Novel amidino substituted benzimidazole and benzothiazole benzo[ b ]thieno-2-carboxamides exert strong antiproliferative and DNA binding properties

Applications of innovative synthetic strategies in anticancer drug discovery: The driving force of new chemical reactions

The discovery of novel anticancer agents remains a critical goal in medicinal chemistry, with innovative synthetic methodologies playing a pivotal role in advancing this field. Recent breakthroughs in CH activation reactions, cyclization reactions, multicomponent reactions, cross-coupling reactions, and photo- and electro-catalytic reactions have enabled the efficient synthesis of new molecular scaffolds exhibiting potent biological activities, including anticancer properties. These methodologies have facilitated the functionalization of natural products, the modification of bioactive molecules, and the generation of entirely new compounds, many of which demonstrate strong antitumor activity. This review summarizes the latest synthetic strategies employed over the past five years for discovering anticancer agents, focusing on their influence on drug design. Additionally, the role of new chemical reactions in expanding chemical space and overcoming challenges, such as drug resistance and selectivity, is highlighted, further emphasizing the importance of discovering novel reactions as a key trend in future drug development.

Multitarget Pharmacology of Sulfur-Nitrogen Heterocycles: Anticancer and Antioxidant Perspectives

Cancer and oxidative stress are interrelated, with reactive oxygen species (ROS) playing crucial roles in physiological processes and oncogenesis. Excessive ROS levels can induce DNA damage, leading to cancer, and disrupt antioxidant defenses, contributing to diseases like diabetes and cardiovascular disorders. Antioxidant mechanisms include enzymes and small molecules that mitigate ROS damage. However, cancer cells often exploit oxidative conditions to evade apoptosis and promote tumor growth. Antioxidant therapy has shown mixed results, with timing and cancer-type influencing outcomes. Multifunctional drugs targeting multiple pathways offer a promising approach, reducing side effects and improving efficacy. Recent research focuses on sulfur-nitrogen heterocyclic derivatives for their dual antioxidant and anticancer properties, potentially enhancing therapeutic efficacy in oncology. The newly synthesized compounds often do not demonstrate both antioxidant and anticancer properties simultaneously. Heterocyclic rings are typically combined with phenyl groups, where hydroxy substitutions enhance antioxidant activity. On the other hand, electron-withdrawing substituents, particularly at the p-position on the phenyl ring, tend to enhance anticancer activity.

Design, Synthesis and Biological Activity of Novel Methoxy- and Hydroxy-Substituted N-Benzimidazole-Derived Carboxamides

This work presents the design, synthesis and biological activity of novel N-substituted benzimidazole carboxamides bearing either a variable number of methoxy and/or hydroxy groups. The targeted carboxamides were designed to investigate the influence of the number of methoxy and/or hydroxy groups, the type of substituent placed on the N atom of the benzimidazole core and the type of substituent placed on the benzimidazole core on biological activity. The most promising derivatives with pronounced antiproliferative activity proved to be N-methyl-substituted derivatives with hydroxyl and methoxy groups at the phenyl ring and cyano groups on the benzimidazole nuclei with selective activity against the MCF-7 cell line (IC50 = 3.1 μM). In addition, the cyano-substituted derivatives 10 and 11 showed strong antiproliferative activity against the tested cells (IC50 = 1.2-5.3 μM). Several tested compounds showed significantly improved antioxidative activity in all three methods compared to standard BHT. In addition, the antioxidative activity of 9, 10, 32 and 36 in the cells generally confirmed their antioxidant ability demonstrated in vitro. However, their antiproliferative activity was not related to their ability to inhibit oxidative stress nor to their ability to induce it. Compound 8 with two hydroxy and one methoxy group on the phenyl ring showed the strongest antibacterial activity against the Gram-positive strain E. faecalis (MIC = 8 μM).

Synthesis and Biological Evaluation of Novel Amino and Amido Substituted Pentacyclic Benzimidazole Derivatives as Antiproliferative Agents

Newly designed pentacyclic benzimidazole derivatives featuring amino or amido side chains were synthesized to assess their in vitro antiproliferative activity. Additionally, we investigated their direct interaction with nucleic acids, aiming to uncover potential mechanisms of biological action. These compounds were prepared using conventional organic synthesis methodologies alongside photochemical and microwave-assisted reactions. Upon synthesis, the newly derived compounds underwent in vitro testing for their antiproliferative effects on various human cancer cell lines. Notably, derivatives 6 and 9 exhibited significant antiproliferative activity within the submicromolar concentration range. The biological activity was strongly influenced by the N atom's position on the quinoline moiety and the position and nature of the side chain on the pentacyclic skeleton. Findings from fluorescence, circular dichroism spectroscopy, and thermal melting assays pointed toward a mixed binding mode-comprising intercalation and the binding of aggregated compounds along the polynucleotide backbone-of these pentacyclic benzimidazoles with DNA and RNA.

