Synthesis, characterization, and antibacterial evaluation of some new 1,3,5-trisubstituted pyrazole derivatives

Dr. Alok Pal Jain


Objective: The objective of the paper was to design, synthesis, and characterization of new 1,3,5-trisubstituted-2-pyrazolines derivative and evaluate for antibacterial activity. Materials and Methods: The 1,3,5-tri-substituted-2-pyrazolines derivatives have been synthesized by the reaction of chalcone derivatives with succinic hydrazide in the environment of pyridine. A total of 20 compounds have been synthesized and characterized by the infrared, 1H-nuclear magnetic resonance, and mass spectral analysis. Antibacterial activity of the compounds carried out on five Gram-positive bacterial strains, that is, Staphylococcus aureus, Staphylococcus faecalis, Bacillus subtilis, Proteus vulgaris, and Bacillus pumilus and two Gram-negative bacterial strains, that is, Escherichia coli and Klebsiella pneumoniae in two different concentrations, that is, 50 and 100 μg/ml by agar diffusion method using cup-plate method. Norfloxacin and ciprofloxacin were used as standard antibacterial drug. Results and Discussion: The data of antibacterial activity against the Gram-positive bacterial strains (S. aureus, S. faecalis, B. subtilis, P. vulgaris, and B. pumilus) suggested the order of activity of compounds: BR-3 >BR-2>BR-1>CL-4>BR-4>CL-3> CL-2>CL-5>CL-6>ME-3>ME-2>ME-4>ME-5>ME-6>ME-7>CL-7>CL-8>CL-1>ME-8>ME-1. The compounds series BR-1 to BR-4 has shown the highest activity. Compound ME-8, CL-8, CL-7, CL-1, ME-5, ME-6, and ME-1 have showed mild activity, compounds CL-2, CL-5, ME-4, CL-6, ME-3, ME-2, and ME-7 showed moderate activity, and compounds BR-3, BR-2, BR-1, CL-4, BR-4, and CL-3 have showed good activity against Gram-negative bacteria. The result data of antibacterial activity suggested that Cl, Br, F, and nitro substitution at the third and fifth position may enhance the antibacterial activity of the compounds but the methyl and methoxy substitution may result in reduction of the activity.

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