Potent, orally active heterocycle-based combretastatin A-4 analogues: synthesis, structure-activity relationship, pharmacokinetics, and in vivo antitumor activity evaluation

The protocatechuic acid-based deep eutectic solvent-mediated green synthesis of 1,2,4,5-tetrasubstituted imidazoles

A novel protocatechuic acid-based deep eutectic solvent (ETPPBr/PCA-DES) was prepared by mixing ethyltriphenylphosphonium bromide (ETPPBr) and protocatechuic acid (PCA = 3,4-dihydroxybenzoic acid), and its structure was fully investigated by using the FT-IR, TGA/DTA, densitometer, eutectic point and 1H NMR techniques. Different molar ratios of ETPPBr to PCA were examined and the eutectic point phase diagram showed that the best ratio for the synthesis of the new DES is the one-to-one ratio of the two starting materials (ETPPBr and PCA). Then, the novel DES was used as a new and capable catalyst for the green synthesis of diverse 1,2,4,5-tetrasubstituted imidazoles a1-a12 from the four-component condensation reaction of phenanthrene-9,10-dione, aromatic amine, aromatic aldehyde, and ammonium acetate with high yields and very short reaction times. High yields and very short reaction times are two advantages of our proposed method compared with the previous reported methods.

Synthesis, Characterization, Molecular Docking, and Investigation of Antibacterial Properties of New Derivatives of 1-H-Phenanthro [9,10-d] Imidazole

In this study, several imidazole derivatives in one pot multicomponent reaction from various aldehydes 1(a-z), 9,10-phenanthrenequinone, or benzyl (2), and ammonium acetate (3) were synthesized in the presence of acetic acid (AcOH) under reflux conditions at 120 °C. Also, the photochromic properties of synthesized compounds were investigated in AcOH as a solvent under laboratory conditions at a temperature of 120 °C. Moreover, the antibacterial activity of the synthesized compounds was investigated. The structure of the products was confirmed using FT-IR, UV-Vis, 1H-NMR, and 13CNMR spectroscopy. The antimicrobial activity of these compounds against gram-positive bacteria including Bacillus subtilis (B. subtilis) and gram-negative bacteria including Escherichia coli (E.coli) bacteria was evaluated by the Well diffusion (WD) method, and the compounds 4 o showed significant results for both antibacterial activity. To gain insight into how these compounds interact with two types of targets, i. e., human topoisomerase II alpha (5GWK) and acetylcholinesterase (7AIX), binding calculations have been used that provide significant results for both targets and show that most ligands can effectively bind to cleft nucleotides. Interfere in the first one or be well placed in them. Hydrophobic pocket in the dimension, which can ultimately lead to high scores achieved.

Modular synthesis of functional libraries by accelerated SuFEx click chemistry

Accelerated SuFEx Click Chemistry (ASCC) is a powerful method for coupling aryl and alkyl alcohols with SuFEx-compatible functional groups. With its hallmark favorable kinetics and exceptional product yields, ASCC streamlines the synthetic workflow, simplifies the purification process, and is ideally suited for discovering functional molecules. We showcase the versatility and practicality of the ASCC reaction as a tool for the late-stage derivatization of bioactive molecules and in the array synthesis of sulfonate-linked, high-potency, microtubule targeting agents (MTAs) that exhibit nanomolar anticancer activity against multidrug-resistant cancer cell lines. These findings underscore ASCC's promise as a robust platform for drug discovery.

3,4-Diarylisoxazoles-Analogues of Combretastatin A-4: Design, Synthesis, and Biological Evaluation In Vitro and In Vivo

Focusing on the molecular docking results, a series of 3,4-diarylisoxazoles, analogues of Combretastatin A4, bearing various substituents at the fifth position of the isoxazole ring and pharmacophore groups bioisosteric to methoxy substituent at ring B, were synthesized in good yields and high regioselectivity. Depending on the substituent at C5, three approaches were chosen for the construction of isoxazole ring, including nitrosation of gem-dihalocyclopropanes, nitrile oxide synthesis, and difluoromethoxylation of isoxazolone to afford 5-haloisoxazoles, 5-unsubstituted isoxazoles, and 5-difluoromethoxyisoxazoles, respectively. Isoxazoles 43 and 45 showed selective cytotoxicity and antitubulin inhibition properties in vitro, with pharmacodynamic profiles closely related to that of CA-4. Both of them slow down tumor growth (66-74%) in mouse xenografts and slightly exceed in effectiveness Combretastatin A4-phosphate itself.

