Reactions hydrolytic

Hydrolytic reactions, which are best documented, include saponification of esters, hydrolysis of amides, and hydrolysis of ethers (glycosides). Except for ester saponification, all the other reactions proceed at a measurable rate only by enzymic catalysis. Hydrolytic enzymes are regular constituents of the digestive tract and lysosomes. They are responsible for the biodegradation of polyesters, polyamides (including polypeptides), polysaccharides and, probably, polyurethanes. 

Disappearance, lost of weight, surface corrosion, changes in the mechanical parameters, etc. have been described with insoluble polymers implanted in the body However, there is very little direct data available on the degradation of soluble polymers in vivo. With natural polymers, the endoenzymes are usually very specific therefore, preferential degradation from the ends can be expected with synthetic polymers, except for cases where specific sequences are inserted for purposes of degradation in the chain 

We used a synthetic polypeptide, a,P-poly[N-(2-hydroxyethyl)-D,L-aspartamide], which was prepared by aminolysis with aminoethanol of D,L-poly uccinimide obtained by thermal polycondensation The polysuccinimide is fully racemic and the aminolysis results in random opening of the succinimide rings, as demonstrated by the C-NMR spectrum As enzymes hydrolyze only the peptide bond 

The experiment was carried out using sewage water microflora as a well known 

An example of a hydrolytic reaction which proceeds very efficiently in the presence of ice [1] is the transformation of relatively inert atmospheric forms of chlorine (HCl and ClONOj) into CXy. 

An important atmospheric heterogeneous reaction is the hydrolysis of N2O5 which originates from gas-phase recombination of NO2 and NO3 radicals [1, 3]  

This reaction can proceed in droplets of water or, more probably, of water solutions of sulfuric acid (which are present in the atmosphere in large quantities) even at temperatures as low as 220K [1]. Volcanic eruptions producing huge clouds of sulfur-containing aerosols are assumed to make a large contribution to the above hydrolytic processes [1]. 

The hydrolytic reactions are of great importance from the viewpoint of chemical degradation of some water pollutants [14-17]. Both inorganic and organic water pollutants frequently have a chemical structure which renders them liable to hydrolysis. 

Alcaligenes denitrificans strain NTB-1 is able to use 4-chloro-, 4-bromo-, and 4-iodoben-zoates as sole sources of carbon and energy. The pathway involves hydrolytic dehalogenation to 4-hydroxybenzoate followed by hydroxylation to 3,4-dihydroxybenzoate (van den Tweel et al. 1987). 

A comparable pathway was used by Arthrobacter sp. strain TM-1, which was able to grow with 4-chlorobenzoate and 4-bromobenzoate (Marks et al. 1984). 

A strain of Acinetobacter sp. 4-CBl is able to dehalogenate 4-chlorobenzoate with the formation of 4-hydroxybenzoate after the initial formation of the 4-chlorobenzoyl CoA ester (Copley and Crooks 1992). 

Enzymatic hydrolysis has been widely studied and several examples of the asymmetric hydrolysis of esters catalyzed by single amino acids, polypeptides, and dendrimers catalyzed have been reported [46]. 

Uoeka and coworkers focused their efforts on the development of a catalytic system of a dipeptide or tripeptide containing L-histidine [47]. An enhanced enan-tioselective hydrolysis was obtained with a tripeptide catalyst in a mixed surfactant system. The tripeptide Z-L-Phe-L-His-L-Eeu-OH was the most efficient catalyst for the hydrolytic cleavage of p-nitrophenyl N-acylphenylalanylates. 

Conformational studies on the tripeptide Z-L-Phe-L-His-L-heu-OH and the dipeptide Z-L-Phe-L-His-OH show that both compounds share the same specific circular dichroism patterns. The tripeptide shows an a-helix-like CD spectrum. 

In addition, their ease of synthesis and modular nature allows for a simple tuning of the catalytic activity through the synthesis of combinatorial libraries of catalysts, thus allowing optimization of their structure with respect to the substrate and reaction under investigation. 

In conclusion, oligopeptides are being established as a versatile alternative to enzymes and small synthetic catalysts in many different reactions and can be expected to prove valuable asymmetric catalysts for more and more synthetically useful transformations in the next decade. 

Hydrolysis is a major biotransformation pathway for drugs containing an ester functionality. This is because of the relative case of hydrolyzing the ester linkage. A classic example of ester hydrolysis is the metabolic conversion of aspirin (acetylsalicylic acid) to salicylic acid. Of the two aslcr moieties present in cocaine, it appears that, in general, the methyl group is hydrolyzed preferentially to yield ben-roylecgoninc os the major human urinary metabolite. The 

Amides are hydrolyzed slowly in comparison to esters. Consequently, hydrolysis of the amide bond of procainamide is relatively slow compared with hydrolysis of the etster linkage in procaine. Drugs in which amide cieavage has been reported to occur, to some extent, include lidocaine. carbainazepine. indomethacin. and prazosin (Mini- 

