Efficient asymmetric synthesis of α-amino acids through hydrogenation of α,β-dehydroamino acid residue in cyclic dipeptides

Abstract

A series of cyclo (Δaminoacyl-L-Ala) ( 4 ) (Δ=α,β-dehydro) were prepared from cyclo(Gly-L-Ala) and corresponding aldehyde, and hydrogenated with Pd black in MeOH. Chiral inductions producing cyclo (L-aminoacyl-L-Ala) ( 5 ) from 4 were 96–99% in the case of L-Aba (2-aminobutanoic acid), L-Val, L-Leu, and L-App (2-amino-5-phenylpentanoic acid) as an L-aminoacyl moiety in 5 . Pure L-Leu, L-Aba, and L-App were synthesized in preparative scale from corresponding 4 through asymmetric hydrogenation and acid-hydrolysis.