Modifications of peptides by chelate Claisen rearrangements of manganese enolates

Deprotonation of allylic esters of peptides at -70 degrees C in the presenc e of metal salts results in the formation of metal peptide enolate complexe s, which undergo Claisen rearrangement on warming to room temperature to pr oduce stereoselectively modified peptides. By far the best results are obta ined with manganese enolates. With these enolates, the amino acids incorpor ated in the peptide chain have no significant influence on the rearrangemen t, neither on the yield nor on the stereochemical outcome. Therefore, this protocol is extremely suitable for the stereoselective modification of pept ides by using esters of chiral allylic alcohols. alpha-Alkylated amino acid s can be incorporated into peptides as well.