3-Substituted 2-Phenylimidazo[2,1-b]benzothiazoles: Synthesis, Anticancer Activity, and Inhibition of Tubulin Polymerization

Oxidative annulation of acetophenones and 2-aminobenzothiazoles catalyzed by reusable nickel-doped LaMnO3 perovskites

Synthesis of imidazole[2,1-b]benzothiazoles often suffers from the use of pre-functionalized substrates and/or homogeneous, non-recyclable catalytic systems. Herein we report a method for direct coupling of acetophenones and 2-aminobenzothiazoles in the presence of reusable perovskites, namely LaMn_0.95Ni_0.05O₃. Imidazole[2,1-b]benzothiazoles were obtained in moderate to good yields and contained an array of useful functionalities. Control experiments indicated that the perovskites played pivotal roles in halogenation and condensation steps.

Design, synthesis and biological evaluation of benzo-[d]-imidazo-[2,1-b]-thiazole and imidazo-[2,1-b]-thiazole carboxamide triazole derivatives as antimycobacterial agents

In the search for new anti-mycobacterial agents, we revealed the importance of imidazo-[2,1-b]-thiazole and benzo-[d]-imidazo-[2,1-b]-thiazole carboxamide derivatives. We designed, in silico ADMET predicted and synthesized four series of novel imidazo-[2,1-b]-thiazole and benzo-[d]-imidazo-[2,1-b]-thiazole carboxamide analogues in combination with piperazine and various 1,2,3 triazoles. All the synthesized derivatives were characterized by ¹H NMR, ¹³C NMR, HPLC and MS spectral analysis and evaluated for in vitro antitubercular activity. The most active benzo-[d]-imidazo-[2,1-b]-thiazole derivative IT10, carrying a 4-nitro phenyl moiety, displayed IC₉₀ of 7.05 μM and IC₅₀ of 2.32 μM against Mycobacterium tuberculosis (Mtb) H37Ra, while no acute cellular toxicity was observed (>128 μM) towards the MRC-5 lung fibroblast cell line. Another benzo-[d]-imidazo-[2,1-b]-thiazole compound, IT06, which possesses a 2,4-dichloro phenyl moiety, also showed significant activity with IC₅₀ 2.03 μM and IC₉₀ 15.22 μM against the tested strain of Mtb. Furthermore, the selected hits showed no activity towards a panel of non-tuberculous mycobacteria (NTM), thus suggesting a selective inhibition of Mtb by the tested imidazo-[2,1-b]-thiazole derivatives over the selected panel of NTM. Molecular docking and dynamics studies were also carried out for the most active compounds IT06 and IT10 in order to understand the putative binding pattern, as well as stability of the protein–ligand complex, against the selected target Pantothenate synthetase of Mtb.

In the search for new anti-mycobacterial agents, we revealed the importance of imidazo-[2,1-b]-thiazole and benzo-[d]-imidazo-[2,1-b]-thiazole carboxamide derivatives.

Antiproliferative effect, alteration of cancer cell cycle progression and potential MET kinase inhibition induced by 3,4-dihydropyrimidin-2(1H)-one C5 amide derivatives

Cancer continues to be the second leading cause of death worldwide. Discovery of novel therapeutic agents has crucial importance for improvement of our medical management capabilities. Dysregulation of the MET receptor tyrosine kinase pathway plays an important role in cancer progression, making this receptor an attractive molecular target for anticancer drug discovery. In this study, twenty-seven 3,4-dihydropyrimidin-2(1H)-one C5 amide derivatives were synthesized and their cancer cell growth inhibitory activity was examined against MCF-7, HT-29 and MOLT-4 cells and also NIH/3T3 non-cancer cells by MTT assay. The antiproliferative effect of the most potent derivatives were tested against MET-dependent EBC-1 and MKN-45, lung and gastric cancer cell lines, respectively. MET kinase inhibition was measured by a Homogenous Time Resolved Fluorescence (HTRF) Assay. The influence of the test compounds on cell cycle was examined by RNase/PI flow cytometric assay. A number of compounds exhibited considerable antiproliferative effects against breast and colon cancer and leukemia cell lines, relatively sparing non-cancer cells. Some derivatives bearing benzothiazolyl carboxamide moiety at C5 position (15, 21, 23, 31, and 37) showed the highest activities with IC₅₀ values as low as 10.9 μM. These compounds showed antiproliferative effects also against MET-amplified cells and dose-dependently inhibited MET kinase activity. They also induced G0/G1 cell cycle arrest at lower doses and apoptosis at higher doses. Molecular docking and dynamics simulation studies confirmed the interaction of compound 23 with the active site of the MET receptor. These findings demonstrate that 3,4-dihydropyrimidin-2(1H)-one analogues may represent promising targeted anticancer agents.

