Aspartate proteases peptide synthesis

Peptide aldehydes are important biochemical tools for specific and reversible inhibition of serine, cysteine, and aspartate proteases in-vitro and in-vivo. Whereas several methods for the preparation of peptide aldehydes have been described [26-28], their reliable parallel synthesis remained a tedious endeavor. Peptide aldehydes suffer from configurational lability in the a-carbonyl position and from high chemical reactivity. 

Thermolysin, which is another protease, will also catalyse peptide synthesis, and a new plant will shortly use this enzyme for the manufacture of the artificial sweetener Aspartame, at a scale of2,000 tonnes per year. In this reaction the L-enantiomer of racemic phenylalanine methyl ester reacts specifically with the a-carboxyl group of JV-protected L-aspartate (Scheme 6.26). Thus both the separation of the enantiomers of the phenylalanine and the protection of the y-carboxyl group of the L-aspartate are unnecessary, which simplifies the synthesis. Although the equilibrium favours hydrolysis rather than synthesis, the peptide product, which is the JV-protected precursor ester of Aspartame, forms an insoluble salt with the... 

Metalloproteases and glutamic and aspartic proteases, on the other hand, do not form covalent intermediates, but activate a water molecule that directly attacks the carbonyl carbon of the peptide bond and displaces the amide nitrogen [49]. These enzymes are often the preferred catalysts for thermodynamically controlled coupling (Figure 15.1). An example of a metalloprotease applied for peptide synthesis is thermolysin, which contains a HExxH+E sequence motif that coordinates a zinc ion and a water molecule. Zinc polarizes the carbonyl group and facilitates deprotonation of the... 

The serine, cysteine, and aspartic proteases and the metalloproteases have all been applied in peptide synthesis. Nevertheless, shortcomings still exist and at an industrial scale chemoenzymatic peptide synthesis is certainly not always the preferred method. Since the properties of the catalyst to a large extent determine the feasibility of industrial application, the discovery and engineering of better variants are an intensive field of research. 

A protease ean be used to catalyze the synthesis of a peptide bond (Scheme 7). When the stoichiometry of the reactions is such that two moles of phenylalanine methyl ester (PM) are used with one mole of Z-aspartic acid, the Z-APM-PM... 

Proteases - Proteases have been applied to several synthetic purposes the most Important of which are peptide bond synthesis and protein semisynthesis. Recent extensive reviews cover this area. Prote-ases have been used in ester synthesis and resolution. Semisynthesis of human insulin has been achieved by enzymic removal and replacement of one amino acid in porcine insulin. All peptide bonds in the N-termlnal octapeptide of dynorphln [H-Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-OH] have been formed using proteases.A precursor of aspartame has been made by themolysin-catalyzed condensation of benzyloxycarbonyl-L-aspartic acid and L-phenylalanlne methyl ester. 

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