A Journey from Amino Acid and Peptide Chemistry to Palladium and Back

Chelated metal enolates of amino acid esters are extremely suitable for the synthesis of unsaturated amino acid derivatives, e. g. via Claisen rearrangement or palladium catalyzed allylic alkylation. Due to the fixed enolate geometry, as a result of chelate formation, these processes proceed with a high degree of diastereo selectivity. Starting from chiral allylic alcohols, which are used for the preparation of the allylic esters and carbonates, optically active amino acids are obtained. This chirality transfer can also be used for stereoselective peptide modifications. If tosylated peptide allylic esters are subjected to Claisen rearrangement, the chirality of the peptide chain can be used as a stereocontrolling element. Another possibility to transfer chirality is given by the rearrangement in the presence of chiral ligands. The palladium catalyzed allylic alkylation is suitable for the introduction of allylic functionalities on the α-carbon and on the nitrogen as well. Therefore the combination of these approaches with ring closing metathesis results in straightforward protocols for the construction of cyclic amino acids and peptides.

enolates - Claisen rearrangement - peptides - palladium - ring closing metathesis