Ultrasound assisted synthesis of tetrazole based pyrazolines and isoxazolines as potent anticancer agents via inhibition of tubulin polymerization

In search of new active molecules against MCF-7, A549 and HepG2, tetrazole based pyrazoline and isoxazoline derivatives under both conventional and ultrasonic irradiation method were designed and efficiently synthesized. Structures of newly synthesized compounds 5a-h and 6a-h were characterized by ¹H NMR, ¹³C NMR, MS and elemental analysis. Several derivatives were found to be excellent cytotoxic against MCF-7, A549 and HepG2 cell lines characterized by lower IC₅₀ values (0.78-3.12 µg/mL). Compounds 5b and 5c demonstrated an antiproliferative effect comparable to that of CA-4. Western blot analysis revealed that, reported compounds accumulate more tubulin in the soluble fraction. Docking studies suggested that, binding of these compounds mimics at the colchicine site of tubulin. In vitro study revealed that the tetrazole based pyrazolines and isoxazolines may possess ideal structural requirements for further development of novel therapeutic agents.

Biological Evaluation and Molecular Modeling of 3,4-dihydropyrimidine- 2(1H)-one Derivatives as Cytotoxic Agents on Breast Cancer In Vitro

Background:

Kinesins and tubulin inhibitors have attracted researchers’ attention as hopeful targets for achieving effective anticancer agents. Dihydropyrimidine-2-ones (DHPMs) inhibit motor proteins Eg5 in the polymerization process of tubulin, also scaffold bearing benzothiazole heterocycle can block tubulin polymerization/depolymerization.

Objective:

In this study, the cytotoxic effects and molecular modeling of newly synthesized derivatives of DHPM that were designed by the Scaffold-hopping approach were investigated as potential dual-inhibitors of Eg5 and tubulin.

Methods:

We investigated the cytotoxic effects of DHPMs derivatives by MTT assay and measureing the Caspase 3 activity. Also, molecular modeling studies were performed by AutoDock4 and GROMACS 4.5.6.

Results:

According to the results, the d2 derivative (IC50 = 68.58 ± 7, SI = 2.57) eliminates MDA-MB- 231 cells in a dose-dependent manner through caspase-dependent and caspase-independent cell death pathways. Molecular docking studies revealed that the d2 compound could interact with both Eg5 and tubulin key residues. MD simulation also demonstrated the stability of the studied ligand-receptor complexes during the 30 ns of the production run. The effectiveness of substitutions at C4 of the DHPM ring was obtained 4-acetoxy-phenyl, 4-methoxyphenyl, and 4-nitrophenyl, respectively.

Conclusion:

The findings of the present study provide evidence that DHPM C5 amide derivatives bearing benzothiazole ring might be considered as promising lead compounds for the discovery of novel and multi-target antitumor agents.

Synthesis of Benzo[d]imidazo[2,1-b]thiazole-Propenone Conjugates as Cytotoxic and Apoptotic Inducing Agents

BACKGROUND

Cancer can be considered as a disease in which normal cells start behaving badly, multiplying uncontrollably, ignoring signals to stop and accumulating to form a mass that is generally termed as a tumor. Apoptosis or programmed cell death is a physiological process that enables organisms to control their cell numbers in many developmental and physiological settings and to eliminate unwanted cells and it plays essential role in chemotherapy-induced tumor-cell killing. The correct balance between apoptosis and inhibition of apoptosis is important in animal development as well as in tissue homeostasis. The aim of this paper is to introduce the readers about the design strategy and synthesis of effective cytotoxic and apoptotic inducing agents based on benzo[d]imidazo[2,1-b]thiazole scaffold.

METHODS

Benzo[d]imidazo[2,1-b]thiazole-propenone conjugates were synthesized by the condensation of 7- methoxy-2-(aryl)benzo[d]imidazo[2,1-b]thiazol-3-yl)prop-2-yn-1-ones with aryl/hetero aryl amines in ethanol at room temperature. These in turn were obtained from 7-methoxy-2-(aryl)benzo[d]imidazo[2,1-b]thiazole-3- carbaldehydes on treatment with ethynylmagnesium bromide followed by oxidation.

RESULTS

3-Arylaminopropenone linked 2-arylbenzo[d]imidazo[2,1-b]thiazole conjugates prepared in this investigation exhibited significant cytotoxic activity and arrested HeLa cancer cells in G1 phase. The treatment of the conjugate led to 40% of loss of mitochondrial membrane potential (DΨm) in HeLa cells and 4 fold increase in the levels of reactive oxygen species (ROS). In addition, it induces apoptosis in HeLa cells, this was examined by the wound healing assay, Actin filaments and Hoechst staining assay.

CONCLUSION

The encouraging biological profile exhibited by these 3-arylaminopropenone 2-aryl linked benzo[d]imidazo[2,1-b]thiazole conjugates demonstrate that they have the potential to be developed as a lead by further structural modifications to obtain potential chemotherapeutic agents that are likely to target the HeLa cancer cells.

