Optically active amino acid complex ions

Yasui et al found that the CD curve in the first band region for a series of typical optically active amino acid complex ions of the type [Co(NH3)4(aa)] (aa = amino acid anion) were of the same form as reported for the vicinal effect of optically active amino acids in complex ions of the type [Co(en)2(aa)] (Fig. 1). Cyclic amino acids and some others gave different types of CD curves. The CD curves for vicinal effects are also of the same type for some isomers of [Co trien(aa)] complex ions, vide infra. The combination of such an effect with the configurational contribution can account for the appearance of one or two CD peaks in the first band region for complex ions of the [Co(en)2aa] type without assuming a change in frequency interval for the two transitions. 

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. 

The coordination of optically active amino acids and their methyl esters to nickel(II) complexes of l,2-bis(2-(5)-aminomethyl-l-pyrrolidinyl)ethane (24 R = H) and l,2-bis(2-(S)-N-methyl-aminomethyl-l-pyrrolidinyl)ethane (24 R=Me) has been studied.98 Some amino acidate ions coordinate stereoselectivity, as do their methyl esters, so that base hydrolysis of the esters proceeds stereoselectively. 

In addition to this we have several examples of which the polymer conformation of the polymeric complex leads the asymmetrical selectivity Hydrogenation reactions of 1-methylcinnamic acid and 1-acetamidocinnamic acid by several poly(L-amino acid)-Pd complexes are observed (142-144). Poly(L-valine) (/3-form) and poly(/3-benzyl-L-aspartate) (a-helix, sinistral) give dextrorotative products, and poly(L-leucine) and poly( 3-benzyl-L-aspartate) (a-helix, dextral) do levo-rotatory products. Also, optical active poly-/3-hydroxyl esters-Raney Ni catalyst (145) and Ion-exchange resin modified by optical active amino acid-metal complex (146,147) are observed in asymmetrically selective hydrogenations. 

The immohilization of the cage complexes on the surface through apical groups offers interesting application possibilities. This approach enables one to obtain ion-exchange resins especially selective for metal ions. The immobilized optically active cations allow one to obtain ion-exchange resins for the separation of optical isomers, such as racemic amino acids or optically active complexes. 

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