Enzymatic hydrolysis, natural

Rolinson, G. N., F. R. Batchelor, D. Butterworth, J. Cameron-Wood, M. Cole, G. C. Eustace, M. V. Hart, M. Richards, and E. B. Chain Formation of 6-Aminopenicillanic Acid from Penicillin by Enzymatic Hydrolysis Nature 187, 236... 

Enzymatic hydrolysis is also used for the preparation of L-amino acids. Racemic D- and L-amino acids and their acyl-derivatives obtained chemically can be resolved enzymatically to yield their natural L-forms. Aminoacylases such as that from Pispergillus OTj e specifically hydrolyze L-enantiomers of acyl-DL-amino acids. The resulting L-amino acid can be separated readily from the unchanged acyl-D form which is racemized and subjected to further hydrolysis. Several L-amino acids, eg, methionine [63-68-3], phenylalanine [63-91-2], tryptophan [73-22-3], and valine [72-18-4] have been manufactured by this process in Japan and production costs have been reduced by 40% through the appHcation of immobilized cell technology (75). Cyclohexane chloride, which is a by-product in nylon manufacture, is chemically converted to DL-amino-S-caprolactam [105-60-2] (23) which is resolved and/or racemized to (24)... 

A number of examples of monoacylated diols produced by enzymatic hydrolysis of prochiral carboxylates are presented in Table 3. PLE-catalyzed conversions of acycHc diesters strongly depend on the stmcture of the substituent and are usually poor for alkyl derivatives. Lipases are much less sensitive to the stmcture of the side chain the yields and selectivity of the hydrolysis of both alkyl (26) and aryl (24) derivatives are similar. The enzyme selectivity depends not only on the stmcture of the alcohol, but also on the nature of the acyl moiety (48). 

Resolution of Racemic Amines and Amino Acids. Acylases (EC3.5.1.14) are the most commonly used enzymes for the resolution of amino acids. Porcine kidney acylase (PKA) and the fungaly3.spet i//us acylase (AA) are commercially available, inexpensive, and stable. They have broad substrate specificity and hydrolyze a wide spectmm of natural and unnatural A/-acyl amino acids, with exceptionally high enantioselectivity in almost all cases. Moreover, theU enantioselectivity is exceptionally good with most substrates. A general paper on this subject has been pubUshed (106) in which the resolution of over 50 A/-acyl amino acids and analogues is described. Also reported are the stabiUties of the enzymes and the effect of different acyl groups on the rate and selectivity of enzymatic hydrolysis. Some of the substrates that are easily resolved on 10—100 g scale are presented in Figure 4 (106). Lipases are also used for the resolution of A/-acylated amino acids but the rates and optical purities are usually low (107). 

Enzymes are the catalyst per excellence for reactions in water, which is their natural habitat. Moreover, the use of enzymes often circumvents the need for functional group protection and deprotection steps. For example, enzymatic hydrolysis of penicillin G to 6-APA (Fig. 2.30) proceeds in one step at ambient temperature while chemical deacylation requires three steps, a temperature of - 40 C and various stoichiometric reagents, leading to a high E factor. 

Another interesting target for this type of inhibitors is the dipeptidyl peptidase IV (DPP IV). This exodipeptidase, which can cleave peptides behind a proline residue is important in type 2 diabetes as it truncates the glucagon-like peptide 1. Taking into account the P2-Pi( Pro)-P,1 cleavage and the requirement for a free terminal amine, the synthesis of a suicide inhibitor was planned. It looked as if the the e-amino group of a P2 lysine residue could be cyclized because of the relative little importance of the nature of the P2 residue on the rate of enzymatic hydrolysis of known synthetic substrates. Therefore, anew series of cyclopeptides 11 was synthesized (Fig. 11.8). 

The relevance of the palladium-catalyzed amidocarbonylation for natural product synthesis has been demonstrated with the multi gram-scale preparation of the central amino acid of chloropeptin I ((S)-3,5-dichloro-4-hydroxyphenylglycine) as well as methionine and p-chlorophenyl alanine via the combination of amidocarbonylation and enzymatic hydrolysis (Table 4) [44]. 

In the field of food sciences, numerous ACE inhibitory peptides have been isolated from the digestion or enzymatic hydrolysis of natural... 

