Selectivity of the enzymatic synthesis of ampicillin by E. coli PGA in the presence of high concentrations of substrates

Selectivity and kinetic modeling of penicillin G acylase variants for the synthesis of cephalexin under a broad range of substrate concentrations

The kinetics of cephalexin synthesis and hydrolysis of the activated acyl-donor precursor phenylglycine methyl ester (PGME) were characterized under a broad range of substrate concentrations. A previously developed model by Youshko-Svedas involving the formation of the acyl-enzyme complex followed by binding of the nucleophilic β-lactam donor does not fully estimate the maximum reaction yields for cephalexin synthesis at different concentrations using initial-rate data. 7-aminodesacetoxycephalosporanic acid (7-ADCA) was discovered to be a potent inhibitor of cephalexin hydrolysis, which may account for the deviation from model predictions. Three kinetic models were compared for cephalexin synthesis, with the model incorporating competitive inhibition due to 7-ADCA yielding the best fit. Additionally, the βF24A variant and Assemblase® did not exhibit significantly different kinetics for the synthesis of cephalexin compared to the wild-type, for the concentration range evaluated and for both initial-rate experiments and time-course synthesis experiments. Lastly, a continuous stirred-tank reactor for cephalexin synthesis was simulated using the model incorporating competitive inhibition by 7-ADCA, with clear tradeoffs observed between productivity, fractional yield, and PGME conversion.

Strategies to Improve the Biosynthesis of β-Lactam Antibiotics by Penicillin G Acylase: Progress and Prospects

β-Lactam antibiotics are widely used anti-infection drugs that are traditionally synthesized via a chemical process. In recent years, with the growing demand for green alternatives, scientists have turned to enzymatic synthesis. Penicillin G acylase (PGA) is the second most commercially used enzyme worldwide with both hydrolytic and synthetic activities toward antibiotics, which has been used to manufacture the key antibiotic nucleus on an industrial level. However, the large-scale application of PGA-catalyzed antibiotics biosynthesis is still in the experimental stage because of some key limitations, such as low substrate concentration, unsatisfactory yield, and lack of superior biocatalysts. This paper systematically reviews the strategies adopted to improve the biosynthesis of β-lactam antibiotics by adjusting the enzymatic property and manipulating the reaction system in recent 20 years, including mining of enzymes, protein engineering, solvent engineering, in situ product removal, and one-pot reaction cascade. These advances will provide important guidelines for the future use of enzymatic synthesis in the industrial production of β-lactam antibiotics.

Hydrophobic Adsorption Followed by Desorption with Ethanol-Water for Recovery of Penicillin G from Fermentation Broth

The hydrophobic adsorption is an alternative to traditional organic solvent extraction for the recovery and purification of Penicillin G (PenG). However, there is a lack of information concerning the effect of process variables and technical feasibility while balancing product degradation. After assessing the integrity of PenG under different conditions, Amberlite XAD-4 was selected from among three different adsorbents. During the batch process using only 0.05 g_XAD-4/mL_medium, the adsorption yield increased from 36% at pH 6 to 44% at pH 4. More than 90% of the antibiotic was captured from the fermentation broth using 0.083 g_XAD-4/mL_medium in a 45 min batch performed at pH 4 and 4 °C. Moreover, there was no PenG degradation. The desorption conditions were evaluated, and 95% of the antibiotic could be recovered in only one batch using water-ethanol, which is an unexplored PenG desorption process. The results showed selective adsorption, indicating that the process can also be useful for purification purposes. Hydrophobic adsorption with ethanol desorption is efficient, scalable, and green and could be used in place of traditional methods or in extractive fermentation.

Poly-lysine supported cross-linked enzyme aggregates of penicillin G acylase and its application in synthesis of β-lactam antibiotics

