Facile and efficient one-pot synthesis of benzimidazoles using lanthanum chloride

Unlocking the Pharmacological Potential of Benzimidazole Derivatives: A Pathway to Drug Development

Heterocyclic molecules have fascinated a massive interest in medicinal chemistry. They are heterocyclic compounds that have gained significance due to their diverse variety of pharmacological activities. Benzimidazole is a heterocyclic compound consisting of benzene and imidazole rings. The ease of synthesis and the structural versatility of benzimidazole make it a promising scaffold for drug development. Many biological actions of benzimidazole derivatives have been well documented, including antibacterial, antiviral, anticancer, anti-inflammatory, antitubercular, and anthelmintic properties. The mechanism of action of benzimidazole derivatives varies with their chemical structure and target enzyme. This review has explored numerous methods for producing benzimidazole derivatives as well as a broad range of pharmacological activities. SAR investigations are also discussed in this review as they provide crucial details regarding the essential structural qualities that benzimidazole derivatives must have in order to be biologically active, which could aid in the rational design of new drug candidates. Benzimidazole scaffold is an exclusive structure in drug design and discovery. Many new pharmaceutical drugs containing benzimidazole are anticipated to be available within the next ten years as a result of the extensive therapeutic applications of benzimidazole and its derivatives. This review inspired many researchers to develop more biologically active compounds bearing benzimidazole, expanding the scope of finding a remedy for other diseases. From this study, we concluded that 2-substituted benzimidazole was considered more extensively by researchers.

Facile one pot synthesis of 2-substituted benzimidazole derivatives under mild conditions by using engineered MgO@DFNS as heterogeneous catalyst

Benzimidazole derivatives are considered as important heterocyclic motifs that show a wide range of pharmaceutical applications. In view of their wide-ranging bioactivities, it is imperative to direct research on the sustainable catalytic synthesis of benzimidazole. Therefore, herein, we report a novel approach for the synthesis of benzimidazole and its derivatives with engineered MgO supported on dendritic fibrous nano silica (MgO@DFNS) as a sustainable heterogeneous catalyst. The catalyst MgO@DFNS was thoroughly characterized to understand its physio-chemical properties using XRD, FE-SEM, XPS, FT-IR, zeta potential, HR-TEM, TGA, TPR and TPD. The obtained results suggested that the catalyst MgO@DFNS prepared well and have the desired characteristics in it. After the successful characterisation of the prepared catalyst MgO@DFNS, it was applied in the synthesis of benzimidazole derivatives via condensation of o-phenylenediamine, and various aromatic and aliphatic aldehydes under ambient temperature. The catalyst produced a clean reaction profile with excellent yields in a shorter time under the umbrella of green chemistry. The effect of reaction parameters such as the effect of time, catalyst dosage, loading of MgO, effect of solvents and effect of different homo and heterogeneous catalyst were also tested. Furthermore, to understand the scope of the catalyst different substituted diamines and substituted aldehydes were reacted and obtained desired products in good to efficient yield. In addition, a recyclability study was also conducted and it was observed that the catalyst could be recycled for up to six cycles without noticeable changes in the morphology and activity. We believe that the present methodology gave several advantages such as an eco-friendly method, easy work-up, good selectivity, high yields and quick recovery of catalyst. MgO@DFNS is highly stable for several cycles without significant loss of its activity, which possibly demonstrates its applicability at the industrial scale.

Heterogeneous catalyst SiO2-LaCl3·7H2O: characterization and microwave-assisted green synthesis of α-aminophosphonates and their antimicrobial activity

Silica-supported lanthanum (III) chloride (SiO₂-LaCl₃·7H₂O) was prepared and characterized by infrared spectroscopy, X-ray diffraction analysis, scanning electron microscope, energy-dispersive X-ray spectroscopy, thermogravimetric analysis and differential thermal analysis techniques. The catalytic activity of this silica-supported lanthanum (III) chloride was investigated in a one-pot three-component Kabachnik-Fields reaction. A library of new α-aminophosphonates was prepared employing various benzothiazole and thiadiazole amines, different substituted aldehydes and diethylphosphite under solvent-free conditions using conventional/microwave methods with good to excellent yields (85-97%). The advantages of this catalyst are that it is environmentally benign, economically inexpensive, and easy to prepare, gives high yields and high purity is less time-consuming, offers easy purification is reusable and enables products to be obtained by simple recrystallization without column chromatography.

