Use of enzymes in the production of semi-synthetic penicillins and cephalosporins: drawbacks and perspectives.

Semi-synthetic ß-lactamic antibiotics are the most used anti-bacteria agents, produced in hundreds tons/year scale. It may be assumed that this situation will even increase during the next years, with new ß-lactamic antibiotics under development. They are usually produced by the hydrolysis of natural antibiotics (penicillin G or cephalosporin C) and the further amidation of natural or modified antibiotic nuclei with different carboxylic acyl donor chains. Due to the contaminant reagents used in conventional chemical route, as well as the high energetic consumption, biocatalytic approaches have been studied for both steps in the production of these very interesting medicaments during the last decades. Recent successes in some of these methodologies may produce some significant advances in the antibiotics industry. In fact, the hydrolysis of penicillin G to produce 6-APA catalyzed by penicillin G acylase is one of the most successful historical examples of the enzymatic biocatalysis, and much effort has been devoted to find enzymatic routes to hydrolyze cephalosporin C. Initially this could be accomplished in a quite complex system, using a two enzyme system (D-amino acid oxidase plus glutaryl acylase), but very recently an efficient cephalosporin acylase has been designed by genetic tools. Other strategies, including metabolic engineering to produce other antibiotic nuclei, have been also reported. Regarding the amidation step, much effort has been devoted to the improvement of penicillin acylases for these reactions since 1960. New reaction strategies, continuous product extraction or new penicillin acylases with better properties have proven to be the key to have competitive biocatalytic processes. In this review, a critical discussion of these very interesting advances in the application of enzymes for the industrial synthesis of semi-synthetic antibiotics will be presented.

Preparation of benzylpenicilloyl-polylysine: a preliminary study.

The manufacturing of PrePen (benzylpenicilloyl-polylysine) was suspended from September 2000 through November 2001 because of Food and Drug Administration intervention. PrePen is penicilloyl bound to polylysine and is considered to be the major determinant of penicillin metabolism; it is used as a skin-testing reagent to detect immunoglobulin E antibodies in people with a history of penicillin allergy. Because of the uncertainty of whether PrePen would be made available in the future, we attempted to make benzylpenicilloyl-polylysine in our laboratory using a modification of a previously described method. Subsequently, we compared our preparation with PrePen by enzyme-linked immunosorbent assay and skin testing. Using a patient previously documented to have a positive reaction to PrePen by history and intradermal skin testing, a puncture test to PrePen as well as dilutions of benzylpenicilloyl-polylysine was negative. Positive intradermal tests were performed on PrePen and benzylpenicilloyl-polylysine at 5 mg/mL. The enzyme-linked immunosorbent assay was performed to compare the antigenicity of PrePen and benzylpenicilloyl-polylysine and revealed similar binding to both. Subsequently, cutaneous testing on 10 additional penicillin-allergic people was performed, with corroborative results. Our benzylpenicilloyl-polylysine production methodology could prove useful to those who do not have access to PrePen or another similar reagent.

Intramolecular general acid catalysis in the aminolysis of beta-lactam antibiotics.

The rate of aminolysis of benzylpenicillin and cephaloridine by hydroxylamine, unlike other amines, shows only a first order dependence on amine concentration. The rate enhancement compared with that predicted from a Bronsted plot for other primary amines with benzylpenicillin is greater than 10(6). This is much more than an alpha-effect and is compatible with rate-limiting formation of the tetrahedral intermediate due to a rapid intramolecular general acid catalysed breakdown of the intermediate. For cephaloridine, the rate enhancement is greater than 10(4) which demonstrates that beta-lactam C-N bond fission and expulsion of the leaving group at C3' are not concerted.

Enzymatic synthesis of beta-lactam antibiotics via direct condensation.

In this paper, the feasibility of precipitation driven synthesis of acidic and zwitterionic beta-lactam antibiotics is studied. As an example of the first type, penicillin G was produced in good yield (160 mmol kg(-1)) directly from the free acid and amine aqueous substrate suspension, where the synthesis product precipitated. Such a precipitation driven synthesis via direct reversal of the hydrolytic reaction is thermodynamically unfavourable for zwitterionic beta-lactam antibiotics, such as amoxicillin. In this paper, a novel method is suggested to help favour precipitation of (poorly soluble) product salts by deliberate addition of certain counter-ions. After screening a number of different counter-ions, it was found that the amoxicillin anion forms a poorly soluble salt with Zn(2+). Despite increased beta-lactam degradation due to the presence of zinc ions, in a synthetic reaction with 0.1 M ZnSO(4) present the synthetic yield could be increased at least 30-fold.

Acyloxymethyl as a drug protecting group. Part 7: Tertiary sulfonamidomethyl ester prodrugs of benzylpenicillin: chemical hydrolysis and anti-bacterial activity.

