Résumé
The straightforward synthesis of chiral (R)- and (S)-difluoroalanine (DfAla) is reported. The key step is a Strecker-type reaction on a (R)-difluorophenethylimine followed by hydrogenolysis, Fmoc protection and acidic hydrolysis. Peptide coupling reactions at its N- and C-terminal position provide diastereomerically pure tripeptides. Based on hydrophobicity index measurements, the hydrophobic contribution of difluoroalanine in a peptide chain was found to be quite similar to that of isoleucine for a smaller van der Waals volume of the side chain.