Naturally occurring cellulose is extremely mechanically stable and is highly resistant to chemical and enzymatic hydrolysis. These properties are due to the conformation of the molecules and their supramolecular organization. The unbranched pi 4 linkage results in linear chains that are stabilized by hydrogen bonds within the chain and between neighboring chains (1). Already during biosynthesis, 50-100 cellulose molecules associate to form an elementary fibril with a diameter of 4 nm. About 20 such elementary fibrils then form a microfibril (2), which is readily visible with the electron microscope. 

Various diastereomeric di-, tri-, and tetrapeptides that carry the sterically demanding trifluoromethyl group instead of the natural a-proton at different positions within these short peptide sequences have been designed, and their stability towards enzymatic hydrolysis has been investigated. The structures of the a-trifluoromethyl (aTfm)-substituted amino acids are shown in Scheme 1. From these studies we gained valuable information on how a-trifluoromethyl-substi-tuted peptides may interact with proteins. The aTfm amino acids used in this study combine the conformational restrictions [49-52] of C -dialkylation with the unique stereoelectronic properties of the fluorine atom and have shown interesting effects on peptide-enzyme interactions [53,54]. 

Enzymatic Hydrolysis Reactions of Esters. Xenobiotic compounds containing esters or other acid derivatives in their structures (e.g., amides, carbamates, ureas, etc., see Table 17.3) are often readily hydrolyzed by microorganisms. To understand how enzymatic steps can be used to transform these substances, it is instructive to consider the hydrolases (i.e., enzymes that catalyze hydrolysis reactions) used by organisms to split naturally occurring analogs (e.g., fatty acid esters in lipids or amides in proteins). The same chemical processes, and possibly even some of the same enzymes themselves, are involved in the hydrolysis of xenobiotic substrates. 

What reasons are there for mixing polymerizable lipids with natural ones Polymerized membrane systems, especially those based on diacetylenic lipids, have proven to be excessively rigid and to show no phase transition. Addition of natural lipids could help to retain a certain membrane mobility even in the polymerized state, with almost unaffected stability. Furthermore, natural lipids can provide a suitable environment for the incorporation of membrane proteins into polymerizable membranes (see 4.2.3). Besides this, enzymatic hydrolysis of the natural membrane component can be used for selectively opening up a vesicle in order to release entrapped substances in a defined manner (see 4.2.2). Therefore, it is interesting to learn about the miscibility of polymerizable and natural lipids and also about the polymerization behavior of these mixtures. Investigations on this subject have thus far focused on mixtures of natural lipids with polymerizable lipids carrying diacetylene moieties. 

Enzymatic Hydrolysis of Natural Lipids in Polymeric Membranes... 

In addition to enzymatic hydrolysis of natural lipids in polymeric membranes as discussed in chapter 4.2.2., other methods have been applied to trigger the release of vesicle-entrapped compounds as depicted in Fig. 37. Based on the investigations of phase-separated and only partially polymerized mixed liposomes 101, methods to uncork polymeric vesicles have been developed. One specific approach makes use of cleavable lipids such as the cystine derivative (63). From this fluorocarbon lipid mixed liposomes with the polymerizable dienoic acid-containing sulfolipid (58) were prepared in a molar ratio of 1 9 101115>. After polymerization of the matrix forming sulfolipids, stable spherically shaped vesicles are obtained as demonstrated in Fig. 54 by scanning electron microscopy 114>. 

Although some forms are detected when tomatine is extracted from the plant, these glycosides are probably either products of enzymatic hydrolysis during extraction or natural intermediates in the biosynthesis and/or degradation of tomatine. 

A few animals (especially ruminants and termites) are able to metabolize cellulose, but even these animals depend on appropriate microorganisms in their intestinal tracts to hydrolyze the -1,4 links other animals, including man, cannot utilize cellulose as food because they lack the necessary hydrolytic enzymes. However, such enzymes are distributed widely in nature. In fact, deterioration of cellulose materials —textiles, paper, and wood —by enzymatic degradation (such as by dry rot) is an economic problem that is not yet adequately solved. Efforts to turn this to advantage through enzymatic hydrolysis of cellulose to glucose for practical food production have not been very successful (see Section 25-12). 

FIGURE 3 Several hypothetical scenarios which might explain resistance of organic macromolecules to extracellular enzymatic hydrolysis (a) natural substrates are not a good fit for enzyme active sites, perhaps because of biological or chemical modifications (b) specific substrates are too dilute to induce enzymes under most circumstances (c) substrates are physically protected from hydrolysis (e.g., Mayer, 1994 Keil et al., 1994). Enzymes may also be complexed, hindering their activities (Wetzel, 1993). 

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