A Crystal Structure of an Oligoproline Hexamer with a Zig‐zag Arrangement

Abstract Oligoprolines adopt the well‐defined polyproline II (PPII) helical conformation, even at a short chain length of six residues. These rigid peptides are versatile molecular rulers and scaffolds, yet there has been great difficulty in obtaining single crystals for X‐ray crystal structure analysis to probe their conformation in the solid state. Here, we report a crystal structure of an oligoproline hexamer bearing an N‐terminal terephthalic acid moiety. Comparison with that of a previously obtained crystal structure of a closely related hexaproline revealed influence of the terminal functional groups and the solvent on the crystal packing.