Efficient Solution Phase Synthesis of PPII Helix Mimicking Ena/VASP EVH1 Inhibitors from Proline‐Derived Modules (ProMs)

Abstract

In the search for efficient inhibitors for the enabled/ vasodilator stimulated phosphoprotein homology 1 (EVH1) domain to reduce cell motility in metastatic cancer, we previously developed a toolkit of proline derived modules (ProMs), which mimic the PPII helix found in the natural ‐FPPPP‐ binding motif of EVH1. In this work, we describe the modular assembly of these ProM‐based penta­peptidic EVH1 ligands through liquid phase peptide synthesis. We initially used pentafluorophenyl (Pfp) active esters for amide bond formation and built up the growing peptide chain from the C‐ to the N‐terminus. Switching to HATU/DIPEA coupling conditions and changing the directionality of the synthesis from the N‐ to the C‐terminus afforded the target ligands with improved overall yields and purity. Employing a Fmoc‐protected (instead of the N‐acetylated) phenylalanine derivative as N‐terminal building block significantly reduced epimerization. In contrast to the originally used solid phase peptide synthesis (SPPS), the developed solution phase method allowed for a facile alteration of the C‐terminal ProM unit and the production of various pentapeptidic ligands in an efficient fashion even on a multigram scale.