Agro-waste sourced catalyst as an eco-friendly and sustainable approach for Knoevenagel condensation reaction

Background:

The present work describes an eco-friendly and sustainable approach for the Knoevenagel condensation of an aromatic aldehyde with ethyl cyanoacetate, and salicylaldehyde with Meldrum acid for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin (2-oxo-2H-1-benzopyran) derivatives, respectively. The reaction performed under greener catalytic media Water Extract of Watermelon Fruit Peel Ash (WEWFPA) is an eco-friendly protocol derived from the agro-waste feedstock. Various protocols have been reported for the synthesis of Knoevenagel condensation reaction using a hazardous catalyst or/and solvent found toxic to the environment, reaction time longer, poor yield, and required purification of the final product. The present method provides several added advantages of being completely greener, economic, giving high yield, inexpensive catalyst, and the final product isolated in pure form with good yield.

Objective:

The objective of the study was to develop a green methodology for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives.

Results:

The agro-waste based catalyst developed avoids the use of external inorganic/organic base, additives, and solvent-free synthesis of Knoevenagel condensation of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives under rt and microwave irradiation, respectively described. The microwave irradiation condition requires less time for the completion of the reaction and also gave better yield isolation

Methods:

We have demonstrated WEWFPA as a greener homogenous agro-waste is employed under rt stirring and microwave irradiation for the economic synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives. The developed method was found robust, non-hazardous and solvent-free with simple work-up gave target product.

Conclusion:

In conclusion, we have established an efficient, simple, agro-waste based catalytic approach for the synthesis of ethylbenzylidenecyanoacetate and 3-carboxy coumarin derivatives employing WEWFPA as an efficient catalyst under rt stirring and microwave synthesis, respectively. The method is a greener, economical and eco-friendly approach for the synthesis of Knoevenagel condensation products. The advantages of the present approach are solvent-free, no external metal, chemical base free, short reaction time and isolated product in good to excellent yields. The catalyst is agro-waste derived, which has abundant in natural sources, thus making the present approach a greener one.

Ultrasound-Promoted Sustainable Synthesis and Antimicrobial Evaluation of 2-Aryl Benzimidazoles Catalyzed by BPAE at Room Temperature

Background:

Present-day chemists are more interested in developing and using green chemistry protocol for various organic transformations, which employ natural feedstock extracts, and solvent-free, and greener catalysts; they are well known for their non-hazardous nature and have replaced many organic and inorganic based catalysts. In literature, the reported homogenous catalytic approaches have been employed for various bioactive heterocycle syntheses, which follow the green chemistry principle established for various organic transformations catalyzed by WERSA, BFE, WEPPA, WEMFSA, WEMPA, and Eichhorniacrassipes. Among them, 2-aryl benzimidazole derivatives have emerged as prominent molecules with a wide variety of applications in biological and material science.

Methods:

The agro-waste sourced from the banana peel is utilized for the preparation of BPAE catalyst, which is employed for the synthesis of 2-aryl benzimidazole derivatives under ultrasound waves at room temperature.

Results:

Here, 2-Aryl benzimidazoles synthesized through the reaction of a substituted o-phenylene diamine with substituted benzoyl chloride catalyzed by BPAE under ultrasound waves at room temperature are described. Furthermore, catalyst BPAE is characterized by flame emission spectrometry, SEM-EDX, and XRD techniques.

Conclusion:

The present work established an eco-friendly, sustainable and novel approach for the synthesis of 2-aryl benzimidazoles using natural feedstock BPAE. The major merits of BPAE include its use as an agro-waste-derived catalyst. It is also highly abundant, inexpensive, yields faster reactions, has a simple workup, and does not require the use of column chromatography.

