Resolution of a-Amino Acids by Chiral Polymer Complexes

Resolution of a-Amino Acids by Chiral Polymer Complexes 

Stereoselective complex formation of a labile metal ion with o-amino acids is well known73 Since the equilibrium of a labile metal complex is established very rapidly, it seems possible that the stereoselectivity of the metal complex formation could be used to resolve optically active amino acids. 

Davankov et al.74) prepared the polymer containing L-proline units 34 by the 

They further observed the stereoselective effect in several other systems containing other amino acids as the polymer ligands74, and identified certain prerequisites for effective resolution (i) mixed complexes are more stable and it is better to use Cu(II) or Ni(II), (ii) the sum of the dentation of the polymer ligands and the mobile ligands (amino acids) should be equal to the coordination number of the central metal ion. The difference in free energy of formation of the two dia-stereomeric complexes with L- and D-proline was estimated to be 0.4 to 0.5 kcal/mol for the L-proline-Cu resin. It was emphasized that the stereoselectivity of this process was sufficient for the complete resolution of racemic a-amino acids74.  

Snyder et al.7S bound N-carboxymethyl-L-valine to a styrene-divinylbenzene copolymer 35 and used its Cu complex to resolve racemic amino acids. With all 

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