Acetic acid, p-Nitrophenyl

Alternatively, borane in tetrahydrofuran (BH/THF) is a useful reagent for reducing carboxylic acids to primary alcohols. Reaction of an acid with BH3/THF occurs rapidly at room temperature, and the procedure is often preferred to reduction with LiAlH because of its relative ease, safety, and specificity. Borane reacts with carboxylic acids faster than with any other functional group, thereby allowing selective transformations such as that shown below on p-nitrophenylacetic acid. If the reduction of p-nitrophenyl-acetic acid were done with LiAlH4, both nitro and carboxyl groups would be reduced. 

When Jencks reacted hydroxylamine with p-nitrophenyl acetate, p-nitrophenolate ion was released at a rate faster than that at which acetohydroxamic acid was formed. This burst effect is evidence for a two-step reaction. In this case the intermediate is O-acetylhydroxylamine, which subsequently reacts with hydroxylamine to form the hydroxamic acid. 

Figure 6-8 is a pH-rate profile for the hydrolysis of p-nitrophenyl acetate. The slopes of the straight-line portions are —1,0, and -L 1, reading in the acid to base direction, and this system can be described by... 

In analogy to the derivative prepared by Breslow and Overman, the cyclohexaamylose-iV-methylhydroxamic acid displays a pronounced specificity for p-nitrophenyl acetate as opposed to n-nitrophenyl acetate. This specificity is probably again derived from the geometry of the inclusion complex i.e., a more favorable location of the reactive center of the para-isomer relative to the hydroxamate function within the inclusion complex. 

The hydrolysis of esters by the nickel derivative (271) provided an early example of the use of a metal-capped cyclodextrin as a catalyst (shown here as its p-nitrophenyl acetate inclusion complex) (Breslow Overman, 1970 Breslow, 1971). The synthesis of this host involves the following steps (i) covalent binding of the pyridine dicarboxylic acid moiety to cyclodextrin, (ii) coordination of Ni(n) to this species, and (iii)... 

Manecke and his collaborators have synthesized polymers of vinylimid-azole hydroxamic acid (75) (22, 23, 24). Hydrolysis of p-nitrophenyl acetate... 

The late discovery of acetyl xylan and feruloyl esterases has been partly due to the lack of suitable substrates. Xylans are often isolated by alkaline extraction, in which ester groups are saponified. Treatment of plant materials under mildly acidic conditions, as in steaming or aqueous-phase thermomechanical treatment, leaves most of the ester groups intact. These methods, however, partly hydrolyze xylan to shorter fragments (63,69). Polymeric acetylated xylan can be isolated from delignified materials by dimethyl sulfoxide extraction (70). The choice of substrate is especially important in studies of esterases for deacetylation of xylans. The use of small chromophoric substrates (p-nitrophenyl acetate, a-naphthyl acetate, and methylumbelliferyl acetate) analogously to the assays of disaccharidases may lead to the monitoring of esterases unable to deacetylate xylan (33, 63, 64). 

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... 

The rate of hydrolysis of a carboxylic ester in strong sulphuric acid generally shows one of the three types of dependence on acid concentration illustrated in Fig. 1. The simplest behaviour, a continuous increase in hydrolysis rate with increasing acid concentration, is shown by esters of tertiary alcohols, which are hydrolyzed very rapidly even in moderately concentrated acid, and by phenol esters, which are somewhat less reactive, but are hydrolyzed much faster than esters of simple primary and secondary alcohols with above about 60% H2S04. Substituted phenyl acetates behave very much like the parent compound, the p-chlorophenyl ester being hydrolyzed at almost the same rate as the unsubstituted compound, while p-nitrophenyl acetate is somewhat less reactive at low acid concentrations, but more reactive in above 70% sulphuric acid. 

Tee s group has reported on the catalysis of enolization of indan-2-one (200) by a-CD, [1-CD, y-CD, hydroxyethyl-jS-CD, and hydroxypropy I -/i-C D, all of which accelerate the reaction by up to 22-fold, but dimethyl-jS-CD slows it by about half.170 These workers have also looked at the effect of alcohols on the basic cleavage of m-nitrophenyl hexanoate by /1-CD.171 Finally, they have been examining the reaction of a-amino acid anions with p-nitrophenyl acetate and hexanoate in the presence of [1-CD.172... 

N-Succinimidyl-p-nitrophenyl acetate (SNPA) derivatization of amines and amino acids... 

