Experimental and theoretical data indicate that, for α-fluoroamides, the FCC(O)N(H) moiety adopts an antiperiplanar conformation. In addition, a gauche conformation is favoured between the vicinal CF and CN(CO) bonds in N-β-fluoroethylamides. This study details the synthesis of a series of fluorinated β-peptides (1–8) designed to use these stereoelectronic effects to control the conformation of β-peptide bonds. X-ray crystal structures of these compounds revealed the expected conformations: with fluorine β to a nitrogen adopting a gauche conformation, and fluorine α to a CO group adopting an antiperiplanar conformation. Thus, the strategic placement of fluorine can control the conformation of a β-peptide bond, with the possibility of directing the secondary structures of β-peptides.
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