N-Acetyl-L-tyrosine ethyl ester

The protease a-chymotrypsin has been used for transesterification reactions by two groups (Entries 7 and 8) [35, 36]. N-Acetyl-l-phenylalanine ethyl ester and N-acetyl-l-tyrosine ethyl ester were transformed into the corresponding propyl esters (Scheme 8.3-2). 

N-Acetyl-L-tyrosine ethyl ester 7 xlO"4 1.43xl03 193 2.7x10s... 

In the first step, we showed by analytical studies that compound 28 was a donor substrate for transketolase in the presence of D-ribose-5-phosphate as acceptor substrate and that in the second step, the hydroxylated aldehyde released 29 led to the P-elimination of protected L-tyrosine. We showed that the free L-tyrosine can thus be obtained by enzymatic deprotection of N-acetyl-L-tyrosine ethyl ester using acylase and subtilisine. In this conditions, it should be possible to carry out this assay in vivo in the presence of host cells overexpressing transketolase and auxotrophic for L-tyrosin. This strategy should offer the first stereospecific selection test of transketolase mutants. The principle of this assay may be extended to other enzymes that can release aldehydes P-substituted by L-tyrosine. 

Iborra and co-workers (Entry 8) examined the transesterification of N-acetyl-L-tyrosine ethyl ester in different ionic liquids and compared their stabilizing effect relative to that found with 1-propanol as solvent [36]. Despite the fact that the enzyme activity in the ionic liquids tested reached only 10 to 50 % of the value in 1-propanol, the increased stability resulted in higher final product concentrations. Fixed water contents were used in both studies. 

C,3H,.N04 N-Acetyl-L-tyrosine ethyl ester N-Acety 1- L-tyrosi n-dthy I-ester- 30.002/00.262 Jl/4... 

Free and immobilized chymotrypsin were assayed using 2mM of N-acetyl-L-tyrosine ethyl ester (ATEE) in 0.05M PBS at pH 8.0. The absorbance of the solution or the supernatant at 256 nm was plotted against the enzyme weight in the reaction mixture. The initial slope of the curve was used to evaluate the activity. 

N-acetyl-L-phenylalanine ethyl ester Transesterification of N-acetyl-L-tyrosin ethyl 39... 

The following abbreviations are used in the text DEAE-cellulose, diethylamino-ethyl-cellulose CM-cellulose, carboxymethyl-cellulose DFP, diisopropylphospho-fluoridate ATEE, acetyl-n-tyrosine ethyl ester BAEE, benzoyl-L-arginine ethyl ester Tris, tris(hydroxymethyl)aminomethane. 

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