Cephalexin synthesis

Fig. 13.14 Cephalexin synthesis cooperation of chemical, enzymatic and fermentative conversions [24].

Figure 2.17a reports in more detail the process simplification possible by biocatalysis in the case of cephalexin synthesis [154]. Figure 2.17b shows the results of a life cycle analysis (Chapter 5) of the old chemical route versus the new white biotech route [154]. The significant improvement in the sustainability of the new process is clearly evidenced. 

Illanes A, Wilson L, Raiman L (1999) Design of immobilized enzyme reactors for the continuous production of fructose syrup from whey permeate. Bioproc Eng 21 509-515 Illanes A, Wilson L, TomaseUo G (2000) Temperature optimization for reactor operation with chitin-immobiUzed lactase under modulated inactivation. Enzyme Microb Technol 27 270-278 Illanes A, Anjari S, Altamirano C et al. (2004) Optimization of cephalexin synthesis with immobilized penicillin acylase in ethylene glycol medium at low temperatures. J Mol Catal B Enzym 30 95-103... 

Illanes A, Anjarf S, Altamirano C et al. (2004) Optimization of cephalexin synthesis with immobihzed penicillin acylase in ethylene glycol medium at low temperatures. J Mol Catal B Enzym... 

Nys 2002 Pan and Syu 2005 Giordano et al. 2006). We developed a model for describing batch reactor performance with immobilized penicillin acylase for the KCS of cephalexin from 7ADCA and PGME based on the kinetic mechanism proposed by Nam et al. (1985). The rate of cephalexin synthesis can be expressed as ... 

KaUenbeig A, van Rantwijk F, Sheldon R (2005) ImmobDization of penicillin G acylase the key to optimum performance. Adv Synth Catal 347 905-926 Kasche V (1985) AmpicUlin and cephalexin synthesis catalyzed by E. coli peniciUin amidase. 

Schroen CGPH, Mohy Eldin MS, Janssen AE et al. (2001b) Cephalexin synthesis by immobilized penicillin acylase under non-isothermal conditions reduction of diffusion limitation. J Mol Catal B Enzym 15 163-172... 

The oral activity and clinical acceptance of cephalexin (14) has led to the appearance of a spate of similar molecules. Cefadroxyl (16) is an example. The design of this drug would seem to have derived from the success of amoxycillin. The synthesis of cefadroxyl was accomplished by N-acylation of 7-aminodesacetyl-cephalosporanic acid (7 ADCA) after blocking the carboxy group with (CH30)2CH3SiCl (to 15). The... 

Cefadroxil Cefadroxil, [6/ -[6a,7)3(7 )]]-3-methyl-8-oxo-7-[[amino(4-hydroxyphenyl) acetyl]amino]-5-thia-l-azabicyclo[4.2.0]oct-2-en-2-carboxylic acid (32.1.2.14), is an analog of cephalexin and differs only in the presence of a hydroxyl group in the fourth position of the phenyl ring of phenylglycine, and is synthesized by a scheme analogous to the scheme of cephradin synthesis [90-96],... 

Cephalosporins Have a nucleus that is similar to that of (3-lactams and similarly dismpt the synthesis of the peptidoglycan layer. This layer is important in maintaining cell wall integrity in gram-positive bacteria. Omnicef (Cefdinir) Cefzil (Cefprozil) Cephalexin (Keflex) Bioavailabihty is dose dependent is only about 16-21%. About 90% is excreted as the parent compound. It is well absorbed by the body and 90% of the dmg is excreted unchanged. 

PGME ADCA Cephalexin Thermodynamically controlled synthesis 100 Very high substrate concentrations (>750mM) with PGME/ADCA = 3. 85... 

Recently, the kinetically controlled synthesis of cephalexin with penicillin amidase was studied at very high concentrations of substrates to the limit of... 

This approach can be extended by working in highly condensed systems formed with mainly undissolved substrates for the enzymatic synthesis of ampicilhn and cephalexin, where the reaction mixture had no aqueous phase for dispersion of the reagents, and no organic solvents were used. The absence of an apparent aqueous phase in the reaction mixture reduces the incidence of the hydrolytic reaction [86-87]. 

