Derivatives of Ribosome-Inhibiting Antibiotic Chloramphenicol Inhibit the Biosynthesis of Bacterial Cell Wall

Here, we describe the preparation and evaluation of α,β-unsaturated carbonyl derivatives of the bacterial translation inhibiting antibiotic chloramphenicol (CAM). Compared to the parent antibiotic, two compounds containing α,β-unsaturated ketones (<b>1</b> and <b>4</b>) displayed a broader spectrum of activity against a panel of Gram-positive pathogens with a minimum inhibitory concentration range of 2–32 μg/mL. Interestingly, unlike the parent CAM, these compounds do not inhibit bacterial translation. Microscopic evidence and metabolic labeling of a cell wall peptidoglycan suggested that compounds <b>1</b> and <b>4</b> caused extensive damage to the envelope of <i>Staphylococcus aureus</i> cells by inhibition of the early stage of cell wall peptidoglycan biosynthesis. Unlike the effect of membrane-disrupting antimicrobial cationic amphiphiles, these compounds did not rapidly permeabilize the bacterial membrane. Like the parent antibiotic CAM, compounds <b>1</b> and <b>4</b> had a bacteriostatic effect on <i>S. aureus</i>. Both compounds <b>1</b> and <b>4</b> were cytotoxic to immortalized nucleated mammalian cells; however, neither caused measurable membrane damage to mammalian red blood cells. These data suggest that the reported CAM-derived antimicrobial agents offer a new molecular scaffold for development of novel bacterial cell wall biosynthesis inhibiting antibiotics