Synthesis,Molecular Docking and Preliminary Antileukemic Activity of 4-Methoxybenzyl Derivatives Bearing Imidazo[2,1-b][1,3,4]thiadiazole

In this study, we synthesized 22 compounds in a series with various substitution on imidazo[2,1-b][1,3,4]thiadiazole. The potential cytotoxic activity of these compounds investigated in leukemia cell lines by Differential Nuclear Staining (DNS). Our results identified two compounds, 2-(4-methoxybenzyl)-6-(2-oxo-2H-chromen-3-yl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl thiocyanate and 6-(4-chlorophenyl)-2-(4-methoxybenzyl)imidazo[2,1-b][1,3,4]thiadiazole-5-carbaldehyde, exhibited the most cytotoxic effect against murine leukemia cells (L1210), human T-lymphocyte cells (CEM) and human cervix carcinoma cells (HeLa) with IC₅₀ values ranging between 0.79 and 1.6 μM. The results indicate that 2-(4-methoxybenzyl)-6-(2-oxo-2H-chromen-3-yl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl thiocyanate is inducing phosphatidylserine externalization and caspase-3 activation which are both a hallmark of apoptosis. Docking studies showed that 2-(4-methoxybenzyl)-6-(2-oxo-2H-chromen-3-yl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl thiocyanate binds within the active sites of transforming growth factor beta (TGF-β) type I receptor kinase domain by strong hydrogen binding and hydrophobic interactions.     

Anticancer profile of newly synthesized BRAF inhibitors possess 5-(pyrimidin-4-yl)imidazo[2,1-b]thiazole scaffold

In this work, a new series of imidazo[2,1-b]thiazole was designed and synthesized. The new compounds are having 3-fluorophenyl at position 6 of imidazo[2,1-b]thiazole and pyrimidine ring at position 5. The pyrimidine ring containing either amide or sulphonamide moiety attached to a linker (ethyl or propyl) at position 2 of the pyrimidine ring. The final compounds were selected by NCI for in vitro cytotoxicity screening. Most derivatives showed cytotoxic activity against colon cancer and melanoma cell lines. In addition, IC₅₀s of the target compounds were determined over A375 and SK-MEL-28 cell lines using sorafenib as positive control. Compounds12b, 12c, 12e, 12f, 15a, 15d, 15f, 14g and 15h exhibited superior activity when compared to sorafenib. The most potent compounds were tested against wild type BRAF, v600e BRAF, and CRAF. Compound 15h exhibited a potential inhibitory effect against^V600EBRAF (IC₅₀?=?9.3?nM).     

Synthesis of carbon-11-labeled 4-(phenylamino)-pyrrolo[2,1-f][1,2,4]triazine derivatives as new potential PET tracers for imaging of p38α mitogen-activated protein kinase

The reference standards methyl 4-(2-methyl-5-(methoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylate (10a), methyl 4-(2-methyl-5-(ethoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylate (10b) and corresponding precursors 4-(2-methyl-5-(methoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylic acid (11a), methyl 4-(2-methyl-5-(ethoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylic acid (11b) were synthesized from methyl crotonate and 3-amino-4-methylbenzoic acid in multiple steps with moderate to excellent yields. The target tracer [¹¹C]methyl 4-(2-methyl-5-(methoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylate ([¹¹C]10a) and [¹¹C]methyl 4-(2-methyl-5-(ethoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylate ([¹¹C]10b) were prepared from their corresponding precursors with [¹¹C]CH₃OTf under basic condition through O-[¹¹C]methylation and isolated by a simplified solid-phase extraction (SPE) method in 50–60% radiochemical yields at end of bombardment (EOB) with 185–555 GBq/μmol specific activity at end of synthesis (EOS).     

Synthesis and anticancer evaluation of 3-aryl-6-phenylimidazo[2,1-b]thiazoles

A series of new 3,6-diphenylimidazo[2,1-b]thiazole derivatives (4a–l) are synthesized and evaluated for their anticancer activity. Some of the synthesized compounds have shown potent anti-proliferative activity against HeLa, MDA-MB-231, A549 and THP1 human cancer cell lines. Among the active compounds, 3-(3-trifluoromethylphenyl)-6-phenylimidazo[2,1-b]thiazole (4j) has caused significant cytotoxicity in HeLa cells, with IC₅₀ as low as 6.5 μM. Compound 4j has induced caspase-3 and caspase-8 activation, leading to an apoptotic cell death. FACS analysis has revealed that compound 4j arrests cells in G0/G1 phase. The presence of 3-(3-trifluoromethylphenyl)- or 3-(3-chlorophenyl)-substituent, in that order, on the 6-phenylimidazo[2,1-b]thiazole impacts more positively than other aryl-substituents, on the anti-proliferative properties of these compounds.     

