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. Author manuscript; available in PMC: 2016 May 27.
Published in final edited form as: J Am Chem Soc. 2015 May 14;137(20):6484–6487. doi: 10.1021/jacs.5b03382

Figure 2.

Figure 2

Structures of tetramers 1a-c depicting H-bonds observed in the crystal structures. Enantiomers of 1b and 1c are shown. α Residues are shaded in yellow, γ residues in green, and protecting groups in gray. 12-Atom H-bonds are shown in red, and 10-atom H-bonds in blue. Geometric criteria used for all H-bond assignment are distance N⋯O < 4.0 Å and angle N–H⋯O > 130°.