Exploring antibiofilm potential of some new imidazole analogs against C. albicans: synthesis, antifungal activity, molecular docking and molecular dynamics studies

A series of 1, 2, 4, 5-tetrasubstituted imidazole derivatives were synthesized and their antibiofilm potential against Candida albicans was evaluated in vitro. Two of the synthesized derivatives 5e (IC50 = 25 µg/mL) and 5m (IC50 = 6 µg/mL),displayed better antifungal and antibiofilm potential than the standard drug Fluconazole (IC50 = 40 µg/mL) against C. albicans. Based on the in vitro results, we escalated the real time polymerase chain reaction (RT-PCR) analysis to gain knowledge of the enzymes expressed in the generation and maintenance of biofilms and the mechanism of biofilm inhibition by the synthesized analogues. We then investigated the possible interactions of the synthesized compounds in inhibiting agglutinin-like proteins, namely Als3, Als4 and Als6 were prominently down-regulated using in-silico molecular docking analysis against the previously available crystal structure of Als3 and constructed structure of Als4 and Als6 using the SWISS-MODEL server. The stability and energy of the agglutinin-like proteins-ligand complexes were evaluated using molecular dynamics simulations (MDS). According to the 100 ns MDS, all the compounds remained stable, formed a maximum of 3, and on average 2 hydrogen bonds, and Gibb's free energy landscape analysis suggested greater affinity of the compounds 5e and 5m toward Als4 protein.Communicated by Ramaswamy H. Sarma.

Development of QTMP: A promising anticancer agent through NP-Privileged Motif-Driven structural modulation

In this study of creating new molecules from clinical trial agents, an approach of Combretastatin structural modulation with the installation of NP-privileged motifs was considered, and a series of trimethoxyphenyl-2-aminoimidazole with functionalized quinolines and isoquinolines was investigated. An exciting method of quinoline C3-H iodination coupled with imidazopyridine-C3-H arylation and hydrazine-mediated fused-ring cleavage enabled synthesizing a class of compounds with two specific unsymmetric aryl substitutions. Interestingly, three compounds (6, 11, and 13) strongly inhibited HeLa cell proliferation with a half-maximal inhibitory concentration (10-46 nM). Among the compounds, compound 6 (QTMP) showed stronger antiproliferative ability than CA-4 (a clinical trial agent) in various cancer cell lines, including cervical, lung, breast, highly metastatic breast, and melanoma cells. QTMP inhibited the assembly of purified tubulin, depolymerized microtubules of A549 lung carcinoma cells, produced defective spindles, and arrested the cells in the G2/M phase. Further, QTMP binds to the colchicine site in tubulin with a dissociation constant of 5.0 ± 0.6 µM. QTMP displayed higher aqueous stability than CA-4 at 37 °C. Further, in silico analysis of QTMP indicated excellent drug-like properties, including good aqueous solubility, balanced hydrophilicity-lipophilicity, and high GI-absorption ability. The results together suggest that QTMP has anticancer potential.

Novel Indole-Pyrazole Hybrids as Potential Tubulin-Targeting Agents; Synthesis, antiproliferative evaluation, and molecular modeling studies

Structurally diverse indole-3-pyrazole-5-carboxamide analogues (10-29) were designed, synthesized, and evaluated for their antiproliferative activity against three cancer cell lines (Huh7, MCF-7, and HCT116) using the sulforhodamine B assay. Some of the derivatives showed anticancer activities equal to or better than sorafenib against cancer cell lines. Compounds 18 showed potent activity against the hepatocellular cancer (HCC) cell lines, with IC50 values in the range 0.6-2.9 μM. Compound 18 also exhibited moderate inhibitory activity against tubulin polymerization (IC50 = 19 μM). Flow cytometric analysis of cultured cells treated with 18 also demonstrated that the compound caused cell cycle arrest at the G2/M phase in both Huh7 and Mahlavu cells and induced apoptotic cell death in HCC cells. Docking simulations were performed to determine possible modes of interaction between 18 and the colchicine site of tubulin and quantum mechanical calculations were performed to observe the electronic nature of 18 and to support docking results.

