Dual DHFR and DNA Gyrase Inhibitory Potency of Some Novel Pyridine Hybrids Linked to Pyrazolo[1,5-a]Pyrimidine Units: Antibacterial Screening and SAR Study.

Bacterial infections are significant issues that endanger public health and deplete financial resources. A potential strategy to combat these infections is molecular hybridization, which combines pharmacophores from potential drugs to produce hybrid scaffolds that are more effective. The preparation of pyridines attached to pyrazolopyrimidine units with promising antimicrobial potency and dual inhibitory capacity against DNA gyrase and dihydrofolate reductase (DHFR) is the aim of this work. A green procedure was conducted by reacting the suitable 2-cyanoacetamides with aromatic aldehydes and malononitrile in refluxing ethanol for 5-8 h containing choline hydroxide to give pyrazolopyrimidine-linked 4-arylpyridine-3,5-dicarbonitrile hybrids 1 and 2 in 74%-94% yields. In general, 5,7-diphenylpyrazolopyrimidine-linked pyridines 2 showed slightly more increased antibacterial activity, particularly against methicillin-resistant Staphylococcus aureus (MRSA), compared to 5,7-dimethylpyrazolopyrimidine-linked pyridines 1. The presence of para-substituted arene units at pyridine-C4 connected to electron-withdrawing groups resulted in increased efficacy. Pyridines 1d and 2d, attached to 4-nitrophenyl groups, showed good potency with MIC/MBC of 2.52/5.04 and 2.03/4.07 µM against S. aureus and Escherichia coli, and with MIC/MBC of 5.04/20.17 and 4.07/16.26 µM against MRSA. 1d and 2d showed promising potency with IC50 of 3.296 and 3.002 μM against S. aureus DNA gyrase, IC50 of 3.702 and 3.304 μM against E. coli DNA gyrase, and IC50 of 0.171 and 0.162 µM against E. coli DHFR.