Tunicamycin is lethal to bacteria and eukaryotes either by blocking cell wall biosynthesis or protein N-glycosylation, respectively. The tunicamycin uracil group mimics the UDP-HexNAc donor substrate, binding to a uridyl binding pocket within PNPT translocase enzymes. This is stabilized by a noncovalent π–πstacking interaction with a conserved Phe within the PNPT active site. We have structurally modified tunicamycins (TunR1 and TunR2) to be less toxic to animal cells, but which retain the antibacterial activity. TunR1 and TunR2 are also potent enhancers of the β-lactam family of antibiotics, resulting in increased activity of penicillins, cephems, and carbapenems. TunR2 in which the uridyl group is converted to a 5,6-dihydrouridyl has low eukaryotic toxicity, and enhanced aminothiazolidyl cephalosporins by >128-fold against B. subtilis and several pathogenic mycobacterial strains.