Imidazolylpyrrolone-Based Small Molecules as Anticancer Agents for Renal Cell Carcinoma

An in silico study focused on known cancer-related target proteins, identified a selection of imidazo[4,5-b]pyrrolo[3,4-d]pyridines as potentially active. These compounds were prepared by a novel synthetic approach, designed and developed in-house, based on the reaction of 5-amino-4-cyanoformimidoyl imidazoles with N-substituted cyanoacetamides. The substituted imidazolylpyrrolones obtained, were cyclized intramolecularly to generate the intended imidazo[4,5-b]pyrrolo[3,4-d]pyridines in a process catalyzed by DBU. Treating the imidazolylpyrrolones with an excess of triethyl orthoformate and heating at 80 °C in the presence of acid catalysis led to imidazopyrrolodiazepines. These compounds were screened for their anticancer potential, using the renal cell carcinoma cell line model (A498 and 786-O cell lines). Two compounds exhibited IC₅₀ values in the low micromolar range with a good selectivity index, when compared to non-neoplastic kidney cell line HK2 and the reference compounds rapamycin, cediranib and sunitinib.     

Copper‐Catalyzed Cascade Reactions of Substituted 4‐Iodopyrazolecarbaldehydes with 1,2‐Phenylenediamines and 2‐Aminophenols

A new approach for the synthesis of novel annulated‐pyrazoles is presented. This protocol includes an intermolecular condensation followed by a copper‐mediated intramolecular C N or C O coupling reaction. The method is applied to a range of substituted 4‐iodopyrazolecarbaldehydes which react with 1,2‐phenylenediamines or 2‐aminophenols to yield substituted 2,4‐ or 1,4‐dihydrobenzo[b]pyrazolo[4,3‐e][1,4]diazepines or substituted‐2H‐ or 1H‐benzo[b]pyrazolo[3,4‐f][1,4]oxazepines, respectively.     

Structure-Based Design,Synthesis, and Biological Evaluation of Imidazo[4,5-b]Pyridin-2-one-Based p38 MAP Kinase Inhibitors: Part 2

We identified novel potent inhibitors of p38 mitogen-activated protein (MAP) kinase using a structure-based design strategy, beginning with lead compound, 3-(butan-2-yl)-6-(2,4-difluoroanilino)-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one ( 1 ). To enhance the inhibitory activity of 1 against production of tumor necrosis factor-α (TNF-α) in human whole blood (hWB) cell assays, we designed and synthesized hybrid compounds in which the imidazo[4,5-b]pyridin-2-one core was successfully linked with the p-methylbenzamide fragment. Among the compounds evaluated, 3-(3-tert-butyl-2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridin-6-yl)-4-methyl-N-(1-methyl-1H-pyrazol-3-yl)benzamide ( 25 ) exhibited potent p38 inhibition, superior suppression of TNF-α production in hWB cells, and also significant in vivo efficacy in a rat model of collagen-induced arthritis (CIA). In this paper, we report the discovery of potent, selective, and orally bioavailable imidazo[4,5-b]pyridin-2-one-based p38 MAP kinase inhibitors.     

Structure-Based Design,Synthesis, and Biological Evaluation of Imidazo[4,5-b]pyridin-2-one-Based p38 MAP Kinase Inhibitors: Part 1

We identified a lead series of p38 mitogen-activated protein kinase inhibitors using a structure-based design strategy from high-throughput screening of hit compound 1 . X-ray crystallography of 1 with the kinase showed an infrequent flip of the peptide bond between Met109 and Gly110, which was considered to lead to high kinase selectivity. Our structure-based design strategy was to conduct scaffold transformation of 1 with maintenance of hydrogen bond interactions with the flipped hinge backbone of the enzyme. In accordance with this strategy, we focused on scaffold transformation to identify imidazo[4,5-b]pyridin-2-one derivatives as potent inhibitors of the p38 MAP kinase. Of the compounds evaluated, 21 was found to be a potent inhibitor of the p38 MAP kinase, lipopolysaccharide-induced tumor necrosis factor-α (TNF-α) production in human monocytic leukemia cells, and TNF-α-induced production of interleukin-8 in human whole blood cells. Herein we describe the discovery of potent and orally bioavailable imidazo[4,5-b]pyridin-2-one-based p38 MAP kinase inhibitors that suppressed cytokine production in a human whole blood cell-based assay.     

