Optically Active 3-Amino-2H-azirines as Synthons for Enantiomerically Pure alpha,alpha-Disubstituted alpha-Amino Acids: Synthesis of the alpha-Methylphenylalanine Synthons and Some Model Peptides The synthesis of a novel 2-benzyl-2-methyl-3-amino-2H-azirine derivative with a chiral amino group is described. Chromatographic separation of the diastereoisomer mixture yielded the pure diastereoisomers 9a and 9b (Scheme 4 ) which are the D- and L-2-methylphenylalanine ((alpha-Me)Phe) synthons, respectively. The reaction of 9a and 9b with thiobenzoic acid and with Z-leucine yielded the monothiodiamides 10a and 10b (Scheme 5 ) and the dipeptide derivatives 11a and 11b (Scheme 6), respectively. Methanolysis of 11b yielded 12b. The absolute configuration of 10a was established by X-ray crystallography. The absolute configuration of (alpha-Me)Phe in 12b has been deduced from the known configuration of L-leucine.