Incorporation of Trifluoromethylated Proline and Surrogates into Peptides: Application to the Synthesis of Fluorinated Analogues of the Neuroprotective Glycine-Proline-Glutamate (GPE) Tripeptide.

The incorporation into a peptide chain of highly hindered and weakly nucleophilic trifluoromethylated prolines, pseudoprolines and oxazolidines has been achieved. As an application, the synthesis of a new class of fluorinated analogues of the neuroprotective tripeptide glycine-proline-glutamate (GPE) is reported. These analogues have been elaborated from a panel of five-membered ring trifluoromethylated amino acids (Tfm-AAs) through the coupling reaction with a glutamate residue at the C-terminus and a glycine at the N-terminus. Although the peptide coupling reaction at the C-terminal position of the fluorinated amino acid was conveniently performed under standard conditions, the very challenging coupling reaction at the highly deactivated N-terminal position proved to be much more problematic. A methodological study was needed to identify suitable reaction conditions for this difficult peptide coupling.