P-Nitrophenyl ester

The initial evidence for the formation of an acyl-enzyme ester intermediate came from studies of the kinetics with which chymotrypsin hydrolyzed analogs of its normal polypeptide substrates. The enzyme turned out to hydrolyze esters as well as peptides and simpler amides. Of particular interest was the reaction with the ester p-nitrophenyl acetate. This substrate is well suited for kinetic studies because one of the products of its hydrolysis, p-nitrophenol, has a yellow color in aqueous solution, whereas p-nitrophenyl acetate itself is colorless. The change in the absorption spectrum makes it easy to follow the progress of the reaction. When rapid-mixing techniques are used to add the substrate to the enzyme, an initial burst of p-nitrophenol is detected within the first few seconds, before the reaction settles down to a constant rate (fig. 8.8). The amount of p-nitrophe-... 

GLYCINE, N-CARBOXY-, N-BENZYL ESTER, p-NITROPHENYl ESTER... 

The addition of PVMI was expected to enhance the hydroxide-ion catalyzed hydrolysis of the anionic ester, since both the hydroxide ions and the negatively charged ester are attracted to the polycation so that the rate of their mutual collision is increased. For any given polyelectrolyte concentration the increase in the rate of hydrolysis should be independent of pH. And this is what has actually been found at pH values greater than 9. At lower pH values, however, a completely unexpected behavior resulted, i. e. the polycation was found to increase the rate of hydrolysis of NABS by the largest factor in that pH range (pH s 6) in which direct water attack on the ester makes the dominant contribution to the overall reaction rate (Fig. 8). The influence of hydrophobic forces appears to be ruled out in this case since PVMI has no effect on the solvolytic rate of the neutral ester p-nitrophenyl acetate and p-nitrophenyl hexanoate. Thus, the causes of the above-mentioned phenomenon are obscure this very fact adds, in the author s opinion, further interest to the study of reactions in polyelectrolyte solutions. The examination of such factors as the enthalpy and entropy of activation may be of particular relevance for a deeper insight into these complex reaction systems. 

Baldwin et al. (1995) surveyed the effect of various mineral phases on the rate of hydrolysis of the model organophosphate ester p-nitrophenyl phosphate. They found that, normalized for the number of independently determined phosphate adsorption sites, the manganese oxides were most effective in catalysing the hydrolysis reaction, followed by iron and titanium oxides, with a small effect for alumina. No effect was... 

Mixed carbonic anhydride N-Carboxyanhydride N-Thiocarboxyamino acid anhydride Benzhydroxamic acid ester Cyanomethyl ester 8-Hydroxyquinoline ester p-Nitrophenyl ester Phenylazophenyl ester Pentachlorophenyl ester Pentafluorophenyl ester Phenyl ester... 

As a prelude to the discussion of reactions at micellar interfaces and in the interstices of micelles we should examine what is special about the nature of reactions at liquid-liquid interfaces. Adsorption of substances at interfaces can lead to an ordering of molecules that is not encountered in bulk solution. The topic has been reviewed by Menger [3,4] who has illustrated the possibilities of reactions at interfaces by investigation of the reaction of the water-insoluble ester p-nitrophenyl laurate in heptane with imidazole in an adjacent aqueous phase. Because of the insolubility of the ester in water any reaction between the species must occur at the interface. Migration of the reactants to the interface was partially rate-determining small amounts of laurate ion which adsorb at the interface retarded the interfacial hydrolysis of the ester. The adsorbed laurate ion probably impedes the transport of one or more of the reactants to the interface, suggesting a means of control of reactions not available in normal bulk reactions. 

Glycine p-nitrophenyl ester hydrobromide. [7413-60-7] M 277.1, m 214" (dec). Recryst from MeOH by adding diethyl ether. [Alners et al. Biochem Preps 13 22 1971]. 

If, however, the /7-nitrophenyl ester of iV-henzoyl-L-leucine is treated with 1-methyl-piperidine in chloroform for 30 min and then coupled with glycine ethyl ester, the dipeptide isolated is almost completely racemic. Furthermore, treatment of the p-nitrophenyl ester of iV-benzoyl-L-leucine with 1-methylpiperidine alone leads to the formation of a crystalline material, C13H15NO2, having strong IR bands at 1832 and 1664 cm . Explain these observations, and suggest a reasonable stmcture for the crystalline product. 

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. 

Remove the Z protecting group from the ethyl ester of Z-Phe-Gly by hydrogenolysis. Couple with the p-nitrophenyl ester of Z-Leu then remove the Z group of the ethyl ester of Z-Leu-Phe-Gly. 

A solution of 88.5 parts of L-phenylalanine methyl ester hydrochloride in 100 parts of water is neutralized by the addition of dilute aqueous potassium bicarbonate, then is extracted with approximately 900 parts of ethyl acetate. The resulting organic solution is washed with water and dried over anhydrous magnesium sulfate. To that solution is then added 200 parts of N-benzyloxycarbonyl-L-aspartic acid-a-p-nitrophenyl, -benzyl diester, and that reaction mixture is kept at room temperature for about 24 hours, then at approximately 65°C for about 24 hours. The reaction mixture is cooled to room temperature, diluted with approximately 390 parts of cyclohexane, then cooled to approximately -18°C in order to complete crystallization. The resulting crystalline product is isolated by filtration and dried to afford -benzyl N-benzyloxycarbonvI-L-aspartyl-L-phenylalanine methyl ester, melting at about 118.5°-119.5°C. 

