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Amidations hydrolytic

Ester and amide hydrolytic reactions are mediated principally by carboxylesterases (GES), though other esterases play a role in the hydrolysis of a limited number of esters. Other key biotransformations include oxidations and conjugation reactions. [Pg.169]

Keywords Amide-bond formation Dehydrogenative amidation Hydrolytic amidation Nitrile hydration Rearrangements Ruthenium catalysts... [Pg.81]

Perhaps the most extensively studied catalytic reaction in acpreous solutions is the metal-ion catalysed hydrolysis of carboxylate esters, phosphate esters , phosphate diesters, amides and nittiles". Inspired by hydrolytic metalloenzymes, a multitude of different metal-ion complexes have been prepared and analysed with respect to their hydrolytic activity. Unfortunately, the exact mechanism by which these complexes operate is not completely clarified. The most important role of the catalyst is coordination of a hydroxide ion that is acting as a nucleophile. The extent of activation of tire substrate througji coordination to the Lewis-acidic metal centre is still unclear and probably varies from one substrate to another. For monodentate substrates this interaction is not very efficient. Only a few quantitative studies have been published. Chan et al. reported an equilibrium constant for coordination of the amide carbonyl group of... [Pg.46]

Inspired by the many hydrolytically-active metallo enzymes encountered in nature, extensive studies have been performed on so-called metallo micelles. These investigations usually focus on mixed micelles of a common surfactant together with a special chelating surfactant that exhibits a high affinity for transition-metal ions. These aggregates can have remarkable catalytic effects on the hydrolysis of activated carboxylic acid esters, phosphate esters and amides. In these reactions the exact role of the metal ion is not clear and may vary from one system to another. However, there are strong indications that the major function of the metal ion is the coordination of hydroxide anion in the Stem region of the micelle where it is in the proximity of the micelle-bound substrate. The first report of catalysis of a hydrolysis reaction by me tall omi cell es stems from 1978. In the years that... [Pg.138]

The conversion of alcohols to esters by O-acylation and of amines to amides by N-acylation are fundamental organic reactions. These reactions are the reverse of the hydrolytic procedures discussed in the preceding sections. Section 3.4 in Part B discusses these reactions from the point of view of synthetic applications and methods. [Pg.484]

The hydrogeh atom bound to the amide nitrogen in 15 is rather acidic and it can be easily removed as a proton in the presence of some competent base. Naturally, such an event would afford a delocalized anion, a nucleophilic species, which could attack the proximal epoxide at position 16 in an intramolecular fashion to give the desired azabicyclo[3.2.1]octanol framework. In the event, when a solution of 15 in benzene is treated with sodium hydride at 100 °C, the processes just outlined do in fact take place and intermediate 14 is obtained after hydrolytic cleavage of the trifluoroacetyl group with potassium hydroxide. The formation of azabi-cyclo[3.2.1]octanol 14 in an overall yield of 43% from enone 16 underscores the efficiency of Overman s route to this heavily functionalized bicycle. [Pg.649]

The specificity of enzyme reactions can be altered by varying the solvent system. For example, the addition of water-miscible organic co-solvents may improve the selectivity of hydrolase enzymes. Medium engineering is also important for synthetic reactions performed in pure organic solvents. In such cases, the selectivity of the reaction may depend on the organic solvent used. In non-aqueous solvents, hydrolytic enzymes catalyse the reverse reaction, ie the synthesis of esters and amides. The problem here is the low activity (catalytic power) of many hydrolases in organic solvents, and the unpredictable effects of the amount of water and type of solvent on the rate and selectivity. [Pg.26]

Polymers used in medicine fall into two main categories those that are sufficiently inert to fulfill a long-term structural function as biomaterials or membranes, and those that are sufficiently hydrolytically unstable to function as bioeradible materials, either in the form of sutures or as absorbable matrices for the controlled release of drugs. For the synthetic organic polymers widely used in biomedicine this often translates to a distinction between polymers that have a completely hydrocarbon backbone and those that have sites in the backbone that are hydrolytically sensitive. Ester, anhydride, amide, or urethane linkages in the backbone usually serve this function. [Pg.163]

