Synthesis of 3₁₀-Helix-Inducing Constrained Analogues of <scp>l</scp>-Proline

Abstract

A bicyclic indolizidinone carboxylic acid and a tricyclic constrained analogue of l-proline were synthesized and evaluated for their ability to induce helix formation as l-Ala tetrapeptides. Variable-temperature NMR, DMSO titration, CD spectra, and X-ray structure analyses, in conjunction with molecular modeling, confirmed the existence of 3(10)-helical motifs with di- and tetrapeptides of l-Ala.