Overview of the New Bioactive Heterocycles as Targeting Topoisomerase Inhibitors Useful Against Colon Cancer

Colorectal cancer (CRC) is the third most common cancer globally, with high mortality. Metastatic CRC is incurable in most cases, and multiple drug therapy can increase patients' life expectancy by 2 to 3 years. Efforts are being made to understand the relationship between topoisomerase enzymes and colorectal cancer. Some studies have shown that higher expression of these enzymes is correlated to a poor prognosis for this type of cancer. One of the primary drugs used in the treatment of CRC is Irinotecan, which can be used in monotherapy or, more commonly, in therapeutic schemes such as FOLFIRI (Fluorouracil, Leucovorin, and Irinotecan) and CAPIRI (Capecitabine and Irinotecan). Like Camptothecin, Irinotecan and other compounds have a mechanism of action based on the formation of a ternary complex with topoisomerase I and DNA providing damage to it, therefore leading to cell death. Thus, this review focused on the principal works published in the last ten years that demonstrate a correlation between the inhibition of different isoforms of topoisomerase and in vitro cytotoxic activity against CRC by natural products, semisynthetic and synthetic compounds of pyridine, quinoline, acridine, imidazoles, indoles, and metal complexes. The results revealed that natural compounds, semisynthetic and synthetic derivatives showed potential in vitro cytotoxicity against several colon cancer cell lines, and this activity was often accompanied by the ability to inhibit both isoforms of topoisomerase (I and II), highlighting that these enzymes can be promising targets for the development of new chemotherapy against CRC. Pyridine analogs were considered the most promising for this study, while the evaluation of the real potential of natural products was limited by the lack of information in their work. Moreover, the complexes, although promising, presented as the main limitation the lack of selectivity.

Synthesis and Biological Activity of 2-Benzo[b]thienyl and 2-Bithienyl Amidino-Substituted Benzothiazole and Benzimidazole Derivatives

Novel benzo[b]thienyl- and 2,2'-bithienyl-derived benzothiazoles and benzimidazoles were synthesized to study their antiproliferative and antitrypanosomal activities in vitro. Specifically, we assessed the impact that amidine group substitutions and the type of thiophene backbone have on biological activity. In general, the benzothiazole derivatives were more active than their benzimidazole analogs as both antiproliferative and antitrypanosomal agents. The 2,2'-bithienyl-substituted benzothiazoles with unsubstituted and 2-imidazolinyl amidine showed the most potent antitrypanosomal activity, and the greatest selectivity was observed for the benzimidazole derivatives bearing isopropyl, unsubstituted and 2-imidazolinyl amidine. The 2,2'-bithiophene derivatives showed most selective antiproliferative activity. Whereas the all 2,2'-bithienyl-substituted benzothiazoles were selectively active against lung carcinoma, the benzimidazoles were selective against cervical carcinoma cells. The compounds with an unsubstituted amidine group also produced strong antiproliferative effects. The more pronounced antiproliferative activity of the benzothiazole derivatives was attributed to different cytotoxicity mechanisms. Cell cycle analysis, and DNA binding experiments provide evidence that the benzimidazoles target DNA, whereas the benzothiazoles have a different cellular target because they are localized in the cytoplasm and do not interact with DNA.

2-Aminobenzothiazoles in anticancer drug design and discovery

Cancer is one of the major causes of mortality and morbidity worldwide. Substantial research efforts have been made to develop new chemical entities with improved anticancer efficacy. 2-Aminobenzothiazole is an important class of heterocycles containing one sulfur and two nitrogen atoms, which is associated with a broad spectrum of medical and pharmacological activities, including antitumor, antibacterial, antimalarial, anti-inflammatory, and antiviral activities. In recent years, an extraordinary collection of potent and low-toxicity 2-aminobenzothiazole compounds have been discovered as new anticancer agents. Herein, we provide a comprehensive review of this class of compounds based on their activities against tumor-related proteins, including tyrosine kinases (CSF1R, EGFR, VEGFR-2, FAK, and MET), serine/threonine kinases (Aurora, CDK, CK, RAF, and DYRK2), PI3K kinase, BCL-XL, HSP90, mutant p53 protein, DNA topoisomerase, HDAC, NSD1, LSD1, FTO, mPGES-1, SCD, hCA IX/XII, and CXCR. In addition, the anticancer potentials of 2-aminobenzothiazole-derived chelators and metal complexes are also described here. Moreover, the design strategies, mechanism of actions, structure-activity relationships (SAR) and more advanced stages of pre-clinical development of 2-aminobenzothiazoles as new anticancer agents are extensively reviewed in this article. Finally, the examples that 2-aminobenzothiazoles showcase an advantage over other heterocyclic systems are also highlighted.

