Synthesis, characterization of nitro or amino substituted pyridyl ligands bridged by an ester or ether bond, and their antibacterial assessment against drug resistant bacteria

A series of ester and ether bridged compounds bearing the nitro and amino moieties were synthesized and characterized, in order to assess their ability to potentially serve as antibacterial agents against drug resistant bacteria. All the compounds were obtained at considerable yields while characterization techniques confirmed their successful synthesis. Furthermore, their antimicrobial assessments showed that all the compounds exhibited antibacterial activity against the Gram-negative bacterial strains, both Klebsiella pneumoniae and its drug resistant counterpart. On the contrary, they were poorly active against S. aureus and MRSA. According to the MIC data, all the compounds showed activity of 0.22 to 0.24 mM towards MDR-K. pneumoniae which was higher than the 0.13 mM of the control AgSD. As for K. pneumoniae, the nitro derivatives L1 and L4 showed significantly higher MIC of 0.23 and 0.26 mM, respectively; while the amino derivatives L2 and L3 were more active, with MIC values of 0.16 mM that was better than the 0.18 mM of the control AgSD. Finally, the time kill kinetics study showed that L2, L3 and the control AgSD were bacteriostatic, while L1 and L4 initially showed a bactericidal trend towards K. pneumoniae but eventually changed to an exponential growth. However, all the compounds were bactericidal towards MDR- K. pneumoniae.