Copper borate (CuB4O7)-promoted multi-component green synthesis of 2,4,5-triarylimidazole derivatives and evidence of in situ conversion of copper borate (CuB4O7) into Cu(OAc)2 in the presence of NH4OAc

A green, efficient, and straightforward methodology for the three-component synthesis of 2,4,5-triarylimidazole has been developed under solvent-free conditions using unconventional CuB₄O₇ as a promoter. This green approach encouragingly provides access to a library of 2,4,5-tri-arylimidazole. Also, we have been able to isolate the compound (5) and (6) in situ, which provides an insight into the direct conversion of CuB₄O₇ into copper acetate in the presence of NH₄OAc under solvent-free condition. The main advantage of this protocol includes an easy reaction procedure, short reaction time, and easy work up of the product without using any tedious separation method.

Exploring the untapped catalytic application of a ZnO/CuI/PPy nanocomposite for the green synthesis of biologically active 2,4,5-trisubstituted imidazole scaffolds

This work is focused on designing an innovative, efficient, and reusable heterogeneous ZnO/CuI/PPy nanocomposite via the self-assembly approach where pyrrole is oxidized into polypyrrole (PPy) and pyrrole also behaves as a reductant in the presence of KI. This so-obtained material was characterized by XRD, FTIR, FESEM, EDX, TEM, XPS, and ICP. TEM clearly shows a spherical morphology with the particle size ranging between 18 and 42 nm. The fabricated nanomaterial was tested for one-pot catalytic synthesis of biologically active 2,4,5-trisubstituted imidazoles under solvent-free conditions. The present work includes the benefits of an easy work-up procedure, higher product yield, shorter reaction duration, and no additional additive requirement under green and sustainable conditions. Moreover, the catalyst exhibited reusability for six runs with no considerable reduction in the respective yields and reactivity (confirmed by XRD, SEM, and TEM of the recycled catalyst). The ICP study shows very low leaching of copper (2.08 ppm) and zinc (0.12 ppm) metals. The approach also presented better values of green metrics like the E-factor, process mass intensity, carbon efficiency and reaction mass efficiency.

Ligand-Directed Photocatalysts and Far-Red Light Enable Catalytic Bioorthogonal Uncaging inside Live Cells

Described are ligand-directed catalysts for live-cell, photocatalytic activation of bioorthogonal chemistry. Catalytic groups are localized via a tethered ligand either to DNA or to tubulin, and red light (660 nm) photocatalysis is used to initiate a cascade of DHTz oxidation, intramolecular Diels-Alder reaction, and elimination to release phenolic compounds. Silarhodamine (SiR) dyes, more conventionally used as biological fluorophores, serve as photocatalysts that have high cytocompatibility and produce minimal singlet oxygen. Commercially available conjugates of Hoechst dye (SiR-H) and docetaxel (SiR-T) are used to localize SiR to the nucleus and microtubules, respectively. Computation was used to assist the design of a new class of redox-activated photocage to release either phenol or n-CA4, a microtubule-destabilizing agent. In model studies, uncaging is complete within 5 min using only 2 μM SiR and 40 μM photocage. In situ spectroscopic studies support a mechanism involving rapid intramolecular Diels-Alder reaction and a rate-determining elimination step. In cellular studies, this uncaging process is successful at low concentrations of both the photocage (25 nM) and the SiR-H dye (500 nM). Uncaging n-CA4 causes microtubule depolymerization and an accompanying reduction in cell area. Control studies demonstrate that SiR-H catalyzes uncaging inside the cell, and not in the extracellular environment. With SiR-T, the same dye serves as a photocatalyst and the fluorescent reporter for microtubule depolymerization, and with confocal microscopy, it was possible to visualize microtubule depolymerization in real time as the result of photocatalytic uncaging in live cells.

