Of aspartic acid

Aza-T-allylpalladium is formed from the Schiff base 193 and reacts with malonate to give a derivative of aspartic acid 194 after hydrolysis of the pro-duct[121]. 

FIGURE 27 3 Application of electrophoresis to the separation of aspartic acid alanine and lysine according to their charge type at a pH corresponding to the isoelectric point (pi) of alanine... 

The carboxamidomethyl ester was prepared for use in peptide synthesis. It is formed from the cesium salt of an A-protected amino acid and a-chloroacetamide (60-85% yield). It is cleaved with 0.5 M NaOH or NaHCOa in DMF/H2O. It is stable to the conditions required to remove BOC, Cbz, Fmoc, and r-butyl esters. It cannot be selectively cleaved in the presence of a benzyl ester of aspartic acid. ... 

The r-butyl ester is a relatively hindered ester, and many of the methods reported below should be—and in many cases are—equally effective for the preparation of other hindered esters. The related 1- and 2-adamantyl esters have been used for the protection of aspartic acid. ... 

Graf, L., et al. Selective alteration of substrate specificity by replacement of aspartic acid 189 with lysine in the binding pocket of trypsin. Biochemistry 26 ... 

This ester was designed as a base-labile protective group. Monoprotection of aspartic acid was achieved using the DCC/DMAP protocol. Cleavage is... 

Relative Lability of Aspartic Acid )8-Carboxyl Protective Groups ... 

Aspartame is a dipeptide, made up of aspartic acid and phenylalanine. Identify all the chiral atoms in aspartame and assign R/S stereochemistry to each. Is the stereochemistry the same as in the natural forms of aspartic acid andphenylalaninel... 

The metabolic breakdown of triacylglycerols begins with their hydrolysis to yield glycerol plus fatty acids. The reaction is catalyzed by a lipase, whose mechanism of action is shown in Figure 29.2. The active site of the enzyme contains a catalytic triad of aspartic acid, histidine, and serine residues, which act cooperatively to provide the necessary acid and base catalysis for the individual steps. Hydrolysis is accomplished by two sequential nucleophilic acyl substitution reactions, one that covalently binds an acyl group to the side chain -OH of a serine residue on the enzyme and a second that frees the fatty acid from the enzyme. 

Q The enzyme active site contains an aspartic acid, a histidine, and a serine. First, histidine acts as a base to deprotonate the -OH group of serine, with the negatively charged carboxylate of aspartic acid stabilizing the nearby histidine cation that results. Serine then adds to the carbonyl group of the triacylglycerol, yielding a tetrahedral intermediate. 

Figure 29.2 MECHANISM Mechanism of action of lipase. The active site of the enzyme contains a catalytic triad of aspartic acid, histidine, and serine, which react cooperatively to carry out two nucleophilic acyl substitution reactions. Individual steps are explained in the text.

Merck s thienamycin synthesis commences with mono (V-silylation of dibenzyl aspartate (13, Scheme 2), the bis(benzyl) ester of aspartic acid (12). Thus, treatment of a cooled (0°C) solution of 13 in ether with trimethylsilyl chloride and triethylamine, followed by filtration to remove the triethylamine hydrochloride by-product, provides 11. When 11 is exposed to the action of one equivalent of tm-butylmagnesium chloride, the active hydrogen attached to nitrogen is removed, and the resultant anion spontaneously condenses with the electrophilic ester carbonyl four atoms away. After hydrolysis of the reaction mixture with 2 n HC1 saturated with ammonium chloride, enantiomerically pure azetidinone ester 10 is formed in 65-70% yield from 13. Although it is conceivable that... 

The noteworthy successes of a relevant model study12 provided the foundation for Merck s thienamycin syntheses. In the first approach (see Schemes 2 and 3), the journey to the natural product commences from a readily available derivative of aspartic acid this route furnishes thienamycin in its naturally occurring enantiomeric form, and is noted for its convergency. During the course of this elegant synthesis, an equally impressive path to thienamycin was under parallel development (see Schemes 4 and 5). This operationally simple route is very efficient (>10% overall yield), and is well suited for the production of racemic thienamycin on a commercial scale.. x... 

