Design, Synthesis, and Structural Analysis of D,L-Mixed Polypyrrolinones. 1. From Nonpeptide Peptidomimetics to Nanotubes

To expand the potential conformational space available to the polypyrroline structural motif, an open chain, D,L-alternating hexapyrrolinone was designed and synthesized. Structural studies, including solution NMR and X-ray crystallographic analysis, revealed that the hexapyrrolinone adopts a turn conformation both in solution and in the solid state, with aggregation in solution and a nanotube-like quaternary structure in the crystal.