Cytotoxic and apoptotic effects of some (R)-carvone-isoxazoline derivatives on human fibrosarcoma and carcinoma cells: experimental evaluation for cytotoxicity, molecular docking and molecular dynamics studies

This study aimed to analyze the cytotoxic and apoptotic effects of isoxazoline derivatives with monoterpene scaffold 9a-e in HT-1080 fibrosarcoma, MCF-7, and MDA-MB-231 breast carcinoma, and A-549 lung carcinoma. The cytotoxic effects data revealed that compounds 9a-e generally induced significant cell growth inhibition in all cell lines, with IC₅₀ ranging from 10 to 30 µM. However, for compounds 9c and 9e, the IC₅₀ reached a value of 100 µM in HT-1080 cells. Compounds 9a, 9b, and 9d could induce apoptosis in HT-1080 cells as demonstrated by Annexin-V labeling and Caspase-3/7 activity. The apoptotic effect was accompanied by cell cycle arrest in the S phase. Molecular docking and molecular dynamics confirmed the empirical assay results and confirmed the stability of the complex with the inhibition of the anti-apoptotic protein, leading to cancer cell death. Overall, these data suggest that the proposed isoxazoline derivatives may be potential candidates for further investigation to evaluate their efficacy and optimal use in cancer treatment.Communicated by Ramaswamy H. Sarma.

Recent Advances of Tubulin Inhibitors Targeting the Colchicine Binding Site for Cancer Therapy

Cancer accounts for numerous deaths each year, and it is one of the most common causes of death worldwide, despite many breakthroughs in the discovery of novel anticancer candidates. Each new year the FDA approves the use of new drugs for cancer treatments. In the last years, the biological targets of anticancer agents have started to be clearer and one of these main targets is tubulin protein; this protein plays an essential role in cell division, as well as in intracellular transportation. The inhibition of microtubule formation by targeting tubulin protein induces cell death by apoptosis. In the last years, numerous novel structures were designed and synthesized to target tubulin, and this can be achieved by inhibiting the polymerization or depolymerization of the microtubules. In this review article, recent novel compounds that have antiproliferation activities against a panel of cancer cell lines that target tubulin are explored in detail. This review article emphasizes the recent developments of tubulin inhibitors, with insights into their antiproliferative and anti-tubulin activities. A full literature review shows that tubulin inhibitors are associated with properties in the inhibition of cancer cell line viability, inducing apoptosis, and good binding interaction with the colchicine binding site of tubulin. Furthermore, some drugs, such as cabazitaxel and fosbretabulin, have been approved by FDA in the last three years as tubulin inhibitors. The design and development of efficient tubulin inhibitors is progressively becoming a credible solution in treating many species of cancers.

2-Amino-4-aryl-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitriles with microtubule disruptive, centrosome declustering and antiangiogenic effects in vitro and in vivo

A series of fifteen 2‐amino‐4‐aryl‐5‐oxo‐4,5‐dihydropyrano[3,2‐c]chromene‐3‐carbonitriles (1 a–o) were synthesized via a three‐component reaction of 4‐hydroxycoumarin, malononitrile, and diversely substituted benzaldehydes or pyridine carbaldehydes. The compounds were tested for anticancer activities against a panel of eight human tumor cell lines. A few derivatives with high antiproliferative activities and different cancer cell specificity were identified and investigated for their modes of action. They led to microtubule disruption, centrosome de‐clustering and G2/M cell cycle arrest in 518 A2 melanoma cells. They also showed anti‐angiogenic effects in vitro and in vivo.

