( S )-α-methyl,α-amino acids: a new stereocontrolled synthesis

A new and convenient stereocontrolled synthesis of the optically pure ( S )-α-methyl,α-amino acids 6 ( a – d ) that exploits the chiral synthon 1,4- N , N -[( S )-1-phenylethyl]-piperazine-2,5-dione ( 1 ) is described. The ( S )-1-phenylethyl group, bonded to each of the N -atoms of the 2,5-diketopiperazine, acts as a chiral inductor in the first alkylation, while the steric hindrance appears to be the determining factor of stereocontrol in third and forth alkylation.