42406-53-1Relevant articles and documents
Synthesis and characterization of new optically active copoly(amid-imide)s based on N-phthalimido-l-aspartic acid and aromatic diamines
Faghihi, Khalil,Alimohammadi, Hamidreza
, p. 407 - 411 (2010)
In this article, six new optically active copoly(amide-imide)s (10a-f) were synthesized through the direct polycondensation reaction of N-phthalimido-l-aspartic acid (4) with 1,5-diamino naphthalene (8), 3,4-diamino benzophenone (9) in the presence of therphthalic acid (7), fumaric acid (6) and adipic acid (5) as a second diacid in a medium consisting of N-methyl-2-pyrrolidone, triphenyl phosphite, calcium chloride and pyridine. The resulting copolymers were fully characterized by means of FT-IR spectroscopy, elemental analyses, inherent viscosity, solubility tests and UV-vis spectroscopy. Thermal properties of resulting copolymers (10a-c) containing three different second diacid in the main chain were compared by using TGA and DTG thermograms.
Acylation is rate-limiting in glycosylasparaginase-catalyzed hydrolysis of N4-(4′-substituted phenyl)-L-asparagines
Du, Wenjun,Risley, John M.
, p. 1900 - 1905 (2007/10/03)
Glycosylasparaginase catalyzes the hydrolysis of the N-glycosylic bond between N-acetyl-D-glucosamine and L-asparagine in the catabolism of glycoproteins. The mechanism has been proposed to resemble that of serine proteases involving an acylation step where a nucleophilic attack by a catalytic Thr residue on the carbonyl carbon of the N-glycosylic bond gives rise to a covalent β-aspartyl-enzyme intermediate, and a deacylation step to give the final products. The question posed in this study was: Is the acylation step the rate-limiting step in the hydrolysis reaction as in serine proteases? To answer this question a series of mostly new substituted anilides was synthesized and characterized, and their hydrolysis reactions catalyzed by glycosylasparaginase from human amniotic fluid were studied. Five N4-(4′-substituted phenyl)-L-asparagine compounds were synthesized and characterized: 4′-hydrogen, 4′-ethyl, 4′-bromo, 4′-nitro, and 4′-methoxy. Each of these anilides was a substrate for the enzyme. Hammett plots of the kinetic parameters showed that acylation is the rate-limiting step in the reaction and that upon binding the electron distribution of the substrate is perturbed toward the transition state. This is the first direct evidence that acylation is the rate-limiting step in the enzyme-catalyzed reaction. A Bronsted plot indicates a small, negative charge (-0.25) on the nitrogen atom of the leaving group anilines containing electron-withdrawing groups, and a small, positive charge (0.43) on the nitrogen atom of the leaving group anilines containing electron-donating groups. The free energy (incremental) change of binding (ΔΔGb) in the enzyme-substrate transition state complexes shows that substitution of a substituted phenyl group for the pyranosyl group in the natural substrate results in an overall loss of binding energy equivalent to a weak hydrogen bond, the magnitude of which is dependent on the substituent group. The data are consistent with a mechanism for glycosylasparaginase involving rapid formation of a tetrahedral structure upon substrate binding, and a rate-limiting breakdown of the tetrahedral structure to a covalent β-aspartyl-enzyme intermediate that is dependent on the electronic properties of the substituent group and on the degree of protonation of the leaving group in the transition state by a general acid.
SOME DERIVATIVES OF ASPARTIC AND GLUTAMIC ACIDS.
BOSE,STRUBE
, p. 847 - 851 (2007/10/04)
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