Derivatives of imidazotriazine and pyrrolotriazine C-nucleosides as potential new anti-HCV agents

Previous investigations identified 2′-C-Me-branched ribo-C-nucleoside adenosine analogues, 1, which contains a pyrrolo[2,1-f][1,2,4]triazin-4-amine heterocyclic base, and 2, which contains an imidazo[2,1-f][1,2,4]triazin-4-amine heterocyclic base as two compounds with promising anti-HCV in vitro activity. This Letter describes the synthesis and evaluation of a series of novel analogues of these compounds substituted at the 2-, 7-, and 8-positions of the heterocyclic bases. A number of active new HCV inhibitors were identified but most compounds also demonstrated unacceptable cytotoxicity. However, the 7-fluoro analogue of 1 displayed good potency with a promising cytotherapeutic margin.     

Design,synthesis and biological evaluation of imidazo[2,1-b]thiazole and benzo[d]imidazo[2,1-b]thiazole derivatives as Mycobacterium tuberculosis pantothenate synthetase inhibitors

In the present study, we have designed imidazo[2,1-b]thiazole and benzo[d]imidazo[2,1-b]thiazole derivatives from earlier reported imidazo[1,2-a]pyridine based Mycobacterium tuberculosis (MTB) pantothenate synthetase (PS) inhibitors. We synthesized thirty compounds and they were evaluated for MTB PS inhibition study, in vitro anti-TB activities against replicative and non-replicative MTB, in vivo activity using Mycobacterium marinum infected Zebra fish and cytotoxicity against RAW 264.7 cell line. Among them compound 2-methyl-N′-(4-phenoxybenzoyl)benzo[d]imidazo[2,1-b]thiazole-3-carbohydrazide (5bc) emerged as potent compound active against MTB PS with IC₅₀ of 0.53 ± 0.13 μM, MIC of 3.53 μM, 2.1 log reduction against nutrient starved MTB, with 33% cytotoxicity at 50 μM. It also showed 1.5 log reduction of M. marinum load in Zebra fish at 10 mg/kg.     

Synthesis and biological evaluation of pyrano[4,3-b][1]benzopyranone derivatives as monoamine oxidase and cholinesterase inhibitors

A series of eighteen pyrano[4,3-b][1]benzopyranone derivatives (1a-9b) were synthesized, and structure-activity relationships of their monoamine oxidase (MAO) A and B, acetylcholinesterase (AChE), and butyrylcholinesterase (BChE) inhibitory activities were evaluated. Most of the synthesized compounds exhibited weak inhibitory activity toward MAO-A, whereas compounds 2a, 2b, 4a, 4b, 5a, 5b, 6a, 6b, 8a and 8b showed potent inhibitory activities toward MAO-B. Intriguingly, compounds 5a, 5b, and 8a showed inhibitory activities comparable to pargylin, used as a positive control for MAO-B. Substitution of butoxy at the C3 position or of chlorine at the C8 position of pyrano[4,3-b][1]benzopyranone increased the inhibitory activity of the compound toward MAO-B. The results of a molecular docking study supported this structural effect. Most of the compounds exhibited no or slight inhibitory activity toward AChE and BChE, with exo type compounds bearing a butoxy group, such as compounds 2b, 5b and 8b, showing weak but distinct inhibitory activities toward BChE. This report is the first to identify pyrano[4,3-b][1]benzopyranone derivatives as potent and selective MAO-B inhibitors. 3-Butoxy-8-chloro-pyrano[4,3-b][1]benzopyranone (5b) may be useful as a lead compound for the development of MAO-B inhibitors.     

Structure-based discovery of cellular-active allosteric inhibitors of FAK

In order to develop potent and selective focal adhesion kinase (FAK) inhibitors, synthetic studies on pyrazolo[4,3-c][2,1]benzothiazines targeted for the FAK allosteric site were carried out. Based on the X-ray structural analysis of the co-crystal of the lead compound, 8-(4-ethylphenyl)-5-methyl-1,5-dihydropyrazolo[4,3-c][2,1]benzothiazine 4,4-dioxide 1 with FAK, we designed and prepared 1,5-dimethyl-1,5-dihydropyrazolo[4,3-c][2,1]benzothiazin derivatives which selectively inhibited kinase activity of FAK without affecting seven other kinases. The optimized compound, N-(4-tert-butylbenzyl)-1,5-dimethyl-1,5-dihydropyrazolo[4,3-c][2,1]benzothiazin-8-amine 4,4-dioxide 30 possessed significant FAK kinase inhibitory activities both in cell-free (IC₅₀ = 0.64 μM) and in cellular assays (IC₅₀ = 7.1 μM). These results clearly demonstrated a potential of FAK allosteric inhibitors as antitumor agents.     

