Synthesis of hexafluorovaline-containing di- and tripeptides

A new strategy for the synthesis of peptides incorporating racemic hexafluorovaline (hfVal) is presented. The synthetic pathway relies on the anti-Michael addition of benzyl amine derivatives to ad hoc prepared beta-bis-trifluoromethyl-acryloyl-alpha-amino esters which proceeds in mild condition, high yields, even if with low stereo- control. The following elaboration of the intermediates, namely deprotection of the benzyl moiety and coupling with alpha-amino esters allowed us to synthetize the targeted tripeptides in four overall synthetic steps, resulting in a synthetic pathway more favorable respect to those appeared in literature based on the synthesis and isolation of racemic Boc-hfVal-OH (eight synthetic steps).