Chemical Mediators:  The Remarkable Structure and Host-Selectivity of Depsilairdin, a Sesquiterpenic Depsipeptide Containing a New Amino Acid

The chemical structure determination of depsilairdin, a highly selective phytotoxin produced by the plant pathogenic fungus Leptosphaeria maculans/Phoma lingam, is described. The elucidation of the unusual chemical structure used a combination of NMR spectral data and X-ray crystallography. The absolute configuration was established using chemical degradation and synthesis of (3S,6R)-3,6-diisopropyl-2,5-morpholinedione and its (3R,6S) and (3R,6R) stereoisomers. Similar to the fungal pathogen, depsilairdin caused strong lesions only on brown mustard leaves but not on related species.