Design,synthesis, and evaluation of novel VEGFR2 kinase inhibitors: Discovery of [1,2,4]triazolo[1,5-a]pyridine derivatives with slow dissociation kinetics

For the purpose of discovering novel type-II inhibitors of vascular endothelial growth factor receptor 2 (VEGFR2) kinase, we designed and synthesized 5,6-fused heterocyclic compounds bearing a anilide group. A co-crystal structure analysis of imidazo[1,2-b]pyridazine derivative 2 with VEGFR2 revealed that the N1-nitrogen of imidazo[1,2-b]pyridazine core interacts with the backbone NH group of Cys919. To retain this essential interaction, we designed a series of imidazo[1,2-a]pyridine, [1,2,4]triazolo[1,5-a]pyridine, thiazolo[5,4-b]pyridine, and 1,3-benzothiazole derivatives maintaining a ring nitrogen as hydrogen bond acceptor (HBA) at the corresponding position. All compounds thus designed displayed strong inhibitory activity against VEGFR2 kinase, and the [1,2,4]triazolo[1,5-a]pyridine 13d displayed favorable physicochemical properties. Furthermore, 13d inhibited VEGFR2 kinase with slow dissociation kinetics and also inhibited platelet-derived growth factor receptor (PDGFR) kinases. Oral administration of 13d showed potent anti-tumor efficacy in DU145 and A549 xenograft models in nude mice.     

Synthesis and biological evaluation of imidazo[2,1-b]thiazole-benzimidazole conjugates as microtubule-targeting agents

A series of imidazo[2,1-b]thiazole-benzimidazole conjugates were synthesized and evaluated for their antiproliferative activity against four human cancer cell lines i.e.; HeLa (cervical), A549 (lung), MCF-7 (breast) and DU-145 (prostate) along with normal HEK-293 cell line. Amongst them, conjugate 6d displayed significant cytotoxicity against human lung cancer cell line, A549 with IC₅₀ value 1.08 µM. Further, cell cycle analysis revealed that this compound arrested the cell cycle at G2/M phase in A549 cells. Furthermore, the tubulin polymerization assay results suggest that this conjugate (6d) exhibits significant inhibitory effect on the tubulin assembly with an IC50 value of 1.68 µM. Moreover, the apoptotic inducing properties of compound 6d was confirmed by Hoechst staining, measurement of mitochondrial membrane potential (ΔΨm) and annexin V-FITC assay. Further, molecular docking studies revealed that compound 6d occupied the colchicine binding site.     

Synthesis,anticancer assessment on human breast,liver and colon carcinoma cell lines and molecular modeling study using novel pyrazolo[4,3-c]pyridine derivatives

The key intermediate 3-aminopyrazolo[4,3-c]pyridine-4,6-dione (2) is considered as a precursor for some novel pyrazolo[4,3-c]pyridines 4a-c, arylhydrazopyrazolo[4,3-c]pyridines 8a-e, pyrazolo[4,5,1-ij][1,6]naphthyridines 11a-e and pyrido[4′,3′:3,4]pyrazolo[1,5-a]-pyrimidines 15a-d through Knovenegal condensation, coupling reaction and Michael addition. Some of the newly synthesized pyrazolo[4,3-c]pyridine derivatives were investigated for anticancer activity. The results of the cytotoxic activity revealed that compound 6b was the most active compound against the breast and liver carcinoma cell lines which gives IC₅₀ values of 1.937 and 3.695 µg/mL, respectively compared to reference drug (doxorubicin) with IC₅₀ values of 2.527 and 4.749 µg/ml, respectively. Moreover, compound 6c was potent compound against the colon carcinoma cell line which gives the value of IC₅₀ = 2.914 µg/ml compared to doxorubicin with IC₅₀ value of 3.641 µg/ml. Some selected of the novel synthesized compounds were docked inside the active site of ERK2 enzyme and were found display a suitable binding with the active site amino acids according to their bond lengths, angles and conformational energy.     

