Amino peptide coupling reactions

Twenty one rhena-/3-ketoimine derivatives of 14 different amino acids and one dipeptide have also been synthesized (37,38). The amino acid derivatives are prepared according to Eq. (3) in which the primary amine is an amino acid ester. A dipeptide derivative is formed via normal peptide coupling reactions, as shown in Eq. (4). In this reaction sequence, the ethyl... 

J Coste, E Frerot, P Jouin, B Castro. NCA A troublesome by-product in difficult amino acid coupling reactions, in CH Schneider, AN Eberle, eds. Peptides 1992. Proceedings of the 22nd European Peptide Symposium, Escom, Leiden 1993, pp 245-246. 

Exercise 25-21 How could an optically pure W-acylamino acid racemize and lead to racemic W-acylpeptides as the result of a peptide coupling reaction wherein the carboxyl group of the amino acid was converted to an anhydride group (Review Section 25-5A.)... 

E.C. 3.5.1.4) used to prepare amino acids, usually through resolution, and also penicillin G acylase (penicillin G amidohydrolase) (E.C. 3.5.1.11), used in the manufacture of semisynthetic penicillins.152 153 Immobilized penicillin G acylase has most recently been used to catalyze the formation of. V-a-phenylacetyl amino acids, which can then be used in peptide coupling reactions (see Section 19.2.3.2).154 Bacterial aminoacylase I (.V-acyl-i.-amino acid amidohydrolase, E.C. 3.5.1.14) has also been used to acylate chiral amines with poor to moderate enantioselectively.155... 

TABLE 19.2 Peptide Coupling Reactions Using Unnatural Amino Acids in Both the Acyl Donor and Acceptor Sites (the Arrow Indicates the Peptide Bond That Was Synthesized) ... 

Amino-acid Protection. - Carboxyamidomethyl (CAM) esters have been shown to be useful protecting groups in a-chymotrypsin and papain-catalysed peptide hydrolysis and synthesis.5 10 1,3-Dioxans (582) can be obtained from Na-protected serine derivatives by acid-catalysed transacetalation and are sufficiently robust to survive both amino deprotection and peptide coupling reactions. 11 (L)-Histidine benzyl ester can be prepared as the ditosylate salt... 

Yet we have to differentiate between the two tasks to determine a maximal amount of amino functions on polymer to monitor the total capacity of the support, e.g., after deprotection/deprotonation on one side, and on the other to detect only traces of amino groups remaining eventually after the peptide coupling reaction. In the first case the analytical methods employed are not limited by the presence of labile N-tenninal protecting groups as in controlling the completion of the peptide synthesis step. 

The restricted applicability of commercially available proteases for peptide coupling reactions warrants the continuous importance of mining natural resources for enzymes with novel properties, such as a broad substrate range, acceptance of nonproteinogenic amino acids, high coupling efficiency, and robustness xmder reaction conditions. 

Carbamates can be used as protective groups for ammo acids to minimize race-mization in peptide synthesis. Raccmi/ation occurs during the base-catalyzed coupling reaction of an W-protected, catboxyl-uc ivated amino acid, and takes place in the intermediate oxazolone that foro S readily from an N-acyl protected amino... 

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