Acetic acid 4-nitrophenyl ester

The reduction of o-nitrophenyl acetic acids or esters leads to cyclization to oxindoles. Several routes to o-nitrophenylacetic acid derivatives arc available, including nitroarylation of carbanions with o-nitroaryl halides[2l,22] or trif-late[23] and acylation of o-nitrotoluenes with diethyl oxalate followed by oxidation of the resulting 3-(u-nitrophenyl)pyruvate[24 26]. 

Activated esters of A-alkoxycarbonylamino acids are prepared by two approaches, activation of the acid followed by reaction with the hydroxy compound, and trans-esterification. Most of the products are stable enough to be purified by washing a solution of the ester in an organic solvent with aqueous solutions. A few that are not crystalline are purified by passage through a column of silica. The commonly used method for their preparation is addition of dicyclohexylcarbodiimide to a cold mixture of the reactants in dimethylformamide or ethyl acetate. The first Boc-amino acid nitrophenyl esters were obtained using pyridine as solvent. Pyridine generates the nitrophenoxide ion that is more reactive. For one type of ester, 2-hydroxypyridino... 

Dihydroxy-3 nitrophenylacetic acid methyl ester P. s. papulans c9h9no6 2-(2,5-Dihydroxy-3-nitrophenyl)acetic acid methyl ester... 

Nitrobenzoic acid Et ester, in N-00093 (4-Nitrophenyl)acetic acid Me ester, in... 

On addition of the acetic acid, a small amount of black solid settles out, but this dissolves when the solution is swirled for several minutes. The potassium salt of ethyl o-nitrophenyl-pyruvate, although it undergoes no apparent change in color, does not keep indefinitely in the dry state. After 3 weeks of storage at room temperature, the salt still produced a yellow solution when dissolved in acetic acid, but, after 3 months of storage, the dry salt produced a deep-red solution from which an oil, rather than crystalline ester, was obtained after catalytic hydrogenation. 

Several crown ethers that possess side chains with terminal mercapto groups enhance the rate of transesterification of amino-acid p-nitrophenyl esters. Matsui and Koga (1978) reported the reactions of a number of amino-acid p-nitrophenyl ester hydrobromides dissolved in mixtures of ethanol and dichloromethane (1 4) and buffered with acetic acid and pyridine (pH 4.60 in... 

Methyl 5-methoxyindole-2-acetate lndole-2-acetic acid, 5-methoxy-, methyl ester (8) 1H-lndole-2-acetic acid, 5-methoxy-, methyl ester (9) (27798-66-9) 5-Methoxy-2-nitrophenylacetic acid Acetic acid, (5-methoxy-2-nitrophenyl)- (8) Benzeneacetic acid, 5-methoxy-2-nitro- (9) (20876-29-3)... 

Reaction of the m-nitrophenyl ester of pyridine-2,5-dicarboxylic acid with cyclodextrin (see Section 3) gives a picolinate ester [52] of a cyclodextrin secondary hydroxyl group (Breslow, 1971 Breslow and Overman, 1970) which will bind metal ions or a metal ion-pyridine carboxaldoxime complex. Such a complex will catalyse hydrolysis of p-nitrophenyl acetate bound within the cyclodextrin cavity leading to a rate constant approximately 2000-fold greater at... 

To a stirred soln of (2-nitrophenyl)acetic acid (lg, 5.5 mmol) in benzene (10 mL) (CAUTION carcinogen ) was added anhyd MeOH (3.5 mL) followed by three drops of coned H2S04. The mixture was refluxed for 8h with an azeotropic distillation device. TLC (CH2C12) showed quantitative conversion into the corresponding methyl ester (Rf 0.28). Purification by chromatography (silica gel, hexanes/ EtOAc) gave the methyl ester as a white solid yield 0.95 g (95%). 

To a solution of isopropyl ester of 6-formyl-5-methoxycarbonyl-2-methyl-4-(3-nitrophenyl)-l,4-dihydropyridine- 3-carboxylic acid (4.5 g) in acetic acid (35 ml) were added hydroxylamine hydrochloride (0.97 g) and sodium acetate (1.43 g), and the mixture was stirred at ambient temperature for 2.5 hours. After acetic anhydride (4.14 g) was added to this reaction mixture, the mixture was stirred at ambient temperature for 1.5 hours and at 95-100°C for additional 4 hours. The acetic acid and the excess of acetic anhydride were removed in vacuum, followed by adding water to the residue and it was neutralized with a saturated aqueous solution of sodium bicarbonate. This aqueous suspension was extracted twice with ethyl acetate, and the combined extract was washed with water, dried over anhydrous magnesium sulfate and evaporated to dryness under reduced pressure to give a reddish-brown oil (4.88 g), which was chromatographed over silica gel (150 g) with a mixture of... 

