Elucidation of the Microwave-Assisted Synthesis and Characterization of Heteronuclear Complexes of Bisbenzimidazole Derivatives and Their Biological Activities by In Vitro and In Silico Assays

A novel and efficient protocol for the microwave-assisted synthesis of diversely substituted 2,2′-bisbenzimidazol-5,6′-dicarboxylic acid (BIMCA) from the reaction of 3,4-diaminobenzoic acid with oxalic acid has been developed, which proceeds through sequential nucleophilic addition and electrophilic substitution in accordance with the Philips method. The synthetic utility of this strategy was demonstrated by the concise, one-pot synthesis of (BIMCA) and metal complexes. (BIMCA) with a [{Fe(salen)}₂O] Schiff base ligand complex and new benzimidazole coordination compounds with double oxygen [(BIMCA){Fe(salen)}₂] ligand complexes were obtained. The resulting [(BIMCA){Fe(salen)}₂] ligand complex was then synthesized from Co(CH₃COO)₂.4H₂O, Ni(CH₃COO)₂.4H₂O and Cu(CH₃COO)₂.H₂O heteronuclear complexes. The condensations proceed with good yield to give products that, in certain instances, are not readily attainable by conventional condensation techniques. The structures of the compounds were identified by Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), elemental analysis and magnetic susceptibility. The mutagenic potential of the synthesized chemicals was evaluated by the Ames test towards mutant Salmonella typhimurium strains TA98 and TA100. It was recorded that these chemicals had no mutagenic action. Also, antimicrobial activities were screened by broth microdilution test. It was seen that the minimum inhibitory concentration (MIC) against Klebsiella pneumoniae, Staphylococcus aureus and Staphylococcus epidermidis was 0.195 mg/mL, followed by a MIC value of 0.390 mg/mL against Escherichia coli and Salmonella typhimurium. [(BIMCA){Fe(salen)}₂Co(II)] demonstrated significant antimicrobial activity against Proteus mirabilis and Staphylococcus aureus, with an MIC of 0.195 mg/mL, followed by an MIC of 0.390 mg/mL against Pseudomonas aeruginosa, K. pneumonia and Salmonella typhimurium. The antioxidant properties were examined using various chemical assays, and [(BIMCA){Fe(salen)}₂O] and (BIMCA) exhibited greater 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability, when compared with other compounds. Enzyme inhibitory effects were tested against acetylcholinesterase (AChE), amylase, butyrylcholinesterase (BChE) and tyrosinase. [(BIMCA){Fe(salen)}₂Cu(II)] displayed the best AChE (IC₅₀ 0.51 mg/mL), BChE (IC₅₀ 0.51 mg/mL) and tyrosinase (IC₅₀ 1.52 mg/mL) inhibitory effects. Furthermore, molecular docking calculations were performed to gain insights into the interaction between [(BIMCA){Fe(salen)}₂] and AChE, and between [(BIMCA){Fe(salen)}₂Cu(II)] and amylase. Both compounds showed the potential inhibition of the protein targets.