New benzothienopyran and benzothienopyranopyrimidine derivatives as topoisomerase I inhibitors: Design, synthesis, anticancer screening, apoptosis induction and molecular modeling studies

New benzothienopyran and benzothienopyranopyrimidine derivatives were synthesized based on the structural requirements of topoisomerase I inhibitors. All target compounds exhibited strong cytotoxic activity with GI₅₀ range of 70.62 %-87.29 % in one dose NCI (USA) screening against 60 human tumor cell lines. Among the tested derivatives, eight compounds namely 4d, 4e, 4f, 5b, 5e, 6b, 6d, and 6f demonstrated broad spectrum and potent anticancer efficacy in five dose screening against all tested panels. DNA relaxation assay for the latter compounds showed that 4d, 5b, and 6f exhibited excellent inhibitory activity with IC₅₀ range of 2.553-4.495 µM as compared to indenoisoquinoline reference drug (IC₅₀ = 3.911 ± 0.21 µM). Moreover, the most active compounds were investigated for being topoisomerase poisons or catalytic inhibitors using DNA nicking assay. Compounds 4d and 6f were found to be potential Topo I poisons, whereas compound 5b has acted as Topo I suppressor. Analyzing cell cycle and induction of apoptosis for the most active compound 4d, revealed growth arrest at the S phase in MDA-MB-435 cells similarly to indenoisoquinoline reference drug. Additionally, in silico molecular modeling study for eight most active cytotoxic compounds in five dose screening demonstrated interaction with DNA as well as distinctive binding pattern similar to the reference indenoisoquinoline, indicating that the newly discovered targets are supposed to be promising candidates as Topo I inhibitors.

Biological evaluation of novel amidino substituted coumarin-benzazole hybrids as promising therapeutic agents

Herein we present the design and the synthesis of novel substituted coumarin-benzimidazole/benzothiazole hybrids bearing a cyclic amidino group on the benzazole core as biologically active agents. All prepared compounds were evaluated for their in vitro antiviral and antioxidative activity as well as for their in vitro antiproliferative activity against a panel of several human cancer cell lines. Coumarin-benzimidazole hybrid 10 (EC50 9.0-43.8 μM) displayed the most promising broad spectrum antiviral activity, while two other coumarin-benzimidazole hybrids 13 and 14 showed the highest antioxidative capacity in the ABTS assay, superior to the reference standard BHT (IC50 0.17 and 0.11 mM, respectively). Computational analysis supported these results and demonstrated that these hybrids benefit from the high C-H hydrogen atom releasing tendency of the cationic amidine unit, and the pronounced ease with which they can liberate an electron, promoted by the electron-donating diethylamine group on the coumarin core. The coumarin ring substitution at position 7 with a N,N-diethylamino group also caused a significant enhancement of the antiproliferative activity, with the most active compounds being derivatives with a 2-imidazolinyl amidine group 13 (IC50 0.3-1.9 μM) and benzothiazole derivative with a hexacyclic amidine group 18 (IC50 1.3-2.0 μM).

