Benzimidazole Derivatives: A Comprehensive Review Of Synthesis, Biological Evaluation, And Therapeutic Potential In Anticancer And Neuroprotective Applications

Benzimidazole is an important heterocyclic scaffold in medicinal chemistry due to its structural similarity to purines, ability to donate and accept hydrogen bonds, and favorable electronic properties that facilitate interactions with various biological targets. Structurally, it consists of a fused benzene and imidazole ring system, enabling strong binding within enzyme active sites and receptor pockets. Owing to these characteristics, benzimidazole derivatives have found extensive pharmaceutical applications. Several clinically important drugs, including omeprazole and lansoprazole (proton pump inhibitors), mebendazole and albendazole (anthelmintic), and candesartan (antihypertensive agent), are based on the benzimidazole nucleus. Furthermore, numerous studies have reported anticancer, antimicrobial, antiviral, anti-inflammatory, analgesic, and neuroprotective activities among benzimidazole derivatives. [7,8,18,23,24]

The biological activity of benzimidazole derivatives is significantly influenced by the nature of substituents attached to the core structure. Aliphatic substituents such as methyl, ethyl, and propyl groups can enhance lipophilicity, membrane permeability, and pharmacokinetic properties, whereas aromatic substituents including phenyl, chlorophenyl, hydroxyphenyl, and methoxyphenyl groups improve planarity and electronic conjugation, facilitating interactions with DNA and protein targets. This review highlights findings from two complementary studies that demonstrate the versatility of the benzimidazole scaffold. Keser et al. (2026) investigated aliphatically substituted benzimidazole derivatives as potential anti-breast cancer agents through apoptosis induction and cell cycle arrest mechanisms, while Raka et al. (2022) synthesized aromatic benzimidazole derivatives using a green chemistry approach and evaluated their analgesic, anti-inflammatory, antioxidant, antimicrobial, acetylcholinesterase inhibitory, and computationally predicted biological activities. [7,8,18,23,24]

2. Chemistry: Synthesis and Structural Characterization

2.1 Synthesis of Aliphatic-Substituted Benzimidazole Derivatives

Keser et al. synthesized a series of benzimidazole derivatives starting from a common precursor (Compound 1) containing benzimidazole, methyl, and thienyl groups. Reaction of Compound 1 with phenyl isocyanate and p-chlorophenyl isocyanate produced urea derivatives (2a and 2b), which were further cyclized under basic conditions to form triazole derivatives (3a and 3b). Additionally, treatment of 2a with sulfuric acid resulted in the formation of Compound 4, a 1,3,4-oxadiazole derivative that emerged as an important lead compound. [1]

Further structural diversification was achieved through aldehyde condensation reactions, yielding Schiff base derivatives (5a–5c), while reaction with carbon disulfide and potassium hydroxide produced a thiooxadiazole derivative (6). All synthesized compounds were characterized using ¹H-NMR, ¹³C-NMR, and LC-MS/TOF techniques. The successful preparation of urea, triazole, oxadiazole, Schiff base, and thiooxadiazole derivatives from a single precursor highlights the versatility of the benzimidazole scaffold for developing pharmacologically active molecules. [1]

2.2 Synthesis of Aromatic-Substituted Benzimidazole Derivatives

Raka et al. developed an environmentally friendly method for synthesizing benzimidazole derivatives using solvent-free or aqueous reaction conditions and inexpensive, eco-friendly catalysts. The key reaction involved the condensation of o-phenylenediamine with aromatic aldehydes or glycolic acid. Disubstituted benzimidazole derivatives (3a–3c) were synthesized using iodine/water or SiO?/ZnCl? catalytic systems, providing hydroxyphenyl, chlorophenyl, and methoxyphenyl substituted products in good to excellent yields. [2]

A monosubstituted benzimidazole derivative (4) was obtained using boric acid as a selective catalyst, while compound 6 (a benzyl ether derivative) was synthesized through a two-step process involving the formation of 2-hydroxymethyl-1H-benzimidazole (5) followed by benzylation. The use of water as a reaction medium and mild catalysts demonstrates the principles of green chemistry. All synthesized compounds were purified by column chromatography and characterized using IR, ¹H NMR, and ESI-MS spectroscopy. [2]

