Acidic amino acids and their amides

Based on the properties of the side chains, the 20 amino acids can be put into six general classes. The first class contains amino acids whose side chains are aliphatic, and is usually considered to include glycine, alanine, valine, leucine, and isoleucine. The second class is composed of the amino acids with polar, nonionic side chains, and includes serine, threonine, cysteine, and methionine. The cyclic amino acid proline (actually, an imino acid) constitutes a third class by itself. The fourth class contains amino acids with aromatic side chains tyrosine, phenylalanine, and tryptophan. The fifth class has basic groups on the side chains and is made up of the three amino acids lysine, arginine, and histidine. The sixth class is composed of the acidic amino acids and their amides aspartate and asparagine, and glutamate and glutamine. 

Acidic Amino Acids and Their Amides (ASP and GLU strongly acid, ASN and GLN polar but not charged. All prefer exterior of protein)... 

Acidic amino acids and their amides Source Stevenson (1994). 

Heaton AE, Moision RM, Armentrout PB. Experimental and theoretical studies of sodium cation interactions with the acidic amino acids and their amide derivatives. J Phys Chem A. 

Figure 6. Proposed inner wall structure of the nicotinic acetylcholine receptor-channel composite from a2pY8 subunit assembly. The channel mouth is constructed from charged amino acids and their amides such as Asp, Glu, and Gin. A Lys is located at just the inner mouth. The lower half is covered by the amino acids having hydroxyl such as Ser and Thr, while the upper half is lined up with hydrophobic residues such as Leu, Val, Ala, lie, and Phe.

Binding of iron by dietary fiber is strongly inhibited by ascorbic acid, citrate, cysteine, EDTA or phytate in concentrations as lew as 100 >uMols/Liter (A3). The inhibitors have the common property of being able to form soluble complexes with iron. The decarbox-ylic amino acids and their amides inhibit binding moderately as do lysine and histidine. Other amino acids either do not interfere with binding of iron fiber or do so only weakly. Calcium (as acetate) and phosphate act as moderate inhibitors. The detergents sodium lauryl sulfonate or cetyltrimethylammonium bromide had no effect on iron binding by fiber (A2). 

Scheme 12.28. A representation of the use of sodium azide as a nucleophile to convert a-halo carboxylic acids and their amide and nitrile derivatives to the corresponding amino compounds. The example shows the formation of glycine (Gly, G) by this method.

Classical enzymes employed for peptide coupling of the serine hydrolase family are chymotrypsin, trypsin, and subtilisin. Chymotrypsin and trypsin are secreted in the mammalian gut as inactive precursors, which are activated by autoproteolysis and structural reorganization. The use of chymotrypsin for peptide synthesis has been reported since the 1930s [50]. Most early examples concern peptide s)mthesis using amides or (m)ethyl esters as acyl donors and free amino acids and their amides, short peptides, or short peptide amides as nucleophilic acyl acceptors [3]. These studies revealed that a high pH, high nucleophile concentration, and low product solubility stimulate the formation of synthetic product. Ethyl esters appeared suitable acyl donors in kinetically controlled conversions, and amino acid amides act better as nucleophilic acyl acceptors than the free amino acids [4]. Furthermore, tripeptides often performed better than dipeptides or amino acids as acyl acceptors. 

In the mid-1970s an enzymatic process for the production of enantiopure a-hydrogen containing L- or D-amino acids (and their amides) has been developed at DSM using whole cells of Pseudomonas putida ATCC 12633. The process is based on the kinetic resolution of racemic amino acid amides and has been commercialized since 1988 for the production of several L- and D-amino acids [1,17b]. The scope and limitations of this process will be discussed, together with enzyme purification, characterization, and the overexpression of the gene coding for the enzyme in an E. coU K-12 strain. 

Electrophilic substitution of the ring hydrogen atom in 1,3,4-oxadiazoles is uncommon. In contrast, several reactions of electrophiles with C-linked substituents of 1,3,4-oxadiazole have been reported. 2,5-Diaryl-l,3,4-oxadiazoles are bromi-nated and nitrated on aryl substituents. Oxidation of 2,5-ditolyl-l,3,4-oxadiazole afforded the corresponding dialdehydes or dicarboxylic acids. 2-Methyl-5-phenyl-l,3,4-oxadiazole treated with butyllithium and then with isoamyl nitrite yielded the oxime of 5-phenyl-l,3,4-oxadiazol-2-carbaldehyde. 2-Chloromethyl-5-phenyl-l,3,4-oxadiazole under the action of sulfur and methyl iodide followed by amines affords the respective thioamides. 2-Chloromethyl-5-methyl-l,3,4-oxadia-zole and triethyl phosphite gave a product, which underwent a Wittig reation with aromatic aldehydes to form alkenes. Alkyl l,3,4-oxadiazole-2-carboxylates undergo typical reactions with ammonia, amines, and hydrazines to afford amides or hydrazides. It has been shown that 5-amino-l,3,4-oxadiazole-2-carboxylic acids and their esters decarboxylate. 

The first example of a dynamic flux analysis was a study performed in the 1960s [269]. In the yeast Candida utilis, the authors determined metabolic fluxes via the amino acid synthesis network by applying a pulse with 15N-labeled ammonia and chasing the label with unlabeled ammonia. Differential equations were then used to calculate the isotope abundance of intermediates in these pathways, with unknown rate values fitted to experimental data. In this way, the authors could show that only glutamic acid and glutamine-amide receive their nitrogen atoms directly from ammonia, to then pass it on to the other amino acids. 

These polymers possessing amide linkages are Important examples of synthetle fibres and are termed as nylons. The general method of preparation eonslsts of the condensation polymerisation of diamines with dlearboxylle aelds and also of amino acids and their laetarns. 

A potential versatile route into a-amino acids and their derivatives is via a combination of (i) nitrile hydratase/amidase-mediated conversion of substituted malo-nonitriles to the corresponding amide/acid followed by (ii) stereospecific Hofmann rearrangement of the amide group to the corresponding amine. Using a series of a,a-disubstituted malononitriles 14, cyanocarboxamides 15 and bis-carboxamides 16, the substrate specificity of the nitrile hydratase and amidase from Rhodococcus rhodochrous IF015564 was initially examined (Scheme 2.7). The amidase hydrolyzed the diamide 16 to produce (R)-17 with 95% conversion and 98%e.e. Amide 17 was then chemically converted to a precursor of (S)-a-methyldopa. It was found... 

A number of syntheses of pyrrolizidine derivatives are based on cyclization of amino acids such as /3-(pyrrolidin-2-yl)propionic acid, 4-aminopimelic acid, and their homologues to give 3-oxo- and 3,5-dioxo-pyrrolizidines. Reduction of these cyclic amides leads to pyrrolizidines. 

Alanine and aspartate are synthesized from pyruvate and oxaloacetate, respectively, by transamination from glutamate. Asparagine is synthesized by amidation of aspartate, with glutamine donating the NH4. These are nonessential amino acids, and their simple biosynthetic pathways occur in all organisms. 

The residues have been listed in the tables in the following order the acidic amino acids (Asp and Glu) and their amides (Asn and Gin) are listed first, followed by His and then the basic amino acids (Lys and Arg). They are followed by the remaining amino acids in, broadly, their order of increasing hydrophobicity. This order is a crude consensus order based on the several hydrophobicity scales discussed by Edsall and McKenzie (1983). 

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