Amino acids acid hydrolysis

CW Gehrke, LL Wall, JS Absheer, FE Kaiser, RW Zumwalt. Sample preparation for chromatography of amino acids acid hydrolysis of proteins. J Assoc Off Anal Chem 68(5) 811-821, 1985. 

Compared with the /V-substituted glycosylamines, the l-amino-l-deoxy-2-ketoses are more stable to moist acid atmospheres, but are still heat-labile and decompose rapidly in mild alkali. They exert greater reducing power, although less than reduc-tones. They brown more easily with amino acids. Acid hydrolysis gives much compared with little HMF, but no hexose is recovered, in keeping with the reaction s being irreversible (however, see below). 

Amino acids Acid hydrolysis (HCI 6N) followed by chromatography. There are many methods with variants in duration (24-48 hours) and temperature (110-I45°C). Methionine and cystine are obtained after performic acid oxidation and tryptophan after alkaline hydrolysis. 

The mixture of D and L optical forms of this hydroxy analogue of methionine is converted to the calcium salt which is used in animal feed supplements. Cyanohydrins react with ammonium carbonate to form hydantoins (2), which yield amino acids upon hydrolysis. Commercial DL-methionine [59-57-8] is produced by hydrolysis of the hydantoin of 3-meth5ithiopropionaldehyde [3268-49-3]. 

Amino Acids via Hydrolysis of /V-Galactosvlamino Acid rerf-Bulylamidc Derivatives74 ... 

The electron-deficient alkene (5.2 mmol) in MeCN (5 ml) is added to an intimate mixture of powdered K2C03 (1 g) and NaOH (0.2 g), the (S)-menthone-protected ethyl glycine (1.27 g, 5 mmol), and TBA-Br (0.16 g, 0.5 mmol) in MeCN (20 ml). The mixture is stirred for 1 h at 0°C and then filtered. The solid is washed with MeCN (10 ml) and the combined organic solutions are evaporated and the residue is taken up in Et20. The ethereal solution is washed well with H20, dried (MgS04), and evaporated to produce the alkylated imine, which can be converted into the amino acid upon hydrolysis with aqueous acid. 

The double bond of 2,2-bis(trifluoromethyl)-5(2f/)-oxazolone 71 reacts with ynamines and the resulting cycloadduct 81 is converted into the corresponding amino acid after hydrolysis. The procedure constitutes a new route to 3-alkyl-substituted aspartic acid derivatives 83 (Scheme 7.20 Table 7.14, Fig. 7.15). 

Formation of an amide bond (peptide bond) will take place if an amine and not an alcohol attacks the acyl enzyme. If an amino acid (acid protected) is used, reactions can be continued to form oligo peptides. If an ester is used the process will be a kinetically controlled aminolysis. If an amino acid (amino protected) is used it will be reversed hydrolysis and if it is a protected amide or peptide it will be transpeptidation. Both of the latter methods are thermodynamically controlled. However, synthesis of peptides using biocatalytic methods (esterase, lipase or protease) is only of limited importance for two reasons. Synthesis by either of the above mentioned biocatalytic methods will take place in low water media and low solubility of peptides with more than 2-3 amino acids limits their value. Secondly, there are well developed non-biocatalytic methods for peptide synthesis. For small quantities the automated Merrifield method works well. 

Use of benzyl alcohol resulted in formation of the benzyl ether corresponding to allyl ethers 52, but attempted Claisen rearrangement resulted in an 82 % yield of the product of a 1,3-benzyl shift (see Section 5.1.3.).20 To demonstrate the utility of the methodology outlined in Table 14, x-oxoester 53a was converted into the corresponding x-amino acid by hydrolysis and reductive animation.20... 

The Strecker Synthesis is a preparation of a-aminonitriles, which are versatile intermediates for the synthesis of amino acids via hydrolysis of the nitrile. 

N.N -dibenzylasparagine (I) is converted by standard reactions into 2, an activated (5-homoserine equivalent. Reaction of 2 with R2CuLi gives 3 in 50-70% yield. The final step to a (5-amino acid involves hydrolysis of the nitrile group and deprotection of nitrogen. 

Water, however, carries both nucleophilic and electrophilic centers. This means that water reacts with many biomolecules in a way that damages them. In the case of proteins, as noted above, water reacts with the amide backbone to degrade proteins, generating amino acids as hydrolysis products (see Figure 2.13). This can be disadvantageous if the protein is desired, as it requires that the protein be re-synthesized. The turnover of proteins is important, however, in any system living in a dynamic environment. Thus, the hydrolytic instability of proteins in water is key to maintaining life. 

Real peptides are usually poor drugs because we have our own peptidases which quickly cut up ingested proteins into their constituent amino acids by hydrolysis of the amide link. Drugs that imitate peptides may avoid this ignominious fate by replacing the amide bond with another bond less susceptible to hydrolysis. This part structure of one HIV protease inhibitor makes the point. 

Simple proteins yield only amino acids on hydrolysis and include the following classes ... 

Histidine participation in catalysis was suggested originally by the pH dependence shown in hydrolyses of simple, neutral substrates such as the methyl ester of an N-benzoyl amino acid. The hydrolysis rate typically increases from nearly zero at pH 5 to a maximum value at pH 8. The rate of change is consistent with that of a catalytic process whose rate-limiting step depends on an ionization with an apparent acid dissociation constant, pKa, close to 7. This is a typical value for the dissociation of a proton from a protonated imidazole group ... 

Step [3] Regenerate the amino acid by hydrolysis of the amide. 

Woodin (1956). Values corrected for destruction of DNP-amino acids during hydrolysis. 

Figure 25.1. Salvage and de Novo Pathways. In a salvage pathway, a base is reattached to a ribose, activated in the form of 5-phosphoribosyl-1-pyrophosphate (PRPP). In de novo synthesis, the base itself is synthesized from simpler starting materials, including amino acids. ATP hydrolysis is required for de novo synthesis.

---