Versatile Stereoselective Synthesis of Completely Protected Trifunctional α‐Methylated α‐Amino Acids Starting from Alanine

A new route to completely protected α‐methylated α‐amino acids starting from alanine is described (see Scheme ). These derivatives, which are obtained via base‐catalyzed opening of the oxazolidinones (2 S ,4 R )‐ and (2 R ,4 S )‐ 2 , can be directly employed in peptide synthesis. The synthesis of both enantiomers of Z‐protected α‐methylaspartic acid β‐( tert ‐butyl)ester ( O 4 ‐( tert ‐butyl) hydrogen 2‐methylaspartates ( R ) or ( S )‐ 4a ), α‐methyl‐glutamic acid γ‐( tert ‐butyl) ester ( O 5 ‐( tert ‐butyl) hydrogen 2‐methylglutamate ( R )‐ or ( S )‐ 4b ), and of N ε ‐bis‐Boc‐protected α‐methyllysine ( N 6 , N 6 ‐bis[( tert ‐butyloxy)carbonyl]‐2‐methyllysine ( R )‐ or ( S )‐ 4c ) is described in full detail.