Enzymatic aminolysis reaction

Surprisingly, the 7t-system geometry in a substrate has a notable influence in the enzymatic aminolysis of esters. The reaction of diethyl fumarate with different amines or ammonia in the presence of CALB led to the corresponding trans-amidoesters with good isolated yields, but in the absence of enzyme, a high percentage of the corresponding Michael adduct is obtained (Scheme 7.9). Enzymatic aminolysis of diethyl maleate led to the recovery of the same a, P-unsaturated amidoester, diethyl fumarate, and diethyl maleate. The explanation of these results can be rationalized via a previous Michael/retro-Michael type isomerization of diethyl maleate to fumarate, before the enzymatic reaction takes place. In conclusion, diethylmaleate is not an adequate substrate for this enzymatic aminolysis reaction [23]. 

The resolution of racemic ethyl 2-chloropropionate with aliphatic and aromatic amines using Candida cylindracea lipase (CCL) [28] was one of the first examples that showed the possibilities of this kind of processes for the resolution of racemic esters or the preparation of chiral amides in benign conditions. Normally, in these enzymatic aminolysis reactions the enzyme is selective toward the (S)-isomer of the ester. Recently, the resolution ofthis ester has been carried out through a dynamic kinetic resolution (DKR) via aminolysis catalyzed by encapsulated CCL in the presence of triphenylphosphonium chloride immobilized on Merrifield resin (Scheme 7.13). This process has allowed the preparation of (S)-amides with high isolated yields and good enantiomeric excesses [29]. 

Gotor, V. (2000) Pharmaceuticals Through Enzymatic Transesterification and Enzymatic Aminolysis Reactions, Biocat. Biotrans. 18, 87-103. 

Over the past years, interest in the preparation of chiral amines and amides by enzymatic ammonolysis or aminolysis reactions [4] has greatly increased for academic and industrial sectors. The role that the enzymatic acylation of amines or ammonia plays for the preparation of some pharmaceuticals is noteworthy [5]. 

Although the aminolysis of esters to amides is auseful synthetic operation, usually it presents some disadvantages in terms of drastic reaction conditions, long reaction times or strong alkali metal as catalyst, which are usually not compatible with other functional groups in the molecule [6]. For this reason, enzymatic aminolysis of carboxylic acid derivatives offers a clean and ecological way for the preparation of different kind of amines and amides in a regio-, chemo-, and enantioselective manner. 

The strategy described here explains the different possibilities of enzymatic ammonolysis and aminolysis reaction for resolution of esters or preparation of enantiomerically pure amides, which are important synthons in organic chemistry. This methodology has been also applied for the synthesis of pyrrolidinol derivatives that can be prepared via enzymatic ammonolysis of a polyfunctional ester, such as ethyl ( )-4-chloro-3-hydroxybutanoate [30]. In addition, it is possible in the resolution of chiral axe instead of a stereogenic carbon atom. An interesting enzymatic aminolysis of this class of reaction has been recently reported by Aoyagi et al. [31[. The side chain of binaphthyl moiety plays an important role in the enantiodis-crimination of the process (Scheme 7.14). 

Other authors have described the lipase-catalyzed chemoselective acylation of alcohols in the presence of phenolic moities [14], the protease-catalyzed acylation of the 17-amino moiety of an estradiol derivative [15], the chemoselectivity in the aminolysis reaction of methyl acrylate (amide formation vs the favored Michael addition) catalyzed by Candida antarctica lipase (Novozym 435) [16], and the lipase preference for the O-esterification in the presence of thiol moieties, as, for instance, in 2-mercaptoethanol and dithiotreitol [17]. This last finding was recently exploited for the synthesis of thiol end-functionalized polyesters by enzymatic polymerization of e-caprolactone initiated by 2-mercaptoethanol (Figure 6.2)... 

Polyethylene glycol is used to make the enzymes soluble in organic solvents [88], and high reaction yields have been obtained with polyethylene-glycol-modified chymotrypsin [89], and papain in benzene [90], Enzymatic modification reactions with deacylation, via aminolysis, of an intermediate covalent acyl-enzyme also support the mechanism of transpeptidation in kinetically controlled peptide syn-... 

Aso et al. [95] studied a model system in order to obtain basic information on the mechanism of amino acid incorporation during an enzymatic modification reaction in the presence of papain. They found that the amino acid ester reacted as a nucleophile in the aminolysis of the acyl-enzyme intermediate to result in the formation of new peptides. Several proteases used in enzymatic peptide bond synthesis are known to form transitory acyl-enzyme intermediates during the hydrolysis of proteins. However, the acyl groups can be transferred to other nucleophiles (amino terminals of peptides or amino acids), synthesizing new peptide bonds [71]. With full knowledge of the above-mentioned facts, covalent amino acid enrichment of proteins can result in... 

Gotor V (1992) Enzymatic aminolysis, hydrazinolysis and oximolysis reactions. In Servi S (ed) Microbial Reagents in Organic Synthesis, Nato ASI Series C, vol 381. Kluwer, Dordrecht, p 199... 

Although, the enzymatic reaction of esters with amines or ammonia have been well documented, the corresponding aminolysis with carboxylic acids are rarer, because of the tendency of the reactants to form unreactive salts. For this reason some different strategies have been used to avoid this problem. Normally, this reaction has been used for the preparation of amides of industrial interest, for instance, one of the most important amides used in the polymer industry like oleamide has been produced by enzymatic amidation of oleic acid with ammonia and CALB in different organic solvents [10]. 

Here, we have selected a few representative examples of the enzymatic resolution of esters by aminolysis or ammonolysis reactions. On the other hand, the enzymatic acylation of racemic amines is also of great utility for the preparation of optically pure... 

In the kinetic approach, the serine or cysteine peptidase rapidly reacts with a suitable acyl donor ester to form the acylenzyme intermediate, which can be deacylated competitively by the added nucleophilic amine component and water. The ratio between aminolysis and hydrolysis of the acyl donor ester is of great importance for the outcome of the synthesis route.This selectivity is essentially determined by the S subsite specificity of the enzyme as shown above. To establish an optimum synthesis strategy, it is useful to know the basic kinetic parameters for the reaction course, in particular those obtained by S subsite mapping are of great importance for planning and optimization of the enzymatic synthesis. 

Proteolytic reactions take place in general in aqueous media, with the equilibrium in the direction of hydrolysis [87]. However, with decreased water activity, the equilibrium of the reaction is shifted toward synthetic reactions [74]. The use of organic media provides a potentially useful approach to the enzymatic modification of food protein. It has been already established that proteinases are active in organic media. They catalyze ester synthesis or aminolysis by synthesizing new peptide bonds preferentially to hydrolysis. 

In general, naturally occurring (IV-protected) L-amino acid esters of short-chain alcohols, such as methyl and ethyl esters are usually sufficiently reactive as acceptors to achieve reasonable reaction rates in enzymatic peptide synthesis via aminolysis. For less reactive (nonnatural) analogs, such as a-substituted [313] or D-configured amino acids [314], activated esters are recommended, among them, 2-haloethyl (e.g., 2-chloroethyl, trifluoroethyl) [315], p-nitrophenyl [316], or guanidinophenyl esters [317]. For the use of cyclic activated esters [5(47/)-oxazolones] see below. 

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