Bacitracin A: Structure-activity relationship

The single imidazole nucleus of L-histidine residue in bacitracin-A seems to be important for the anti-bacterial activity of the molecule, since iodination, carboxymethylation and coupling of diazobenzene sulphonic acid to the histidine residue in the antibiotic caused 90–94% loss of antibacterial activity of the antibiotic. In contrast, the bacitracin sulphone and sulphoxide derivatives are as active as the parent antibiotic.