Microbial O‐demethylation of sinesetin and antimutagenic activity of the metabolite

Biotransformation of sinesetin by Aspergillus niger afforded 4′‐hydroxy‐5,6,7,3′‐tetramethoxyflavone on the basis of its spectroscopic data including IR, heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bond connectivity (HMBC) analysis. Sinesetin and the metabolite showed antimutagenic activity against chemical mutagens 4‐dimethyl‐3H‐imidazo[4,5‐f]quinolin‐2‐amine (MeIQ) and 3‐amino‐14‐dimethyl‐5H‐pyrido[4,3‐b]indole (Trp‐P‐1) in the umu test using Salmonella typhimurium TA1535/pSK1002. Copyright © 2005 Society of Chemical Industry     

Synthesis and in vivo Evaluation of Fluorine‐18 and Iodine‐123 Pyrazolo[4,3‐e]‐1,2,4‐triazolo[1,5‐c]pyrimidine Derivatives as PET and SPECT Radiotracers for Mapping A2A Receptors

Imaging agents that target adenosine type 2A (A_2A) receptors play an important role in evaluating new pharmaceuticals targeting these receptors, such as those currently being developed for the treatment of movement disorders like Parkinson′s disease. They are also useful for monitoring progression and treatment efficacy by providing a noninvasive tool to map changes in A_2A receptor density and function in neurodegenerative diseases. We previously described the successful evaluation of two A_2A‐specific radiotracers in both nonhuman primates and in subsequent human clinical trials: [¹²³I]MNI‐420 and [¹⁸F]MNI‐444. Herein we describe the development of both of these radiotracers by selection from a series of A_2A ligands, based on the pyrazolo[4,3‐e]‐1,2,4‐triazolo[1,5‐c]pyrimidine core of preladenant. Each of this series of 16 ligands was found to bind to recombinant human A_2A receptor in the low nanomolar range, and of these 16, six were radiolabeled with either fluorine‐18 or iodine‐123 and evaluated in nonhuman primates. These initial in vivo results resulted in the identification of 7‐(2‐(4‐(4‐(2‐[¹⁸F]fluoroethoxy)phenyl)piperazin‐1‐yl)ethyl)‐2‐(furan‐2‐yl)‐7H‐pyrazolo[4,3‐e][1,2,4]triazolo[1,5‐c]pyrimidin‐5‐amine ([¹⁸F]MNI‐444) and 7‐(2‐(4‐(2‐fluoro‐4‐[¹²³I]iodophenyl)piperazin‐1‐yl)ethyl)‐2‐(furan‐2‐yl)‐7H‐imidazo[1,2‐c]pyrazolo[4,3‐e]pyrimidin‐5‐amine ([¹²³I]MNI‐420) as PET and SPECT radiopharmaceuticals for mapping A_2A receptors in brain.     

Synthesis of heterocyclic phosphonato esters by reaction between triphenyl phosphite and acetylenic diesters in the presence of sulfur-containing heterocyclic compounds

The reaction between triphenyl phosphite and acetylenic esters in the presence of some heterocyclic compounds such as oxazolo[4,5-b]pyridine-2(3H)-thione, 2-mercaptobenzothiazole or 2-mercaptopyrimidine led to the formation of phosphonato esters in high yield.     

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.     

An Improved Synthesis of Imidazo[4,5‐b]pyridines and Imidazo[4,5‐b]pyrazines by Palladium Catalyzed Amidation using Xantphos in a 1,4‐Dioxane:tert‐Amyl Alcohol Solvent System

Herein an improved protocol for the synthesis of imidazo[4,5‐b]pyridines and imidazo[4,5‐b]pyrazines using a palladium‐catalyzed amidation that utilizes Xantphos as an ancillary phosphine ligand is reported. The use of a binary solvent system comprised of 1,4‐dioxane and tert‐amyl alcohol was crucial in eliminating unwanted by‐products.

     

Pyridine-2(1H)-thione in heterocyclic synthesis: synthesis and antimicrobial activity of some new thio-substituted ethyl nicotinate,thieno[2,3-b]pyridine and pyridothienopyrimidine derivatives

