Biomimetic enterobactin analogue mediates iron-uptake and cargo transport into and .

The design, synthesis and biological evaluation of the artificial enterobactin analogue and several fluorophore-conjugates thereof are described. provides an attachment point for cargos such as fluorophores or antimicrobial payloads. Corresponding conjugates are recognized by outer membrane siderophore receptors of Gram-negative pathogens and retain the natural hydrolyzability of the tris-lactone backbone. Initial density-functional theory (DFT) calculations of the free energies of solvation (Δ(sol)) and relaxed Fe-O force constants of the corresponding complexes indicated a similar iron binding constant compared to natural enterobactin (). The synthesis of was achieved an iterative assembly based on a 3-hydroxylysine building block over 14 steps with an overall yield of 3%. A series of growth recovery assays under iron-limiting conditions with and mutant strains that are defective in natural siderophore synthesis revealed a potent concentration-dependent growth promoting effect of similar to natural . Additionally, four cargo-conjugates differing in molecular size were able to restore growth of indicating an uptake into the cytosol. displayed a stronger uptake promiscuity as six different cargo-conjugates were found to restore growth under iron-limiting conditions. Imaging studies utilizing BODIPY-conjugates, demonstrated the ability of to overcome the Gram-negative outer membrane permeability barrier and thus deliver molecular cargos the bacterial iron transport machinery of and .