In order to facilitate the site specific incorporation of fluorinated amino acids into proteins, two methods are currently applied in our group, (i) in vitro non-sense suppression based protein expression and (ii) total chemical synthesis. In the first approach, an amber stop codon is introduced into a desired position in the protein encoding DNA sequence, and a fluorinated amino acid is chemically coupled to a suppressor tRNA (Ye, Beilstein J. Org. Chem., 2010). Subsequently, protein expression is carried out by means of a cell-free translation system. In the second approach, peptide fragments are synthesized by solid phase peptide synthesis, and the full-length protein is generated by means of native chemical ligation. To investigate fluorine induced effects in the context of protease-inhibitor interactions, our group is currently investigating the basic bovine pancreatic trypsin inhibitor (BPTI) and various proteases. When substituted at a site of the inhibitor that directly interacts with chymotrypsin, DfeGly increases protein stability and preserves inhibition.