3-(4-Bromophenyl)-2-cyanoprop-2-enethioamide (1) reacted with ethyl 3-oxo-3-phenylpropanoate (2) to give ethyl 4-(4-bromophenyl)-5-cyano-2-phenyl-6-thioxo-1,6-dihydropyridine-3-carboxylate (3). Compound 3 was taken as a starting material for the synthesis of thio-substituted ethyl nicotinate derivatives 5a–d, which underwent cyclization to the corresponding thieno[2,3-b]pyridines 6a–d. Also 3 reacted with hydrazine hydrate to give the pyrazolo[3,4-b]pyridine derivative 7, which upon diazotization gave the diazonium derivative 8. Compound 6a condensed with dimethylformamide–dimethylacetal to afford thieno[2,3-b]pyridine derivative 9, which reacted with different amines 10a–e to afford the pyridothienopyrimidine derivatives 12a–e through the Dimroth rearrangement. Moreover, compound 6a reacted with different reagents to give pyridothienopyrimidine derivatives 14a and b, 17 and pyrazolothienopyridine derivative 18. In addition, acetylating compound 6c with chloroacetylchloride afforded the 3-[(2)-chloroacetylamino]thieno[2,3-b]pyridine derivative 20, which upon cyclization yielded the corresponding 2-chloromethylpyrido[3′,2′:4,5]thieno[3,2-d]pyrimidine derivative 21. Some of the newly synthesized compounds were screened in vitro for their antimicrobial activities.

     

Critical Intermediates Reveal New Biosynthetic Events in the Enigmatic Colibactin Pathway

Colibactin is a potent genotoxin that induces DNA double‐strand breaks; it is produced by Escherichia coli strains harboring a pks+ island. However, the structure of this compound remains elusive. Here, using transformation‐associated recombination (TAR) cloning to perform heterologous expression, we took advantage of the significantly increased yield of colibactin pathway‐related compounds to determine and isolate a series of vital (pre)colibactin intermediates. The chemical structures of compounds 8 , 10 and 11 were identified by NMR and MSⁿ analyses. The new 1H‐pyrrolo[3,4‐c]pyridine‐3,6(2H,5H)‐dione‐ and thiazole‐containing compound 10 provides new insights regarding the biosynthetic pathway to (pre)colibactin and establishes foundations for future investigation of the intriguing (pre)colibactin structures and its modes of action.     

[6,7]‐Heterocycle‐Fused 14‐Hydroxymorphinan Derivatives: Design,Synthesis, and Opioid Receptor Activity

A series of new 14‐hydroxymorphinan analogues with a thiazole or imidazo[2,1‐b]thiazole fragment as the heterocyclic function fused to ring C were designed and synthesized. These compounds can be viewed as the result of a direct modification at ring C of the 14‐hydroxymorphinan scaffold. Among these compounds, three were identified as having potent binding affinity (～1 nM ) at both κ and μ receptors, and acting as agonists at κ and partial agonists or antagonists at μ receptors. In view of the promising results from studies on compounds with mixed κ and μ receptor activities, these new compounds warrant further investigation.     

3-substituted 2-phenylimidazo[2,1-b]benzothiazoles: synthesis, anticancer activity, and inhibition of tubulin polymerization

A new series of 3‐substituted 2‐phenylimidazo[2,1‐b]benzothiazoles ( 3 a – h ) were synthesized by C‐arylation of 2‐arylimidazo[2,1‐b]benzothiazoles using palladium acetate as catalyst, and the resulting compounds were evaluated for their anticancer activity. Compounds 3 a , 3 e , and 3 h exhibited good antiproliferative activity, with GI₅₀ values in the range of 0.19–83.1 μM . Compound 3 h showed potent anticancer efficacy against 60 human cancer cell lines, with a mean GI₅₀ value of 0.88 μM . This compound also induced cell‐cycle arrest in the G₂/M phase and inhibited tubulin polymerization followed by activation of caspase‐3 and apoptosis. A high‐throughput tubulin polymerization assay showed that the level of inhibition for compound 3 h is similar to that of combretastatin A‐4. Molecular modeling studies provided a molecular basis for the favorable binding of compounds 3 a , 3 e , and 3 h to the colchicine binding pocket of tubulin.     

Palladium‐Catalyzed Direct Arylations of 1,2‐Azolo[1,5‐a]pyridines using Copper(I) Chloride as a Lewis Acid Activator and the Synthesis of 2,6‐Disubstituted Pyridines

A direct method for the arylation of 1,2‐azolo[1,5‐a]pyridines has been developed. In the process, the fused pyridines react with aryl halides in the presence of the palladium complex Pd(OAc)₂(Phen) as a catalyst and copper(I) chloride (CuCl) as a Lewis acid to form arylated derivatives. While pyrazolo[1,5‐a]pyridines and [1,2,4]triazolo[1,5‐a]pyridines are arylated at ortho‐positions of their pyridine rings using this method, in situ ring‐opening of the formed C‐7 arylated [1,5‐a]pyridine takes place to generate the 2,6‐disubstituted pyridine. Also, upon treatment with lithium diisopropylamide (LDA), C‐7 arylated pyrazolo[1,5‐a]pyridine‐3‐carboxylates react to produce diversely substituted 2,6‐disubstituted pyridines. Finally, a sequential C‐3 arylation was accomplished through a two‐step sequence involving hydrolysis of pyrazolo[1,5‐a]pyridine‐3‐carboxylates followed by the bimetallic Pd/Cu‐catalyzed decarboxylative coupling reaction with aryl bromide.