Carboxylic acids, acyl chlorides, and sulfonyl chlorides used for deri-vatization of 4-aminophenylalanine and >-4-am i n op h e ny I a I a n i n e are as follows 5-hydantoinacetic acid, / ran, v - 4 - co t i n i n ec a r b o xy I i c acid, isonicotinic acid, 3-pyridinepropionic acid, 4-hydroxyphenylacetic acid, 2-butynoic acid, 2-pyrazinecarboxylic acid, cyclopropanecarboxylic acid, 3-hydroxy-2-qui-noxaline carboxylic acid, 5-bromovaleric acid, propargyl chloroformate, 3,4-dimethoxybenzoyl chloride, 2-thiophenesulfonyl chloride, 3-thiophene-carboxylic acid, 2-thiophenecarboxylic acid, 2-methylbutyric acid, 2-thio-pheneacetyl chloride, benzoic acid, furylacrylic acid, 4-nitrophenyl acetic acid, 2,5-dimethoxyphenylacetic acid, p-toluenesulfonyl chloride, 4-(di-methylamino)phenylacetic acid, 3-indolepropionic acid, phenoxyacetic acid, 3-(dimethylamino)benzoic acid, cyclohexanecarboxylic acid, naphtha-lenesulfonyl chloride, 4-bromophenylacetic acid, 4-bromobenzoic acid, 2-phenoxybutyric acid, 3,4-dichlorophenylacetic acid, (l-naphthoxy)acetic acid. 

Alkaline hydrolysis rates of a series of thiophenyl 4-X-benzoates (47 X = H, Me, N02) was significantly enhanced in the presence of cyclodextrins (CDs), and this was attributed to strong binding of the benzoyl moiety within the CD cavity and covalent catalysis by secondary hydroxy groups of the CDs (48).63 The effect of MeCN and MeOH on the alkaline hydrolysis of acetylsalicylic acid in aqueous micellar solutions was reported.64 Butylaminolysis of p-nitrophenyl acetate in chlorobenzene in the presence of different kinds of phase-transfer catalysts (crown ethers and gly-mes) supported the existence of a novel reaction pathway exhibiting a first-order dependence on the concentration of the phase-transfer catalyst and a second-order... 

Acidic proteinoids accelerate the hydrolysis of the unnatural substrate, p-nitrophenyl acetate 7,8). P-Nitrophenyl acetate has been used as a substrate for both natural esterases and esterase models. The imidazole ring of histidine is involved in the active site of a variety of enzymes, including hydrolytic enzymes. Histidine residues of proteinoid play a key role in the hydrolysis, the contribution to activity of residues of lysine and arginine is minor, and no activity is observed for proteinoid containing no basic amino acid 7). 

Proteinoids were tested after being stored in the dry state for 5 to 10 years. Acidic proteinoids effective in catalyzing the hydrolysis of p-nitrophenyl acetate showed the same levels of activity as observed 10 years earlier19>. Lysine-rich proteinoids which catalyzed the decarboxylation of oxaloacetic acid were found to be insoluble in assay medium after 5 years of storage in the dry state. Their activity, however, had increased by 32 to 145%, and the activity of the lysine-rich proteinoids was largely associated with the insoluble portion 19). 

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... 

Small fatty acids, for example, bind strongly to HSA and, as shown in Figure 2, strongly inhibit its reaction with p-nitrophenyl acetate (29). In each case, and as is particularly obvious with decanoate ion, complete inhibition appears to require a single carboxylate ion, each, however, having a different affinity in proportion to its hydrophobicity. 

Figure 3. Inhibition of the reaction between p-nitrophenyl acetate and HSA by drugs. Data for oxazepam (0), fiufenamic acid (D), and naproxen (O) obtained at pH 7.4 in 0.03M triethanolamine/HCl at 25°C with 3.5 X 10 5M HSA. Dissociation constants are given in Table II.

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... 

Finally, an aspartic acid residue is necessary for full catalysis and this residue is thought to use its CO2 group as a general base. A chemical model shows that the hydrolysis of p-nitrophenyl acetate in aqueous acetonitrile containing sodium benzoate and imidazole follows the rate law ... 

The catalytic activity of artificial chymotrypsin in the hydrolysis of m-tert-butylphenyl acetate (k = 2.8xl02 s 1, KM = 13xl05M) was found to be close to the activity of chymotrypsin in the hydrolysis of p-nitrophenyl acetate (k,.at = l.lxlO2 s 1, KM = 4x105M). Another example of mimicking enzyme catalysis by P-cyclodextrin is general acid-base-catalyzed hydrolysis and nitrosation of amines by alkyl nitrites (Iglesias, 1998). 

Aldridge, W.N. (1953). Two types of esterase (A and B) hydrolysing p-nitrophenyl acetate, propionate and butyrate, and a method for their determination. Biochem. J. 53 110-17. Aldridge, W.N., Reiner, E. (1972). Enzyme Inhibitors as Substrates, Interaction of Esterases with Esters of Organo-phosphorus and Carbamic Acids. North-Holland, Amsterdam. Andersen, R.A., Mikalsen, A., Saetre, T. (1983). Cholinesterase levels in two stocks of Wistar rats, effect of hypophysectomy. Gen. Pharmacol. 14 285-6. 

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