New benzimidazolequinones as trypanosomicidal agents

Herein, the design and synthesis of new 2-phenyl(pyridinyl)benzimidazolequinones and their 5-phenoxy derivatives as potential anti-Trypanosoma cruzi agents are described. The compounds were evaluated in vitro against the epimastigotes and trypomastigote forms of Trypanosoma cruzi. The replacing of a benzene moiety in the naphthoquinone system by an imidazole enhanced the trypanosomicidal activity against Trypanosoma cruzi. Three of the tested compounds (11a-c) showed potent trypanosomicidal activity and compound 11a, with IC₅₀ of 0.65 μM on the trypomastigote form of T. cruzi, proved to be 15 times more active than nifurtimox. Additionally, molecular docking studies indicate that the quinone derivatives 11a-c could have a multitarget profile interacting preferentially with trypanothione reductase and Old Yellow Enzyme.

Montmorillonite K10: An Efficient Organo-Heterogeneous Catalyst for Synthesis of Benzimidazole Derivatives

The use of toxic solvents, high energy consumption, the production of waste and the application of traditional processes that do not follow the principles of green chemistry are problems for the pharmaceutical industry. The organic synthesis of chemical structures that represent the starting point for obtaining active pharmacological compounds, such as benzimidazole derivatives, has become a focal point in chemistry. Benzimidazole derivatives have found very strong applications in medicine. Their synthesis is often based on methods that are not convenient and not very respectful of the environment. A simple montmorillonite K10 (MK10) catalyzed method for the synthesis of benzimidazole derivatives has been developed. The use of MK10 for heterogeneous catalysis provides various advantages: the reaction yields are decidedly high, the work-up procedures of the reaction are easy and suitable, there is an increase in selectivity and the possibility of recycling the catalyst without waste formation is demonstrated. The reactions were carried out in solvent-free conditions and in a short reaction time using inexpensive and environmentally friendly heterogeneous catalysis. It has been shown that the reaction process is applicable in the industrial field.

Synthesis and insight into the structure-activity relationships of 2-phenylbenzimidazoles as prospective anticancer agents

In order to explore and develop new anticancer agents, three series of 2-phenylbenzimidazoles, 15-46, were condensed under simple and mild conditions using sodium metabisulfite as an oxidation agent and another series, 47-55, were obtained via a reduction reaction using sodium borohydride. All the compounds synthesized were evaluated for their in vitro anticancer activities against three human cancer cell lines. The novel compound 38 was found to be the most potent multi cancer inhibitor against A549, MDA-MB-231, and PC3 cell lines (IC50 values 4.47, 4.68 and 5.50 μg mL-1, respectively). In addition, compound 40 exhibited the best IC50 value of 3.55 μg mL-1 against the MDA-MB-231 cell line. The results demonstrated that introducing a new substituent to compounds 37-55 could improve their antiproliferative activities.

Amide–imine conjugate involving gallic acid and naphthalene for nano-molar detection, enrichment and cancer cell imaging of La3+: studies on the catalytic activity of the La3+ complex

A single crystal X-ray structurally characterized amide–imine conjugate (GAN) derived from gallic acid and naphthalene selectively recognizes La³⁺ ion via TURN ON fluorescence through ESIPT and CHEF mechanisms.

Extending the Hierarchy of Heterogeneous Catalysis to Substituted Derivatives of Benzimidazole Synthesis: Transition Metals Decorated CNTs

A simple and practical procedure has been adopted for one pot synthesis of benzimidazole derivatives under mild reaction conditions, starting from cinnamyl alcohol (COH) with bimetallic nanoparticles (BNPs) and supported bimetallic nanoparticles of Cu, Ti, Zn, Mn, Ag, and Co. All the catalysts were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), X-Ray Diffractometry (XRD), Brunauer Emmett-Teller (BET) surface area, and pore size analyzer. The products were identified/quantified with 1HNMR, FT-IR, and MS. 98% yield of substituted derivatives of benzimidazole was obtained with Cu–Ti supported on FMWCNTs in ethanol with excellent selectivity. Quantum chemical calculations of molecular reactivity of substituted cinnamaldehyde (CHO) and ortho phenylenediamine (OPD) have good consistency with experimental results. The returns of this work were the use of readily available catalysts, high yield, short reaction time, and simplicity of the process.