A substantial number of bioactive molecules, such as polypeptides, N-acetyl-DL-penicillamine, p-(dipropylsulfamoyl)benzoic acid, and nicotinic acid, contain a carboxylic acid function, and this provides a site for linkage to a polyphosphazene chain. A number of prototype polymers have been synthesized in which pendent amino groups provide coupling sites for the carboxylic acid (34). The amide linkages so formed are potentially bioerodible, but the use of a hydrolytic sensitizing cosubstituent would be expected to accelerate the process. [Pg.179]

The hydrolytic stability of water soluble poly[N-(4-sulfo-phenyDdimethacrylamide] (PSPDM) was studied at 90 C in aqueous solutions at pH 7, pH 1.2 (0.1M HC1), and pH 12.3 (0.1M NaOH). PSPDM, which possesses predominantly 5-mem-bered ring imides, was prepared by the cyclopolymerization and subsequent sulfonation of N-phenyldimethacrylamide. No detectable PSPDM imide hydrolysis occurred after 30 days at pH 7 or pH 1.2. Under basic conditions, however, complete hydrolysis to amic acid occurred after one day. The resulting Nsubstituted amide was extremely stable to further basic hydrolysis. [Pg.291]

The pseudobenzylisoquinoline alkaloids are fairly widespread in nature, being found among members of Berberidaceae, Annonaceae, Fumariaceae, and Ranunculaceae. The biogenesis of the pseudobenzylisoquinoline alkaloids assumes their formation from protoberberinium salts by C-8—C-8a bond scission in a Baeyer-Villiger-type oxidative rearrangement to produce the enamides of type 73 and 74. These amides may be further biotransformed either to rugosinone (76) type alkaloids by hydrolytic N-deformylation followed by oxidation or to ledecorine (75) by enzymatic reduction. These transformations were corroborated by in vitro studies (80-82). It is suggested that enamide seco alkaloids may be precursors of aporphine alkaloids (80), on one hand, and of cularine alkaloids (77), on the other. [Pg.257]

A monodentate palladium(II) complex trans-[Pd(py)2(H202)]2+ hydrolyzes Met-Aa amide bonds with a rate comparable with that promoted by [Pd(H20)3(0H)]+. Unlike Pd(H20)3(0H)]+, //chelated complex containing temed (A,A,AAA -tctramcthylcthylenediamine) hydrolyzes Met-Aa amide bonds with hydrolytic rate controlled by temed release. The action of the other two complexes, c -[Pd(ED-TA)C12] (EDTA = ethylene diaminetetraacetic acid) and cis-1,2-bis(2-formylglycinebenzene-sulfenyl)ethane Pd11 chloride differs from the action of similar complexes of U,v-[Pd(en)Cl2] and cw-[Pd(dtco-3-OH)Cl2] (dtco-3-OH = l,5-dithiacycooctan-3-ol).448... [Pg.592]

Selective cleavage of peptides and proteins is an important procedure in biochemistry and molecular biology. The half-life for the uncatalyzed hydrolysis of amide bonds is 350 500 years at room temperature and pH 4 8. Clearly, efficient methods of cleavage are needed. Despite their great catalytic power and selectivity to sequence, proteinases have some disadvantages. Peptides 420,423,424,426 an(j proteins428 429 can be hydrolytically cleaved near histidine and methionine residues with several palladium(II) aqua complexes, often with catalytic turnover. [Pg.593]


See other pages where Amidations hydrolytic is mentioned: [Pg.349]    [Pg.550]    [Pg.214]    [Pg.293]    [Pg.424]    [Pg.773]    [Pg.82]    [Pg.349]    [Pg.550]    [Pg.214]    [Pg.293]    [Pg.424]    [Pg.773]    [Pg.82]    [Pg.311]    [Pg.203]    [Pg.275]    [Pg.129]    [Pg.525]    [Pg.526]    [Pg.743]    [Pg.408]    [Pg.150]    [Pg.88]    [Pg.177]    [Pg.172]    [Pg.188]    [Pg.139]    [Pg.36]    [Pg.245]    [Pg.38]    [Pg.3]    [Pg.22]    [Pg.269]    [Pg.122]    [Pg.433]    [Pg.369]    [Pg.242]    [Pg.293]    [Pg.298]    [Pg.167]    [Pg.700]    [Pg.458]    [Pg.556]   
See also in sourсe #XX -- [ Pg.81 , Pg.93 ]




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