A good example of a white biotech process in the pharmaceutical area is our route to the antibiotic cephalexin, practiced on a large industrial scale for several years now. By advanced enzyme and metabolic engineering we were able to replace the traditional 10-step, mainly chemical synthesis (Fig. 29.3A) by a fermentative route followed by two mild enzymatic steps (Fig. 29.3 B). The white biotech process has been shown recently to use far less energy (-65%), less input of (harsh) chemicals (-65%), is water-based, generates less waste, and is very cost-effective (-50%) (Bruggink, A.). Again, this is a bio-based process where environmental and economic benefits go hand in hand and for which there is no competitive chemical alternative (EuropaBio and McKinsey Company, 2003 DSM position document, 2004). 

Use of 2-azetidinones as building blocks in organic synthesis is now well established. However, cephalosporins have rarely been used as intermediates for the synthesis of non-/3-lactam products. Cephalosporins with an ct-amino group on the 7-/3-acyl substituent, cefaclor 11 and cephalexine 12, have been aminolyzed and the initial, unstable... 

Besides being used for the production of the precursors 6-APA and 7-ADCA, penicillin amidases are also able to couple 6-APA and 7-ADCA with D-phenyl-glycine ester or amide in a kinetically controlled enzymatic peptide synthesis forming ampicillin or cephalexin (38, 39). These reactions (Scheme 21) have a great potential for being commercialized in the near future [95]. 

The replacement of the chemical synthesis route for cephalexin, which consisted of ten difficult chemical steps starting from peniciUin G, by the enzymatic synthesis or green route (six steps) has led to a more sustainable water-based... 

In Chapter 1 (Section 1.6.1, Bio-based Economy) it was noted how white biotechnologies contribute to sustainability. We may cite, as an additional example, that DSM s route to the antibiotic cephalexin (a combination of a fermentation and an enzymatic reaction with respect to multistep chemo-synthesis) reduces of 65% the materials and energy used, and about 50% the variable costs [153]. Other examples of biocatalysis and white biotechnologies used industrially by DSM are summarized in Table 2.5. 

More recently, a biocatalytic manufacturing route was developed in which deacylation was accomplished by penicillin G acylase in water at room temperature, requiring no protection and deprotection (Scheme 8.9) [58]. Moreover, through reaction engineering, penicillin G acylase also catalyzes the acylation of 6-APA with either amino esters or aminoamides to produce a wide range of semi-synthetic P-lactam antibiotics such as amoxicillin and ampicillin. A similar approach could be applied to the synthesis of the 7-ADCA derivatives cefaclor, cephalexin, and cefadroxil. 

F. Knauseder, N. Palma, Enzymatic Synthesis of Cephalexin by Immobilized Penicillin Acylase from E. Colt, ECB-3 Mtinchen, Part 1,1984, pp. 431-438. 

Semisynthetic Cephalosporins. Once the structure of cephalosporin C became known (98), attempts were made to find chemically modified analogs having superior biological properties. This was successfully achieved with the synthesis of cephalothin, cephaloridine, cephalogly-cine, and cephalexin (Figure 20). In the first two, in vitro potency was enhanced as much as 10,000 fold (99), in the latter two oral absorption... 

Transpeptidation, septum cross-1 wall synthesis Nonseptate filamentous cells Cephalexin, cefuroxine, aztronam... 

Chemferm is one of among several companies which apply penicillin acylase for the kinetically controlled industrial synthesis of semisynthetic antibiotics in aqueous environments (Scheme 37) [109-111]. Ampicillin (119) and amoxicillin (120) can be obtained by the enzyme-catalyzed condensation of 6-aminopenicillic acid (6-APA, 117) with the amide or ester of D-(-)-4-hydrox-yphenylglycine and D-(-)-phenylglycine, respectively. In a similar way, cephalexin (121) can be obtained by reaction of D-(-)-phenylglycine with 7-aminodesacetoxycephalosporanic acid (7-ADCA, 118). Penicillin acylase from diverse microbial strains such as E. colU Klyveromyces citrophiluy and Bacillus megabacterium was successfully applied for this transformation and was used in its immobilized form based on a gelatin carrier. The immobilization allows an easy separation from the reaction medium and the reuse of the enzyme for at least 50 cycles. Impressive characteristics of this transformation are yields >90%, a selectivity of >95%, and an optical purity of >99% ee. The industrial manufacture takes place in repetitive batch reactors at many locations worldwide with an annual production volume of 2,000 t. 

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