Mag: a C-alpha-methylated, side-chain unsaturated alpha-amino acid. Introduction into model peptides and conformational preference

By a chemo-enzymatic approach we synthesized the chiral, Cα-methylated α-amino acid Mag, characterized by a side-chain CγCδ bond. We also prepared a series of model peptides containing Mag in combination with Aib and Ala. All of the peptides were fully characterized and their conformational preference was determined in solution by FT-IR absorption and 1H NMR investigations. X-Ray diffraction analyses of l-Mag, a derivative and three peptides are also presented. We find that this Cα-methylated α-amino acid is an excellent β-turn and 310-helix former. A peptide with two Mag residues one on top of the other after one complete turn of the 310-helix has been synthesized and characterized.