N-substitution Reactions of 2-Aminobenzimidazoles to Access Pharmacophores

Benzimidazole (BI) and its derivatives are interesting molecules in medicinal chemistry because several of these compounds have a diversity of biological activities and some of them are even used in clinical applications. In view of the importance of these compounds, synthetic chemists are still interested in finding new procedures for the synthesis of these classes of compounds. Astemizole (antihistaminic), Omeprazole (antiulcerative), and Rabendazole (fungicide) are important examples of compounds used in medicinal chemistry containing BI nuclei. It is interesting to observe that several of these compounds contain 2-aminobenzimidazole (2ABI) as the base nucleus. The structures of 2ABI derivatives are interesting because they have a planar delocalized structure with a cyclic guanidine group, which have three nitrogen atoms with free lone pairs and labile hydrogen atoms. The 10-π electron system of the aromatic BI ring conjugated with the nitrogen lone pair of the hexocyclic amino group, making these heterocycles to have an amphoteric character. Synthetic chemists have used 2ABI as a building block to produce BI derivatives as medicinally important molecules. In view of the importance of the BIs, and because no review was found in the literature about this topic, we reviewed and summarized the procedures related to the recent methodologies used in the N-substitution reactions of 2ABIs by using aliphatic and aromatic halogenides, dihalogenides, acid chlorides, alkylsulfonic chlorides, carboxylic acids, esters, ethyl chloroformates, anhydrides, SMe-isothioureas, alcohols, alkyl cyanates, thiocyanates, carbon disulfide and aldehydes or ketones to form Schiff bases. The use of diazotized 2ABI as intermediate to obtain 2-diazoBIs was included to produce Nsubstituted 2ABIs of pharmacological interest. Some commentaries about their biological activity were included.

Design, synthesis, biological evaluation and QSAR analysis of novel N-substituted benzimidazole derived carboxamides

As a result of our previous research focussed on benzimidazoles, herein we present design, synthesis, QSAR analysis and biological activity of novel N-substituted benzimidazole derived carboxamides. Carboxamides were designed to study the influence of the number of methoxy groups, the type of the substituent placed at the benzimidazole core on biological activity. Pronounced antioxidative activity displayed unsubstituted 28 (IC₅₀ ≈ 3.78 mM, 538.81 mmolFe²⁺/mmolC) and dimethoxy substituted derivative 34 (IC₅₀ ≈ 5.68 mM, 618.10 mmolFe²⁺/mmolC). Trimethoxy substituted 43 and unsubstituted compound 40 with isobutyl side chain at N atom showed strong activity against HCT116 (IC₅₀ ≈ 0.6 µM, both) and H 460 cells (IC₅₀ ≈ 2.5 µM; 0.4 µM), being less cytotoxic towards non-tumour cell. Antioxidative activity in cell generally confirmed relatively modest antioxidant capacity obtained in DPPH/FRAP assays of derivatives 34 and 40. The 3D-QSAR models were generated to explore molecular properties that have the highest influence on antioxidative activity.

Synthetic Approaches to Biologically Active C-2-Substituted Benzothiazoles

Numerous benzothiazole derivatives are used in organic synthesis, in various industrial and consumer products, and in drugs, with a wide spectrum of biological activity. As the properties of the benzothiazole moiety are strongly affected by the nature and position of substitutions, in this review, covering the literature from 2016, we focus on C-2-substituted benzothiazoles, including the methods of their synthesis, structural modification, reaction mechanisms, and possible pharmacological activity. The synthetic approaches to these heterocycles include both traditional multistep reactions and one-pot atom economy processes using green chemistry principles and easily available reagents. Special attention is paid to the methods of the thiazole ring closure and chemical modification by the introduction of pharmacophore groups.

Biological Activity of Newly Synthesized Benzimidazole and Benzothizole 2,5-Disubstituted Furane Derivatives

Newly designed and synthesized cyano, amidino and acrylonitrile 2,5-disubstituted furane derivatives with either benzimidazole/benzothiazole nuclei have been evaluated for antitumor and antimicrobial activity. For potential antitumor activity, the compounds were tested in 2D and 3D cell culture methods on three human lung cancer cell lines, A549, HCC827 and NCI-H358, with MTS cytotoxicity and BrdU proliferation assays in vitro. Compounds 5, 6, 8, 9 and 15 have been proven to be compounds with potential antitumor activity with high potential to stop the proliferation of cells. In general, benzothiazole derivatives were more active in comparison to benzimidazole derivatives. Antimicrobial activity was evaluated with Broth microdilution testing (according to CLSI (Clinical Laboratory Standards Institute) guidelines) on Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Additionally, Saccharomyces cerevisiae was included in testing as a eukaryotic model organism. Compounds 5, 6, 8, 9 and 15 showed the most promising antibacterial activity. In general, the compounds showed antitumor activity, higher in 2D assays in comparison with 3D assays, on all three cell lines in both assays. In natural conditions, compounds with such an activity profile (less toxic but still effective against tumor growth) could be promising new antitumor drugs. Some of the tested compounds showed antimicrobial activity. In contrast to ctDNA, the presence of nitro group or chlorine in selected furane-benzothiazole structures did not influence the binding mode with AT-DNA. All compounds dominantly bound inside the minor groove of AT-DNA either in form of monomers or dimer and higher-order aggregates.