2.3 Structural Comparison and Chemical Insights

The two series of synthetics vary greatly from each other in their modes of substitution on the core structure benzimidazole. In the case of the aliphatic substituted compounds prepared by Keser et al., the dimethyl groups are introduced on the N-substituted carbons of the benzimidazole ring, leading to spatial restrictions in conformation due to steric hindrance. This is followed by the addition of the oxadiazole, triazole, or Schiff base units to the side-chain moiety, contributing additional pharmacophoric features to the molecule. [1,2]

The structure of compound 4 in the series Keser, the anti-cancer lead, is notably described by the hybridization of the 1,3,4-oxadiazole ring that creates a rigid, electron-withdrawing heteroatom system, allowing for particular interactions with potential biological targets. Indeed, the use of an oxadiazole moiety is widely used as a bioisosteric substitution in medicine chemistry, being a good alternative to both amide and ester linkages, increasing drug metabolic stability while retaining the biological activity of the molecule towards its target. [1,2]

3. Anticancer Biological Evaluation

3.1 Cytotoxicity Assessment — MTT Assay

Cytotoxic activity of all nine synthetic aliphatic substituted benzimidazole compounds was determined using the MTT assay in three different cells: MCF-7 (hormone receptor positive breast carcinoma), MDA-MB-231 (triple negative breast cancer) and MCF-10A (normal breast cells) following exposure for 72 hours. Results of IC50 values are shown in Table 1 below. [1]

Table 1. IC50 values (µM) of synthesized compounds in breast cancer and normal cell lines after 72 h treatment.^[1]

Among the synthesized compounds, Compound 4 showed the strongest anticancer activity against both MCF-7 and MDA-MB-231 breast cancer cell lines, with IC?? values comparable to the standard drug cisplatin. Importantly, Compound 4 displayed lower toxicity toward normal MCF-10A cells, indicating a degree of selectivity for cancer cells, which is a desirable characteristic for potential anticancer agents. Compound 3a also demonstrated notable cytotoxic activity but exhibited greater toxicity toward normal cells, suggesting poorer selectivity. [1] In contrast, compounds 2a, 3b, 5a–5c, and 6 showed weak to moderate cytotoxic effects, while Compound 2b was largely inactive. The superior activity of Compound 4 is attributed to the presence of the 1,3,4-oxadiazole ring, which enhances interactions with biological targets, and dimethyl substituents that increase lipophilicity and facilitate cellular uptake. These structural features likely contribute to its enhanced anticancer potential. [1]

3.2 Cell Cycle Analysis

In an effort to determine the mechanism by which compound 4 exhibits antiproliferative properties, a flow cytometric study was carried out through PI staining of cells cultured at IC50 concentration for 72 hours. [1] MCF-7 untreated control cells had a normal proliferation cycle pattern of 55.6% G0/G1 phase, 31.5% S phase, and 9.9% G2/M phase. Likewise, for MDA-MB-231 control cells, the percentages of the phases are 58.1%, 30.7%, and 9.2%, respectively. Significant changes were noted in both cell lines after being exposed to compound 4 for 72 hours. [1] For the case of MCF-7 cells, there was a decrease in the G0/G1 phase from 38% to 40%, an increase in the S-phase from 45% to 47%, and an increase in G2/M from 12% to 14%. MDA-MB-231 cells were observed to have a similar G0/G1 decrease from 40% to 42%, with an increase in S-phase from 43% to 45%, and a G2/M increase from 13% to 15%. This significant increase in the S-phase indicates that 4 affects the processes of DNA synthesis and replication, thus causing DNA replication stress-induced cell cycle arrest. [1]

3.3 Apoptosis Induction

Flow cytometry analysis using Annexin V/PI staining showed that Compound 4 effectively induced apoptosis in both MCF-7 and MDA-MB-231 breast cancer cells after 72 hours of treatment at its IC?? concentration. Treatment significantly reduced cell viability and increased both early and late apoptotic cell populations compared with untreated controls. The observed induction of apoptosis, together with S-phase cell cycle arrest, suggests that Compound 4 triggers replication stress-mediated cell death, potentially through activation of the mitochondrial apoptotic pathway, a mechanism commonly associated with benzimidazole derivatives. [1]

4. Molecular Docking and MM-GBSA Analysis

4.1 Docking Studies of Anticancer Compound 4

Docking studies for the interaction between compound 4 and four proteins involved in regulating apoptosis and cell cycles were performed by employing AutoDockVina (v4.2.5.1): Bcl-2 (PDB: 2W3L), Bcl-xL (PDB: 2YXJ), CDK2 (PDB: 2VU3), and Cyclin E (PDB: 2B9R). Preparation of protein and ligand optimization were done with the help of Protein Preparation Wizard and Gaussian 09 W with the OPLS 2005 force field, respectively, at pH of physiological condition. [1]