I2/DMSO mediated multicomponent reaction for the synthesis of 2-arylbenzo[d]imidazo[2,1-b] thiazole derivatives

Synthesis of a series of 2-arylbenzo[d]imidazo[2,1-b] thiazoles tethered with barbituric acid moiety has been reported from the three component reaction of 2-aminobenzothiazoles, barbituric acids and terminal aryl acetylenes or aryl methyl ketones in the presence of I2 in DMSO medium. Both conventional and microwave heating conditions can be used for this multicomponent reaction. The salient features of this methodology are: (i) formation of one C-C and two C-N bonds in one-pot under metal-free oxidation followed by cyclization, (ii) selective formation of the fused imidazole ring, (iii) wide substrate scope, (iv) easy purification of the products, (v) products having more than one pharmaceutically important motifs and (vi) gram scale synthesis possible.

Regioselective oxidative cross-coupling of benzo[d]imidazo[2,1-b]thiazoles with styrenes: a novel route to C3-dicarbonylation

A novel I₂ promoted, highly efficient metal-free and peroxide-free greener domino protocol for the C3-dicarbonylation of benzo[d]imidazo[2,1-b]thiazoles (IBTs) with styrenes has been developed via oxidative cleavage of the C(sp²)-H bond, followed by C3-nucleophilic attack of IBT and oxidation. Interestingly, under these conditions 2-(benzo[d]imidazo[2,1-b]thiazol-2-yl)aniline gave the benzo[4',5']thiazolo[2',3':2,3]imidazo[4,5-c]quinoline derivative via oxidative cleavage of the C(sp²)-H bond, followed by Pictet-Spengler cyclization and aromatization. This method offers the advantages of broad substrate scope, ecofriendly feature and high atom economy apart from higher yields.

Rational design and synthesis of 2-anilinopyridinyl-benzothiazole Schiff bases as antimitotic agents

Based on our previous results and literature precedence, a series of 2-anilinopyridinyl-benzothiazole Schiff bases were rationally designed by performing molecular modeling experiments on some selected molecules. The binding energies of the docked molecules were better than the E7010, and the Schiff base with trimethoxy group on benzothiazole moiety, 4y was the best. This was followed by the synthesis of a series of the designed molecules by a convenient synthetic route and evaluation of their anticancer potential. Most of the compounds have shown significant growth inhibition against the tested cell lines and the compound 4y exhibited good antiproliferative activity with a GI₅₀ value of 3.8µM specifically against the cell line DU145. In agreement with the docking results, 4y exerted cytotoxicity by the disruption of the microtubule dynamics by inhibiting tubulin polymerization via effective binding into colchicine domain, comparable to E7010. Detailed binding modes of 4y with colchicine binding site of tubulin were studied by molecular docking. Furthermore, 4y induced apoptosis as evidenced by biological studies like mitochondrial membrane potential, caspase-3, and Annexin V-FITC assays.

Aryl-imidazothiadiazole analogues as microtubule disrupting agents

Disruption of tubulin polymerization and the docked pose of 5k in the colchicine binding site of tubulin.

Synthesis and biological evaluation of novel pyrano[3,2-c]carbazole derivatives as anti-tumor agents inducing apoptosis via tubulin polymerization inhibition

A series of novel pyrano[3,2-c]carbazole derivatives have been synthesized and antiproliferative activity of the derivatives were investigated on various cancer cell lines.

Synthesis of β-carboline-benzimidazole conjugates using lanthanum nitrate as a catalyst and their biological evaluation

A series of β-carboline-benzimidazole conjugates bearing a substituted benzimidazole and an aryl ring at C3 and C1 respectively were designed and synthesized. The key step of their preparation was determined to involve condensation of substituted o-phenylenediamines with 1-(substituted phenyl)-9H-pyrido[3,4-b]indole-3-carbaldehyde using La(NO3)3·6H2O as a catalyst and their cytotoxic potential was evaluated. Conjugates 5a, 5d, 5h and 5r showed enhanced cytotoxic activity (GI50 values range from 0.3 to 7.1 μM in most of the human cancer cell lines) in comparison to some of the previously reported β-carboline derivatives. To substantiate the cytotoxic activity and to understand the nature of interaction of these conjugates with DNA, spectroscopy, DNA photocleavage and DNA topoisomerase I inhibition (topo-I) studies were performed. These conjugates (5a, 5d and 5r) effectively cleave pBR322 plasmid DNA in the presence of UV light. In addition, the effect of these conjugates on DNA Topo I inhibition was studied. The mode of binding of these new conjugates with DNA was also examined by using both biophysical as well as molecular docking studies, which supported their multiple modes of interaction with DNA. Moreover, an in silico study of these β-carboline-benzimidazole conjugates reveals that they possess drug-like properties.

