Esterification amino acids

Figure 14.7 Principal derivatisation strategies for the GC C IRMS of lipids [trimethylsiylation (cholesterol) and esterification (fatty acids)] and amino acids (esterification acylaction)...

Ionic liquids are emerging as viable media, in in roving various organic reactions as green solvents or catalysts, and have shown promising applications in many chemical processes. This study, for the first time, shows the use of ionic liquid [EtPy][Cp3COO] as an excellent catalyst for the esterification of amino acids. Esterification of several amino acids was achieved with very good yields. 

Predict products of the following reactions of amino acids esterification, acylation, reaction with ninhydrin. 

REACTIONS OF a-AMINO ACIDS Esterification of the a-Carboxyl Group Acetylation of the a-Amino Group... 

The exchange resins 6nd application in (i) the purification of water (cation-exchange resin to remove salts, followed by anion-exchange resin to remove free mineral acids and carbonic acid), (ii) removal of inorganic impurities from organic substances, (iii) in the partial separation of amino acids, and (iv) as catalysts in organic reactions (e.g., esterification. Section 111,102, and cyanoethylation. Section VI,22). 

This procedure is restricted mainly to aminodicarboxyhc acids or diaminocarboxyhc acids. In the case of neutral amino acids, the amino group or carboxyl group must be protected, eg, by A/-acylation, esterification, or amidation. This protection of the racemic amino acid and deprotection of the separated enantiomers add stages to the overall process. Furthermore, this procedure requires a stoichiometric quantity of the resolving agent, which is then difficult to recover efficiendy. Practical examples of resolution by this method have been pubUshed (50,51). 

Esterification, Amidation, and Acid Chloride Formation. Amino acids undergo these common reactions of the carboxyl group with due regard for the need for A/-protection. 

The procedure described is essentially that of Shioiri and Yamada. Diphenyl phosphorazidate is a useful and versatile reagent in organic synthesis. It has been used for racemlzatlon-free peptide syntheses, thiol ester synthesis, a modified Curtius reaction, an esterification of a-substituted carboxylic acld, formation of diketoplperazines, alkyl azide synthesis, phosphorylation of alcohols and amines,and polymerization of amino acids and peptides. - Furthermore, diphenyl phosphorazidate acts as a nitrene source and as a 1,3-dipole.An example in the ring contraction of cyclic ketones to form cycloalkanecarboxylic acids is presented in the next procedure, this volume. 

Amino acids undergo reactions characteristic of the amino group (e.g., amide formation) and the carboxyl group (e.g., esterification). Amino acid side chains undergo reactions characteristic of the functional groups they contain. 

In the case of simple amino acids and dipeptides, esterification of the carboxyl groups occurs on heating in toluene with the appropriate bis(triorganotin) oxide or triorganotin hydroxide 481, 482), the water being removed azeotropically. 

Each functional group of an amino acid exhibits all of its characteristic chemical reactions. For carboxylic acid groups, these reactions include the formation of esters, amides, and acid anhydrides for amino groups, acylation, amidation, and esterification and for —OH and —SH groups, oxidation and esterification. The most important reaction of amino acids is the formation of a peptide bond (shaded blue). 

Solid Acid Catalysed Esterification of Amino Acids and Other Bio-Based Acids... 

Four different amino acids have been selected for esterification to study the effect of R-group substituent of amino acid on rate and ease of esterification. The four acids are alanine, serine, aspartic acid and lysine. Their respective esters were prepared by reported methods to authenticate and compare with those prepared by our method. Alanine was esterified with ethanol to yield the ethyl ester, keeping -NH3+ group intact. This was also confirmed by acidity of final reaction mixture (pH- 3.2). There was about 50% conversion of alanine to its ethyl ester. Further work on ester formation, including qualitative and quantitative analysis, is in process. 

H. Kise and H. Shirato, Enzymatic reactions in aqueous-organic media. V. Medium effect on the esterification of aromatic amino acids by a-chymotrypsin. Enzyme Microb. Technol. 10, 582-585 (1988). 

First law of thermodynamics, 24 645-648 First limiting amino acid, 2 601 First-order irreversible chemical kinetics, 25 286-287, 292-293 First-principle approach, in particle size measurement, 13 153 First sale doctrine, 7 793 Fischer, Emil, 16 768 Fischer carbene reaction, 24 35-36 Fischer esterification, 10 499 Fischer formula, 4 697 Fischer-Indole synthesis, 9 288 Fischer lock and key hypothesis, 24 38 Fischer-Tropsch (FT) synthesis, 6 791, 827 12 431... 

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