Penicillin enzymatic cleavage

The industrial production of 6-aminopenicillanic acid (6-APA), the key building block for all semisynthetic variations (1957) 6-APA is readily available from high-producing strains of Penidllium chrysogenum by enzymatic cleavage of penicillin G with penicillin acylase (see Section 2.03.11). 

Except for penicillin G (phenylacetyl side chain) and penicillin V (phenoxyacetyl side chain), which can be industrially produced by fermentation, the other penicillins are obtained by coupling the required side chain to 6-APA (see Table 1). 6-APA is an important industrial intermediate produced on a large scale by enzymatic cleavage... 

Amoxicillin (21) is a semi-synthetic penicillin antibiotic. The penicillin portion is derived from fermentation of either penicillin-V or penicillin-G, and then the sidechain is removed to afford 6-APA. This transformation can be done chemically.69 207 The alternative, which is growing in importance, is to perform an enzymatic cleavage under mild conditions.208 The D-p-hydroxyphenylglycine is then attached as the new sidechain chemical and enzymatic methods are available to achieve this (Scheme 31.16).209 215 The phenylglycine amino acid is obtained by a resolution (Chapters 2, 7, and 25) or by enzymatic hydrolysis of a hydantoin (Chapter 2, 6, and 19).216-220... 

In contrast, enzymatic cleavage of penicillin G (Fig. 1.37) is performed in water at 37 °C and the only reagent used is NH3 (0.9 kg per kg of 6-APA), to adjust the pH. The enzymatic process currently accounts for the majority of the several thousand tons of 6-APA produced annually on a world-wide basis. 

An enzyme-labile so-called safety catch linker 452 was used successfully in various palladium-catalyzed cross-coupling reactions [592]. The linker 452, which releases a hydroxy or an amino functionality on enzymatic cleavage of its phenylacetamide moiety and subsequent rapid lactam formation, was attached to a soluble POE 6000 (polyethylene oxide) polymer and its free phenylacetic acid moiety was transformed to an m-iodobenzyl ester. The thus immobilized m-iodobenzyl alcohol was Heck-coupled with tert-butyl acrylate, and the coupling product 453 was cleaved off the solid support with penicillin G acylase under very mild conditions (pH 7, 37°C) (Scheme 8.84). 

As in the penicillin studies, the possibility of further improving the chemotherapeutic properties of cephalosporin C was apparent if the 7-ACA nucleus could be obtained. Enzymatic cleavage of the side chain failed, as did the use of precursors to generate new... 

A. is a central building block of penicillins and is produced either by fermentation Penicillium chry-sogenum or Pleurotis astreatus) in the absence of suitable side-chain precursors or by chemical or enzymatic cleavage of penicilline G (phenoxy-methylpenicilline). 

For the enzymatic cleavage, immobilized penicillin acylase is used. Alternatively, the fresh enzyme or resting cells can be used. 

This ester is conveniently formed from a penicillinic acid with PhCH2C02CH2Cl and TEA. Cleavage is accomplished by enzymatic hydrolysis with penicillin G. acylase in 70-90% yield. 

Preparation of PhAcOZ amino acids proceeds from the chloroformate, and cleavage is accomplished enzymatically with penicillin G acylase (pH 7 phosphate buffer, 25°, NaHS03, 40-88% yield). In a related approach, the 4-ace-toxy derivative is used, but in this case deprotection is achieved using the lipase, acetyl esterase, from oranges (pH 7, NaCl buffer, 45°, 57-70% yield). 

Figure 6.14 Enzymatic side chain cleavage of penicillins. 6-Aminopenicillanic acid, a valuable intermediate for the production of various semi-synthetic penicillins, can be obtained through enzyme-mediated hydrolysis of the phenylacety group of penicillin G or the phenoxyacetyl group of penicillin V. The active site of the enzyme recognises the aromatic side chain and the amide linkage, rather than the penidllin nucleus. Chemical entitles other than penicillins are therefore often good substrates, as long as they contain the aromatic acetamide moiety.

About one-third of the commercial cephalosporins are derived from 7-ADCA. Due to the lower cost of penicillin, 7-ADCA is usually produced from penicillin G by ring expansion of a penicillin sulfoxide ester to yield a cephalosporin ester. The removal of the ester group is followed by cleavage of the phenylacetyl side chain to give 7-ADCA. Two-thirds of the commercial cephalosporins are derived from 7-ACA, that is produced from CPC by either chemical or enzymatic deacylation. 

Examples of this, in addition to the above acrylamide example and the related enzymatic conversion of 3-cyanopyridine to nicotinamide, are die amidase cleavage of penicillins to produce 6-aminopenicillanic acid (6-APA) and the corresponding (more complex) process for converting cephalosporin C to 7-aminocephalosporanic acid (7-ACA) (see Chapter 9, footnote 8.)... 

In the first step, an enzymatic C-H bond cleavage occurs in the cysteine residue with formation of a C-N bond. From the intermediate 3, which is bound to the enzyme, penicillin is formed by a C-H bond cleavage in the valine residue and subsequently a C-S linkage (3 4) is formed. 

Cleavage of the amide bond of the aminoadipyl side chain of cephalosporin C affords the 7-aminocephalosporanic acid (7-ACA) nucleus (180). This was first achieved in small yield by direct acid hydrolysis (151). The inability to cleave the side chain enzymatically as in the penicillins (6) resulted in much effort to find an efficient chemical method to provide (180), since this is the source of many clinically important semi-synthetic cephalosporins. Many of these compounds have advantages over the penicillins in terms of acid stability and resistance to P-lactamases. 

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