A novel one-pot synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave irradiation

An overview of imidazole and its analogues as potent anticancer agents

The quest for novel, physiologically active imidazoles remains an exciting topic of research among medicinal chemists. The imidazole ring is a five-membered aromatic heterocycle that is found in both natural and synthesized compounds. Multiple anticancer drug classes are currently available on the market, but concerns including toxicity, limited efficacy and solubility have lowered the overall therapeutic index. Therefore, the hunt for new potential chemotherapeutic agents persists. The development of imidazole as a reliable and safer alternative to anticancer treatment is generating much attention among experts. Tubulin or microtubule polymerization inhibition and changes in the structure and function of DNA, VEGF, topoisomerase, kinases, histone deacetylases and certain other proteins that affect gene expression are among the putative targets.

Synthesis, antioxidant activity, antimicrobial efficacy and molecular docking studies of 4-chloro-2-(1-(4-methoxyphenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol and its transition metal complexes

Herein, a one-pot synthesis of tetra-substituted imidazole, 4-chloro-2-(1-(4-methoxyphenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol (HL), is reported by the reaction of benzil, 5-bromosalicylaldehyde, ammonium acetate and anisidine. The synthesized imidazole was reacted with salts of 1st row transition metals (Co(ii), Ni(ii), Cu(ii), Mn(ii) and Zn(ii)) to obtain metal complexes. The structure of the compounds was confirmed using various spectroscopic and analytical techniques. HL, which is crystalline, was characterized by SC-XRD. Subsequently, the synthesized compounds were evaluated for their antioxidant and antimicrobial activities. Antimicrobial studies revealed the more noxious nature of metal complexes compared to ligand against various strains of bacteria and fungi. Molecular docking results based on the binding energy values also supported the experimental results of the antioxidant activities of the compounds. HL was found to be a better antioxidant than metal complexes. For a better insight into the structure, computational studies of the compounds were also carried out. A clear intra-molecular charge transfer was perceived in the ligand and its metal complexes. The transfer integral values for holes (36.48 meV) were found to be higher than the electron transfer integrals (24.76 meV), which indicated that the ligand would be a better hole transporter. According to the frontier molecular orbitals of the dimer, the charge transfer within the molecule is found from monomer 1 to 2.

Microwave-assisted preparation of polysubstituted imidazoles using Zingiber extract synthesized green Cr2O3 nanoparticles

Cr₂O₃ nanoparticles were prepared using Zingiber officinal extract which were used as an efficient and reusable catalyst in the practical synthesis of polysubstituted imidazoles by means of a convenient reaction of aromatic aldehydes with ammonium acetate and benzil under microwave irradiation and H₂O as solvent. The structure of the compounds was studied by IR and ¹H-NMR spectrum. The most important benefits of this process are operational simplicity, reasonable reaction times, and excellent yield of products. The results show that the optimal conditions for the formation of imidazole derivatives are as follow: power of 400 W, reaction time of 4-9 min, H₂O as a solvent, and 15 mmol of catalyst amount.

One Pot Synthesis and Pharmacological Evaluation of Aryl Substituted Imidazoles as Potential Atypical Antipsychotics

Background:

Second generation or “atypical” antipsychotics demonstrate an improved therapeutic profile over conventional neuroleptics. These are effective in both positive and negative symptoms of the disease and have a lower propensity to induce adverse symptoms.

Objective:

The main objective of the research was in silico design and synthesis of potential atypical antipsychotics with combined antiserotonergic / antidopaminergic effect.

Methods:

A one pot synthesis of aryl substituted imidazole derivatives was carried out in green solvent PEG-400 and the prepared compounds were evaluated for atypical antipsychotic activity in animal models for dopaminergic and serotonergic antagonism. The compounds were designed based on their 3D similarity studies to standard drugs and in silico (docking studies) with respect to 5-HT2A and D2 receptors.

Results:

Results from the docking studies with respect to 5-HT2A and D2 receptors suggested a potential atypical antipsychotic profile for the test compounds. Theoretical ADME profiling of the compounds based on selected physicochemical parameters suggested an excellent compliance with Lipinski’s rules. The potential of these compounds to penetrate the blood brain barrier (log BB) was computed through an online software program and the values obtained for the compounds suggested a good potential for brain permeation. Reversal of apomorphine induced mesh climbing behaviour coupled with inactivity in the stereotypy assay indicates antidopaminergic effect and a potential atypical profile for the test compounds 1-5. Further, the activity of compounds in DOI assay indicated a 5-HT2 antagonistic profile (5-HT2 antagonism).