Yb/Chitosan Catalyzed Synthesis of Highly Substituted Piperidine Derivatives for Potential Nuclease Activity and DNA Binding Study

BACKGROUND

Herein, a new chitosan-supported ytterbium nano-catalyst has been prepared and used in a mild, efficient, and expeditious method for the synthesis of substituted piperidine derivatives via threecomponent condensation of substituted anilines, formaldehyde and different cyclic/acyclic active methylene compounds at room temperature.

METHODS

The catalyst was characterized by FTIR, XRD, SEM, EDX, TEM, ICP-AES and the stability of the catalyst was evaluated by TG analysis. The synthesized compound 3,3,11,11-Tetramethyl-15-(phenyl)-15- azadispiro[5.1.5.3]hexadecane-1,5,9,13-tetrone (3a) was explored for pBR322 DNA cleavage activity and genotoxicity. Further, the interaction of 3a with CT-DNA was investigated through UV-vis, fluorescence and viscosity.

RESULTS

The preparation of Yb/chitosan nano-catalyst was verified and the catalyst was found effective towards substituted piperidine formations with the catalyst reusability. Compound 3a was successfully tested for DNA cleavage activity. In addition, fluorescence results revealed that compound 3a interacted with DNA with a binding affinity of 4.84 x 10⁴ M^-1.

CONCLUSION

Our findings suggest that compounds bearing spiro-piperidine scaffold, synthesized using reusable nano-catalyst, could be effective biological agents.

Amidino substituted 2-aminophenols: biologically important building blocks for the amidino-functionalization of 2-substituted benzoxazoles

Unlike the closely related and widely investigated amidino-substituted benzimidazoles and benzothiazoles with a range of demonstrated biological activities, the matching benzoxazole analogues still remain a largely understudied and not systematically evaluated class of compounds. To address this challenge, we utilized the Pinner reaction to convert isomeric cyano-substituted 2-aminophenols into their amidine derivatives, which were isolated as hydrochlorides and/or zwitterions, and whose structure was confirmed by single crystal X-ray diffraction. The key step during the Pinner synthesis of the crucial carboximidate intermediates was characterized through mechanistic DFT calculations, with the obtained kinetic and thermodynamic parameters indicating full agreement with the experimental observations. The obtained amidines were subjected to a condensation reaction with aryl carboxylic acids that allowed the synthesis of a new library of 5- and 6-amidino substituted 2-arylbenzoxazoles. Their antiproliferative features against four human tumour cell lines (SW620, HepG2, CFPAC-1, HeLa) revealed sub-micromolar activities on SW620 for several cyclic amidino 2-naphthyl benzoxazoles, thus demonstrating the usefulness of the proposed synthetic strategy and promoting amidino substituted 2-aminophenols as important building blocks towards biologically active systems.

Recent Progress of Benzimidazole Hybrids for Anticancer Potential

This review presents the detailed account of factors leading to cancer and design strategy for the synthesis of benzimidazole derivatives as anticancer agents. The recent survey for cancer treatment in Cancer facts and figures 2017 American Chemical Society has shown progressive development in fighting cancer. Researchers all over the world in both developed and developing countries are in a continuous effort to tackle this serious concern. Benzimidazole and its derivatives showed a broad range of biological activities due to their resemblance with naturally occurring nitrogenous base i.e. purine. The review discussed benzimidazole derivatives showing anticancer properties through a different mechanism viz. intercalation, alkylating agents, topoisomerases, DHFR enzymes, and tubulin inhibitors. Benzimidazole derivatives act through a different mechanism and the substituents reported from the earlier and recent research articles are prerequisites for the synthesis of targeted based benzimidazole derivatives as anticancer agents. The review focuses on an easy comparison of the substituent essential for potency and selectivity through SAR presented in figures. This will further provide a better outlook or fulfills the challenges faced in the development of novel benzimidazole derivatives as anticancer.