Synthesis and characterization of novel combretastatin analogues of 1,1-diaryl vinyl sulfones, with antiproliferative potential via in-silico and in-vitro studies

Novel 1,1-diaryl vinyl-sulfones analogues of combretastatin CA-4 were synthesized via Suzuki-Miyaura coupling method and screened for in-vitro antiproliferative activity against four human cancer cell lines: MDA-MB 231(breast cancer), HeLa (cervical cancer), A549 (lung cancer), and IMR-32 (neuroblast cancer), along with a normal cell line HEK-293 (human embryonic kidney cell) by employing 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. The compounds synthesised had better cytotoxicity against the A549 and IMR-32 cell lines compared to HeLa and MDA-MB-231 cell lines. The synthesized compounds also showed significant activity on MDA-MB-231 cancer cell line with IC₅₀ of 9.85-23.94 µM, and on HeLa cancer cell line with IC₅₀ of 8.39-11.70 µM relative to doxorubicin having IC₅₀ values 0.89 and 1.68 µM respectively for MDA-MB-231 and HeLa cell lines. All the synthesized compounds were not toxic to the growth of normal cells, HEK-293. They appear to have a higher binding affinity for the target protein, tubulin, PDB ID = 5LYJ (beta chain), relative to the reference compounds, CA4 (- 7.1 kcal/mol) and doxorubicin (- 7.2 kcal/mol) except for 4E, 4M, 4N and 4O. The high binding affinity for beta-tubulin did not translate into enhanced cytotoxicity but the compounds (4G, 4I, 4J, 4M, 4N, and 4R, all having halogen substituents) that have a higher cell permeability (as predicted in-silico) demonstrated an optimum cytotoxicity against the tested cell lines in an almost uniform manner for all tested cell lines. The in-silico study provided insight into the role that cell permeability plays in enhancing the cytotoxicity of this class of compounds and as potential antiproliferative agents.

Imidazole Analogs of Vascular-Disrupting Combretastatin A-4 with Pleiotropic Efficacy against Resistant Colorectal Cancer Models

Specific targeting of the tumoral vasculature by vascular-disrupting agents (VDA), of which combretastatin A-4 (CA-4) is a main representative, has been considered a new therapeutic strategy against multidrug-resistant tumors. In addition, CA-4 and analogs are tubulin-targeting agents and can exert direct antitumor effects by different mechanisms. Herein, we analyzed a series of synthetic CA-4 analogs featuring N-methylimidazole-bridged Z-alkenes with different halo- or amino-substituted aryl rings in vitro and in vivo, focusing on models of colorectal cancer. Combined in vitro/in vivo structure-activity relationship studies using cell lines and xenograft tumors susceptible to VDA-induced vascular damage demonstrated a clear association of cytotoxic and vascular-disrupting activity with the ability to inhibit tubulin polymerization, which was determined by specific substitution constellations. The most active compounds were tested in an extended panel of colorectal cancer (CRC) cell lines and showed activity in CA-4-resistant and chemotherapy-resistant cell lines. The bromo derivative brimamin was then compared with the known fosbretabulin (CA-4P) by activity tests on DLD-1- (multidrug-resistant) and HT29- (CA-4-resistant) derived xenograft tumors. Treatment did not induce pronounced vascular-disrupting effects in these tumors. Histological analyses revealed distinct tumor substructures and vessel compositions of DLD-1/HT29 tumors, which clearly differed from the tumor models susceptible to VDA treatment. Even so, brimamin effectively retarded the growth of DLD-1 tumors, overcoming their resistance to standard treatment, and it inhibited the outgrowth of disseminated HT29 tumor cells in an experimental metastasis model. In conclusion, combretastatin analogous N-methylimidazoles proved capable of inducing vascular-disrupting effects, comparable to those of CA-4P. In addition, they showed antitumor activities in models of drug-resistant colorectal cancer, independent of vascular-disrupting effects.

