Novel pyrazolo[1,5- a ]pyrimidine-based pyridine hybrids: Synthesis, antibacterial evaluation, dual anti-DHFR and anti-DNA gyrase activity, and SAR study

Molecular hybridization offers a possible approach to create hybrids with increased antibacterial efficacy. Synthesis of new pyrazolo[1,5-a]pyrimidine-based pyridines as potential antibacterial agents with dual anti-DNA gyrase and anti-DHFR activity is the aim of this work. The proper pyrazolo[1,5-a]pyrimidine-linked 2-cyanoacetamides were reacted with various aldehydes and malononitrile in refluxing ethanol for 6–10 h containing choline hydroxide (0.7 mL, 46 wt%) to produce pyrazolo[1,5-a]pyrimidine-based 6-amino-4-arylpyridine-3,5-dicarbonitrile hybrids 1 and 2 in 71–94% yields. Generally, 3-(phenyldiazenyl)pyrazolopyrimidine-linked pyridines demonstrated twofold more antibacterial efficacy compared to 3-benzylpyrazolo[1,5-a]pyrimidine-based pyridine. Improved potency was due to p-substituted arene units at pyridine-C4 linked to electron-withdrawing groups. Hybrids 1d and 2d, connected to 4-nitrophenyl groups at pyridine-C4, demonstrated good efficacy with MIC/MBC of 4.16/8.33 and 2.25/4.50 µM against S. aureus and E. coli. Hybrids 1d/2d demonstrated remarkable efficacy with IC50 of 3.546/3.227, 3.926/3.558, and 0.172/0.165 μM, respectively, against S. aureus DNA gyrase, E. coli DNA gyrase, and E. coli DHFR.