2- ethyl ester protect acids

Sultana R, Ravagna A, Mohmmad-Abdul H, Calabrese V, Butterfield DA. 2005. Ferulic acid ethyl ester protects neurons against amyloid beta-peptide(l-42)-induced oxidative stress and neurotoxicity Relationship to antioxidant activity. J Neurochem 92 749-758. 

Sultana, R., Ravagna, A., Mohmmad-Abdul, H., Calabrese, V. and Butterfield, D. A., 2005. Femlic acid ethyl ester protects neurons against amyloid P-peptide (1-42)-induced oxidative stress and neiuotoxicity relationship to antioxidant activity. Journal of Neurochemistry 92(4), 749-758. 

Carboxyl groups of ammo acids and peptides are normally protected as esters Methyl and ethyl esters are prepared by Fischer esterification Deprotection of methyl and ethyl esters is accomplished by hydrolysis m base Benzyl esters are a popular choice because they can also be removed by hydrogenolysis Thus a synthetic peptide protected at both... 

In the second major method of peptide synthesis the carboxyl group is activated by converting it to an active ester, usually a p-nitrophenyl ester. Recall from Section 20.12 that esters react with ammonia and amines to give fflnides. p-Nitrophenyl esters are much more reactive than methyl and ethyl esters in these reactions because p-nitrophenoxide is a better (less basic) leaving group than methoxide and ethoxide. Simply allowing the active ester and a C-protected amino acid to stand in a suitable solvent is sufficient to bring about peptide bond formation by nucleophilic acyl substitution. 

The methyl ether was introduced after the Wittig reaction which used a protected carboxylic acid (ethyl ester). p-Nitrophenol is available and is one of the products of the nitration of phenol. 

Carbohydrate lactones have been used as the carbonyl reagent in the Reformatsky reaction. Thus, 2,3 5,6-di-O-cyclohexylidene-D-mannono-1,4-lactone [44, obtained by oxidation of the mannofuranose derivative (49)] reacted with ethyl bromoacetate and zinc to give the protected 2-deoxy-3-octulosonic acid ethyl ester (45a) in 69% yield (50). Ketonic hydrolysis with potassium hydroxide in aqueous methanol, followed by acidification and heating, afforded the 1-deoxyheptulose derivative 45b. Similarly, starting from compound 44, the 1-C-substituted allyl and propar-gyl lactols were prepared on reaction with allyl or propaigyl bromides in the presence of zinc (51). 

Furthermore, attempted cyclization of N-carboxymethyl meroquinene ethyl ester failed to afford any of the enone, suggesting that the carboxylic acid was an intermediate. The N-protecting groups, in addition to benzoyl, that are tolerated include CC Me, pivaloyl, acetyl, toluenesulfonyl, CBz, and alkyl. 

Parmar et al have developed a method for resolving racemic mixtures of a variety of natural and nonnatural amino acids using the ethyl ester of the amino acid protected at the amino position hy the formation of a Schiff base with an aromatic aldehyde such as /)-chlorobenzaldehyde. Both chymotrypsin and Lip such as porcine Lip gave good yields of the L-amino acid which precipitates out of solution as the amino acid ester released from the imine is cleaved by the hydrolase. 

Carboxyl protection of the second amino acid is usually achieved by conversion to an ester using an appropriate alcohol and acidic catalyst (see Section 7.9.1). Although methyl and ethyl esters... 

Enalapril Enalapril, (S)-l-[iV-[l-(ethoxycarbonyl)-3-phenylpropyl]-L-alanyl]-L-proline (22.7.12), is synthesized by reacting the benzyl ester of L-alanyl-L-proline with the ethyl ester of 3-benzoylacrylic acid, which forms the product 22.7.11, the reduction of which with hydrogen using a Raney nickel catalyst removes the protective benzyl group, giving the desired enalapril (22.7.12) [24], Alternative methods of syntheses have also been proposed [25-29]. 

Reacting this with thiourea in the classic scheme of thiazole synthesis by reacting of a-halogencarbonyl compounds with thioamides forms the ethyl ester of (Z)-2-(2-aminoth-iazole-4-yl)-2-hydroxyminoacetic acid (32.1.2.74). The amino group in this molecule is protected by a reaction with triphenylchloromethane in dimethylformamide in the presence of triethylamine, which gives the ethyl ester of (Z)-2-(2-tritylaminothiazole-4-yl)-... 

Scheme 6.86 Typical 2-aryl-2,5-dihydropyrrole derivatives prepared with the asymmetric [3 + 2] cycloaddition between buta-2,3-dienoic acid ethyl ester and various DPP-protected (hetero)aromatic imines catalyzed by phosphinothiourea 75.

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