A simple method of preparation of labelled peptides possessing antibiotic properties.

Preparation of derivatives of peptide antibiotics polymyxin B and Colistinsubstituted on free amino groups by aminoacyl residues is described. The first procedure is based on the condensation of the antibiotic with active ester of a suitably protected amino acid. The second one makes use of W o o d w a r d's reagent by condensation of the antibiotic with a protected amino acid. The following compounds were prepared: glycyl-14C-polymyxin B and glutaminyl-polymyxin B and glycylcolistin, also under conditions suitable for a radioactive synthesis. All the preparations preserve a substantial part of the biological activity comparable with polymyxin B and Colistin.