Synthesis, antioxidant, and antimicrobial activities of new 2-(1,5,6-trimethyl-1H-benzo[d]imidazole-2-carbonyl)-2,3-dihydro-1H-pyrazole-4-carbonitriles, (1,3,4-oxadiazol-2-yl)-1H-benzo[d]imidazol-5-yl)(phenyl)methanones, and (1,3,4-oxadiazol-2-yl)-1,5-dihydro-[1,2,4]triazolo[1,5-a]pyridine-8-carbonitriles ( QSAR and molecular docking analysis)

Abstract

Objectives A new series of 2-(1,5,6-trimethyl-1H-benzo[d]imidazole-2-carbonyl)-2,3-dihydro-1H-pyrazole-4-carbonitrile (6a,b), (1,3,4-oxadiazol-2-yl)-1H-benzo[d]imidazol-5-yl)(phenyl) methanone (9–11), and (1,3,4-oxadiazol-2-yl)-1,5-dihydro-[1,2,4]triazolo[1,5-a]pyridine-8-carbonitrile (14–16) derivatives were synthesized and evaluated for their antioxidant and antimicrobial activities; in addition, their quantitative structure–activity relationships and molecular docking were investigated. Methods The target compounds 6a,b were synthesized by the following method: reaction of 5,6-dimethyl-1H-benzoimidazole-2-carbohydrazide (2) with 4-(dimethyl amino)benzaldehyde or anthracene-9-carbaldehyde yielded Schiff’s bases 3a,b, which were reacted with ethyl cyanoacetate to yield 1H-pyrazole-4-carbonitriles 4a,b; N-methylation of 4a,b afforded 5a,b, which reacted with 4-aminoantipyrine to give 6a,b. In addition, 5-benzoyl-1H-benzo[d]imidazole-2-carbohydrazide (8) or 8-cyano-6-isocyano-5-oxo-7-phenyl-1,5-dihydro-[1,2,4]triazolo[1,5-a]pyridine-2-carbohydrazide (13) reacted with different carboxylic acids such as crotonic acid, 3,4-diaminobenzoic acid, and 6-hydroxy-4-methoxybenzofuran-5-carboxylic acid to form compounds 9–11 and 14–16, respectively. The synthesized compounds were evaluated for their antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay, and the diffusion plate method for antimicrobial activity. Results and conclusion Among other tested compounds, compounds 15, 11, and 10 possessed the highest antioxidant activity, whereas compounds 4a, 5b, 6b, 10, and 11 displayed high activity against Staphylococcus aureus, Salmonella typhimurium, and Candida albicans. The quantitative structure–activity relationships of the studied compounds 4a, 4b, 5b, 6b, 10, 11, 14, 15, and 16 indicated a high correlation (r 2 =0.82) between the predicted and actual activities as obtained from molecular descriptors and the inhibitory activity of this set of tested molecules measured as antioxidant activity. Moreover, the three-dimensional (3D) pharmacophore was generated, and docking of the most active antibacterial compound 4a against the dihydropteroate synthase enzyme gave comparable scores for hydrogen bond interaction (−13.5 kcal/mol) and binding mode to the reference antibiotic sulfamethoxazole (−13.00 kcal/mol).