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, C-alpha-methylated alpha-amino acid Mag, characterized by a side-chain C-gamma=C-delta bond. We also prepared a series of model peptides containing Mag in combination w ith Aib and Ala. All of the peptides were fully characterized and their con formational preference was determined in solution by FT-IR absorption and H -1 NMR investigations. X-Ray diffraction analyses of L-Mag, a derivative an d three peptides are also presented. We find that this C-alpha-methylated a lpha-amino acid is an excellent beta-turn and 3(10)-helix former. A peptide with two Mag residues one on top of the other after one complete turn of t he 3(10)-helix has been synthesized and characterized. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.