Synthesis of bis-α,α′-amino acids through diastereoselective bis-alkylations of chiral Ni(II)-complexes of glycine

The Ni(II) complex derived from glycine Schiff base with (S)-N-(benzylprolyl)-2-aminobenzophenone can be effectively alkylated with alpha,omega-dibromide reagents to furnish the corresponding bis-alkylated products. This method presents a direct approach for the preparation of the corresponding bis-alpha,alpha'-amino acids with high biological importance. Heterogeneous (phase-transfer) as well as homogeneous conditions for the alkylation reactions have been investigated and the latter proved to be more efficient in terms of stereochemical outcome. In particular, alkylation of the glycine Schiff base Ni(II) complex with 1,3-dibromopropane followed by acid-catalysed hydrolysis of the resulting bis-alkylation product, allowed for the preparation of naturally occurring (2S,6S)-diaminopimelic acid in high overall yield.