Preclinical in vitro screening of newly synthesised amidino substituted benzimidazoles and benzothiazoles

Newly synthesised benzimidazole/benzotiazole derivatives bearing amidino, namely 3,4,5,6-tetrahydropyrimidin-1-ium chloride, substituents have been evaluated for their potential antitumor activity in vitro. Compounds and standard drugs (doxorubicin, staurosporine and vandetanib) were tested on three human lung cancer cell lines A549, HCC827 and NCI-H358. We tested compounds in MTS citotoxicity assay and in BrdU proliferative assay performed on 2 D and 3 D assay format. Because benzmidazole scaffold is similar to natural purines, we tested the most active compounds for ability to induce cell apoptosis of A549 by binding to DNA in comparison with doxorubicin and saturosporine. Additionally, the ADME properties of the most active benzothiazole/benzimidazole and non-active compounds were determined to see if the different ADME properties are the cause of different activity in 2 D and 3 D assays, as well as to see if the tested active compounds have drug like properties and potency for further profilation. ADME characterisation included solubility, lipophilicity, permeability, metabolic stability and binding to plasma proteins. In general, the benzothiazole derivatives were more active in comparison to their benzimidazole analogues. The exception was 2-phenyl substituted benzimidazole 6a being active with very pronounced activity especially towards HCC827 cells. All active compounds have similar mode of action on A549 cell line as standard compound doxorubicin, which binds to nucleic acids with the DNA double helix. Tested active benzothiazole compounds were characterised by moderate to good solubility, good metabolic stability, low permeability and high binding to plasma proteins. One tested active benzimidazole derivative showed ADME properties, but lower lipophilicity resulted in low PPB and higher metabolic instability. In addition, no significant difference was observed in ADME profile between active and non-active compounds.

Synthesis, anti-inflammatory and analgesic evaluation of thiazole/oxazole substituted benzothiazole derivatives

Non-Steroidal biologically active heterocyclic compounds 4-(2-(4-chlorophenyl) benzo[d]thiazol-3(2H)-yl)-N-((3-substituted-2-hydrobenzo[d]thiazol-2-yl)methylene) thiazol-2-amine (3a-3d), 4-(2-(4-chlorophenyl)benzo[d]thiazol-3(2H)-yl)-N-((3-substituted - 2-hydrobenzo [d]thiazol-2-yl)methylene)oxazol-2-amine (3a'-3d'), (Z)-N'-(4-(2-(4-chlorophenyl)benzo[d]thiazol-3(2H)-yl)thiaol-2-yl)-N-(4-substituted phenylimino)-3-substituted-2-hydrobenzo[d]thiazole-2-carboxamidine (4a-4 h) and (Z)-N'-(4-(2-(4-chlorophenyl)benzo[d]thiazol-3(2H)-yl)oxazol-2-yl)-N-(4-substituted phenylimino) - 3-substituted-2-hydrobenzo[d]thiazole-2-carboxamidine (4a'-4h') were synthesized starting from 2-chloro-1-(2-(4-chlorophenyl)benzo[d]thiazol-3(2H)-yl) ethanone (1). The structure configuration of newly synthesized compounds has been determined by elemental analysis and various spectroscopic (IR, ¹HNMR and GCMS) techniques. These compounds were tested for their anti-inflammation, analgesic, ulcerogenic, acute toxicity and free radical scavenging action and compared with reference drugs in albino rats. Compound 4-(2-(4-chlorophenyl)benzo[d]thiazol-3(2H)-yl)-N-((3-substituted-2-hydrobenzo [d]thiazol-2-yl)methylene)thiazol-2-amine (3c) was the most active compound than reference drug at a dose of 50 mg/kg p.o.

Antiproliferative benzothiazoles incorporating a trimethoxyphenyl scaffold as novel colchicine site tubulin polymerisation inhibitors

Tubulin polymerisation inhibitors exhibited an important role in the treatment of patients with prostate cancer. Herein, we reported the medicinal chemistry efforts leading to a new series of benzothiazoles by a bioisosterism approach. Biological testing revealed that compound 12a could significantly inhibit in vitro tubulin polymerisation of a concentration dependent manner, with an IC₅₀ value of 2.87 μM. Immunofluorescence and EBI competition assay investigated that compound 12a effectively inhibited tubulin polymerisation and directly bound to the colchicine-binding site of β-tubulin in PC3 cells. Docking analysis showed that 12a formed hydrogen bonds with residues Tyr357, Ala247 and Val353 of tubulin. Importantly, it displayed the promising antiproliferative ability against C42B, LNCAP, 22RV1 and PC3 cells with IC₅₀ values of 2.81 μM, 4.31 μM, 2.13 μM and 2.04 μM, respectively. In summary, compound 12a was a novel colchicine site tubulin polymerisation inhibitor with potential to treat prostate cancer.

