Assessment of the rules related to gaining activity against Gram-negative bacteria

In the search for new antibacterial compounds, we repositioned an antimalarial compound class by derivatising it based on the so-called "eNTRy" rules for enhanced accumulation into Gram-negative bacteria. We designed, synthesised and evaluated a small library of amino acid modified compounds together with the respective Boc-protected analogues, leading to no substantial improvement in antibacterial activity against wild-type K12, whereas more distinct activity differences were observed in mutant strains Δ, D22, Δ and BL21(DE3)omp8. A comparison of the activity results of the mutants with respect to the known rules related to enhanced activity against Gram-negative bacteria revealed that applicability of the rules is not always ensured. Out of the four amino acids used in this study, glycine derivatives showed highest antibacterial activity, although still suffering from efflux issues.