Penicillin G acylase (PGA) from Providencia rettgeri PX04 (PrPGA) was utilized to synthesize β-lactam antibiotics. Poly-lysine supported cross-linked enzyme aggregates (PL-CLEAs) were prepared using PGA. Addition of poly-lysine significantly increased retention of PGA activity in CLEAs, with a decrease in the synthesis/hydrolysis (S/H) ratio. PL-CLEAs with 0.56 mg/mL poly-lysine retained 83% of free PGA activity, and displayed a higher S/H ratio than that of the free enzyme. Both PL-CLEAs and CLEAs exhibited high pH and thermal stabilities. PL-CLEAs possessed the best stability profile, and the lowest α value [(k_cat/K_m)_Ps/(k_cat/K_m)_AD], and was most effective at amoxicillin synthesis. A >94% yield of amoxicillin was achieved using a D-HPGME/6-APA ratio of 1.2:1 (240 mM, 200 mM), with fed-batch addition of D-HPGME. PL-CLEAs displayed excellent operational stability during amoxicillin synthesis. Over 97% of initial conversion was retained after twenty rounds of catalysis. PL-CLEAs exhibited greater potency than CLEAs in practical catalysis, permitting a higher concentration of reactants.

Penicillin acylase-catalyzed synthesis of N-bromoacetyl-7-aminocephalosporanic acid, the key intermediate for the production of cefathiamidine

BACKGROUND

Enzymatic approaches have become promising alternatives to chemical methods for the production of semi-synthetic β-lactam antibiotics. In this work, enzymatic synthesis of N-bromoacetyl-7-aminocephalosporanic acid (N-bromoacetyl-7-ACA), the key intermediate for the production of cefathiamidine, was reported for the first time.

RESULTS

Of the immobilized penicillin acylases (PAs) tested, PGA-750 was the best biocatalyst. Optimization of the biocatalytic process was conducted. The optimal acyl donor, molar ratio of acyl donor to 7-ACA, pH, temperature, 7-ACA concentration, and enzyme dosage were methyl bromoacetate, 3, 7.5, 20 °C, 50 mmol/L and 4 U/mL, respectively. Under the optimal conditions, enzymatic N-acylation of 7-ACA with methyl bromoacetate afforded the desired product with the yield of 85% in 2 h, where the synthesis/hydrolysis (S/H) ratio was approximately 1.5. The immobilized enzyme PGA-750 exhibited good operational stability, and the relative yields of approximately 90% and 63% were achieved, respectively, when it was reused in 7th and 11th batch.

CONCLUSIONS

An enzymatic approach to N-bromoacetyl-7-ACA, the key intermediate for the industrial production of cefathiamidine, has been developed successfully in a fully aqueous medium. The present work may open up a novel opportunity for the production of cefathiamidine through a simple and green process.Graphical abstractEnzymatic synthesis of N-bromoacetyl-7-ACA, the key intermediate for the production of cefathiamidine, was reported for the first time.

The Kinetics of Ampicillin Release from Hydroxyapatite for Bones Regeneration

Semisynthetic beta-lactam antibiotics are among the most used pharmaceuticals. Their use in veterinary and human medicine is in continuous expansion. There is a growing need for developing bioactive implants. Advantages of implantable drug delivery tools can include high release efficiency, precise dose control, low toxicity, and allow to overcome disadvantages connected with conventional methods. In this respect, hydroxyapatite (HA) is an elective material. It enables to produce architectures similar to those of real bones. Here we studied a kinetic model to describe ampicillin release from HA. In the course of adsorption experiment, ampicillin was dissolved, maintained at and shaken at 60 strokes/minute. Samples were withdrawn periodically for analysis and then returned to the mixture. Adsorbed amounts were measured by the difference of the concentration of the antibiotics before and after adsorption using UV adsorption at 225 nm. The aim of this work was to evaluate its application as ampicillin delivery carrier.

Kinetics of β-lactam antibiotics synthesis by penicillin G acylase (PGA) from the viewpoint of the industrial enzymatic reactor optimization

Competition with well-established, fine-tuned chemical processes is a major challenge for the industrial implementation of the enzymatic synthesis of beta-lactam antibiotics. Enzyme-based routes are acknowledged as an environmental-friendly approach, avoiding organochloride solvents and working at room temperatures. Among different alternatives, the kinetically controlled synthesis, using immobilized penicillin G acylase (PGA) in aqueous environment, with the simultaneous crystallization of the product, is the most promising one. However, PGA may act either as a transferase or as a hydrolase, catalyzing two undesired side reactions: the hydrolysis of the acyl side-chain precursor (an ester or amide, a parallel reaction) and the hydrolysis of the antibiotic itself (a consecutive reaction). This review focuses specially on aspects of the reactions' kinetics that may affect the performance of the enzymatic reactor.