An artificial tris-catecolate siderophore with a tripodal backbone and its conjugates with ampicillin and amoxicillin were synthesized. Both conjugates exhibited significantly enhanced in vitro antibacterial activities against Gram-negative species compared to the parent drugs, especially against Pseudomonas aeruginosa. The conjugates appeared to be assimilated by an induced bacterial iron transport process as their activities were inversely related to iron concentration. The easily synthesized tris-catecolate siderophore has great potential for future development of various drug conjugates to target antibiotic-resistant Gram-negative bacteria.