Table 2. Molecular docking analysis of compound 4 with apoptosis and cell cycle regulatory proteins.^[1]

Molecular docking studies revealed that Compound 4 exhibited strong binding affinities toward multiple protein targets, suggesting a multitarget mechanism of action. The strongest interaction was observed with CDK2, where Compound 4 formed several hydrogen bonds and hydrophobic interactions within the ATP-binding region. These interactions may inhibit ATP binding and kinase activity, thereby disrupting cell cycle progression and reducing cancer cell proliferation. [1] Compound 4 also showed favorable binding to the anti-apoptotic proteins Bcl-xL and Bcl-2, potentially blocking their ability to suppress apoptosis and promoting cancer cell death. In addition, interactions with Cyclin E at the Cyclin E–CDK2 interface may contribute to G1/S phase cell cycle arrest. Together, these findings support the observed apoptotic and antiproliferative effects of Compound 4 in breast cancer cells. [1]

4.2 MM-GBSA Binding Free Energy Calculations

Energetic validation of the docking results was performed using Molecular Mechanics/Generalized Born Surface Area (MM-GBSA) method to analyze the energetics of binding. The MM-GBSA calculations include interactions due to van der Waals forces, electrostatic interactions, and solvent. [1]

Table 3. MM-GBSA binding free energy analysis of compound 4 with target proteins.^[1]

Binding free energies showed favorable binding in the four protein receptors. Highest binding energy was noted for CDK2 with ΔGbind = -48.3 kcal/mol and Bcl-2 with ΔGbind = -45.1 kcal/mol. Van der Waals forces played an important role in the energetics of binding (ΔEvdW from -51.8 to -42.5 kcal/mol). This is because of the nature of the extended aliphatic chain that effectively occupies hydrophobic regions. This result supports the mechanism of apoptosis induction and cell cycle inhibition at one site. [1]

4.3 Docking of Neuroprotective Benzimidazole Derivatives

In the Raka study, consensus molecular docking was performed against acetylcholinesterase (AChE, PDB: 4pqe) and butyrylcholinesterase (BChE, PDB: 6esy), enzymes relevant to Alzheimer's disease and neurodegeneration. Multiple docking platforms (AutoDock Vina, Chimera, and Achilles docking server) were used for consensus scoring. [2]

Table 4. Consensus docking scores and key interactions of benzimidazole derivatives with AChE and BChE. [11]

With regard to AChE affinity, compound 3b exhibited high docking scores with a docking energy of -8.50 kcal/mol and was bound by hydrophobic interactions (Pi-Alkyl of residues LEU A:4 and ILE A:16) and Pi-Cation interaction with ARG A:14. Meanwhile, compound 3a was found to be involved in hydrogen bonds with residue GLU A:181, Pro-Alkyl interactions with PRO A:51, and a Pi-Cation interaction with ARG A:9 with docking energy of -8.37 kcal/mol. For BChE affinity, compound 4 had the highest docking energy of -9.20 kcal/mol with docking mechanisms involving hydrogen bonding with LEU A:123 and stacking of pi-pi interaction with HIS A:124 and ASN A:94. [2]

5. Analgesic, Anti-inflammatory, and Neuroprotective Activities

5.1 Central Analgesic Activity

Central analgesia was tested using the radiant heat tail flick test on Swiss albino mice, with morphine serving as the standard positive control agent. The compounds were orally administered to the animals in doses of 25 mg/kg and 50 mg/kg, with tail flick latency times determined at 0 minutes, 30 minutes, 60 minutes, and 90 minutes after administration. [2,12,13]

Table 5. Comparison of central anti-nociceptive activity of key benzimidazole derivatives vs. morphine standard (% elongation of tail-flick latency).^[11,12,13]

Evaluation of central analgesic activity showed that compounds 3a, 3b, and 6 produced significant pain-relieving effects. Among them, Compound 3b demonstrated the strongest activity, exhibiting analgesic effects comparable to the standard drug morphine at higher doses. Compound 3a also showed marked analgesic activity, while Compound 6 produced effects similar to morphine at 60 minutes, indicating that these benzimidazole derivatives possess promising central analgesic potential. [2,12,13]