     

Synthesis and Antimicrobial Activity Evaluation of Imidazole-Fused Imidazo[2,1-b][1,3,4]thiadiazole Analogues

Three series of new imidazole-fused imidazo[2,1-b][1,3,4]thiadiazole analogues (compounds 20 a – g , 21 a – g , and 22 a – g ) have been synthesized, and their antibacterial and antifungal activities have been evaluated. All the target compounds showed strong antifungal activity and high selectivity for the test fungus Candida albicans over Gram-positive and -negative bacteria. N-((4-(2-Cyclopropyl-6-(4-fluorophenyl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl)-5-(6-methyl-pyridin-2-yl)-1H-imidazol-2-yl)methyl)aniline ( 21 a ) showed the highest activity against C. albicans (MIC₅₀=0.16 μg/mL), 13 and three times that of the positive control compounds gatifloxacin and fluconazole, respectively. Compounds 21 a and 20 e did not show cytotoxicity against human foreskin fibroblast-1 cells, and compound 21 a was as safe as the positive control compounds in hemolysis tests. These results strongly suggest that some of the compounds produced in this work have value for development as antifungal agents.     

Parallel Synthesis of Pyrrolo[3,2-f]quinolines (PQQ Skeleton) Library via a One-Pot Three-Component Reaction under Catalyst-Free Conditions

An efficient and straightforward synthetic protocol was developed for the diversity-oriented synthesis of 13-aryl-6,13-dihydrochromeno[4,3-b]pyrrolo[3,2-f]quinolin- 12(3H)-one and 10-aryl-3H-furo[3,4-b]pyrrolo[3,2-f]quinolin-9(7H)-one derivatives (PQQ skeleton) in high yields under catalyst-free conditions. This procedure includes a one-pot three-component reaction of aromatic aldehyde, 1H-indol-5-amine, and 1,3-dicarbonyl compounds to generate total of 25-Membered structurally interesting and pharmacologically significant PQQ skeletons for bio-active screening.     

LEGO‐Inspired Drug Design: Unveiling a Class of Benzo[d]thiazoles Containing a 3,4‐Dihydroxyphenyl Moiety as Plasma Membrane H+‐ATPase Inhibitors

The fungal plasma membrane H⁺‐ATPase (Pma1p) is a potential target for the discovery of new antifungal agents. Surprisingly, no structure–activity relationship studies for small molecules targeting Pma1p have been reported. Herein, we disclose a LEGO‐inspired fragment assembly strategy for the design, synthesis, and discovery of benzo[d]thiazoles containing a 3,4‐dihydroxyphenyl moiety as potential Pma1p inhibitors. A series of 2‐(benzo[d]thiazol‐2‐ylthio)‐1‐(3,4‐dihydroxyphenyl)ethanones was found to inhibit Pma1p, with the most potent IC₅₀ value of 8 μm in an in vitro plasma membrane H⁺‐ATPase assay. These compounds were also found to strongly inhibit the action of proton pumping when Pma1p was reconstituted into liposomes. 1‐(3,4‐Dihydroxyphenyl)‐2‐((6‐(trifluoromethyl)benzo[d]thiazol‐2‐yl)thio)ethan‐1‐one (compound 38 ) showed inhibitory activities on the growth of Candida albicans and Saccharomyces cerevisiae, which could be correlated and substantiated with the ability to inhibit Pma1p in vitro.     

