(alpha Me)Aun: A Highly Lipophilic, Chiral, C-alpha-Tetrasubstituted alpha-Amino Acid. Incorporation into Model Peptides and Preferred Conformation

Using a chemo‐enzymatic approach we prepared the highly lipophilic, chiral, Cα‐methylated α‐amino acid (αMe)Aun. Two series of terminally protected model peptides containing eitherd‐(αMe)Aun in combination with Aib orl‐(αMe)Aun in combination with Gly were synthesized using solution methods and fully characterized. A detailed solution conformational analysis, based on FT‐IR absorption, 1H NMR and CD techniques, allowed us to determine the preferred conformation of this amino acid and the relationship between chirality at its α‐carbon atom and screw sense of the helix that is formed. The results obtained strongly support the view thatd‐(αMe)Aun favors the formation of the left‐handed 310‐helical conformation.