The rates of transacylation were studied between thiol-bearing chiral crown ethers (1—10) and a-amino acid p-nitrophenyl ester salts. Enantioselectivities, kD/kLratios, of 6.5 for valine ester salt, 8.7 for phenylalanine ester salt, and 7.7 for valine ester salt were achieved by 1, 5, and 8, respectively. Saturation phenomena of rate acceleration depending on crown concentration were observed and analysis of these data revealed that the chiral recognition occurs in the step of liberation of p-nitrophenol by intra-complex thiolysis, not in the complex-forming step. A possible mechanism for the enantioselectivity is proposed on the basis of the kinetic data.
All Science Journal Classification (ASJC) codes
- General Chemistry
- Drug Discovery