pathway, involved in cell survival, differentiation, stress response, and apoptosis. ASK1 kinase inhibition has become a promising strategy for the treatment of Non-alcoholic steatohepatitis (NASH) disease. A series of novel ASK1 inhibitors with indazole scaffolds were designed and synthesized, and their ASK1 kinase activities were evaluated. The System Structure Activity Relationship (SAR) study discovered a promising compound 33c, which has a strong inhibitory effect on ASK1. Noteworthy observations included a discernible reduction in lipid droplets within LO2 cells stained with Oil Red O, coupled with a decrease in LDL, CHO, and TG content within the NASH model cell group. Mechanistic inquiries revealed that compound 33c could inhibit the protein expression levels of the upregulated ASK1-p38/JNK signaling pathway in TNF-α treated HGC-27 cells and regulate apoptotic proteins. In summary, these findings suggest that compound 33c may be valuable for further research as a potential candidate compound against NASH.

“Synergistic Innovation: Crafting Indazole Derivatives for Advanced Anticancer, Antioxidant, and Antimicrobial Efficacy through Integrative Design and Holistic Evaluation”

AbstractThis study presents the synthesis and characterization of a newer series of N‐(1‐(2‐(phenylamino) pyrimidin‐4‐yl)‐1H‐indazol‐5‐yl)benzenesulfonamide (6 a–6 n) and N‐(6‐ethoxy‐1‐(2‐(phenylamino) pyrimidin‐4‐yl)‐1H‐indazol‐5‐yl)benzenesulfonamide (7 a–7 c) derivatives through the reaction of N‐(1‐(2‐chloropyrimidin‐4‐yl)‐1H‐indazol‐5‐yl) benzenesulfonamide (4 a–i) and N‐(1‐(2‐chloropyrimidin‐4‐yl)‐6‐ethoxy‐1H‐indazol‐5‐yl) benzenesulfonamide (5 a–i) with various aniline derivatives in isopropanol. The compounds were thoroughly evaluated for their biological activities, encompassing antifungal, antibacterial, and anticancer assays, as well as antioxidant potential in DPPH and ABTS assays. Compound 7 b (IC50: 0.0125 MIC), 6 e (IC50: 0.0128 MIC), and 6 i (IC50: 0.0128 MIC) demonstrated exceptional antibacterial efficacy, while 6 d (IC50: 0.0124 MIC), 6 f (IC50: 0.0125 MIC) and 7 c (IC50: 0.0118 MIC), exhibited notable antifungal activity. Compounds 6 c (IC50: 13.31±0.32 μM, A459) & (IC50: 22.36±1.76 μM, MCF7) displayed significant anticancer activity comparable to established drugs. Moreover, 6 b (IC50: 11.22±0.16 μM, A459) & (IC50: 18.21±1.32 μM, MCF7) and 6 d (IC50: 11.23±0.17 μM, A459) & (IC50: 18.31±1.41 μM, MCF7) showed remarkable anticancer potency. Notably, compound N‐(1‐(2‐(methyl(phenyl)amino)pyrimidin‐4‐yl)‐1H‐indazol‐5‐yl)‐4‐nitrobenzenesulfonamide (IC50:0.1090 μmol/mL for DPPH and IC50: 0.1286 μmol/mL for ABTS) exhibited the most significant antioxidant activity. Computational docking studies revealed robust binding interactions with target enzymes (PDB ID: 4JT3 for anticancer, PDB ID: 1EA1 for antifungal, PDB ID: 1KZN for antibacterial, PDB ID: 3SRG for antioxidant), supported by molecular dynamics simulations indicating consistent stability of the most potent compound within the binding sites of the target proteins. These findings underscore the therapeutic potential of these derivatives, warranting further investigation for potential clinical applications.

Synthesis, Antiproliferative Evaluation, and Molecular Docking of Thieno[3,2-e]indazole Derivatives

Background: Although indazole derivatives are rare and may not be available easily in nature, there are many reports demonstrating their pharmaceutical and other applications. Objective: This study aimed to synthesize new indazole derivatives and evaluate their antiproliferative activity to produce new anti-cancer agents. Method: The 2-aryllidenecyclohexane-1,3-dione derivatives 3a-c were obtained through the reaction of cyclohexane-1,3-dione with aromatic aldehydes used for the synthesis of thieno-[3,2-e]indazole derivatives. These derivatives were characterized by extensive analytical and spectral studies and were further used as starting materials for some heterocyclic transformations to produce biologically active compounds. The antiproliferative activities of the newly synthesized compounds were evaluated against the six cancer cell lines, A549, HT-29, MKN-45, U87MG, SMMC-7721, and H460. Most of the tested compounds exhibited high cytotoxicity except a few compounds. Results: In this study, new compounds were synthesized, characterized, and evaluated toward the selected six cancer cell lines. All tested compounds displayed potent c-Met enzymatic activity with IC50 values ranging from 0.25 to 10.30 nM and potent prostate PC-3 cell line inhibition with IC50 values ranging from 0.17 to 9.31mM. Conclusion: The results obtained in this work demonstrated that the variations in substituents within the aryl moiety, together with the attached heterocyclic ring, have a notable influence on the antiproliferative activity. The results obtained in this work encourage further work in the future.

