Chemoenzymatic synthesis of (S)-hexafluoroleucine and (S)-tetrafluoroleucine.

We have developed a short chemoenzymatic synthesis for both (S)-5,5,5,5',5',5'-hexafluoroleucine (Hfl) and (S)-5,5,5',5'-tetrafluoroleucine (Qfl) on gram scale. Qfl was incorporated into a peptide using standard solid-phase peptide synthesis protocols to measure its helix propensity. The helix propensity for Qfl is 0.68 kcal.mol-1 more favorable compared to Hfl.