Synthesis of New Bis(pyrazolo[1,5-a]pyrimidines) Linked to Different Spacers as Potential MurB Inhibitors.

An efficient protocol was adopted to efficiently prepare three new series of bis(pyrazolo[1,5-a]pyrimidines) linked to different spacers. The new bis(pyrazolo[1,5-a]pyrimidines) were prepared in 80-90 % yields by reacting the respective bis(enaminones) and 4-(4-substituted benzyl)-1H-pyrazole-3,5-diamines in pyridine at reflux temperature for 5-7 h. The new products showed a wide spectrum of antibacterial activity against six different bacterial strains. In general, propane- and butane-linked bis(pyrazolo[1,5-a]pyrimidines), which are attached to 3-(4-methyl- or 4-methoxybenzyl) units, had the best antibacterial activity with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values up to 2.5 and 5.1 µM, respectively. Additionally, the previous products demonstrated promising MurB inhibitory activity with IC50 values up to 7.2 µM.

[3+2] Cycloaddition Synthesis of New Piperazine-Linked Bis(chromene) Hybrids Possessing Pyrazole Units as Potential Acetylcholinesterase Inhibitors.

Two series of piperazine-linked bis(chromene) hybrids that are attached to pyrazole units were synthesized in the current study. Both series are attached to an acyl unit at pyrazole-C3, with one series attached to an acetyl unit and the other to an ethoxycarbonyl unit. A [3+2] cycloaddition protocol was conducted to produce the target hybrids with good yields by reacting the appropriate hydrazonoyl chlorides with chromene-based bis(enaminone) in dioxane containing triethylamine at reflux for 4 h. New hybrids were tested for acetylcholinesterase inhibitory activity at concentrations of 15 and 25 µM, as well as their ability to quench 2,2-diphenylpicrylhydrazyl (DPPH) free radicals at a concentration of 25 µg/mL. In general, the inhibitory activity is related to the electronic properties of the para-substituent that is attached to the arene unit at pyrazole-N1. Furthermore, the acyl unit attached to pyrazole-C3 has a significant effect on the new hybrids' inhibitory activity. At the previous concentrations, the (3-acetylpyrazole)-linked hybrid attached to p-NO2 units demonstrated the best acetylcholinesterase inhibitory activity, with inhibition percentages of 79.7 and 90.2. Furthermore, the previous hybrid demonstrated the most effective DPPH inhibitory activity, with an inhibition percentage of 87.5.

New Arylazo-Based (Chromene-Thiazole) Hybrids as Potential MRSA Inhibitors.

A three-component protocol was established to efficiently synthesize (chromene-thiazole) and related arylazo analogs in good to excellent yields. The desired products were prepared by reacting the appropriate salicylaldehydes, 2-cyanothioacetamide, and chloroacetone or hydrazonyl chlorides. Using piperidine as a mediator in ethanol at 80 °C for 4-6 h, the three-component protocol produce the target hybrids in 87-96 % yields. The newly synthesized products showed a broad range of antibacterial activity. The addition of an arylazo unit at the chromene-C6 position significantly improved the antibacterial activity, while the impact of adding an arylazo group at the thiazole-C5 position varied based on the electronic characteristics of the para-substituted arene unit. Generally, series that is linked to two arylazo units, one at chromene-C6 and the other at thiazole-C5, showed the best activity. Some new hybrids showed effective antibacterial activity than ciprofloxacin with MIC/MBC values up to 1.9/3.9 µM against S. aureus and E. coli. Additionally, they demonstrated better effectiveness against MRSA ATCC:33591 and ATCC:43300 compared to linezolid, with MIC/MBC values up to 4.0/16.1 and 3.9/15.6 µM, respectively. The data predicted for the physicochemical properties, lipophilicity, pharmacokinetics, and drug-likeness of new arylazo-based chromene-thiazole hybrids evaluated by SwissADME. As a result of the above, products that are linked to two arylazo units can be considered drug-like scaffolds.

Tandem synthesis, cytotoxicity, and in silico study of new 1,3,4-oxadiazoles as potential thymidylate synthase inhibitors.