Conclusion:

Compound 5 emerged as important lead compound showing combined antidopaminergic and antiserotonergic (5-HT2A) activity with a potential atypical antipsychotic profile.

Tetrabutylammonium Bromide (TBAB) Catalyzed Synthesis of Bioactive Heterocycles

During the last two decades, tetrabutylammonium bromide (TBAB) has gained significant attention as an efficient metal-free homogeneous phase-transfer catalyst. A catalytic amount of TBAB is sufficient to catalyze various alkylation, oxidation, reduction, and esterification processes. It is also employed as an efficient co-catalyst for numerous coupling reactions. It has also acted as an efficient zwitterionic solvent in many organic transformations under molten conditions. In this review, we have summarized the recent developments on TBAB-catalyzed protocols for the efficient synthesis of various biologically promising heterocyclic scaffolds.

Microwave-assisted efficient synthesis of 3-substituted bis-isoxazole ether bearing 2-chloro-3-pyridyl via 1,3-dipolar cycloaddition

An efficient strategy for synthesizing of 3-substituted bis-isoxazole ether bearing 2-chloro-3-pyridyl under microwave radiation was reported. The reactive regioselectivity was improved by changing mainly the solvent and acid-binding agent. 3-(2-Chloropyridin-3-yl)-5-(((3-substituted phenyl isoxazol-5-yl)methoxy)methyl)isoxazoles were synthesized in 31-92% yields and were characterized by FT-IR, HRMS, ¹H and ¹³C NMR spectroscopy. The single crystal of 3-(2-chloropyridin-3-yl)-5-(((3-(p-tolyl)isoxazol-5-yl)methoxy)methyl)isoxazole was obtained, and the structure of compound has also been determined by X-ray diffraction technique. Weak intra- and intermolecular C-H∙∙∙O interactions and a C-H∙∙∙π interaction link molecules into a three-dimensional network. The results showed that the synthesized compounds belonged to triclinic system, and their regioselectivity depended on the solvent and acid-binding agent. The merits of this method include the environmentally friendly, efficient, simple operation, and higher regional selectivity. An efficient synthesis of 3-substituted bis-isoxazole ethers was developed via 1,3-dipolar cycloaddition reaction starting from 3-substituted phenyl-5-((prop-2-yn-1-yloxy))methyl)isoxazoles and (Z)-2-chloro-N-hydroxynicotinimidoyl chloride using NaHCO3 as an acid-binding agent in THF solvent-dissolved trace water under catalyst-free microwave-assisted conditions.

Synthesis, Antimicrobial Evaluation and Molecular Docking of Some Potential 2,6-disubstituted 1H-Benzimidazoles; Non-Classical Antifolates

BACKGROUND

Dihydrofolate reductase is one of the important enzymes for thymidylate and purine synthesis in micro-organisms. A large number of drugs have been designed to inhibit microbial DHFR but over the period of time, some drugs have developed resistance and cross reactivity towards the enzyme. Over the past few decades, benzimidazoles, triazoles and their derivatives have been grabbing the attention of the synthetic chemists for their wide gamut of antibacterial and antifungal activities targeting microbial protein DHFR.

OBJECTIVE

Our goal behind present investigation is to explore benzimidazoles class of drugs as microbial DHFR inhibitors by studying ligand-receptor binding interactions, in vitro enzyme inhibition assay and confirmation of anti-microbial activity against selected pathogenic microorganisms.

METHODS

A library containing thirty novel 2,6-disubstituted 1H-benzimidazoles was synthesized by one pot condensation of o-nitro aniline or 2,4-dinitro aniline with series of aldehydes or acetophenones using Na2S2O4 or SnCl2 respectively and reflux for 5-6hr. Structures of compounds have been confirmed by spectroscopic methods as 1H and 13C NMR, FT-IR and MS. In vitro DHFR inhibition study was performed by using Epoch microplate reader and IC50 of the test compounds was compared with Trimethoprim. In vitro antimicrobial activity was performed against selected clinical pathogens by agar disk diffusion method and MIC (µg/mL) was reported.

