Purpurolic acid: A new natural alkaloid from Claviceps purpurea (Fr.) Tul.

- A new amino acid, purpurolic acid, is described by MS and NMR characteristics.
- The natural alkaloid contains proline and alanine in non-peptide linkage.
- It is detected in tissue extracts by acidic mobility in ion-exchange autoanalysis.
- It accumulates only in parasitic sclerotial tissue during ergot alkaloid synthesis.
- Purpurolic acid may be a biomarker for ergot contamination in food or feed.

A novel secondary metabolite from the sclerotia of Claviceps purpurea (Fr.) Tul. is described; the structure is based on 1H and 13C NMR spectroscopy and electrospray mass spectrometry. It has an elemental composition C10H16N2O7 and is comprised mainly of proline and alanine moieties, although without peptide linkage. Notably, these amino-acids are also components of the cyclic tripeptide side chain of several classic ergoline alkaloids. Designated as purpurolic acid, the new compound is the principal free amino-acid in ergot and its natural abundance exceeds that of the ergoline alkaloids with which it accumulates in parallel during parasitic development. In contrast, it does not accumulate in the fungus in axenic culture, even when ergotamine is synthesised. The extent to which the compound is a metabolite of other ergot fungi worldwide is unknown. Biological activity and metabolic significance also remain unknown, but purpurolic acid could become a biomarker for detection of ergot contamination in agricultural products of temperate latitudes.

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