Negamycin: Nature's Forgotten Antibiotic.

Negamycin is a natural product antibiotic discovered in 1970 and shown to have a Gram-negative spectrum of activity. It has served as the starting point in drug discovery efforts due in large part to its structural simplicity and novel mode of inhibition of the bacterial ribosome. It follows that negamycin does not show cross-resistance with other antibacterial agents that operate on the ribosome, whether this would be due to target modification, drug efflux, or drug metabolism. Because of the deficiencies of current drug regimens for the treatment of infections caused by Gram-negative pathogens, having a new agent brought to the infectious disease formulary represents a critical medical need, as has been promoted by the World Health Organization and other entities. Negamycin has been the subject of over 20 total syntheses, often highlighting stereoselective chemistry toward installing its two chiral centers on an acyclic chain. Novel synthetic methodologies thereby developed can stimulate the synthesis of novel analogs. With this, progress has been made in devising more potent analogs than negamycin. Structural work has determined that negamycin binds to the A-site of the 30S ribosome encounter complex with tRNA. Advancements have been made to understand the mechanism of transport of negamycin to the bacterial cytoplasm to enable engagement of the ribosome. This review surveys much of what has been published around negamycin and its analogs, including aspects of the biological spectrum of activity and mode of action as well as limitations that have held back clinical development.