Esterification of amino acids

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

FIGURE 3.18 Protection of carboxyl groups by esterification of amino acids (A) by acid-catalyzed reaction with alcohol. [Curtius 1888, Fisher 1906] with X = Cl for H-Xaa-OMe, X-Xaa-OEt, and H-Pro-OCH2Ph ... 

The methylenemalonate moiety was used as an N-protecting group at the esterification of amino acids. After the esterification of the carboxyl group with the appropriate alkyl bromide in acetone in the presence of... 

N-Thiocarbonyl alkyl esters of amino acids were chromatographed by Halpern et al. [286]. Their preparation proceeds according to Scheme 5.29. The reaction sequence includes esterification of amino acids followed by reaction with carbon disulphide and triethylamine, giving rise to dithiocarbamate. Reaction of the latter with chloroformate... 

Q Predict products of the acylation and esterification of amino acids, and their reaction with ninhydrin. Problems 24-34 and 36... 

Esterification of amino acids. The amino group of an amino acid can be protected as the enamine 1, formed by reaction with ethyl acetoacetate and a base in benzene/ DMSO. After alkylation the protective group is removed by addition of an acid, particularly TsOH, to provide amino acid ester salts (equation I). 

Allyl esters are synthesized by the azeotropic esterification of amino acids with allyl alcohol in the presence of TosOH or by reaction of N -protected amino acid cesium salts with allyl bromide.P °l They are also available from N -protected amino acids by treatment with allyl alcohol/DCC in or with diallyl dicarbonate in THF with DMAP as cat-... 

H-Xaa-ODpm-TosOH General Procedure for the Esterification of Amino Acid TosOH Salts with Diazodiphenyhnethane ... 

Esterification of amino acids. Theobald et a/. heated a mixture of an amino acid, 1.1 equivalents of p-toluenesulfonic acid, and a large excess of dimethyl sulfite (5-15 equiv.) to produce the methyl ester p-toluenesuMbnate. In some cases yields... 

Amino acid esiers. The combination of methanol and thionyl chloride is recommended by Brenner for the esterification of amino acids (the Fischer procedure usually is troublesome). A mixture of the amino acid and methanol is treated... 

Excess liquid reagents can be used as solvents in neat reactions. Many PTC reactions have been conducted without organic solvents (see Figure 3.17). Conversions can be very fast and efficient, as in the ethylation of indole [61] (Figure 4.20). The esterification of amino acids in melted octadecanol was also an effective solvent-free reaction (Figure 4.21) [62],... 

FIGURE 4.21. Solvent-free esterifications of amino acids... 

The answer is c. (Murray, pp 452-467. Scriver, pp 3-45. Sack, pp 1-40. Wilson, pp 101—120.) ATP is required for the esterification of amino acids to their corresponding tRNAs. This reaction is catalyzed by the class of enzymes known as aminoacyl-tRNA synthetases. Each one of these enzymes is specific for one tRNA and its corresponding amino acid. 

Esterification of Amino Acids by Using Ionic Liquid as a Green Catalyst... 

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. 

Figure 1 Scheme of acetylation and esterification of amino acid. 

Esterification of amino acids is a difficult reaction because amino acids exist as zwitterions (dipolar ions) and carboxyl group is not a free group (but an anion). Since the esterification reaction is an equilibriiun process, factors that shift the reaction toward the products will benefit the formation of amino acid ester. 

D Cantacuzene, C Guerreiro. Optimization of the papain catalyzed esterification of amino acids by alcohol and diols. Tetrahedron 45(3) 741-748, 1989. 

The water content is also an important factor on the enzymatic synthesis in hydrophilic organic solvents (75). The enzymatic activity in organic solvent depends on water content. Small amount of water is required to reach the maximum activity in hydrophobic solvents. However, hydrophilic organic solvents remove the essential water bound in the protein and inactivate enzyme activity (Figure 14 A) (75). Furthermore, optimum water content of the reaction in hydrophilic organic solvent is known to be higher than that in hydrophobic organic solvent. Kise et al. reported that in esterification of amino acids by a-chymotrypsin in alcohols, optimum water content is about 2% (77). 

Linko et al. 1998). Lipases have been extensively used in the production of surfactants of different chemical nature by esterification of alkyl glycosides and fatty acids, by transesterification of natural oils and alcohols, by transesterification of phospholipids and alcohols, and also by esterification of amino acids and amides (Saxena et al. 1999). Personal care products, hke isopropyl myristate and isopropyl palmitate, have been produced in solvent-free media with immobilized lipase and wax esters (esters from long-chain fatty acids and fatty alcohols) are also being produced with lipases (Hasan et al. 2006). 

The general approach for carboxyl protection is esterification. The simplest solution, the use of methyl or ethyl esters, is suitable for semipermanent blocking, although the commonly applied process of unmasking, alkaline hydrolysis, is far from unequivocal. It is accompanied by racemization, partial hydrolysis of carboxamide groups in the side chain of asparagine and glutamine residues and by several other side reactions which are initiated by proton abstraction (Cf. Chapter VII). Nevertheless, perhaps because of the attractively simple esterification of amino acids... 

Typical derivatives of the first type are the various esters (Me, Et, Pr, iso-Pi, Bu, wo-Bu, cc-Bu, Am, tio-Am, etc.) of A -acyl (acetyl, TEA, PFP, HFB, etc.) amino acids. The butyl esters of iV-TFA amino acids owing to the frequency of their use even have a special abbreviation TAB derivatives. The two-stage process includes the esterification of amino acids by an excess of the corresponding alcohol in the presence of HCl and, after the evaporation of volatile compounds, the treatment of the non-volatile hydrochlorides of alkyl esters by acylating reagents (Fig. 1). 

Protocol 1. Esterification of amino acids on 2-chlorotrityl chloride resin... 

Oligonucleotide Synthesis. Sulfonyl derivatives of 1,2,4-triazole, e.g. (1), are used as efficient coupling reagents in oligonucleotide synthesis by the phosphotriester method. A nitro derivative (2) allows esterification of amino acids onto hydroxymethyl... 

Esterification of Amino Acids. Methyl ester hydrochlorides of amino acids have been prepared in which 2,2-dimethoxypropane has been used as the source of the methoxy group, the reaction solvent, and the reagent for the removal of the water formed by virtue of the hydrolysis of the acetal to methanol and acetone. This procedure has also been used to prepare the methyl esters of fatty acids. ... 

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