MsbA-IN-5 (compound 40) is a potent and highly selective MsbA inhibitor with an IC 50 value of 2 nM. MsbA-IN-5 has inhibitory activity against Escherichia coli , Klebsiella pneumoniae , and Enterobacter cloacae with MICs of 12 μM, 12 μM and 25 μM, respectively. MsbA-IN-5 can be used for researching anti-Gram-negative bacteria.