An Efficient Synthesis of Optically Pure ( R )‐ and ( S )‐2‐(aminomethyl)alanine (( R )‐ and ( S )‐ama) and ( R )‐ and ( S )‐2‐(aminomethyl)leucine (( R )‐ and ( S )‐aml)

An efficient synthesis of enantiomerically pure ( R )‐ and ( S )‐2‐(aminomethyl)alanine (( R )‐ and ( S )‐Ama) 1a and ( R )‐ and ( S )‐2‐(aminomethyl)leucine (( R )‐ and ( S )‐Aml) 1b is described ( Schemes 1 and 2 ). Resolution of the racemic amino acids was achieved using L ‐phenylalanine cyclohexylamide ( 2 ) as chiral auxiliary. The free amino acids 1a, b were converted to the N α ‐Boc, N γ ‐Z‐protected derivatives 11a, b ( Scheme 3 ) ready for incorporation into peptides. Based on the three crystal structures of the diastereoisomeric peptides 8a, 8b , and 9b , the absolute configurations in both series were determined. β‐Turn type‐I geometries were observed for structures 8b and 9b , whereas 8a crystallized in an extended backbone conformation.