N-substituted benzimidazole acrylonitriles as in vitro tubulin polymerization inhibitors: Synthesis, biological activity and computational analysis

We present the design, synthesis and biological activity of novel N-substituted benzimidazole based acrylonitriles as potential tubulin polymerization inhibitors. Their synthesis was achieved using classical linear organic and microwave assisted techniques, starting from aromatic aldehydes and N-substituted-2-cyanomethylbenzimidazoles. All newly prepared compounds were tested for their antiproliferative activity in vitro on eight human cancer cell lines and one reference non-cancerous assay. N,N-dimethylamino substituted acrylonitriles 30 and 41, bearing N-isobutyl and cyano substituents placed on the benzimidazole nuclei, showed strong and selective antiproliferative activity in the submicromolar range of inhibitory concentrations (IC₅₀ 0.2-0.6 μM), while being significantly less toxic than reference systems docetaxel and staurosporine, thus promoting them as lead compounds. Mechanism of action studies demonstrated that two most active compounds inhibited tubulin polymerization. Computational analysis confirmed the suitability of the employed benzimidazole-acrylonitrile skeleton for the binding within the colchicine binding site in tubulin, thus rationalizing the observed antitumor activities, and demonstrated that E-isomers are active substances. It also provided structural determinants affecting both the binding position and the matching affinities, identifying the attached NMe₂ group as the most dominant in promoting the binding, which allows ligands to optimize favourable cation∙∙∙π and hydrogen bonding interactions with Lys352.

2-substituted benzothiazoles as antiproliferative agents: Novel insights on structure-activity relationships

Given the wide spectrum of biological activities, benzothiazoles represent privileged scaffolds in medicinal chemistry, useful in drug discovery programs to modulate biological activities of lead compounds. A large body of knowledge about benzothiazoles has been reported in scientific literature, describing their antimicrobial, anticonvulsant, neuroprotective, anti-inflammatory, and antiproliferative effects. This review summarizes the results obtained in the structure-activity relationship studies on antiproliferative benzothiazoles, focusing on 2-substituted derivatives and on mechanism of action responsible for the antitumor effects of this class of compounds.

Green synthesis and biological evaluation of 6-substituted-2-(2-hydroxy/methoxy phenyl)benzothiazole derivatives as potential antioxidant, antibacterial and antitumor agents

We present a new efficient green synthetic protocol for introduction of substituents to the C-6 position of 2-arylbenzothiazole nuclei. Newly synthesized compounds were designed to study the influence of the hydroxy and methoxy groups on the 2-arylbenzothiazole scaffold, as well as the influence of the type of substituents placed on the C-6 position of benzothiazole moiety on biological activity, including antibacterial, antitumor and antioxidant activity. Modest activity was observed against the tested Gram-positive and Gram-negative bacterial strains for only amidino derivatives 5d and 6d. The tested compounds exhibited moderate to strong antiproliferative activity towards the tumor cell lines tested. The SAR study revealed that the introduction of substituents into the benzene ring of the benzothiazole nuclei is essential for antiproliferative activity, while introduction of the hydroxy group into the 2-aryl moiety of the 2-arybenzothiazole scaffold significantly improved selectivity against tumor cell lines. The observed results revealed several novel 6-substituted-2-arylbenzothiazole compounds, 5b, 5c, 5f and 6f, with strong and selective antiproliferative activity towards HeLa cells in micro and submicromolar concentrations, with the most selective compounds being 6-ammonium-2-(2-hydroxy/methoxyphenyl)benzothiazoles 5f and 6f. The compound 5f bearing the hydroxy group on the 2-arylbenzothiazole core showed the most promising antioxidative activity evaluated by DPPH, ABTS and FRAP in vitro assays. The presence of the amino protonated group attached at the benzothiazole moiety was essential for the antiproliferative and antioxidant activity observed, exerted through a change in the levels of the reactive oxygen species-modulated HIF-1 protein.

Palladium-Catalyzed Ligand-Free C-N Coupling Reactions: Selective Diheteroarylation of Amines with 2-Halobenzimidazoles

2-Aminobenzimidazoles are widely present in a number of bioactive molecules. Generally, the preparation of these molecules could be realized by the mono-substitution of 2-halobenzimidazoles with amines. However, rare examples were reported for the di-substituted products and the selectivity of mono- vs. di-substitution was relatively low. Considering the potential values of the di-substituted products, we accomplished the first selective diheteroarylation of amines with 2-halobenzimidazoles. Notably, this Pd-catalyzed transformation was realized under ligand-free conditions. Accordingly, numerous target products were efficiently produced from various aromatic or aliphatic amines and 2-halobenzimidazoles. It was worth noting that two representative products were further confirmed by X-ray crystallography. More significantly, this catalytic process could be applied to the synthesis and discovery of new bioactive compounds, which demonstrated the synthetic usefulness of this newly developed approach.

