Chemical Dynamic Thermodynamic Resolution and <i>S</i>/<i>R</i> Interconversion of Unprotected Unnatural Tailor-made α‑Amino Acids

Described here is an advanced, general method for purely chemical dynamic thermodynamic resolution and <i>S</i>/<i>R</i> interconversion of unprotected tailor-made α-amino acids (α-AAs) through intermediate formation of the corresponding nickel­(II)-chelated Schiff bases. The method features virtually complete stereochemical outcome, broad substrate generality (35 examples), and operationally convenient conditions allowing for large-scale preparation of the target α-AAs in enantiomerically pure form. Furthermore, the new type of nonracemizable axially chiral ligands can be quantitatively recycled and reused, rendering the whole process economically and synthetically attractive

Chemical Dynamic Thermodynamic Resolution and <i>S</i>/<i>R</i> Interconversion of Unprotected Unnatural Tailor-made α‑Amino Acids

Described here is an advanced, general method for purely chemical dynamic thermodynamic resolution and <i>S</i>/<i>R</i> interconversion of unprotected tailor-made α-amino acids (α-AAs) through intermediate formation of the corresponding nickel­(II)-chelated Schiff bases. The method features virtually complete stereochemical outcome, broad substrate generality (35 examples), and operationally convenient conditions allowing for large-scale preparation of the target α-AAs in enantiomerically pure form. Furthermore, the new type of nonracemizable axially chiral ligands can be quantitatively recycled and reused, rendering the whole process economically and synthetically attractive

Purely Chemical Approach for Preparation of d‑α-Amino Acids via (<i>S</i>)‑to‑(<i>R</i>)‑Interconversion of Unprotected Tailor-Made α‑Amino Acids

Unnatural (<i>R</i>)-α-amino acids (α-AAs) are in growing demand in the biomedical research and pharmaceutical industries. In this work, we present development of a purely chemical approach for preparation of (<i>R</i>)-α-AAs via (<i>S</i>)-to-(<i>R</i>)-interconversion of natural and tailor-made (<i>S</i>)-α-AAs. The method can be used on free, unprotected α-AAs and features a remarkable structural generality including substrates bearing tertiary alkyl chains and reactive functional groups. These attractive characteristics, combined with simplicity of reaction conditions and virtually complete stereochemical outcome, constitute a true methodological advance in this area, rivaling previously reported chemical and biocatalytic approaches