Peptides chemical hydrolysis

An alternative approach to peptide sequencing uses a dry method in which the whole sequence is obtained from a mass spectrum, thereby obviating the need for multiple reactions. Mass spec-trometrically, a chain of amino acids breaks down predominantly through cleavage of the amide bonds, similar to the result of chemical hydrolysis. From the mass spectrum, identification of the molecular ion, which gives the total molecular mass, followed by examination of the spectrum for characteristic fragment ions representing successive amino acid residues allows the sequence to be read off in the most favorable cases. 

See Section IV.1 for alternative methods of chiral resolution. Partial chemical hydrolysis of proteins and peptides with hot 6 M HC1, followed by enzymatic hydrolysis with pronase, leucine aminopeptidase and peptidyl D-amino acid hydrolase, avoids racemiza-tion of the amino acids281. The problems arising from optical rotation measurements of chiral purity were reviewed. Important considerations are the nonideal dependence of optical rotation on concentration and the effect of chiral impurities282. 

The present chapter focuses on specific aspects of these challenges, namely peptide bond hydrolysis (chemical and enzymatic) and intramolecular reactions of cyclization-elimination (Fig. 6.4). This will be achieved by considering, in turn a) the enzymatic hydrolysis of prodrugs containing a peptide pro-moiety (Sect. 6.2), b) the chemical hydrolysis of peptides (Sect. 6.3), c) the enzymatic hydrolysis of peptides containing only common amino acids (Sect. 6.4), d) the hydrolysis of peptides containing nonproteinogenic amino acids (Sect. 6.5), and, finally, e) the hydrolysis of peptoids, pseudopeptides and peptidomimetics (Sect. 6.6). 

The intrinsic inertness of the peptide bond is demonstrated by a study of the chemical hydrolysis of N-benzoyl-Gly-Phe (hippurylphenylalanine, 6.37) [67], a reference substrate for carboxypeptidase A (EC 3.4.17.1). In pH 9 borate buffer at 25°, the first-order rate constant for hydrolysis of the peptide bond ( chem) was 1-3 x 10-10 s-1, corresponding to a tm value of 168 y. This is a very slow reaction indeed, confirming the intrinsic stability of the peptide bond. Because the analytical method used was based on monitoring the released phenylalanine, no information is available on the competitive hydrolysis of the amide bond to liberate benzoic acid. 

Table 6.5. Peptide Sites of Particular Reactivity toward Chemical Hydrolysis. See text for references and further details. ...

A- [(Acy loxy )methyl] derivatization was also examined for its potential to improve the biological stability of peptides. For example, the peptide-like model A-[(benzyloxy )carbonyl]glycine benzylamide (8.171, R = H) was de-rivatized to a few N-/Yacyloxy)methyl] derivatives whose chemical and enzymatic hydrolysis was investigated [225], The results compiled in Table 8.13 indicate a fast chemical hydrolysis, the mechanism of which is depicted as Reaction b in Fig. 8.21. Enzymatic hydrolysis also occurs in human plasma, resulting in short half-lives, with the exception of the pivaloyl analogue. 

Proteins, peptides, and other polymeric macromolecules display varying degrees of chemical and physical stability. The degree of stability of these macromolecules influence the way they are manufactured, distributed, and administered. Chemical stability refers to how readily the molecule can undergo chemical reactions that modify specific amino-acid residues, the building blocks of the proteins and peptides. Chemical instability mechanisms of proteins and peptides include hydrolysis, deamidation, racemization, beta-elimination, disulfide exchange, and oxidation. Physical stability refers to how readily the molecule loses its tertiary and/or sec-... 

This means that peptide bond formation is not a totally unfavorable process but actually corresponds to a change in standard free energy that is close to 0 [102], But this assertion is true within a rather limited pH range only (Fig. 2), where peptide bond formation is a very slow process in the absence of catalyst so that the reversibility of peptide bond hydrolysis revealed by enzymatic catalysis is usually not accessible with purely chemical systems. 

Related applications include peptide/protein hydrolysis, heterogeneous catalysis reactions, acid digestion of samples, (e.g. tissue, implants, catalysts, drugs, etc), for AA / ICP / ICP-MS analysis, solvent extractions, processing and/or destruction of toxic chemicals, chemotherapy and anti-neoplastic agents. 

Chemical Hydrolysis of peptides or amides, release of sugars, etc. Direct physical or chemical analysis, e.g., titrations free substances... 

Can sequence proteins by specific enzyme and chemical hydrolysis to give peptides which can then be nm through sequenators (up to about 100 aa s). 

Fragment aliquots of the polypeptide by enzymatic or chemical hydrolysis and separate the peptide mixtures into individual fragments. (This process will yield overlapping sets of smaller peptides.)... 

The peptide bond is an amide containing an sp carbon atom. The amide is stabilized by electron resonance between the nitrogen and oxygen atoms. The uncatalyzed, or chemical hydrolysis of a peptide bond is illustrated at the top of Figure 10. The most difficult structure to form, or the transition state, consists of the tetrahedral carbon. This would be the structure at the top of the energy diagram in Figure 1. 

However, selective cleavage of this amide bond in the C-terminal position was previously impossible. Both chemical and biochemical methods also led to internal peptide bond hydrolysis, giving rise to difficult separation problems. Consequently the amide group has been rather unattractive for C-terminal protection in peptide synthesis. 

In addition to chemical hydrolysis, hydrolysis by enzymes can operate as an alternative degradation process. It has become widely accepted that biodegradable synthetic polymers tend to be designed to mimic those structures prevailing in nature, since enzymes produced by microbial populations may not discriminate between polymers of similar structure.11 Synthetic nonpolypeptidic, chiral polyamides could mimic natural peptides or proteins, resulting in biodegradable products useful in biomedicine. 

Liquid gelatins (L), produced by intense chemical hydrolysis, have medium-weight molecules M < 10 ), a weak charge and many highly charged peptides. 

The wool fiber consists predominantly of proteins therefore, the reactions of wool are the reactions of the protein backbone (e.g., peptide bond hydrolysis) and the reactions of the side-chains of the 21 different types of amino acid residues of which wool is composed. Six of these amino acids (glycine, alanine, valine, leucine, isoleucine, and proline) are essentially chemically inert so are not normally available for chemical reaction. The reactions of the... 

When it is not known whether the A. a. in the original protein is Asn or Asp, the abbreviation Asx or B is used Glx or Z indicates Glu, Gin, Gla (L-4-car-boxyglutamic acid) or GIp (pyroglutamic acid). These ambiguities arise l cause chemical hydrolysis of peptide bonds also hydrolyses Asn, Gin, Gla and GIp to the corresponding acid. 

Figures. The methods for preparation of peptide aldehydes. Methods 1 and 2 prepare an N-terminal aldehyde peptide by oxidation of an N-terminal Ser-peptide or hydrolysis of a dimethoxyacetate-peptide. Methods 3-7 prepare C-terminal aldehyde peptides. Methods 3 and 4 are known as the n + 1 method. The peptide alkyl ester or alkyl thioester is obtained from different types of resins then a masked amino acid glycodiol ester is introduced by enzymatic synthesis (3a, 3b) or by a chemical method (4) finally, the peptide is treated with TFA to give the aldehyde peptide. In methods 5 and 6, aldehyde peptides are obtained from oxidation of a peptide glycol diol ester. In method 7, treatment of an N-protected peptide thioester resin with Pd" and EtjSIH gives the cleaved C-terminal peptide aldehyde.

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