Chemical deracemization and (S) to (R) interconversion of some fluorine-containing α-amino acids

Several ω-CF3-substituted α-amino acids have been prepared in optically pure form via two complementary approaches. Racemic fluorinated derivatives of 2-aminobutanoic acid, norvaline and norleucine were chemically deracemized by complexation with a Ni(II) salt and a chiral reagent derived from α-(phenyl)ethylamine. Additionally this procedure also allowed the conversion of readily available l-amino acids, CF3-analogs of cysteine and methionine, into the corresponding unnatural d-series. Optically pure amino acids are obtained upon disassembly of the Ni(II) complexes with recovery of the chiral ligand.