Design and discovery of new antiproliferative 1,2,4-triazin-3(2H)-ones as tubulin polymerization inhibitors targeting colchicine binding site

Thirty-five new colchicine binding site inhibitors have been designed and synthesized based on the 1,2,4-triazin-3(2H)-one nucleus. Such molecules were synthesized through a cascade reaction between readily accessible α-amino ketones and phenyl carbazate as a masked N-isocyanate precursor. The synthesized derivatives are cisoid restricted combretastatin A4 analogues containing 1,2,4-triazin-3(2H)-one in place of the olefinic bond, and they have the same essential pharmacophoric features of colchicine binding site inhibitors. The synthesized compounds were evaluated in vitro for their antiproliferative activities against a panel of three human cancer cell lines (MCF-7, HepG-2, and HCT-116), using colchicine as a positive control. Among them, two compounds 5i and 6i demonstrated a significant antiproliferative effect against all cell lines with IC₅₀ ranging from 8.2 - 18.2 µM. Further investigation was carried out for the most active cytotoxic agents as tubulin polymerization inhibitors. Compounds 5i and 6i effectively inhibited microtubule assembly with IC₅₀ values ranging from 3.9 to 7.8 µM. Tubulin polymerization assay results were found to be comparable with the cytotoxicity results. The cell cycle analysis revealed significant G2/M cell cycle arrest of the analogue 5i in HepG-2 cells. The most active compounds 4i, 4j, 5 g, 5i and 6i did not induce significant cell death in normal human lung cells Wl-38, suggesting their selectivity against cancer cells. Also, These compounds upregulated the level of active caspase-3 and boosted the levels of the pro-apoptotic protein Bax by five to seven folds in comparison to the control. Moreover, apoptosis analyses were conducted for compound 5i to evaluate its apoptotic potential. Finally, in silico studies were conducted to reveal the probable interaction with the colchicine binding site. ADME prediction study of the designed compounds showed that they are not only with promising tubulin polymerization inhibitory activity but also with favorable pharmacokinetic and drug-likeness properties.

Synthesis and Biological Evaluation of 2,3,4-Triaryl-1,2,4-oxadiazol-5-ones as p38 MAPK Inhibitors

A series of azastilbene derivatives, characterized by the presence of the 1,2,4-oxadiazole-5-one system as a linker of the two aromatic rings of stilbenes, have been prepared as novel potential inhibitors of p38 MAPK. Biological assays indicated that some of the synthesized compounds are endowed with good inhibitory activity towards the kinase. Molecular modeling data support the biological results showing that the designed compounds possess a reasonable binding mode in the ATP binding pocket of p38α kinase with a good binding affinity.

Combretastatin A-4 sulfur-containing heterocyclic derivatives: Synthesis, antiproliferative activities and molecular docking studies

Combretastatin A-4 inspired heterocyclic derivatives were synthesized and evaluated for their biological activities on tubulin polymerization and cell proliferation. Among the 19 described sulfur-containing compounds, derivatives (Z)-4h and (Z)-4j exhibited interesting in cellulo tubulin polymerization inhibition and antiproliferative activities with IC₅₀ values for six different cell lines between 8 and 27 nM. Furthermore, in silico docking studies within the colchicine/CA-4 binding site of tubulin were carried out to understand the interactions of our products with the protein target. The effects on the cell cycle of follicular lymphoma cells were also investigated at 1-10 nM concentrations showing that apoptotic processes occurred.

Tubulin Inhibitors Binding to Colchicine-Site: A Review from 2015 to 2019

Due to the three domains of the colchicine-site which is conducive to the combination with small molecule compounds, colchicine-site on the tubulin has become a common target for antitumor drug development, and accordingly, a large number of tubulin inhibitors binding to the colchicine-site have been reported and evaluated over the past years. In this study, tubulin inhibitors targeting the colchicine-site and their application as antitumor agents were reviewed based on the literature from 2015 to 2019. Tubulin inhibitors were classified into ten categories according to the structural features, including colchicine derivatives, CA-4 analogs, chalcone analogs, coumarin analogs, indole hybrids, quinoline and quinazoline analogs, lignan and podophyllotoxin derivatives, phenothiazine analogs, N-heterocycle hybrids and others. Most of them displayed potent antitumor activity, including antiproliferative effects against Multi-Drug-Resistant (MDR) cell lines and antivascular properties, both in vitro and in vivo. In this review, the design, synthesis and the analysis of the structure-activity relationship of tubulin inhibitors targeting the colchicine-site were described in detail. In addition, multi-target inhibitors, anti-MDR compounds, and inhibitors bearing antitumor activity in vivo are further listed in tables to present a clear picture of potent tubulin inhibitors, which could be beneficial for medicinal chemistry researchers.

