A straightforward approach for the regioselective synthesis of various derivatives of benzo[e]pyrazolo[5\\\',1\\\':2,3]pyrimido[4,5-b][1,4]diazepine as a novel heterocyclic system from the annulation of 6-bromo-7-chloro-3-cyano-2-(ethylthio)-5-methylpyrazolo[1,5-a]pyrimidine with several 2-amino-N-substituted-benzamides as bident nucleophiles in the presence of K2CO3 and DMF has been disclosed. The right regio-isomer was elucidated by 2D-NOESY NMR spectroscopy, as well. Most of the novel synthetic compounds exhibited antimicrobial activity though relatively at high concentrations against multi-drug resistant Klebsiella pneumoniae and Escherichia coli clinical isolates possessed of strong biofilm formation ability. N-cyclohexyl substituted pyrazolopyrimidobenzodiazepine (3h) as the most potent compound represented 100% growth inhibitory on both types of bacterial strains, which brings promises for further changes to develop potential antimicrobial drugs.

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