BIOSYNTHESE DES PEPTIDTEILS DER MUTTERKORNALKALOIDE VOM CYCLOL–TYP

Abstract

A review is given on the biosynthesis of the peptide moiety in ergot alkaloids. Feeding experiments with labeled amino acids have revealed that phenylalanine, proline, valine and leucine are specifically incorporated into the appropriate constituents of the peptides of ergotamine, ergocornine and ergokryptine, respectively. The α-hydroxy-α-amino acid residue of the ergotoxine alkaloids is derived from valine. In the case of ergotamine alanine or a close relative is the immediate precursor of the hydroxyamino acid fragment.

The exact mechanism of cyclol formation in ergot alkaloid biosynthesis is not yet clarified. Abe's group in Japan has found the intact incorporation of lyser-gylalanine and lysergylvaline in peptide alkaloids of various ergot strains. Furthermore they demonstrated the incorporation of L–leucyl–L–proline lactam and L–phenylalanyl–L–proline-lactam in ergokryptine and ergotamine, respectively. Other authors (Floss, Gröger) did not confirm these results. They have tested the possible involvement of free simple lysergic acid derivatives, various di– and tripeptides as well as the corresponding diketopiperazines. In these experiments the added precursors were split by the fungus into the corresponding compounds (lysergic acid and amino acids) prior to incorporation into the peptide moitety of ergot alkaloids. Based on these results and on inhibitor experiments one may speculate that the synthesis of the peptide portion is a nonribosomal process. Apparently like in the biosynthesis of peptide antibiotics the peptide chain formation takes place on a multienzyme complex.