5.2 Peripheral Analgesic Activity

Peripheral analgesic activity was assessed using acetic acid-induced writhing assay, and diclofenac sodium (25 mg/kg) was used as reference drug. Out of all the test drugs studied, compound 6 exhibited highest peripheral analgesic activity (55.60% writhing inhibition) at dose level of 50 mg/kg, followed by compound 3c (54.10% at 25 mg/kg). Compound 3a and compound 3b exhibited moderate peripheral analgesic activity at dose level of 25 mg/kg (49.25%, 26.87%), respectively (P < 0.001). Compound 4 (monosubstituted) failed to show any significant peripheral analgesic activity. [2]

5.3 Anti-inflammatory Activity

Anti-inflammatory activity was evaluated using the carrageenan-induced paw edema model, with diclofenac sodium as the reference drug. Among the tested compounds, disubstituted benzimidazoles 3b and 3a exhibited the strongest anti-inflammatory effects, with Compound 3b showing inhibition levels comparable to diclofenac after 4 hours. Compounds 3c and 6 displayed moderate activity, whereas Compound 4 showed only weak anti-inflammatory effects. [11,13] The superior activity of compounds 3a and 3b is likely due to their enhanced interaction with cyclooxygenase (COX) enzymes. Their strong analgesic and anti-inflammatory profiles suggest that these compounds may exert their effects through a mechanism similar to that of diclofenac, involving inhibition of the COX pathway. [2,13]

5.4 Cholinesterase Inhibitory Activity

Cholinesterase inhibitory activity was evaluated using Ellman’s assay with donepezil as the reference standard. Among the synthesized compounds, Compound 6 showed the strongest inhibition of AChE, while compounds 3a and 3b exhibited comparatively weaker AChE activity. In contrast, compounds 3a and 3b demonstrated the highest BChE inhibitory effects, with Compound 3a showing notable selectivity toward BChE. These results suggest the potential of these benzimidazole derivatives as lead compounds for developing therapies targeting neurodegenerative disorders. [2,14,15]

5.5 Antioxidant Activity

The antioxidant activities were determined by DPPH free radical scavenging assay using BHT as the reference antioxidant (IC50 value = 14.44 µg/mL). Compound 3a displayed a high antioxidant activity (IC50 value = 16.73 µg/mL), having a similar degree of efficiency compared to BHT. This was due to the phenolic –OH group present on 4-hydroxybenzyl residue, which acts as an important chemical structure responsible for antioxidant activities via donating hydrogen atoms. Moreover, in the lipid peroxidation assay performed using rat brain homogenate as a substrate, compound 3a demonstrated the highest activity among all tested compounds (IC50 value = 75.53 µg/mL versus catechin reference IC50 value = 59.36 µg/mL). The antioxidant activities of compounds 4 and 3b were moderate whereas the antioxidant activities of compounds 6 and 3c were low. [2,16]

5.6 Antimicrobial Activity

Antimicrobial activity was evaluated against several Gram-positive and Gram-negative bacteria as well as fungal strains using the disc diffusion method. Among the tested compounds, only compounds 4 and 6 exhibited weak antimicrobial activity, producing small zones of inhibition against some bacterial strains. In contrast, the disubstituted benzimidazole derivatives (3a, 3b, and 3c) showed no significant antimicrobial effects, suggesting that aromatic substitution may reduce the antibacterial potential of these compounds. [2,21]

5.7 Cytotoxicity (Brine Shrimp Lethality Assay)

The cytotoxicity studies done using the brine shrimp lethality test provided preliminary data for the toxicity of the compounds with vincristine sulfate used as the positive control (LC50 = 1.283 μg/mL). Compound 6 exhibited modest cytotoxicity (LC50 = 16.68 µg/mL) while 3b (LC50 = 21.9 µg/mL) and 3c (LC50 = 35.99 µg/mL) displayed weaker cytotoxicity. Compounds 3a and 4 exhibited minimal cytotoxicity (LC50 = 116.17 and 148.48 µg/mL) in comparison. The cytotoxicity data obtained via brine shrimp test can be supplemented with the findings from MTT test in Keser et al. [2]

6. Comparative ADMET Profiling

Both experiments applied ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) analysis through silico to determine the drug likeness and pharmacokinetics of the compounds. Specifically, the use of AdmetSAR 2.0 web server was made in the Keser study for compound 4, whereas the Raka study used SwissADME and admetSAR to analyze its compounds. These findings are summarized in Table 6 below. [1,2]

Table 6. Comparative ADMET profiles of lead compounds from both studies.