Guanidinophenyl ester

Scheme 5.1.2. Structures of substrates and substrate mimetic moieties for Arg- and Glu-specific proteases. 1. arginine 2. 4-amidinophenyl ester 3. 4-guanidinophenyl ester (OGp) 4. aspartic acid 5. glutamic acid 6. carboxymethyl thioester (SCm).

Table 12.5-8. Clostripain-catalyzed coupling of 4-guanidinophenyl esters of 4-phenylbutyric acid (Pbu-OGp) and benzoyl-fi-alanine (Bz-(S-Ala-OGp), respectively, with various amino acid amides and peptides according to Gunther et al.[,99 .

In general, naturally occurring (IV-protected) L-amino acid esters of short-chain alcohols, such as methyl and ethyl esters are usually sufficiently reactive as acceptors to achieve reasonable reaction rates in enzymatic peptide synthesis via aminolysis. For less reactive (nonnatural) analogs, such as a-substituted [313] or D-configured amino acids [314], activated esters are recommended, among them, 2-haloethyl (e.g., 2-chloroethyl, trifluoroethyl) [315], p-nitrophenyl [316], or guanidinophenyl esters [317]. For the use of cyclic activated esters [5(47/)-oxazolones] see below. 

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