Structures of new peptide antibiotics, plusbacins A1-A4 and B1-B4

The constituent amino acids of plusbacins A1-A4 were determined to be two moles of L-trans-3-hydroxyproline and one mole each of D-threo-beta-hydroxyaspartic acid, L-threo-beta-hydroxyaspartic acid, D-allo-threonine, D-serine, D-alanine and L-arginine. In plusbacins B1-B4, one mole of L-trans-3-hydroxyproline is replaced by L-proline. The fatty acid residue of A1 and B1 was determined to be 3-hydroxy-tetradecanoic acid, for A2 and B2 to be 3-hydroxy-isopentadecanoic acid, for A3 and B3 to be 3-hydroxy-isohexadecanoic acid, and for A4 and B4 to be 3-hydroxy-hexadecanoic acid. A lactone linkage was suggested to reside between L-threo-beta-hydroxyaspartic acid and 3-hydroxy-fatty acid residues by degradation experiments. The amino acid sequences of plusbacins A2 and B2 were confirmed by Edman degradation of their deacylated products, and supported by mass spectrometric studies. From the above, structures of all components of plusbacins were concluded.