AAmino Acids As Chiral Ligands

Various experiments conducted using a-amino acids as a ligand gave marked enantioselective effects for Cu(II) and Ni(II). Table 7.4 illustrates the results for the reaction (1) in Figure 7.8.11'12

TABLE 7.4 Influence of «-Amino Acid Ligands on the Equilibrium Constant for Binding of 3.8c to the Ligand-Cu2+ Complex (K„) and the Second-Order rate Constant (kcat) for Reaction of this Ternary Complex with Diene 2" and the Enantioselectivity of this Reaction in Water6

Structure

Ligand

Name

o nh2 o nh2

o nh2 o nh2

o nh2

Glycine

L-Valine

L-Leucine

L-Phenylalanine

L-Tyrosine

.¿V-Methyl-L-tyrosine

1.16 x 103

6.29 x 102

5.71 x 102

5.14 x 102

8.66 x 102

1.40 x 10J

2.45 x 103

jV-Methyl-p-methoxy-L-phenylalanine 2.04 x 10

2.56

1.90

2.01

2.01

2.07

2.83

o^HQkoh o x h3c ch3

A'^-Dimethyl-L-tyrosine

1.66 x

103

2.92

/tNH

L-Tryptophan

3.02 x

103

1.44

33

5-Hydroxy-L-tryptophan

4.89 x

103

1.15

29

oh /rnh

o nh2Xj

L-Abrinee

5.05 x

103

1.47

74

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