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 Nα‐Boc,Nγ‐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.