I2-DMSO-Mediated Construction of 2,3- and 2,4-Disubstituted Pyrimido[1,2-b]indazole Skeletons.

An efficient synthetic method for constructing 2,3- and 2,4-disubstituted pyrimidio[1,2-b]indazole skeletons through I2-DMSO-mediated and substrate-controlled regioselective [4 + 2] cyclization is reported. The reaction conditions are mild, its operation is simple, and the substrate scope is wide. More than 60 pyrimidio[1,2-b]indazole derivatives have been synthesized, providing a new methodology for constructing related molecules and potentially enriching bioactive-molecule libraries.

In-silico design of novel potential HDAC inhibitors from indazole derivatives targeting breast cancer through QSAR, molecular docking and pharmacokinetics studies

Latest studies confirmed that abnormal function of histone deacetylase (HDAC) plays a pivotal role in formation of tumors and is a potential therapeutic target for treating breast cancer. In this research, in-silico drug discovery approaches via quantitative structure activity relationship (QSAR) and molecular docking simulations were adapted to 43 compounds of indazole derivatives with HDAC inhibition for anticancer activity against breast cancer. The QSAR models were built from multiple linear regression (MLR), and models predictability was cross-validated by leave-one-out (LOO) method. Based on these results, compounds C32, C26 and C31 from model 3 showed superior inhibitory activity with pIC50 of 9.30103, 9.1549 and 9.1549. We designed 10 novel compounds with molecular docking scores ranging from −7.9 to −9.3 kcal/mol. The molecular docking simulation results reveal that amino acid residues ILE1122 and PRO1123 play a significant role in bonding with 6CE6 protein. Furthermore, newly designed compounds P5, P2 and P7 with high docking scores of −9.3 kcal/mol, −8.9 kcal/mol and −8.8 kcal/mol than FDA-approved drug Raloxifene (-8.5 kcal/mol) and aid in establishment of potential drug candidate for HDAC inhibitors. The in-silico ADME functionality is used in the final phase to evaluate newly designed inhibitors as potential drug candidates. The results suggest that newly designed compounds P5, P2 and P7 can be used as a potential anti-breast cancer drug candidate.

Synthesis and evaluation of novel N1-acylated 5-(4-pyridinyl)indazole derivatives as potent and selective haspin inhibitors

Protein kinase dysregulation was strongly linked to cancer pathogenesis. Moreover, histone alterations were found to be among the most important post-translational modifications that could contribute to cancer growth and development. In this context, haspin, an atypical serine/threonine kinase, phosphorylates histone H3 at threonine-3 and is notably overexpressed in various common cancer types. Herein, we report novel 5-(4-pyridinyl)indazole derivatives as potent and selective haspin inhibitors. Amide coupling at N1 of the indazole ring with m-hydroxyphenyl acetic acid yielded compound 21 with an IC50 value of 78 nM against haspin. This compound showed a meaningful selectivity over 15 of the most common off-targets, including Clk 1–3 and Dyrk1A, 1B, and 2. The most potent haspin inhibitors 5 and 21 effectively inhibited the growth of the NCI-60 cancer cell lines, further emphasizing the success of our scaffold as a new selective lead for the development of anti-cancer therapeutic agents.

Regioselective synthesis of 3,4-diarylpyrimido[1,2-b]indazole derivatives enabled by iron-catalyzed ring-opening of styrene oxides.

The first synthesis of 3,4-diarylpyrimido[1,2-b]indazole derivatives from 3-aminoindazoles has been realized. The FeCl3-catalyzed intermolecular epoxide ring-opening reaction altered the order of annulation, with the free primary NH2 groups in 3-aminoindazoles preferentially reacting with styrene oxides instead of aromatic aldehydes. This protocol is further highlighted by its broad substrate compatibility, high chemo- and regioselectivities, and the late-stage modifications of bioactive molecules. Without aromatic aldehydes, the synthesis of 3-aryl-4-acylpyrimido[1,2-b]indazole derivatives can also be accomplished using alternative reaction conditions.