In contrast to 1, isomeric p-nitrophenyl nicotinate shows almost no catalysis. Thus, it is clear that substrate coordination to the metal ion complex plays the critical role for an enormous rate enhancement. The lipophilic ester (R = C5Hn) also undergoes a large rate enhancement indicating the importance of substrate binding into the micellar phase by hydrophobic interaction. A large rate enhancement can also be seen in lipophilic esters which lack the metal coordination site as given below with the enantioselective micellar reactions (Table 9, 10). 

As revealed by IR-spectroscopy, the attachment of the polymer proceeds via acylation of aminopropyls absorbances of both amides (1650 cm-1) and esters (1740 cm-1) contribute to the spectrum of polyacrylate-coated aminopropyl-Aerosil (specific surface area 175 m2/g) [55], During the reaction, the accumulation of p-nitrophenyl ester groups in the support is accompanied by the liberation of p-nitrophenol into the contacting solution. Thus, the evaluation of the conformational state of adsorbing macromolecules can be performed by the simultaneous study of both processes by UV-spectroscopy as shown in Fig. 7. Apparently, at... 

Fig. 7a, b. Kinetics of poly(p-nitrophenyl acrylate) chemical adsorption on aminopropyl-Aerosil at 25 °C in dimethylsulphoxide. Filled circles ester group content (pmol/g support), empty c/rc/ei p-nitrophenol release (pmol/g support), a — l%solution b — 5% solution [55]... 

Porous glass (PG) modified with covalently adsorbed poly(p-nitrophenyl acrylate), as described in Sect. 4.1, turned out to be a highly suitable carrier for immobilization of various biospecific ligands and enzymes. When the residual active ester groups of the carrier were blocked by ethanolamine, the immobilized ligands when bound to the solid support via hydrophilic and flexible poly(2-hydroxyethyl acrylamide). The effective biospecific binding provided by the ligands... 

S.P. solid-phase technique L.P. liquid-phase technique OPTcp pentachlorophenyl ester TEEP tetraethyl pyrophosphit OTCp trichlorophenyl ester ONp p-nitrophenyl ester ONSu N-hydroxysuccinimido ester OPFp pentafluorophenyl ester OQu 8-hydroxyquinyl ester OPy 3-hydroxy-pyridyl ester ODnp 2,4-dinitrophenyl ester DCC dicyclohexylcarbodiimide HOBn 3-hydroxy-4-oxo-3,4-dihydro-l,2,3-benzotriazin Opi JV-hy-droxypiperidine EEDQ 2-ethoxy-l-ethoxycarbonyl-l,2-dihydroquinoline Tos p-toluenesulfonyl PTC propanetricarboxylic acid OBu tm-butyl ester Nva norvaline Aha aminohexanoic acid Om ornithine... 

In the course of this study, the authors determined /Lvalues for dibenzyl, methyl phenyl, methyl p-nitrophenyl, di-p-tolyl, di-isopropyl and tetramethylene sulphoxides and for diethyl, dipropyl and dibutyl sulphites. The /Lscales are applied to the various reactions or the spectral measurements. The /Lscales have been divided into either family-dependent (FD) types, which means two or more compounds can share the same /Lscale, family-independent (FI) types. Consequently, a variety of /Lscales are now available for various families of the bases, including 29 aldehydes and ketones, 17 carboxylic amides and ureas, 14 carboxylic acids esters, 4 acyl halides, 5 nitriles, 10 ethers, 16 phosphine oxides, 12 sulphinyl compounds, 15 pyridines and pyrimidines, 16 sp3 hybridized amines and 10 alcohols. The enthalpies of formation of the hydrogen bond of 4-fluorophenol with both sulphoxides and phosphine oxides and related derivatives fit the empirical equation 18, where the standard deviation is y = 0.983. Several averaged scales are shown in Table 1588. 

THE USE OF POLYSTYRYLSULFONYL CHLORIDE RESIN AS A SOLID SUPPORTED CONDENSATION REAGENT FOR THE FORMATION OF ESTERS SYNTHESIS OF N-[(9-FLUORENYLMETHOXY)CARBONYL]-L-ASPARTIC ACID a tert-BUTYL ESTER, P (2-ETHYL[(lE)-(4-NITROPHENYL)AZO] PHENYL]AMINO]ETHYL ESTER... 

Sulfate monoesters can react by dissociative paths, and this is the favored path. Whether such reactions are concerted or involve a very short-lived sulfur trioxide intermediate has been the subject of debate. ° Benkovic and Benkovic reported evidence suggesting that the nucleophile is present (though there is little bond formation) in the transition state for the reaction of amines with p-nitrophenyl sulfate. Alkyl esters of sulfuric or sulfonic acids normally react with C-0 cleavage only when this is disfavored, as in aryl esters, does one see S-0 cleavage. Sulfate diester... 

For the elongation of the chain starting from 11 toward the N-terminal group, direct condensation of the activated p-nitrophenyl esters of such amino acids as N-protected L-cysteine, L-glutamic acid, glycine, L-leu-cine, L-proline, L-serine, L-tyrosine, andL-valine with 2-acetamido-3,4,6-... 

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