Hydrolysis of recombinant human peptide drugs and hormones at the N- or C-terminal amino acids by carboxy- and 

Chapter 4 Metabolic Changes of Drugs and Related Organic Compounds 111 CHjCHj 

Phase I or functionalization reactions do not always produce hydrophilic or pharmacologically inactive metabolites. Various phase II or conjugation reactions, however, can convert lliese metabolites to mote poltu and water-soluble products. Many conjugativc enzymes accomplish this objective by at- 

more complex applications of hydrolases, such as those involving the formation and/or cleavage of phosphate esters, epoxides, nitriles, and organo-halides, are described elsewhere in this book. In contrast to the group of proteases, esterases and lipases, they have had less impact on organic chemistry, although their synthetic potential should not be underestimated. 

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Resolution of racemic alcohols by acylation (Table 6) is as popular as that by hydrolysis. Because of the simplicity of reactions ia nonaqueous media, acylation routes are often preferred. As ia hydrolytic reactions, selectivity of esterification may depend on the stmcture of the acylatiag agent. Whereas Candida glindracea Upase-catalyzed acylation of racemic-cx-methylhenzyl alcohol [98-85-1] (59) with butyric acid has an enantiomeric value E of 20, acylation with dodecanoic acid increases the E value to 46 (16). Not only acids but also anhydrides are used as acylatiag agents. Pseudomonasfl. Upase (PFL), for example, catalyzed acylation of a-phenethanol [98-85-1] (59) with acetic anhydride ia 42% yield and 92% selectivity (74). 

Hydrolytic reactions can also be performed at the start as well as oxidative and reductive ones They can be earned out by wet chemistry or enzymatically Examples are listed in Table 11... 

Because hydrolytic reactions are reversible, they are seldom carried out in batch wise processes [26,28,36,70]. The reactor is usually a double jacket cylindrical flask fitted with a reflux condenser, magnetic stirrer, and thermometer connected with an ultrathermostat. The catalyst is added to the reaction mixture when the desired temperature has been reached [71,72]. A nitrogen atmosphere is used when the reactants are sensitive to atmospheric oxygen [36]. Dynamic methods require more complicated, but they have been widely used in preparative work as well as in kinetic studies of hydrolysis [72-74]. The reaction usually consists of a column packed with a layer of the resin and carrying a continuous flow of the reaction mixture. The equilibrium can... 

In the chemiluminescence-based HPLC detection system, illustrated schematically in Figure 6, the oxalate ester and hydrogen peroxide are introduced to the eluent stream at postcolumn mixer Mj, which then flows through a conventional fluorescence detector with the exciting lamp turned off or a specially built chemiluminescence detector. The two reagents are combined at mixer Mj, rather than being premixed, to prevent the slow hydrolytic reactions of the oxalate ester. 

Except for extending the toolbox of type 1 BVMOs, it can also be worthwhile to explore other types of Baeyer-Villiger catalysts. As mentioned above, type 11 BVMOs have hardly been explored and new types of BVMOs have been discovered in recent years. Eurthermore, Baeyer-Villiger oxidation activity has also been introduced into enzymes that normally catalyze other (hydrolytic) reactions. " This... 

The reaction of brominated diphenyl ethers with methoxide in dimethyl formamide has been examined, and suggested as a ranking of their susceptibility to hydrolytic reactions under natural conditions (Rahm et al. 2005). The nature of the products was not apparently systematically examined. 

The operation of these hydrolytic reactions is independent of the oxygen concentration of the system so that—in contrast to biotic degradation and transformation—these reactions may occur effectively under both aerobic and anaerobic conditions. 

Xun L, CM Webster (2004) A monooxygenase catalyzes sequential dechlorinations of 2,4,6-trichlorophnel by oxidative and hydrolytic reactions. J Biol Chem 279 6696-6700. 

The first stages for two of these degradations were straightforward hydrolytic reactions. 

Nucleophilic Substitution Hydrolytic Reactions of Halogenated Alkanes and Alkanoates... 

Degradation of substituted triazines is accomplished by a sequence of hydrolytic reactions (Jutzi et al. 1982 Mulbry 1994). Atrazine, which is a representative herbicide, is degraded... 

Another important argument for the use of the organic solvent is the reverse hydrolytic reactions that become feasible [61,75]. The inhibition of the biocatalyst can be reduced, since the substrate is initially concentrated in the organic phase and inhibitory products can be removed from the aqueous phase. This transfer can shift the apparent reaction equilibrium [28,62] and facilitates the product recovery from the organic phase [20,29,33]. A wide range of organic solvents can be used in bioreactors, such as alkanes, alkenes, esters, alcohols, ethers, perfluorocarbons, etc. (Table 1). 

The hydrolytic reaction catalyzed by lipases generally takes place at the oil-water interface. The hydrolytic activity in the presence of triacylglycerols is the basis characteristic of lipases (Table 4). However, hydrolytic activity of different lipases may not always give a good indication of the potential synthesis activity (Table 4). 

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