<jats:title>Abstract</jats:title><jats:p>A new complex of cyclic peptide lactone antibiotics from <jats:italic>Bacillus subtilis</jats:italic>, which we named <jats:italic>Maltacines</jats:italic> has recently been described. The structure elucidation of three of them is reported in this paper. The amino acid sequences and structures of the peptides were found by MS<jats:sup><jats:italic>n</jats:italic></jats:sup> of the ring‐opened linear peptides that gave uninterrupted sequences of B<jats:sub><jats:italic>n</jats:italic></jats:sub> and Y″<jats:sub><jats:italic>n</jats:italic></jats:sub> ions. The identities of four unknown residues in the sequences were solved by a combination of derivatisation with phenylisothiocyanate (PITC), high‐resolution mass spectrometry and H/D exchange. The nature and position of the cyclic structure was disclosed by a chemo‐selective ring opening with Na<jats:sup>18</jats:sup>OH and was found to be a lactone formed between a hydroxyl of residue number 4 and the <jats:italic>C</jats:italic>‐terminal amino acid number 12. For verification of the structure of the B<jats:sub>2</jats:sub><jats:sup>+</jats:sup> ion, peptides with different combinations of P/Q and P/K at the <jats:italic>N</jats:italic>‐terminus were synthesized. The structures of the four peptides is tentatively suggested to be: D1a: cyclo(4,12)‐P‐Q‐Y‐Adip‐A‐E‐T‐Y‐Orn‐HGly‐Y‐I‐OH, D1b: cyclo(4,12)‐P‐Q‐Y‐Adip‐A‐E‐T‐Y‐Orn‐S‐Y‐I‐OH and D1c: cyclo(4,12)‐P‐Q‐Y‐Adip‐A‐E‐T‐Y‐K‐S‐Y‐I‐OH. Adip = aminodihydroxy pentanoic acid and HGly = hydroxyglycine. Copyright © 2005 John Wiley & Sons, Ltd.