A novel,broad-spectrum anticancer compound containing the imidazo[4,5-e][1,3]diazepine ring system

Synthesis and broad-spectrum anticancer activity of a novel heterocyclic compound 1 containing the title imidazo[4,5-e][1,3]diazepine ring system have been reported. The compound shows potent in vitro antitumor activity with low micromolar IC₅₀’s against prostate, lung, breast, and ovarian cancer cell lines tested. The long alkyl chain attached to the six-position of the heterocyclic ring of 1 appears to be necessary for the observed biological activity.     

Imidazo[2′,1′:2,3]thiazolo[4,5-d]pyridazinone as a new scaffold of DHFR inhibitors: Synthesis,biological evaluation and molecular modeling study

New series of thiazolo[4,5-d]pyridazin and imidazo[2′,1′:2,3]thiazolo[4,5-d]pyridazin analogues were designed, synthesized and evaluated for their in vitro DHFR inhibition and antitumor activity. Compounds 13 and 43 proved to be DHFR inhibitors with IC₅₀ 0.05 and 0.06 μM, respectively. 43 proved lethal to OVCAR-3 Ovarian cancer and MDA-MB-435 Melanoma at IC₅₀ 0.32 and 0.46 μM, respectively. The active compounds formed hydrogen bond at DHFR binding site between N₁-nitrogen of the pyridazine ring with Glu30; the carbonyl group with Trp24, Arg70 or Lys64; π-cation interaction with Arg22 and π-π interaction with Phe31 residues. Ring annexation of the active 1,3-thiazole ring analogue 13 into the bicyclic thiazolo[4,5-d]pyridazine (18,19) or imidazo[2,1-b]thiazoles (23–25) decreased the DHFR inhibition activity; while the formation of the tricyclic imidazo[2′,1′:2,3]-thiazolo[4,5-d]pyridazine (43–54) increased potency. The obtained model could be useful for the development of new class of DHFR inhibitors.     

Synthesis and nematicidal activities of 1,2,3-benzotriazin-4-one derivatives containing benzo[d][1,2,3]thiadiazole against Meloidogyne incognita

Based on the characteristic of benzo[d][1,2,3]thiadiazole to induce the systemic acquired resistance and improve the immunity of plants, benzo[d][1,2,3]thiadiazole was introduced into 1,2,3-benzotriazin-4-one, thirty-one novel 1,2,3-benzotriazin-4-one derivatives containing benzo[d][1,2,3]thiadiazole were designed and synthesized. Nematicidal activity showed that most of the synthesized compounds exhibited great inhibitory activity in vivo against Meloidogyne incognita at 20 mg/L. Among 31 tested compounds, A2 and A3 showed an excellent nematicidal activity with the inhibition rate of 50.4% and 53.1% at the concentration of 1.0 mg/L, respectively. The influence of substituent type and position was investigated. The relationship between structure and activity was also preliminary analyzed.     

Synthesis and anti-proliferative activity of a small library of 7-substituted 5H-pyrrole [1,2-a][3,1]benzoxazin-5-one derivatives

In this study, we investigate the anti-proliferative activity of a small library of 7-substituted 5H-pyrrolo[1,2-a][3,1]benzoxazin-5-one derivatives, against a panel of human cancer cell lines. We reported the synthesis of these compounds in a previous work. 7-Bromo-5H-benzo[d]pyrrolo[2,1-b][1,3]oxazin-5-one showed a promising anti-proliferative effect. As starting material for Suzuki-Miyaura cross coupling reaction, it was selected for the design and the synthesis of six further derivatives, with the aim to better define structure-activity relationships. The anti-proliferative MTT assay revealed a dose-dependent reduction of cell viability, especially for 7-([1,1′-biphenyl]-4-yl)-5H-benzo[d]pyrrolo[2,1-b][1,3]oxazin-5-one. Cell cycle and western blotting analysis suggested apoptosis as possible mechanism for its anti-proliferative activity. These preliminary results encourage our interest for further optimizations.     

Optimization of a 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of HIV capsid assembly inhibitors 1: Addressing configurational instability through scaffold modification

The optimization of a 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of inhibitors of HIV-1 capsid assembly that possess a labile stereocenter at C3 is described. Quaternization of the C3 position of compound 1 in order to prevent racemization gave compound 2, which was inactive in our capsid disassembly assay. A likely explanation for this finding was revealed by in silico analysis predicting a dramatic increase in energy of the bioactive conformation upon quaternization of the C3 position. Replacement of the C3 of the diazepine ring with a nitrogen atom to give the 1,5-dihydro-benzo[f][1,3,5]triazepine-2,4-dione analog 4 was well tolerated. Introduction of a rigid spirocyclic system at the C3 position gave configurationally stable 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione analog 5, which was able to access the bioactive conformation without a severe energetic penalty and inhibit capsid assembly. Preliminary structure–activity relationships (SAR) and X-ray crystallographic data show that knowledge from the 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of inhibitors of HIV-1 capsid assembly can be transferred to these new scaffolds.     