A comprehensive review in current developments of benzothiazole-based molecules in medicinal chemistry

Benzothiazole (BTA) and its derivatives are the most important heterocyclic compounds, which are common and integral feature of a variety of natural products and pharmaceutical agents. BTA shows a variety of pharmacological properties, and its analogs offer a high degree of structural diversity that has proven useful for the search of new therapeutic agents. The broad spectrum of pharmacological activity in individual BTA derivative indicates that, this series of compounds is of an undoubted interest. The related research and developments in BTA-based medicinal chemistry have become a rapidly developing and increasingly active topic. Particularly, numerous BTA-based compounds as clinical drugs have been extensively used in practice to treat various types of diseases with high therapeutic potency. This work systematically gives a comprehensive review in current developments of BTA-based compounds in the whole range of medicinal chemistry as anticancer, antibacterial, antifungal, antiinflammatory, analgesic, anti-HIV, antioxidant, anticonvulsant, antitubercular, antidiabetic, antileishmanial, antihistaminic, antimalarial and other medicinal agents. It is believed that, this review article is helpful for new thoughts in the quest for rational designs of more active and less toxic BTA-based drugs, as well as more effective diagnostic agents and pathologic probes.

Design and synthesis of imidazo[2,1-b]thiazole-chalcone conjugates: microtubule-destabilizing agents

A series of chalcone conjugates featuring the imidazo[2,1-b]thiazole scaffold was designed, synthesized, and evaluated for their cytotoxic activity against five human cancer cell lines (MCF-7, A549, HeLa, DU-145 and HT-29). These new hybrid molecules have shown promising cytotoxic activity with IC50 values ranging from 0.64 to 30.9 μM. Among them, (E)-3-(6-(4-fluorophenyl)-2,3-bis(4-methoxyphenyl)imidazo[2,1-b]thiazol-5-yl)-1-(pyridin-2-yl)prop-2-en-1-one (11 x) showed potent antiproliferative activity with IC50 values ranging from 0.64 to 1.44 μM in all tested cell lines. To investigate the mechanism of action, the detailed biological aspects of this promising conjugate (11 x) were carried out on the A549 lung cancer cell line. The tubulin polymerization assay and immunofluoresence analysis results suggest that this conjugate effectively inhibits microtubule assembly in A549 cells. Flow cytometric analysis revealed that this conjugate induces cell-cycle arrest in the G2/M phase and leads to apoptotic cell death. This was further confirmed by Hoechst staining, activation of caspase-3, DNA fragmentation analysis, and Annexin V-FITC assay. Moreover, molecular docking studies indicated that this conjugate (11 x) interacts and binds efficiently with the tubulin protein.

Synthesis of imidazothiadiazole–benzimidazole conjugates as mitochondrial apoptosis inducers

A series of imidazothiadiazole–benzimidazole conjugates (3a–z) were synthesized and evaluated for their cytotoxic activity against a set of four selected human cancer cell lines. Compounds3band3yexhibited significant antiproliferative activity against the ME-180 (cervical) cell line.

DLJ14, a novel chemo-sensitization agent, enhances therapeutic effects of adriamycin against MCF-7/A cells both in vitro and in vivo

OBJECTIVES

We investigated the chemo-sensitization of a ligustrazine derivate, (E)-2-(2, 4-dimethoxystyryl)-3, 5, 6-trimethylpyrazine (DLJ14) on Adriamycin (Adr, Wanle, Shenzhen, China)-resistant human breast cancer (MCF-7/A) cells both in vivo and in vitro.

METHODS

The antitumour effects of DLJ14 and Adr was observed in MCF-7/A cells by 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay in vitro and was evaluated by MCF-7/A xenografts in nude mice. The intracellular Adr accumulation was assessed by mean fluorescence intensity of Adr. The messenger RNA level of glutathione (GSH) S-transferase (GST)π in MCF-7/A cells was determined by real-time reverse transcription PCR assay. The expression of GSTπ, c-jun NH2 -terminal kinase (JNK) and phosphor-JNK (p-JNK) was detected by Western blotting method.

KEY FINDINGS

The MTT results showed that DLJ14 exhibited a weak inhibition on proliferation of both MCF-7 and MCF-7/A cells, in contrast with the strong inhibition of verapamil. When DLJ14 is combined with Adr, the inhibitory effect on MCF-7/A cells and MCF-7/A xenografts was enhanced significantly through increasing intracellular accumulation of Adr by inhibition of GSH level and the activity of GSH peroxidase and GST. Moreover, DLJ14 could downregulate the expression of GSTπ and increase the expression of JNK and p-JNK in MCF-7/A cells or in xenografts.

CONCLUSION

DLJ14 is a promising chemo-sensitization candidate for the reversal of multidrug resistance in cancers.