Experimental and Computational Study of the Antioxidative Potential of Novel Nitro and Amino Substituted Benzimidazole/Benzothiazole-2-Carboxamides with Antiproliferative Activity

We present the synthesis of a range of benzimidazole/benzothiazole-2-carboxamides with a variable number of methoxy and hydroxy groups, substituted with nitro, amino, or amino protonated moieties, which were evaluated for their antiproliferative activity in vitro and the antioxidant capacity. Antiproliferative features were tested on three human cancer cells, while the antioxidative activity was measured using 1,1-diphenyl-picrylhydrazyl (DPPH) free radical scavenging and ferric reducing antioxidant power (FRAP) assays. Trimethoxy substituted benzimidazole-2-carboxamide 8 showed the most promising antiproliferative activity (IC₅₀ = 0.6–2.0 µM), while trihydroxy substituted benzothiazole-2-carboxamide 29 was identified as the most promising antioxidant, being significantly more potent than the reference butylated hydroxytoluene BHT in both assays. Moreover, the latter also displays antioxidative activity in tumor cells. The measured antioxidative capacities were rationalized through density functional theory (DFT) calculations, showing that 29 owes its activity to the formation of two [O•∙∙∙H–O] hydrogen bonds in the formed radical. Systems 8 and 29 were both chosen as lead compounds for further optimization of the benzazole-2-carboxamide scaffold in order to develop more efficient antioxidants and/or systems with the antiproliferative activity.

Identification of 3-(benzazol-2-yl)quinoxaline derivatives as potent anticancer compounds: Privileged structure-based design, synthesis, and bioactive evaluation in vitro and in vivo

Inspired by the common structural characteristics of numerous known antitumor compounds targeting DNA or topoisomerase I, 3-(benzazol-2-yl)-quinoxaline-based scaffold was designed via the combination of two important privileged structure units -quinoxaline and benzazole. Thirty novel 3-(benzazol-2-yl)-quinoxaline derivatives were synthesized and evaluated for their biological activities. The MTT assay indicated that most compounds possessed moderate to potent antiproliferation effects against MGC-803, HepG2, A549, HeLa, T-24 and WI-38 cell lines. 3-(Benzoxazol- -2-yl)-2-(N-3-dimethylaminopropyl)aminoquinoxaline (12a) exhibited the most potent cytotoxicity, with IC₅₀ values ranging from 1.49 to 10.99 μM against the five tested cancer and one normal cell line. Agarose-gel electrophoresis assays suggested that 12a did not interact with intact DNA, but rather it strongly inhibited topoisomerase I (Topo I) via Topo I-mediated DNA unwinding to exert its anticancer activity. The molecular modeling study indicated that 12a adopt a unique mode to interact with DNA and Topo I. Detailed biological study of 12a in MGC-803 cells revealed that 12a could arrest the cell cycle in G2 phase, inducing the generation of reactive oxygen species (ROS), the fluctuation of intracellular Ca²⁺, and the loss of mitochondrial membrane potential (ΔΨm). Western Blot analysis indicated that 12a-treatment could significantly up-regulate the levels of pro-apoptosis proteins Bak, Bax, and Bim, down-regulate anti-apoptosis proteins Bcl-2 and Bcl-xl, and increase levels of cyclin B1 and CDKs inhibitor p21, cytochrome c, caspase-3, caspase-9 and their activated form in MGC-803 cells in a dose-dependent manner to induce cell apoptosis via a caspase-dependent intrinsic mitochondria-mediated pathway. Studies in MGC-803 xenograft tumors models demonstrated that 12a could significantly reduce tumor growth in vivo at doses as low as 6 mg/kg with low toxicity. Its convenient preparation and potent anticancer efficacy in vivo makes the 3-(benzazol-2-yl)quinoxaline scaffold a promising new chemistry entity for the development of novel chemotherapeutic agents.

Therapeutic advancement of benzothiazole derivatives in the last decennial period

Benzothiazole, a fused heterocyclic moiety, has attracted synthetic and medicinal chemists for good reasons. It is a valuable scaffold that possesses diverse biological activities, such as anticancer, anti-inflammatory, antimicrobial, antiviral, antimalarial, and anticonvulsant effects. This review mainly focusses on the recent research work on the different biological activities of benzothiazole-based compounds.