Total structures of colistin minor components.

Structural characterization of the colistin (CL) components were carried out using Frit-fast atom bombardment liquid chromatography/mass spectrometry (Frit-FAB LC/MS), tandem mass spectrometry (MS/MS) and the amino acid analysis proposed by MARFEY, and the total structures of 4 minor components including the absolute configuration of the constituent amino acids were proposed. The structures of the minor components were the same as those of the main component colistin A or B except that L-leucine is replaced by L-valine or L-isoleucine.