New thieno[2,3- <i>b</i> ]pyridine-based 1 <i>H</i> -pyrazole hybrids attached to arylazo units: Synthesis of potential MRSA inhibitors

The goal of this work is to examine the impact of integrating arylazo units to the skeleton of thieno[2,3-b]pyridine-based 1H-pyrazoles on their MRSA inhibitory activity. Using a stoichiometric amount of p-toluenesulfonic acid (p-TSA), the new hybrids were obtained by reacting thieno[2,3-b]pyridine-based carbohydrazides with acetylacetone or its aryldiazenyl-containing derivatives. The protocol was carried out in refluxing ethanol for 3–8 h in the presence of three equivalents of p-TSA. Product 4e, connected to phenyldiazenyl and (4-methoxyphenyl)diazenyl units at thieno[2,3-b]pyridine-C5 and pyrazole-C4, respectively, demonstrates the highest antibacterial potency, which exceeds ciprofloxacin with MIC/MBC of 1.8/3.6 µM against S. aureus and E. coli. Moreover, it exceeds linezolid in efficacy with MIC/MBC of 1.8/7.3 µM against MRSA.