RESULTS

Moderate to good level of DHFR inhibition was observed with IC50 values in the range of 7-23 µM. Compounds B1, B19, B22, B24 and B30 expressed 1.1 to 1.4 folds more prominent DHFR inhibitory activity as compared to standard Trimethoprim. Remarkable antimicrobial activity was exhibited by B1, B19, B22, B24 and B30. Molecular docking study revealed perfect binding of test ligands with key amino acids of DHFR as Phe31, Ile94, Ile5, Asp27, Gln32 and Phe36.

CONCLUSION

Nature of 1H-benzimidazole substituents at position 2 and 6 had influence over magnitude and type of molecular binding and variation in the biological activity. The present series of 1H-benzimidazoles could be considered promising broad-spectrum antimicrobial candidates that deserve in future for preclinical antimicrobial evaluation and development of newer antimicrobial agents targeting microbial DHFR.

Imidazoles as potential anticancer agents

Cancer is a black spot on the face of humanity in this era of science and technology. Presently, several classes of anticancer drugs are available in the market, but issues such as toxicity, low efficacy and solubility have decreased the overall therapeutic indices. Thus, the search for new promising anticancer agents continues, and the battle against cancer is far from over. Imidazole is an aromatic diazole and alkaloid with anticancer properties. There is considerable interest among scientists in developing imidazoles as safe alternatives to anticancer chemotherapy. The present article describes the structural, chemical, and biological features of imidazoles. Several classes of imidazoles as anticancer agents based on their mode of action have been critically discussed. A careful observation has been made into pharmacologically active imidazoles with better or equal therapeutic effects compared to well-known imidazole-based anticancer drugs, which are available on the market. A brief discussion of the toxicities of imidazoles has been made. Finally, the current challenges and future perspectives of imidazole based anticancer drug development are conferred.

An efficient green protocol for the synthesis of tetra-substituted imidazoles catalyzed by zeolite BEA: effect of surface acidity and polarity of zeolite

Zeolite BEA catalyzed synthesis of highly substituted imidazoles via a green approach.

Synthesis of 2,4,5-trisubstituted imidazoles, quinoxalines and 1,5-benzodiazepines over an eco-friendly and highly efficient ZrO2–Al2O3 catalyst

Where, R is alkyl, aryl, alkoxy, N,N-diethyl or halo group.

Current advances in the synthesis and biological potencies of tri- and tetra-substituted 1H-imidazoles

In this report, we review the current chemistry progress and in particular the synthesis approaches of tri- and tetra-substituted imidazoles.

New Conditions for the Effective Synthesis of Tri and Tetrasubstituted Imidazoles Catalysed by Recyclable Indium (III) Triflate and Magnesium Sulfate Heptahydrate

A one-pot three or four component reaction of wide range of aromatic aldehydes, benzil, aliphatic and aromatic primary amines and ammonium acetate is reported for the synthesis of tri/tetra-substituted imidazoles under solvent-free conditions. Indium (III) trifluoromethanesulfonate and magnesium sulfate heptahydrate as two highly efficient and recyclable catalysts perform a key factor to synthesis of imidazole derivatives with high yields.

A highly efficient magnetic solid acid catalyst for synthesis of 2,4,5-trisubstituted imidazoles under ultrasound irradiation

Fe(3)O(4) nanoparticles were prepared by chemical coprecipitation method and subsequently coated with 3-aminopropyltriethoxysilane (APTES) via silanization reaction. Grafting of chlorosulfuric acid on the amino-functionalized Fe(3)O(4) nanoparticles afforded sulfamic acid-functionalized magnetic nanoparticles (SA-MNPs). SA-MNPs was found to be a mild and effective solid acid catalyst for the efficient, one-pot, three-component synthesis of 2,4,5-trisubstituted imidazoles under ultrasound irradiation. This protocol afforded corresponding imidazoles in shorter reaction durations, and in high yields. This green procedure has many obvious advantages compared to those reported in the previous literatures, including avoiding the use of harmful catalysts, easy and quick isolation of the products, excellent yields, short routine, and simplicity of the methodology.

K7Na3P2W18Cu4O68: A Mild, Efficient, and Reusable Catalyst for the One-Pot Synthesis of 1,2,4,5-Tetra Substituted Imidazoles

An efficient method for the synthesis of 1,2,4,5-tetra substituted imidazoles usingK7Na3P2W18Cu4O68as catalyst is reported. This four-component condensation of benzil, aldehydes, amines, and ammonium acetate proceeds under solvent-free conditions. The catalyst is handling and recoverable.