FIGURE 2:

(a) Nucleation of short R-helices by replacement of an N-terminal i and i + 4 hydrogen bond (C=O· ·H−N) with a covalent link (C=X−Y−N). The hydrogen bond surrogate (HBS)-based helices contain a carbon-carbon bond derived from an olefin metathesis reaction. (b) Synthesis of HBS α- and π-helices from a bis-olefin peptide by the ring-closing metathesis (RCM) reaction. R is the amino acid side chain.