A novel series of benzothiazepine derivatives as tubulin polymerization inhibitors with anti-tumor potency

In this work, a series of diaryl benzo[b][1,4]thiazepine derivatives D1-D36 were synthesized and screened as tubulin polymerization inhibitors with anti-tumor potency. They were designed by introducing the seven-member ring benzothiazepine as the linker for CA-4 modification for the first time. Among them, the hit compound D8 showed potential on inhibiting the growth of several cancer cell lines (IC₅₀ values: 1.48 μM for HeLa, 1.47 μM for MCF-7, 1.52 μM for HT29 and 1.94 μM for A549), being comparable with the positive controls Colchicine and CA-4P. The calculated IC₅₀ value of D8 as an tubulin polymerization inhibitor was 1.20 μM. The results of the flow cytometry assay revealed that D8 could induce the mitotic catastrophe and the death of living cancer cells. D8 also indicated the anti-vascular activity. The possible binding pattern was implied by docking simulation, inferring the possibility of introducing interactions with the nearby tubulin chain. Since the novel structural trial has been conducted with preliminary discussion, this work might stimulate new ideas in further modification of tubulin-related anti-cancer agents and therapeutic approaches.

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.

Development of novel and green NiFe2O4/geopolymer nanocatalyst based on bentonite for synthesis of imidazole heterocycles by ultrasonic irradiations

Geopolymers as aluminosilicate inorganic polymers and eco-friendly building materials which can be used as substrate for different kinds of composite. In this research, according to the fabrication of geopolymer based on bentonite as a substrate and embedment of NiFe2O4 nanoparticles in the construction of this polymer, the synthesis of a new magnetic nanocomposite (NiFe2O4/geopolymer) was investigated for the first time. In order to describe its chemistry and morphology features, different analyses such as Fourier transform infrared spectroscopy, field-emission scanning electron microscopy and transmission electron microscopy images, Brunauer-Emmet-Teller adsorption-desorption isotherm, X-ray diffraction pattern, energy-dispersive X-ray analysis, thermogravimetric analysis, and vibrating-sample magnetometer analysis were used. The application of this novel nanocatalyst was studied for one-pot three-component condensation reaction of substituted imidazole derivatives by accelerated ultrasonic irradiations. Compared to the other conventional catalysts which were used for the synthesis of imidazole derivatives, the green synthesis method for fabrication of this heterogeneous and magnetic nanocatalyst, its high thermal stability, being eco-friendly, noticeable efficiency and easy reusability have become privileges to be superior.

Synthesis, biological evaluation, and modeling studies of 1,3-disubstituted cyclobutane-containing analogs of combretastatin A4

With the aim of circumventing the adverse cis/trans-isomerization of combretastatin A4 (CA4), a naturally occurring tumor-vascular disrupting agent, we designed novel CA4 analogs bearing 1,3-cyclobutane moiety instead of the cis-stilbene unit of the parent compound. The corresponding cis and trans cyclobutane-containing derivatives were prepared as pure diastereomers. The structure of the target compounds was confirmed by X-ray diffraction study. The title compounds were evaluated for their cytotoxic properties in human cancer cell lines HepG2 (hepatocarcinoma) and SK-N-DZ (neuroblastoma), and the overall activity was found in micromolar range. Molecular docking studies and molecular dynamics simulation within the colchicine binding site of tubulin were in good agreement with the obtained cytotoxicity data.