The discovery and unique pharmacological profile of RO4938581 and RO4882224 as potent and selective GABAA α5 inverse agonists for the treatment of cognitive dysfunction

Lead optimisation of the imidazo[1,5-a][1,2,4]-triazolo[1,5-d][1,4]benzodiazepine class led to the identification of two clinical leads [RO4882224 (11) and RO4938581 (44)] functioning as novel potent and selective GABA_A α5 inverse agonists. The unique pharmacological profiles and optimal pharmacokinetic profiles resulted in in vivo activity in selected cognition models.     

Development of an anti-hepatitis B virus (HBV) agent through the structure-activity relationship of the interferon-like small compound CDM-3008

Hepatitis B, a viral infectious disease caused by hepatitis B virus (HBV), is a life-threatening disease that leads liver cirrhosis and liver cancer. Because the current treatments for HBV, such as an interferon (IFN) formulation or nucleoside/nucleotide analogues, are not sufficient, the development of a more effective agent for HBV is urgent required.CDM-3008 (1, 2-(2,4-bis(trifluoromethyl)imidazo[1,2-a][1,8]naphthyridin-8-yl)-1,3,4-oxadiazole) (RO8191)) is a small molecule with an imidazo[1,2-a][1,8]naphthyridine scaffold that shows anti-HCV activity with an IFN-like effect. Here, we report that 1 was also effective for HBV, although the solubility and metabolic stability were insufficient for clinical use. Through the structure-activity relationship (SAR), we discovered that CDM-3032 (11, N-(piperidine-4-yl)-2,4-bis(trifluoromethyl)imidazo[1,2-a][1,8]naphthyridine-8-carboxamide hydrochloride) was more soluble than 1 (>30?mg/mL for 11 versus 0.92?mg/mL for 1). In addition, the half-life period of 11 was dramatically improved in both mouse and human hepatic microsomes (T1/2, >120?min versus 58.2?min in mouse, and >120?min versus 34.1?min in human, for 11 and 1, respectively).     

Novel imidazo[2,1-b][1,3,4]thiadiazole (ITD) hybrid compounds: Design,synthesis, efficient antibacterial activity and antioxidant effects

In this study, novel imidazo[2,1-b][1,3,4]thiadiazole (ITD) compounds were synthesized and their antimicrobial and antioxidant capacity was examined. The C-2 position of the ITD structure was fixed with the 3,4-hydroxybenzene ring and the properties of the two series of compounds obtained by phenyl or 4-chlorophenyl in the C-6 position were compared. In the formation of these series, new properties were determined by the addition of different pharmacophore to the target product by binding of the groups known in the literature from the C-5 position to the structure. In the study, it was seen that the compounds 4a, 4b, 5a, 5b, 7f, 10, 12 and 13 had very high anti-tuberculosis activities at low concentrations, 3b was found to exhibit moderate activity while other synthesis compounds exhibited moderate activity. In addition, it showed activity against gram positive and negative bacteria. In the determination of the antioxidant capacities of the newly synthesized compounds by FRAP and DPPH methods, the compounds showing activity were found to be 2, 3a, 3b, 6c, 9, 11 and 13.The structures of all synthesized compounds were solved by spectroscopic methods such as FT-IR, ¹H NMR, ¹³C NMR and mass.     

Synthesis of novel di- and tricationic carbapenems with potent anti-MRSA activity

A new series of 1β-methyl carbapenems possessing a 6,7-disubstituted imidazo[5,1-b]thiazol-2-yl group directly attached to the C-2 position of the carbapenem nucleus was prepared, and their activities against methicillin-resistant Staphylococcus aureus (MRSA) were evaluated. First, a benzyl moiety was introduced at the C-6 position of imidazo[5,1-b]thiazole attached to the carbapenem. These benzylated molecules showed potent anti-MRSA activity, but poor water solubility. In order to overcome this drawback, we designed and synthesized di- and tricationic carbapenems and finally discovered a novel carbapenem (15i), which exhibited excellent anti-MRSA activity and good water solubility.