Pseudodiproline (Pro–Cyp) Oligomers Fold into Helical Polyproline Type secondary structures

The synthesis and conformational properties of oligo-proline mimetics composed of dimeric and tetrameric Pro–Cyp constructs linked by a hydroxymethylene unit are reported. Oligomers were studied both in the solid state and in solution, unveiling right-handed helical conformation depending on the configuration of the vicinally substituted trans-cyclopentane carboxylic acid unit (Cyp). Unlike polyproline oligomers, the alternating synthetic Pro–Cyp counterparts are not stabilized by n–π* interactions but rely instead on the steric demands of the extended backbone conformation within the hydroxymethylene-linked Pro–Cyp repeating units.