A new series of pyrrole-linked mono- and bis(1,3,4-oxadiazole) hybrids, attached to various arene units, was prepared using a two-step tandem protocol. Therefore, a benzohydrazide derivative was condensed with the appropriate aldehydes in ethanol at 80°C for 60-150 min to give the corresponding N-(benzoylhydrazones). Without isolation, the previous intermediates underwent intramolecular oxidative cyclization in dimethyl sulfoxide at 180°C for 90-200 min in the presence of chloramine trihydrate to afford the target hybrids. The cytotoxicity of all hybrids was examined in vitro against the MCF-7, HEPG2, and Caco2 cell lines. Arene-linked hybrids 4i and 4j, attached to p-nitro and p-acetoxy units, were the most potent ones, with IC50 values ranging from 5.47 to 8.80 and 12.75 to 21.22 µM, respectively, when tested on the above cell lines. At the tested concentrations of 5 and 7.5 µM, hybrid 4i inhibited thymidylate synthase (TS) with the best inhibition percentages of 72.3 and 91.3, whereas hybrid 4j displayed comparable inhibitory activity to the reference pemetrexed. Hybrid 4j had inhibition percentages of 62.7 and 82.6, whereas pemetrexed had inhibition percentages of 59.2 and 80.2, respectively. The capability of hybrids 4i and 4j as potential TS inhibitors is supported by molecular docking studies, while SwissADME predicts their efficacy as drug-like scaffolds.

Chloramine Trihydrate-Mediated Tandem Synthesis of New Pyrrole and/or Arene-Linked Mono- and Bis(1,3,4-Oxadiazole) Hybrids as Potential Bacterial Biofilm and MRSA Inhibitors.

A two-step tandem protocol was used to prepare new pyrrole and/or arene-linked bis(1,3,4-oxadiazoles) as well as their mono-analogs. The appropriate aldehydes and benzohydrazides were first condensed in ethanol at 80 °C to yield the corresponding N-benzoylhydrazones. Without isolation, the previous intermediates were subjected to a chloramine trihydrate-mediated oxidative cyclization in DMSO at 180 °C to yield the target molecules. The antibacterial potency of the (pyrrole-arene)-linked hybrids exceeded the arene-linked hybrids, and the bis(1,3,4-oxadiazoles) exceeded their mono-analogs against six different ATCC strains. Furthermore, the antibacterial efficacy of bis(1,3,4-oxadiazoles) 11c, and 11f, which are linked to pyrrole, and (p-tolylthio)methyl units, was highest against S. aureus, E. coli, and P. aeruginosa strains. Their MIC ranged between 3.8 and 3.9 µM, while their MBC values ranged between 7.7 and 15.8 µM. Additionally, they showed promising bacterial biofilm inhibitory activity against the same strains tested, with IC50 values ranging from 4.7 to 5.3 µM. They were also effective against MRSA ATCC : 33591, and ATCC : 43300 strains, with MIC, and MBC values ranging from 3.8-7.9 and 7.7-15.8 µM, respectively. When tested against the MCF-10A cell lines, hybrids 11c, and 11f are cytotoxic at concEntrations that are more than 6 and 13-fold higher than their MIC values against the S. aureus, E. coli, and P. aeruginosa strains, respectively. This lends support to both hybrids' potential as safe antibacterial agents.

3-Aminopyrazolo[3,4-b]pyridine: Effective Precursor for Barium Hydroxide-Mediated Three Components Synthesis of New Mono- and Bis(pyrimidines) with Potential Cytotoxic Activity.

In this study, an efficient one-pot procedure for preparing a new series of pyrazolo[3,4-b]pyridine-fused pyrimidines was described. The target hybrids were developed through a three-component reaction of 3-amino-1H-pyrazolo[3,4-b]pyridine, benzaldehydes, and acetophenones (molar ratio 1 : 1 : 1). The best conditions for the previous reaction were 2.5 equivalents of barium hydroxide in DMF at 150 °C for 6 h. New bis(pyrimidines) were synthesized in high yields using a similar one-pot reaction protocol with some modifications. Thus, two equivalents of each of the appropriate acetophenones and 3-aminopyrazolopyridine were reacted with one equivalent of the appropriate bis(aldehydes). The reaction was carried out at 150 °C for 8 h using 4.5 equivalents of barium hydroxide in DMF. Repeating the previous reaction with the appropriate bis(acetyl) derivatives and benzaldehydes resulted in good yields of the target bis(pyrimidines). The in vitro cytotoxic activity of new pyrimidines against the MCF-7, HEPG2, and Caco2 cell lines was evaluated using the reference doxorubicin (IC50 values of 4.34-6.97 µM). Hybrid 6h had the best activity against Caco2 and MCF-7 cell lines, IC50 values of 12.62 and 14.50 µM, respectively. The IC50 values for hybrids 6c, 6e, and 6f against MCF-7 and Caco2 cell lines were 23.99-41.69 and 33.14-43.33 µM, respectively. Furthermore, hybrid 6e displayed IC50 value of 20.06 µM HEPG2 cell lines, while the hybrids 6c, 6f and 6h exhibited IC50 values ranging between 26.29-50.51 µM. Furthermore, hybrid 6e had an IC50 value of 20.06 µM for the HEPG2 cell lines, whereas hybrids 6c, 6f, and 6h had IC50 values ranging from 26.29 to 50.51 µM.