Tertiary sulfonamidomethyl esters of benzylpenicillin (4) were synthesised and evaluated as a new class of potential prodrugs for beta-lactam antibiotics. Their hydrolysis in aqueous buffers was studied by HPLC and reveal a U-shaped pH rate profile with a pH-independent process extending from ca. pH 2 to ca. pH 10. This pathway is characterised by kinetic data that are consistent with a unimolecular mechanism involving rate-limiting iminium ion formation and penicillinoate expulsion. Benzylpenicillin and the corresponding sulfonamide are the ultimate products detected and isolated, indicating that beta-lactam ring opening is much slower than ester hydrolysis. As expected from the high reactivity, benzylpenicillin esters (4) displayed similar in vitro antibacterial activity to benzylpenicillin itself. Compared to the benzylpenicillin derivatives, sulfonamidomethyl esters of benzoic, clofibric and valproic acids display a much higher stability, giving rise to a Brønsted beta1g value of -0.96 and suggesting that tertiary sulfonamidomethyl esters may be useful prodrugs for carboxylic acid drugs with pKa > 4.

Uptake of phenylacetic acid by two strains of Penicillium chrysogenum.

Uptake of phenylacetic acid, the side-chain precursor of benzylpenicillin, was studied in Penicillium chrysogenum Wisconsin 54-1255 and in a strain yielding high levels of penicillin. In penicillin fermentations with the high-yielding strain, 100% recovery of phenylacetic acid in benzylpenicillin was found, whereas in the Wisconsin strain only 17% of the supplied phenylacetic acid was incorporated into benzylpenicillin while the rest was metabolized. Accumulation of total phenylacetic acid-derived carbon in the cells was nonsaturable in both strains at high external concentrations of phenylacetic acid (250-3500 microM), and in the high-yielding strain at low phenylacetic acid concentrations (2. 8-100 microM), indicating that phenylacetic acid enters the cells by simple diffusion, as concluded earlier for P. chrysogenum by other authors. However, at low external concentrations of phenylacetic acid saturable accumulation appeared in the Wisconsin strain. HPLC-analyses of cell extracts from the Wisconsin strain showed that phenylacetic acid was metabolized immediately after entry into the cells and different [14C]-labeled metabolites were detected in the cells. Up to approximately 50% of the accumulated phenylacetic acid was metabolized during the transport-assay period, the conversion having an impact on the uptake experiments. Nevertheless, accumulation of free unchanged phenylacetic acid in the cells showed saturation kinetics, suggesting the possible involvement of a high-affinity carrier in uptake of phenylacetic acid in P. chrysogenum Wisconsin 54-1255. At high concentrations of phenylacetic acid, contribution to uptake by this carrier is minor in comparison to simple diffusion and therefore, of no importance in the industrial production of penicillin.

Skin testing with penicilloate and penilloate prepared by an improved method: amoxicillin oral challenge in patients with negative skin test responses to penicillin reagents.

BACKGROUND: Penicillin skin testing has been limited by the lack of commercially available penicilloate and penilloate reagents. OBJECTIVE: This project was proposed to produce a stable, well-characterized supply of penicilloate and penilloate for intrastate use by our health maintenance organization and to document clinical safety and efficacy. METHODS: An improved method of extraction for penicilloate and penilloate, which changed the solvents used during recrystallization, was developed. With these newly prepared reagents, penicillin skin testing was performed on 348 subjects. Skin testing was immediately followed by an oral challenge of 250 mg of amoxicillin in 215 of 288 (75%) subjects displaying a negative response to a battery of penicillin skin tests. RESULTS: Nuclear magnetic resonance and mass spectrometry of the newly produced penicilloate and penilloate showed no evidence of organic contamination. Penicillin skin testing resulted in 17.2% (60 of 348) positive test results, with 20% of the subjects with positive results only responding to the newly produced minor determinants. The rate of mild adverse reactions to penicillin skin testing was 1.1% (4 of 348). The rate of mild acute adverse reactions was 5.1% (11 of 215), and the delayed reaction rate was 0.9% (2 of 215) with the amoxicillin challenge. CONCLUSIONS: This improved penicillin minor determinant extraction method allows for the reproducible production of very pure preparations of penicilloate and penilloate. Large-scale penicillin skin testing, followed by amoxicillin challenge if results are negative is feasible in a large group model health maintenance organization operating within a single state with the use of internally produced penicilloate and penilloate and commercially available penicillin, amoxicillin, and penicilloyl polylysine.

Modeling of penicillin G hydrolysis to 6-APA in an immobilized enzyme-ion exchange system.

