Design, synthesis, and antibacterial studies of potent pyrazolinyltriazoles

A library of pyrazolinyltriazole hybrids ( 3a – l , 4a – l ) was synthesized via azide–alkyne dipolar (Huisgen) cycloaddition of azidoacetyl pyrazoline and acetylenedicarboxylic esters under solvent-free condition. The in vitro antibacterial activity of the hybrids was studied against four human pathogens, viz. Escherichia coli (ATCC 25922), Klebsiella pneumonia (ATCC 13883), Proteus mirabilis (ATCC 12453), and Staphylococcus aureus (ATCC 29213), compared with that of ciprofloxacin as standard drug. Six of the 24 compounds synthesised [ 3d , k , l and 4d , k , l with minimum inhibitory concentration (MIC) of 3.9 µg/mL] were found to be more potent than ciprofloxacin. In fact, the high antibacterial activity of all 24 new compounds against S. aureus reveals that such compounds with this pyrazolinyltriazole skeleton may emerge as a new class of potential antibacterial agents. Furthermore, the other three pathogens were also effectively inhibited by most of the synthesized compounds ( 3a , c , d , g , k , l , 4a – e , h – l ). Synthesis of the heterocyclic hybrids 3 , 4 , identification of their core skeleton, and their structure–activity relationship are reported herein. Graphical Abstract