Esters acid-induced ester hydrolysis

Anhydrides react with water to generate carboxylic acids, with alcohols to give esters, and with amines to form amides. Esters behave similarly. There are both acid-catalyzed and base-induced reactions of esters with water (ester hydrolysis) to give carboxylic acids. There are both acid- and base-catalyzed versions of the reaction of esters with alcohols (transesterification) that generate new esters. Esters also react with amines to form amides. 

Even though amides are the least reactive of the acyl compounds, they can nevertheless be hydrolyzed in either acid or base. The mechanisms of these reactions are directly related to those of acid- or base-induced ester hydrolysis. In base, the carbonyl carbon of an amide is attacked to give tetrahedral intermediate A (Fig. 18.39). 

The study of both carbonyl and carbon acid participation in ester hydrolysis has been used by Bowden and Last (1971) to evaluate certain of the factors suggested for important roles in enzymic catalysis. A first model concerns a comparison of the three formyl esters and shows that the proximity of the formyl to the ester group and internal strain increase in passing along the series, 1,2-benzoate, 1,8-naphthoate and 4,5-phenanthroate. The very large rate enhancements result from the proximity of the internal nucleophile once formed and from internal strain. Strain is increased or induced by the primary... 

Acid-catalyzed hydrolysis of esters is the reverse of acid-catalyzed ester formation discussed previously. Base-induced ester hydrolysis (saponification) is an irreversible reaction. The initial step is the attack of hydroxide ion at the carbonyl carbon ... 

The acidity of the vinylic C—H bond is exemplifiedby the hydroxide ion-induced H/D exchange of ester 117 in competition with ester hydrolysis. Synthetically useful... 

Analyses of in situ DNA synthesis of Euglena gracilis identify zinc-dependent steps in the eukaryotic cell cycle and show that the derangements in RNA metabolism are critical determinants of the growth arrest associated with zinc deficiency. Combined use of microwave-induced emission spectrometry and micro gel emulsion chromatography shows the presence of stoichiometric amounts of zinc essential to the function of E. gracilis and yeast RNA polymerases, the reverse transcriptases" from avian myeloblastosis, murine leukemic and woolly type C viruses, and E. coli methionyl tRNA synthetase. These results stress the importance of zinc to both nucleic acid and protein metabolism. Transient-state kinetic studies of carboxypeptidase A show that zinc functions in the catalytic step of peptide hydrolysis and in the binding step of ester hydrolysis. 

The reactivity, fate, and distribution of bound solutes are certainly changed by association with stream humic substances. The rate of photolysis of certain organic compounds (Zepp et al., 1981a,b), the rate of volatilization of polychlorinated biphenyls (Griffin and Chian, 1980), the bioaccumulation of polynuclear aromatic hydrocarbons in fish (Leversee, 1981), the rate of humic acid induced acid-base catalysis (Perdue, 1983), and the rate of microbiological decomposition are some specific examples. The octyl ester of 2,4-D (2,4 DOE) was predicted by theoretical and mathematical models and found by experimentation to be resistant to base hydrolysis when bound to humic substances (Perdue, 1983). The same model predicted the humic acid catalyzed hydrolysis of atrazine as demonstrated by Li and Felbeck 11972). 

The reactions of metailated 2-methyloxazolines with carbonyl compounds to provide adducts constitute the key step in a general procedure for the conversion of carbonyl compounds into 3-hydroxy carboxylic acids and esters or their a,3-unsaturated counterparts (Schemes 21-26). o For example, reaction of the lithiated derivative of (54) with carbonyl compounds provides the adducts (55) in high yield (Scheme 21). Subsequent acid-catalyzed hydrolysis provides the unsaturated carboxylic acids (56) depending upon the severity of the reaction conditions, acid-induced ethanolysis can be performed on the adducts (55) to provide either the unsaturated esters (57) or the 3-hydroxy esters (58) in good yields (Table 7). The main limitation of the method is that extensive retroaldolization occurs upon attempts to hydrolyze adducts (55 R = alkyl), so a-alkyl-3-hydroxy esters and acids do not appear to be accessible. 

The perfection of this strategy makes use of the L-threonine-derived 2S,ZR acid 61 and tert-h xiy iV-(p-methoxybenzyl)glycinate as the active methylene partner [28d]. After condensation to amide 62, base treatment (LHMDS) induced epoxydation (at 0 °C) and then (25 °C) cyclization. This double inversion mechanism produced a single epimer, 63a, which, through acid 63b, was converted to target 11 by silylation, ester hydrolysis, lead tetraacetate and CAN (or peroxydisulfate) oxidation. 

Incorporation of the amino acids L-2,4-diaminobutyric acid (DAB) and homocysteine (HCY) into a PEA backbone was investigated with the aim of imparting stimuli-responsive degradation properties. Studies on model compounds revealed that the pendant y-amine or y-thiol of DAB and HCY esters experimented intramolecular cyclizalions at a much more rapid rate than background ester hydrolysis. Thus, stimuli-induced cyclization reactions (i.e., after deprotection of pendant groups by acids or reducing agents) were effective to cleave ester... 

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