Broad-spectrum antibacterial amphiphilic aminoglycosides: A new focus on the structure of the lipophilic groups extends the series of active dialkyl neamines.

Amphiphilic aminoglycosides (AAGs) constitute a new class of antibacterial compounds targeting the bacterial membranes. We have identified the 3',6-dinonyl neamine 9 as a broad spectrum antibacterial AAG. Here, we report on the synthesis, antibacterial activity and eukaryotic cytotoxicity of new 3',6-dialkyl neamines designed in order to finely delineate the structure-activity relationships relating their activity to a lipophilicity window. New broad-spectrum antibacterial derivatives were obtained carrying two identical linear or branched alkyl groups or two different linear alkyl groups. Two fluorescent antibacterial 3',6-heterodialkyl neamines carrying a pyrenylbutyl fluorophore were also identified as potential tools for mechanistic study. Homodialkyl and heterodialkyl neamines appeared to be more active on Gram-negative bacteria than dinaphthylalkyl neamines. However, branched dialkyl neamines or heterodialkyl derivatives were found to be more cytotoxic on mammalian cells than 9. The exposure of P. aeruginosa over one month to half-MIC of one of the most active derivatives 9 demonstrated the high difficulty of resistance emergence to AAGs.