Chiral differentiation of some cyclic β ‐amino acids by kinetic and fixed ligand methods

Differentiation of β ‐amino acid enantiomers with two chiral centres was investigated by kinetic method with trimeric metal‐bound complexes. Four enantiomeric pairs of β ‐amino acids were studied: c is‐(1 R ,2 S )‐, c is‐(1 S ,2 R )‐, t rans‐(1 R ,2 R )‐ and t rans‐(1 S ,2 S )‐2‐aminocyclopentanecarboxylic acids (cyclopentane β ‐amino acids), and c is‐(1 R ,2 S )‐, c is‐(1 S ,2 R )‐, trans ‐(1 R ,2 R )‐, and trans ‐(1 S ,2 S )‐2‐aminocyclohexanecarboxylic acids (cyclohexane β ‐amino acids). The results showed that the choice of metal ion (Cu 2+ , Ni 2+ ) and chiral reference compound (α‐ and β ‐amino acids) had an effect on the enantioselectivity. Especially, aromaticity of the reference compound was noted to enhance the enantioselectivity. The fixed‐ligand kinetic method, a modification of the kinetic method, was then applied to the same β ‐amino acids, with dipeptides used as fixed ligands. With this method, dipeptide containing an aromatic side chain enhanced the enantioselectivity. Copyright © 2009 John Wiley & Sons, Ltd.