Synthesis, ion complexation study, and 3D-structural analysis of peptides based on crown-carrier, C-alpha-methyl-L-DOPA amino acids

Selected series of terminally protected model peptides to the hexamer level, based on four novel, crown-ether containing Cα-methyl-L-DOPA (L-Mdp) amino acid residues, namely L-Mdp[15-C-5], L-Mdp[18-C-6], L-Mdp[benzo-24-C-8] and L-Mdp[(S)-Binol-20-C-6], combined with either L-Ala or L-Ala/Aib or Gly/Aib, were synthesized by solution methods. An ESI-MS analysis of their alkali metal cation complexation ability was carried out. Their FTIR absorption, 1H NMR, ECD, and VCD spectroscopic properties suggest that all of these crowned amino acids are strong inducers of (left-handed) β-turns and 310-helical structures.(©