Acylation of 3-(N-formylamino)salicylic acids resulted in transacylation with loss of the formyl moiety. The reaction proceeds through a bis-N-acylated intermediate, which undergoes facile deformylation. This transacylation reaction has been employed for the site-specific functionalization of the mitochondrial poison antimycin A, affording several novel derivatives. The selective cytotoxicity of some of these derivatives toward cultured A549 human lung epithelial adenocarcinoma cells, in comparison with WI-38 normal human lung fibroblasts, illustrates one application of this transacylation reaction.