Synthesis of tetra-substituted thiophene derivatives as potential Hits combating antibiotic resistant bacteria ESKAPE

The escalating prevalence of antibiotic-resistant bacteria has led to a serious global public health problem; therefore, there is an urgent need for the development of structurally innovative antibacterial agents. In our study, different series of tetra-substituted thiophene derivatives were designed and synthesized by multi-component reactions (MCRs) in moderate to excellent yields. Some of the designed final compounds were synthesized by both microwave assisted method and traditional synthesis. Thirteen compounds were evaluated against antibiotic resistance bacteria ESKAPE, among which compounds 11, 13 and 17 showed the most potent inhibitory activities against multidrug-resistant Enterococcus faecalis with MIC (minimum inhibitory concentration) values as low as 15.62, 7.61 and 15.62 µg/mL, respectively. Two potent candidates 11 and 13 not only showed rapid bactericidal properties and impeded E. faecalis biofilm formation to effectually relieve the development of drug resistance, but also performed low toxicity toward human normal cells. Moreover, time dependent killing assay was performed that showed the reduction of the concentration of bacteria by 5.0 Log (CFU/mL) within 6 h, stronger than reference drug, ampicillin at the same concentration. Additionally, mechanistic investigation demonstrated that both compounds 11 and 13 could exert inhibitory activity against DHPS with IC₅₀ value of 1.73 and 4.67 µM, respectively and against DNA gyrase enzyme with IC₅₀ value of 0.07 and 0.04 µM, respectively. Moreover, the cytotoxic activity of the most active compound was crucial to be determined that showed IC₅₀ value of 75.42 µM. Molecular docking indicated that the binding of both compounds 11 and 13 to DHPS and DNA gyrase enzymes could hinder their function. These results can provide novel structures of antibacterial drugs chemically different from currently known antibiotics and broaden prospects for the development of effective antibiotics against antibiotic-resistant bacteria.