Cysteinyl-P-alanine

Enantiomeric differentiation during the thiolysis of a-amino acid ester salts by two thiol-bearing 18-crown-6 derivatives prepared from (1/ , 2/ , 35, 45)- and R, 2S, 3R, 45)-camphane-2,3-diols has also been demonstrated [74]. Discrimination by factors of 1.7-1.9 in the rates of p-nitrophenol release from the enantiomers of alanine-p-nitrophenyl ester salts has been observed. By contrast, the tetrakis-L-cysteinyl methyl ester receptor molecule l,l-l,l,l,l-(60) exhibits [75] extremely high... 

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