Chloramphenicol is treated with various carboxylic acids to give esters which can be used as low-toxicity antibiotics. Ca pantothenate (24.1 g.) is suspended in 75 ml. abs. HCONMe2 9.6 ml. ClCO2Et is added dropwise at -5.degree., the mixt. is agitated for 30 min., and the soln. is mixed with 28 g. chloramphenicol in 45 ml. abs. HCONMe2. The mixt. is agitated for 1 hr. at room temp., HCONMe2 is distd. in vacuo, the warm residue is dissolved in iso-PrOH, the soln. is cooled, and the solid material that forms is filtered off. Et2O is added to the filtrate to give the pantothenate deriv., m. 93.degree. (decompn. begins). Also prepd. is 4-(O2N)C6H4CH(OH)CH[NHCOCH(O2CR)Cl]CH2OH in which RCO2 is the pantothenate group.