Novel bis(pyrazole-benzofuran) hybrids possessing piperazine linker: Synthesis of potent bacterial biofilm and MurB inhibitors.

Novel 1,4-bis[(2-(3-(dimethylamino)-1-oxoprop-2-en-1-yl)benzofuran-5-yl)methyl]piperazine was prepared and used as a key synthon for the this study. Therefore, 1,3-dipolar cycloaddition of this synthon with the appropriate hydrazonyl chlorides afforded a new series of bis(1,3,4-trisubstituted pyrazoles), linked via piperazine moiety. Furthermore, it reacted with hydrazine hydrate and phenyl hydrazine individually to afford the corresponding 1,4-bis[(2-(1H-pyrazolyl)benzofuran-5-yl)methyl]piperazines. Different bacterial strains and cell lines were selected to study the in-vitro antibacterial and cytotoxic activities for the new derivatives. 1,4-Bis[((2-(3-acetyl-1-(4-nitrophenyl)-1H-pyrazole-4-yl)carbonyl)benzofuran-5-yl)methyl]piperazine 5e showed the best antibacterial efficacies with MIC/MBC values of 1.2/1.2, 1.2/2.4 and 1.2/2.4 µM against each of E. coli, S. aureus and S. mutans strains, respectively. In addition, the inhibitory activity of some new bis(pyrazoles) as MRSA and VRE inhibitors were studied. Compound 5e gave the best inhibitory activity with MIC/MBC values of 18.1/36.2, 9.0/18.1 and 18.1/18.1 µM, respectively, against MRSA (ATCC:33591 and ATCC:43300) and VRE (ATCC:51575) bacterial strains, respectively. Compound 5e showed more effective biofilm inhibition activities than the reference Ciprofloxacin. It showed IC50 values of 3.0 ± 0.05, 3.2 ± 0.08 and 3.3 ± 0.07 µM against S. aureus, S. mutans and E. coli strains, respectively. Furthermore, experimental study showed excellent inhibitory activities of 1,4-bis[((2-(3-substituted-1-aryl-1H-pyrazole-4-yl)carbonyl)benzofuran-5-yl)methyl]piperazine derivatives, attached to p-NO2 or p-Cl groups, against MurB enzyme. Compound 5e gave the best MurB inhibitory activity with IC50 value of 3.1 µM. The in-silico study was performed to predict the capability of new derivatives as potential inhibitors of MurB enzyme.

Synthesis, in-vitro and in-silico study of novel thiazoles as potent antibacterial agents and MurB inhibitors.

Efficient procedures are herein reported for the synthesis of novel hybrid thiazoles via a one-pot three-component protocol. The protocol involves the reaction of novel aldehyde, thiosemicarbazide and halogen-containing reagents in solvent- and catalyst-free conditions. The structures of the new thiazoles were elucidated by elemental analyses and spectroscopic data. The in-vitro antibacterial screening and MurB enzyme inhibition assays were performed for the novel thiazoles. The thiazol-4(5H)-one derivative 6d, with p-MeO, exhibits the best antibacterial activities with minimum inhibitory concentration values of 3.9, 3.9, 7.8, and 15.6 µg/ml against Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus mutans, and Escherichia coli, respectively, as compared to the reference antibiotic drugs. It also exhibits the highest inhibition of the MurB enzyme with an IC50 of 8.1 µM. The structure-activity relationship was studied to determine the effect of the structures of the newly prepared molecules on the strength of the antibacterial activities. Molecular docking was also performed to predict the binding modes of the new thiazoles in the active sites of the E. coli MurB enzyme.