Conformation of linear homo-oligoprolines

A conformational analysis of Piv-l-Pro-d-Pro-OMe was performed in the solid state using i.r. absorption and X-ray diffraction. The tertiary amide bond is in the trans conformation, whereas the tertiary peptide bond is in the cis conformation. The sequence of the, ø angles is F, F*. The preferred conformations of the pivaloylamino group, the pyrrolidine rings, and the ester moiety are also discussed.