Synthesis,Thermal Stability and Impact Stability of Novel Tetranitro‐Dipyridotetraazapentalene Derivatives

The synthetic details for the construction of three new dipyridotetraazapentalene derivatives, 5H‐pyrido[3″,4″:4′,5′] [1,2,3]triazolo‐ [1′,2′:1,2][1,2,3]triazolo[5,4‐b]pyridin‐6‐ium inner salt ( 8 ), 5H‐pyrido[3″,2″:4′,5′] [1,2,3]triazolo[1′,2′:1,2] [1,2,3]triazolo[5,4‐b]‐pyridin‐6‐ium inner salt ( 15 ) and 5H‐pyrido[2″,3″:4′,5′] [1,2,3]‐triazolo[1′,2′:1,2][1,2,3]triazolo[4,5‐b]pyridin‐6‐ium inner salt ( 16 ) are presented. Nitration of ( 8 ) and ( 15 ) afforded the novel tetranitrodipyridotetraazapentalene derivatives, 2,4,8,10‐tetranitro‐5H‐pyrido[3″,4″:4′,5′][1,2,3]triazolo[1′,2′:1,2][1,2,3]‐triazolo[5,4‐b]‐pyridin‐6‐ium inner salt ( 3 ) and 2,4,8,10‐tetranitro‐5H‐pyrido[3″,2″:4′,5′][1,2,3]triazolo[1′,2′:1,2][1,2,3]‐triazolo[5,4‐b]‐pyridin‐6‐ium inner salt ( 4 ) in good yields. Both isomers, ( 3 ) and ( 4 ), exhibited high thermal stability (differential scanning calorimetric analysis and thermal gravimetric analysis) and were insensitive to impact (hammer/anvil test).     

Design and Synthesis of DNA‐Interactive β‐Carboline–Oxindole Hybrids as Cytotoxic and Apoptosis‐Inducing Agents

A new series of (E)‐3‐[(1‐aryl‐9H‐pyrido[3,4‐b]indol‐3‐yl)methylene]indolin‐2‐one hybrids were synthesized and evaluated for their in vitro cytotoxic activity against a panel of selected human cancer cell lines, namely, HCT‐15, HCT‐116, A549, NCI‐H460, and MCF‐7, including HFL. Among the tested compounds, (E)‐1‐benzyl‐5‐bromo‐3‐{[1‐(2,5‐dimethoxyphenyl)‐9H‐pyrido[3,4‐b]indol‐3‐yl]methylene}indolin‐2‐one ( 10 s ) showed potent cytotoxicity against HCT‐15 cancer cells with an IC₅₀ value of 1.43±0.26 μm and a GI₅₀ value of 0.89±0.06 μm . Notably, induction of apoptosis by 10 s on the HCT‐15 cell line was characterized by using different staining techniques, such as acridine orange/ethidium bromide (AO/EB) and DAPI. Further, to understand the mechanism of anticancer effects, various assays such as annexin V‐FITC/PI, DCFDA, and JC‐1were performed. The flow cytometric analysis revealed that compound 10 s arrests the HCT‐15 cancer cells at the G0/G1 phase of the cell cycle. Additionally, western blot analysis indicated that treatment of 10 s on HCT‐15 cancer cells led to decreased expression of anti‐apoptotic Bcl‐2 and increased protein expression of both pro‐apoptotic Bax and caspase‐3, ‐8, and ‐9, and cleaved PARP with reference to actin. Next, a clonogenic assay revealed the inhibition of colony formation in HCT‐15 cancer cells by 10 s in a dose‐dependent manner. Moreover, upon testing on normal human lung cells (HFL), the compounds were observed to be safer with a low toxicity profile. In addition, viscosity and molecular‐docking studies showed that compound 10 s has typical intercalation with DNA.     

Discovery of Mono‐ and Disubstituted 1H‐Pyrazolo[3,4]pyrimidines and 9H‐Purines as Catalytic Inhibitors of Human DNA Topoisomerase IIα

Human DNA topoisomerase IIα (htIIα) is a validated target for the development of anticancer agents. Based on structural data regarding the binding mode of AMP‐PNP (5′‐adenylyl‐β,γ‐imidodiphosphate) to htIIα, we designed a two‐stage virtual screening campaign that combines structure‐based pharmacophores and molecular docking. In the first stage, we identified several monosubstituted 9H‐purine compounds and a novel class of 1H‐pyrazolo[3,4]pyrimidines as inhibitors of htIIα. In the second stage, disubstituted analogues with improved cellular activities were discovered. Compounds from both classes were shown to inhibit htIIα‐mediated DNA decatenation, and surface plasmon resonance (SPR) experiments confirmed binding of these two compounds on the htIIα ATPase domain. Proposed complexes and interaction patterns between both compounds and htIIα were further analyzed in molecular dynamics simulations. Two compounds identified in the second stage showed promising anticancer activities in hepatocellular carcinoma (HepG2) and breast cancer (MCF‐7) cell lines. The discovered compounds are suitable starting points for further hit‐to‐lead development in anticancer drug discovery.