Aspaityl proteinases are proteinases that utilize the terminal carboxyl moiety of the side chain of aspartic acid to effect peptide bond hydrolysis. 

NMDA (iV-methyl-D-aspartic acid) is a synthetic derivative of aspartic acid and represents the prototypical agonist at the NMDA receptors for which the latter were named. 

E9.3 The deamination of aspartic acid is a reversible reaction catalyzed by the... 

Asp-A-pro tease The amino terminus sides of aspartic acid and glutamic acid... 

A synthesis of aspartic acid is based on this strategy. Disconnection (a) is attractive since acyl-amino malonate (7) is a reagent for synthon (6). Synthon (8) can be represented by allyl bromide. 

While both R—COOH and R—NH R—COOH is a far stronger acid than R—NHj. At physiologic pH (pH 7.4), carboxyl groups exist almost entirely as R—COO and amino groups predomi-nandy as R—NH3. Figure 3-1 illustrates the effect of pH on the charged state of aspartic acid. 

Phosphonic acid analogues of aspartic acid, glutamicacid C-benzy1g1ycine,191 and the phosphor inane (70)1 92 have been studied, also the oxime (71)193 a phosphonopiperidinol - with a very distorted chair structure,194 the phosphonate (72),195 a pyrazole,196 a thiocarbamoy1phosphonate, 97 and two iminobis-(methylphosphonic acids).198 Additionally there have been studies of the new bicyclic sulphur heterocycle (73),199 the oxazaphospho1idine (74)200 and a triaminophosphetanium aluminium betaine.201... 

Noszal, B. Sandor, P., Rota-microspeciation of aspartic acid and asparagine, Anal. Chem. 61, 2631-2637 (1989). 

If the environmental temperature is constant, the racemization process takes place at a uniform rate, which is determined, at any time during the process, by the relative amounts of / and d forms of the amino acid can be measured. As the racemization proceeds and the concentration of the / form amino acid decreases, the rate of racemization gradually slows down. When there is a mixture of 50% of each of the d and / forms, the racemization process stops altogether. The half-life of the racemization of aspartic acid, for example, a common amino acid in proteins, at 20°C is about 20,000 years. This half-life makes it possible to date proteins as old as about 100,000 years. So far, however, the dates obtained with the technique have proved somewhat inconsistent, probably because of the difficulty in verifying whether the temperature of the amino acids has been constant. 

Manley, W. R, G. H. Miller, and J. Czywczynski (2000), Kinetics of aspartic acid racem-ization, in Goodfriend, G. A., M. J. Collins, M. L. Fogel, S. A. Macko, and J. F. Wehmiller (eds.), Perspectives in Amino Acid and Protein Geochemistry, Oxford Univ. Press, New York, pp. 202-218. 

Weiner, S., Z. Kustanovich, E. Gil-Av, and W. Traub (1980), Dead Sea scroll parchments Unfolding of the collagen molecules and racemization of aspartic acid, Nature 287, 820-823. 

Radkiewicz et al.184 explored the mechanism of aspartic acid racemization by means of the DFT(B3LYP)/SCRF calculations. The DFT/SCRF calculations provided quantitative rationalization of the rapid racemization observed at succinimide residues in proteins. The proposed reaction mechanism was supported by the computed increase of the acidity of the succinimide residue in aqueous solution compared to gas phase. 

Radkiewicz, J. L., H. Zipse, S. Clarke, and K. N. Houk. 1996. Acclerated Racemization of Aspartic Acid and Asparagine Residues via Succinimidine Intermediates An ab initio Theoretical Exploration of Mechanism. J. Am. Chem. Soc. 118,9148. 

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