2-(3,4-Dimethoxyphenyl)-N-(4-methoxyphenyl)-1-propyl-1H-benzo[d]imidazole-5-carboxamide

2-(3,4-Dimethoxyphenyl)-N-(4-methoxyphenyl)-1-propyl-1H-benzo[d]imidazole-5-carboxamide was synthesized by the ‘one-pot’ reductive cyclization of N-(4-methoxyphenyl)-3-nitro-4-(propylamino)benzamide with 3,4-dimethoxybenzaldehyde, using sodium dithionite as a reductive cyclizing agent using DMSO as a solvent. The structure of newly synthesized compound was elucidated based on IR, 1H-NMR, 13C-NMR, and LC-MS data.

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

A comprehensive account of recent advances in the synthesis of imidazopyridines, assisted through transition-metal-catalyzed multicomponent reactions, C-H activation/functionalization and coupling reactions are highlighted in this review article. The basic illustration of this review comprises of schemes with concise account of explanatory text. The schemes depict the reaction conditions along with a quick look into the mechanism involved to render a deep understanding of the catalytic role. At some instances optimizations of certain features have been illustrated through tables, i.e., selectivity of catalyst, loading of the catalyst and percentage yield with different substrates. Each of the reported examples has been rigorously analyzed for reacting substrates, reaction conditions and transition metals used as the catalyst. This review will be helpful to the chemists in understanding the challenges associated with the reported methods as well as the future possibilities, both in the choice of substrates and catalysts. This review would be quite appealing to a wider range of organic chemists in academia and industrial R&D sectors working in the field of heterocyclic syntheses. In a nutshell, this review will be a guiding torch to envisage: (i) the role of various transition metals in the domain dedicated towards method development and (ii) for the modifications needed thereof in the R&D sector.

A nanoscopic icosahedral {Mo72Fe30} cluster catalyzes the aerobic synthesis of benzimidazoles

In this study, the catalytic efficiency of amorphous {Mo₇₂Fe₃₀} nanocapsules as a safe Keplerate polyoxometalate in organic synthesis was exploited. The easy-made solid catalyst exhibited high efficiency using a very low dosage (0.02–0.05 mol%) in the catalyzed condensation of various aromatic 1,2-diamines and aldehydes for the aerobic synthesis of benzimidazoles with very small E-factor values (0.11–0.33). The superior catalytic activity of amorphous nanoclusters compared to that of its crystalline counterpart was demonstrated. The high activity and recyclability of heterogeneous catalysts in a green reaction media under oxygen atmosphere, make this environmentally benign organic process appropriate for our applied goals.

Catalytic activity of amorphous {Mo₇₂Fe₃₀} nanoclusters as a safe Keplerate polyoxometalate in aerobic synthesis of benzimidazoles was described.

p-Toluenesulfonic Acid Coated Natural Phosphate as an Efficient Catalyst for the Synthesis of 2-Substituted Benzimidazole

2-Substituted benzimidazoles are selectively synthesised in high yields via the condensation of o-phenylenediamine derivatives with aldehyde derivatives using catalytic amount of p-toluenesulfonic acid coated natural phosphate (NP/PTSA) under mild conditions. The use of NP/PTSA as a reusable catalyst makes this process simple, convenient, and environmentally friendly.

An efficient one-pot conversion of carboxylic acids into benzimidazoles via an HBTU-promoted methodology

Benzimidazole is a privileged, and routinely used pharmacophore in the drug discovery process. Herein, we report a mild, acid-free and one-pot synthesis of indole, alkyl and alpha-amino benzimidazoles through a novel HBTU-promoted methodology. An extensive library of indole-carboxylic acids, alkyl carboxylic acids and N-protected alpha-amino acids has been converted into the corresponding benzimidazoles in 80-99% yield. Since alpha-aminobenzimidazoles are highly useful synthons as chiral ligands for chemical catalysis, as well as for drug discovery endeavors, our reported method provides direct access to this scaffold in a simple, one-pot operation from commercially available carboxylic acids.