Binding free energy chiral discrimination

The more active isomer (where activity refers to binding affinity at a defined receptor) is designated the eutomer, the less active is the distomer. The ratio of activities is the eudismic ratio, and its logarithm, the eudismic index, is then proportional to the difference in binding free energy between the enantiomers. The eudismic index is a quantitative measure of chiral discrimination. 

Still and Liu reported the enantioselective complexation of amino acids and small peptide derivatives by a bowl-shaped C3 macrotricyclic receptor in chloroform (Figure 14). In all cases the receptor showed the largest hitherto reported chiral discrimination, with a preference for the L-configuration of the substrates (with e.g. 99% ee and a AAG 13 kJ/mol for Boc-val-NHMe). The observed free energies of binding were up to AG - 30 kJ/mol in the case of Me02C-ser-0tBu. 

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