Antimicrobial agent-1 (compound 6C) possesses potent activity against TolC mutant E. coli with an MIC value of 2 μg/mL. Antimicrobial agent-1 and Colistin exhibit synergistic activity against Gram-negative bacteria. Antimicrobial agent-1 has no cytotoxicity on mammalian cell lines, with MICs > 128 μg/mL in Caco-2 and Vero cell lines[1].