Synthesis and antibacterial evaluation of fused pyrazoles and Schiff bases

For the discovery of new antibiotic drugs to face the problem of microbial resistance, a series of fused pyrazoles such as pyrazolopyrimidines 15a–f, pyrazoloquinazolines 18a, b and pyrazolotriazines 20a, b was synthesized via the reaction of 5-aminopyrazoles 8a, b with 3-(dimethylamino)-1-aryl-prop-2-en-1-ones 9a–d, 2-((dimethylamino)methylene)-5,5-dimethylcyclohexane-1,3-dione (16) and sodium nitrite (NaNO₂), respectively. Finally, Schiff bases 22a–g were obtained by the condensation of 8a, b with aromatic aldehydes 21a–d. The chemical structure of the new compounds was confirmed by spectroscopy. The structure of 15 b was confirmed by X-ray crystallography analysis. All compounds were screened for antibacterial properties toward multi-drug resistant bacteria (MDRB).