Copper-catalyzed [2+3]-annulation of N-H imines with vinyl azides: access to polyaryl 2H-imidazoles

A practical method for the synthesis of 2H-imidazoles via a [2+3] annulation of N-H imines with vinyl azides using a copper catalyst is developed. In this conversion, environmentally friendly oxygen is used as the sole oxidant and N2 and H2O are the only by-products. The catalytic transformation, operating under mild conditions, is operationally simple and is considered as a readily available catalytic system having good substrate and functional compatibility with high atom-efficiency without the need for additional ligands or additives.

Tubulin inhibitors: Discovery of a new scaffold targeting extra-binding residues within the colchicine site through anchoring substituents properly adapted to their pocket by a semi-flexible linker

Bis-hydrazides 13a-h were designed and synthesized as potential tubulin inhibitors selectively targeting the colchicine site between α- and β-tubulin subunits. The newly designed ring-B substituents were assisted at their ends by 'anchor groups' which are expected to exert binding interaction(s) with new additional amino acid residues in the colchicine site (beyond those amino acids previously reported to interact with reference inhibitors as CA-4 and colchicine). Conformational flexibility of bis-hydrazide linker assisted these 'extra-binding' properties through reliving ligands' strains in the final ligand-receptor complexes. Compound 13f displayed the most promising computational and biological study results in the series: MM/GBSA binding energy of -62.362 kcal/mol (extra-binding to Arg α:221, Thr β:353 & Lys β:254); 34% NCI-H522 cells' death (at 10 µM), IC₅₀ = 0.073 µM (MTT assay); significant cell cycle arrest at G2/M phase; 11.6% preG1 apoptosis induction and 83.1% in vitro tubulin inhibition (at concentration = IC₅₀). Future researchers in bis-hydrazide tubulin inhibitors are advised to consider the 2-chloro-N-(4-substituted-phenyl)acetamide derivatives as compound 13f due to extra-binding properties of their ring B.

Colchicine-Binding Site Inhibitors from Chemistry to Clinic: A Review

It is over 50 years since the discovery of microtubules, and they have become one of the most important drug targets for anti-cancer therapies. Microtubules are predominantly composed of the protein tubulin, which contains a number of different binding sites for small-molecule drugs. There is continued interest in drug development for compounds targeting the colchicine-binding site of tubulin, termed colchicine-binding site inhibitors (CBSIs). This review highlights CBSIs discovered through diverse sources: from natural compounds, rational design, serendipitously and via high-throughput screening. We provide an update on CBSIs reported in the past three years and discuss the clinical status of CBSIs. It is likely that efforts will continue to develop CBSIs for a diverse set of cancers, and this review provides a timely update on recent developments.

Visible light-emitting diode light-driven one-pot four component synthesis of poly-functionalized imidazoles under catalyst- and solvent-free conditions

A visible light-emitting diode light-driven green and sustainable protocol has been demonstrated for the one-pot four component synthesis of poly-functionalized imidazoles under catalyst- and solvent-free conditions.

The Masked Polar Group Incorporation (MPGI) Strategy in Drug Design: Effects of Nitrogen Substitutions on Combretastatin and Isocombretastatin Tubulin Inhibitors

Colchicine site ligands suffer from low aqueous solubility due to the highly hydrophobic nature of the binding site. A new strategy for increasing molecular polarity without exposing polar groups—termed masked polar group incorporation (MPGI)—was devised and applied to nitrogenated combretastatin analogues. Bulky ortho substituents to the pyridine nitrogen hinder it from the hydrophobic pocket while increasing molecular polarity. The resulting analogues show improved aqueous solubilities and highly potent antiproliferative activity against several cancer cell lines of different origin. The more potent compounds showed moderate tubulin polymerization inhibitory activity, arrested the cell cycle of treated cells at the G₂/M phase, and subsequently caused apoptotic cell death represented by the cells gathered at the subG₀/G₁ population after 48 h of treatment. Annexin V/Propidium Iodide (PI) double-positive cells observed after 72 h confirmed the induction of apoptosis. Docking studies suggest binding at the colchicine site of tubulin in a similar way as combretastatin A4, with the polar groups masked by the vicinal substituents. These results validate the proposed strategy for the design of colchicine site ligands and open a new road to increasing the aqueous solubility of ligands binding in apolar environments.