We have made several artificial enzymes that use cyclodextrin to bind a substrate and then react with it by acylating a cyclodextrin hydroxyl group. This builds on earlier work by Myron Bender, who first studied such acylations [83]. We added groups to the cyclodextrin that produced a flexible floor, capping the ring [84]. The result was to increase the relative rate of cyclodextrin acylation by m-t-butylphenyl acetate from 365 relative to its hydrolysis rate in the buffer to a Complex/ buffer of 3300. We changed the substrate to achieve better geometry for the intracomplex acylation reaction, and with a p-nitrophenyl ester of ferroceneacrylic acid 10 we achieved a relative rate for intracomplex acylation of ordinary [3-cyclodextrin vs. hydrolysis of over 50 000 and a Vmax comparable to that for hydrolysis of p-nitrophenyl acetate by chymotrypsin... 

One structure that seemed attractive was ferrocinnamic acid, a ferrocene derivative carrying an acrylic acid chain. The substrate examined was the p-nitrophenyl ester of this acid (I) (12). It was clear from the known binding constants of ferrocene (4) and of p-nitrophenyl acetate that the ferrocene nucleus should be the one... 

The hydrolyses of p-nitrophenyl esters of acetic acid (PNPA), diei lpropionic acid (P ), and lauric acid (PNPL) by Cyclo-(Leu-His), Cyclo-(D-LarfDs), and Cyclo-(Gly-His) as catalyst were carried out (94,103). Following the optical density of p-nitrophenolate ion liberated in the acylation of the imidazole group by the substrate, the seoind-order rate constant (M min ) were determined, and are summarized in Table 16. 

Acylation of fl-cyclodextrin. The acylation of /5-cyclodextrin is modestly accelerated by bound m-nitrophenyl acetate, m-N02C6H40C0CH3. Recently acylation of /3-cyclodextrin at a rate comparable to acylation of chymotrypsin has been reported. The acylating reagent is the p-nitrophenyl ester (1) of ferrocinnamic acid. This reagent was chosen because ferrocene is strongly bound within the cavity of /3-cyclodextrin. The acylation is accelerated by > 50,000-fold compared to hydrolysis of 1 in DMSO-HjO alone buffered at pH 6.8. Thus cyclodextrins can behave as artificial enzymes. 

This ring closure takes place readily whenever the carbonyl and amino groups occur in the relative positions shown above. Reduction of o-nitro-phenylacetonitrile by stannous chloride produces indole rather than the corresponding amino aldehyde. The synthesis is most useful for the preparation of indole-2-carboxylic acid by reduction of o-nitrophenyl-pyruvic acid with ferrous sulfate and ammonia or with sodium hydrosulfite. The ethyl ester is obtained by a similar reduction with zinc and acetic acid or by catalytic hydrogenation of ethyl o-nitrophenyl-pyruvate over platinum oxide catalyst. ... 

Thus, two types of active esters are of interest those formed from an acid and a substituted phenol (12-15) and those formed from an acid and a substituted hydroxylamine (16-19). Both types are reactive by virtue of the electron-withdrawing properties of the OR moiety in 2. The level of activation of the substituted phenyl esters varies directly with the electronic effect going from 4-nitrophenyl to 2,4,5-trichlorophenyl, pentachlorophenyl, and pentafluorophenyl, which corresponds with the increasing acidity of the phenols. A diminution in the rate of aminolysis is caused by the presence of a substituent in the ortho position of the ring.f l An additional phenomenon contributes to the reactivity of the esters formed from substituted hydroxylamines, namely anchimeric assistance. Since the anoinolysis of active esters is a bimolecular reaction, it is dependent on concentration and can be forced to completion by an excess of one of the reactants. Aminolysis is also characterized by a pronounced dependence on the polarity of the solvent in particular for the esters formed from substituted phenols, the half-life of a 2,4,5-trichlorophenyl ester in the presence of benzylamine being one hundred times less in dimethylformamide than in benzene. Furthermore, aminolysis is catalyzed by mild acid such as acetic acid. The rate of anoinolysis is slowed if the side chain of the active ester contains a P-methyl substituent. 

Peptide synthesis. This is an excellent reagent for the preparation of activated p-nitrophenyl esters of N-protected amino acids. A solution of the N-protected ami no acid (2) in acetic acid containing a little pyridine is treated with 1.5 equivalents... 

Peptide synthesis. Esters of 3-hydroxypyridine offer some advantage over the usual p-nitrophenyl esters because the unreacted ester is soluble in dilute acid and hence readily removed. The esiers are readily prepared by coupling the Cb-peptide and 3-hydroxypridine with dicyclohexylcarbodiimide in ethyl acetate in the presence of triethylamine. 

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