A composite system of an immobilized enzyme reactor combined with an ion exchange column was employed for hydrolysis of penicillin G to 6-APA with continuous removal of PAA. In this study, a mathematical model of penicillin G hydrolysis to 6-APA in the composite system was developed based on the compartment model, the profile of concentration in the ion exchange column, and the enzyme kinetics in the immobilized enzyme reactor. After checking the simulation values and experimental data, the effects of the resin volume, the flow rate, and the switching time on the time required to reach the desired conversion rate was also examined by computer simulation.

(2,3)-alpha-Methylenepenams: synthesis and in vitro activity.

A series of alpha-methylene penicillins was synthesized and SAR were studied. The alpha-isomers were found to be chemically reactive and biologically active in contrast to the beta-isomers. In addition, the alpha-isomers have broader spectrum of in vitro activity than the corresponding penicillins. Generally, the alpha-isomers are more active against gram-negative bacteria than the corresponding penicillins, but slightly weaker in potency towards gram-positive organisms.

Brain-specific chemical delivery systems for beta-lactam antibiotics. Synthesis and properties of some dihydropyridine and dihydroiosquinoline derivatives of benzylpenicillin.

Six chemical delivery systems (CDS) were synthesized for benzylpenicillin in order to improve its transport across the blood-brain barrier. The CDS's were based on a dihydropyridine----quaternary pyridinium ion redox system, analogous to the naturally occurring NADH----NAD+ system. Two different types of CDS's were prepared: benzylpenicillin esters of diols in which the other hydroxyl group is esterified by dihydrotrigonelline and benzylpenicillin esters of amino alcohols in which the amine group is acylated by dihydrotrigonelline, or by 1,2-dihydro-2-methyl-4-isoquinolinecarboxylic acid. Lipophilicities of the CDS's were proved to be much higher than those of benzylpenicillin by using Rm values as lipophilicity indexes. Upon oxidation, all of the CDS's gave the quaternary ion forms. Kinetic studies in buffer (pH profiles) indicated that the quaternary salts released benzylpenicillin in pH range of 5-9 via hydrolysis. The CDS's in acidic media yielded as the major reaction product 6-hydroxy-1,4,5,6-tetrahydropyridines as a result of water addition, while in basic conditions benzylpenicillin was released. The water addition reaction was dependent on the CDS's structure, being more prevalent in the case of the "amide-esters". The dihydroisoquinoline CDS was rather stable in the pH range 5-8.

The preparation and determination of structure of benzylpenicilloyl compounds used in skin-testing for penicillin allergy.

The preparation of alpha-D-benzylpenicilloyl-n-propylamine and octa-epsilon-(alpha-D-benzylpenicilloyl)-octa-alpha-L-lysine are described. Their structures were established by chemical and spectroscopic evidence. Proton and carbon-13 nuclear magnetic resonance spectra of these two penicillin derivatives and some related compounds are provided. These compounds are useful in skin testing for penicillin allergy.

Synthesis of a 125I-radiolabeled penicillin for penicillin-binding proteins studies.

Radioiodination of penicillin X (p-hydroxybenzylpenicillin) with 125INa, using the chloramine-T method, is simple and almost quantitative. The product thus obtained can be used without further purification for the penicillin-binding proteins (PBPs) assay. The chemical structure of 125I-penicillin X is very close to that of penicillin G, and the affinity of the two compounds for the PBPs are very similar. 125I-penicillin X can then advantageously replace [14C]penicillin G in these experiments, as its specific radioactivity is 2000 Ci/mol, in our preparations, instead of about 50 Ci/mol; thus, the experimental procedure is simplified and the autoradiography exposure time is reduced to 12-48 h.

[Effect of the quality of regenerated butanol on the process of producing the potassium salt of benzylpenicillin]. / Issledovanie vliianiia kachestva regenerirovannogo butanola na protsess polucheniia kalievoi soli benzilpenitsillina.

The effect of water and butylacetate contained in butanol used in production of potassium benzylpenicillin on the yield and quality of the latter was studied. It was found that normal butyl alcohol with the moisture level not more than 0.2 per cent provided the optimal conditions for the antibiotic production. Butyl acetate contained in butanol in an amount of 25 per cent was shown also to have practically no effect on the yield and quality of benzylpenicillin.

Preparation of 6-epi-ampicillin and of 6-epi-alpha-hydroxybenzylpenicillin.

The preparation of 6-epi-ampicillin by hydrolysis of 6-epihetacillin is described. During this conversion, the formation of a diketopiperazine was also observed. The best yield was obtained at pH 7.0 and room temperature for 3 approximately 7 hours. The lowest yield of 6-epi-ampicillin and the highest formation of the diketopiperazine occurred in pyridine - acetic acid - water. Treatment of ampicillin (with D-aminophenylacetyl side chain) with nitrous acid gave alpha-hydroxybenzylpenicillin with about 66% of L- and 34% mandelyl side chain. Reaction 6-epi-ampicillin gave 6-epi-alpha-hydroxybenzylpenicillin with practically the same ratio of L- and D-isomers.