Amino Acids reaction

Optically active five- or six-membered cyclic A -acyliminium ions of this type are generated from the a-inethoxy derivatives, easily obtainable through anodic methoxylation of intermediates that are prepared via ex-chiral-pool syntheses from certain natural amino acids. Reaction of 5-substituted five-membered cyclic A -acyliminium ions with various nucleophiles leads to the predominant formation of cw-products with moderate selectivity. The trans-selective reaction with alkyl copper reagents appears to be an exception. 

Amino acids, sulphoxide, radiolysis of 909 a-Amino acids, reactions of 776, 777 a-Aminosulphones, synthesis of 176 Aminosulphonyl radicals 1093 Aminosulphoxides rearrangement of 740 synthesis of 336 Andersen synthesis 60 / -Anilinosulphoxides, synthesis of 334, 335 Anion radicals 1048-1050 ESR spectra of 1050-1054 formation of during electrolysis 963 during radiolysis 892-897, 899, 903 Annulation 778, 781, 801, 802 Antibiotics, synthesis of 310 Arenesulphenamides 740 Arenesulphenates 623 reactions of 282 rearrangement of 719 Arenesulphinates 824, 959 chiral 618... 

In an indirect amination process, acyl halides are converted to amino acids. Reaction of the acyl halide with a chiral oxazolidinone leads to a chiral amide, which reacts with the N=N unit of a dialkyl azodicarboxylate [R"02C—N=N—CO2R ]. Hydrolysis and catalytic hydrogenation leads to an amino acid with good enantioselectivity. ... 

The reaction of dipyridyl disulphide with triphenylphosphine to give the stable phosphonium salt (51) has been used in new methods of phosphorylation (reaction A), in peptide synthesis (reaction B), and in the formation of active esters of cx-amino-acids (reaction C). These reactions appear to have synthetic potential. 

In an attempt to form orally active penicillins unrelated to ampicillin, use was made of the fact that certain spiro a-aminoacids, such as 9, are well absorbed orally and transported like normal amino acids. Reaction of cyclohexanone with ammonium carbonate and KCN under the conditions of the Bucherer-Bergs reaction led to hydantoin 10. On acid hydrolysis, a-amino acid 11 resulted. Treatment with phosgene... 

Fig. 8.26. The two-step activation of oxazolidin-5-one derivatives of peptides and N-acy/ amino acids (8.190). Hydrolysis (Reaction a) yields an A-(l-hydroxyalkyl) derivative that breaks down to liberate the peptide or A-acyl amino acid (Reaction b) [247] [248],...

Amino acid Reaction Amino acid Reaction... 

Despite the rather preponderant odds in favor of amino acid reaction,... 

PITC (phenylisothiocyanate) Aabs = 254 nm. Phenylthiocarbamyl amino acid derivatives are moderately stable at room temperature (1 day). PITC reacts well with both primary and secondary amino acids. Reaction time is approximately 5 minutes at room temperature. Excess reagent must subsequently be removed under vacuum. Also, for hydrolyzed samples, hydrochloric acid must be completely removed prior to derivatization. As a result, even though the actual reaction time is reasonably fast, the total time for various sample manipulations can add up to 2 hours. This is partially compensated by the extremely fast separation possible (12 minutes). Detection is by UV absorption only. Detection limits are typically in the high picomole range. Short column life can result due to unreacted PITC getting into the column. Unlike some of the other reagents, PITC quantifies tyrosine and histidine very well. PITC analysis is available as a commercially prepackaged system dubbed Pico-Tag by Waters Corporation. Representative references include 184-188. See Fig. 11 for a typical separation. 

Chemical methods for carboxyl end-group determination are considerably less satisfactory. Treatment of the peptide with anhydrous hydrazine at 100°C results in conversion of all the amino acid residues to amino acid hydrazides except for the carboxyl-terminal residue, which remains as the free amino acid and can be isolated and identified chro-matographically. Alternatively, the polypeptide can be subjected to limited breakdown (proteolysis) with the enzyme carboxypeptidase. This results in release of the carboxyl-terminal amino acid as the major free amino acid reaction product. The amino acid type can then be identified chroma-tographically. 

A modification of the pyridoxal—amino acid reaction (mentioned above) has been made for automatic analysis of amino acids by ligand-exchange chromatography [95]. This technique involves separation of the amino acids prior to fluorimetric reaction and determination. As the amino acids are eluted from the column, they are mixed with the pyridoxal-zinc(II) reagent to produce a highly fluorescent zinc chelate. Amounts of as low as 1 nmole of amino acid may be detected. The first reaction involved is the formation of the pyridoxyl-amino acid (Schiff base) as in Fig.4.46. The zinc then forms a chelate which probably has the structure shown in Fig. 4.48. 

Some authors have indicated that the sugar-amino acid reactions of the Maillard type are of minor importance in citrus juices because of the high acidities involved. Studies in our laboratories (42-44) would tend to indicate that, to the contrary, the amino acids and sugars are of more than just minor importance in the darkening of citrus juices. Huffman (42) treated citrus juices with cationic ion-exchange resins to remove amino acids, proteins, and the mineral cations, then restored the cations. 

In 1911 his first report (3) on peptide synthesis was presented and in 1912 his first report (2 ) on the sugar-amino acid reaction was published. He completed a book (J l) in 1913. 

Useful for such compounds as sugars, phenols, alcohols, amines, thiols, steroids especially recommended for citric acid cycle compounds and amino acids reaction is often carried out in pyridine or dimethyl formamide (the latter being preferred for 17-keto steroids) care must be taken to eliminate moisture lowest silyl donating strength of all common silating reagents... 

Many other compounds have been identified as products of the sugar-amino acid reaction. Amongst these are 2,3-butanedione,195 formaldehyde,196 pyruvaldehyde,20,195, 247, 248 3-hydroxy-2-butanone,248 hydroxy-2-propanone,248 and acetaldehyde.73 Imidazoles,196, 249-251 especially 4(5)-methylimidazole, have also been isolated from the reaction under mild conditions, and could have been formed from a-hydroxy ketones or aldehydes plus amino compounds. Following the early identification247 of pyru-valdehyde as a product of the Maillard reaction, much work was done in an attempt to show that this reactive compound plays a major role in the reaction,249 262 254 but, that this is so is by no means certain.7... 

During the processing of foods, several chemical reactions affect the structure of some amino acids reactions with reducing sugars and polyphenols, interaction of the side chains of the amino acids, oxidation, etc. In some cases, these chemical modifications do not seem to change the nutritional availability of the amino acids involved, while in other cases, they do. In all cases, the presence of the newly formed molecules induces biochemical and physiological changes. 

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