Aspartic acid -esters

Glutamic Acid.—The greater part of the glutamic acid is isolated as hydrochloride before the mixture of amino acids is esterified. It is contained with aspartic acid ester in the aqueous solution after the phenylalanine ester has been extracted by ether, and it is separated from aspartic acid, after hydrolysis by baryta, by conversion into its hydrochloride from this it is obtained by treatment with the calculated quantity of soda to combine with the hydrochloric acid and by crystallisation from water, in which it is soluble with some difficulty. 

When amino acid ester prodrugs of acetaminophen were prepared (Kovach et al., 1975 Pitman, 1976), the hydrobromide salt of the glycine ester showed enhanced solubility in water, but the hydrochloride salt of th -aspartic acid ester exhibited a solubility lower than that of the parent compound. The enhanced solubility resulted from the formation of a salt, while the parent drug is a weakly acidic phenol and behaves as essentially a neutral molecule in solution. The reduced solubility in the case of th0-aspartic acid ester resulted from ionization of the terminal carboxylic acid, which, with the protonated amine, gives a zwitterionic compound. The zwitterion also behaved as a molecule with an overall neutral character, as is commonly observed with zwitterion behavior in aqueous media, but its larger size resulted in a further reduced solubility. 

Typical photoresponsive polypeptides exhibiting a helix-helix transition upon photoirradiation are shown in Fig. 1. These polypeptides are composed of l-aspartates as the amino acid component. The poly(l-aspartic acid esters) are the most thoroughly investigated polypeptides with respect to their ordered structures... 

On the basis of these observations, Ueno et al. designed and synthesized a series of poly(L-aspartic acid ester)-containing azobenzene pendants as the pho-... 

Leucyl-glycine ester Glycyl-aspartic acid ester... 

L-Aspartic acid esters 458 react with diphosgene in dioxane at 55 °C to give the corresponding isocyanate 459 in 62% yield [317]. 

P)—histidine N im (5-cysteine)-2,4-dinitrophenyl bond, coupling by base (p)—y-glutamic acid ester or )8-aspartic acid ester bond -lys-amide, by DCC coupling... 

Hen egg-white lysozyme has been esterified specifically at L-aspartic acid-52 with the affinity label 2,3-epoxypropyl j8-di-iV-acetylchitobioside. The disulphide and L-aspartic acid ester bonds of the derivatized enzyme were then reduced with 1,4-dithiothreitol and sodium borohydride, respectively, resulting in the removal of the affinity label and the formation of homoserine residues. The enzyme obtained on re-oxidation with glutathione was inactive, whereas reduction (with 1,4-dithio-threitol) and re-oxidation (with glutathione) of the original enzyme did not abolish its activity. It was concluded that L-aspartic acid-52 is essential for enzymic activity. 

Alkylbetaine esters [90-92], quaternized aspartic acid esters [23], and polyolesters of betaine [71] have been suggested for use in fabric care. The ester bond in betaine esters is strongly activated by cationic nitrogen in the a position, and therefore these materials can undergo rapid abiotic degradation and have very low aquatic toxicity. 

Marck, K.W., Wildevuur C.H., Sederel W.L., Bantjes, A. and Fejen, J. (1977) Biodegradability and tissue reaction of random copolymers of L-leucine, L-aspartic acid and L-aspartic acid esters, J. Biomed. Mater. Res. 11,405-422. 

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