Rhizocticins — New phosphono‐oligopeptides with antifungal activity

The widely used and well‐known bacterial strain Bacillus subtilis ATCC 6633 was found to produce two novel, antifungal hydrophilic peptide antibiotics, L ‐arginyl‐ L ‐2‐amino‐5‐phosphono‐3‐ cis ‐pentenoic acid ( L ‐Arg‐ L ‐APPA, rhizocticin A) and L ‐valyl‐ L ‐arginyl‐ L ‐2‐amino‐5‐phosphono‐3‐ cis ‐pentenoic acid ( L ‐Val‐ L ‐Arg‐ L ‐APPA, rhizocticin B). Besides rhizocticin A and B, the main components, small amounts of related tripeptides were detected. Instead of the L ‐Val of rhizocticin B they contain L ‐Ile or L ‐Leu and are referred to as rhizocticins C and D, respectively. The C‐terminal residue was identified by NMR spectroscopy as the unsaturated phosphono amino acid L ‐APPA, known till now only as D enantiomer. Enzymatic cleavages of rhizocticin B yielded both L ‐APPA and rhizocticin A.