Batch reactor performance for the enzymatic synthesis of cephalexin: influence of catalyst enzyme loading and particle size

Reactor Design and Optimization of α-Amino Ester Hydrolase- Catalyzed Synthesis of Cephalexin

Pharmaceutical production quality has recently been a focus for improvement through incorporation of end-to-end continuous processing. Enzymatic ß-lactam antibiotic synthesis has been one focus for continuous manufacturing, and α-amino ester hydrolases (AEHs) are currently being explored for use in the synthesis of cephalexin due to their high reactivity and selectivity. In this study, several reactors were simulated to determine how reactor type and configuration impacts reactant conversion, fractional yield toward cephalexin, and volumetric productivity for AEH-catalyzed cephalexin synthesis. The primary reactor configurations studied are single reactors including a continuous stirred-tank reactor (CSTR) and plug flow reactor (PFR) as well as two CSTRS and a CSTR + PFR in series. Substrate concentrations fed to the reactors as well as enzyme concentration in the reactor were varied. The presence of substrate inhibition was found to have a negative impact on all reactor configurations studied. No reactor configuration simultaneously allowed high substrate conversion, high fractional yield, and high productivity; however, a single PFR was found to enable the highest substrate conversion with higher fractional yields than all other reactor configurations, by minimizing substrate inhibition. Finally, to further demonstrate the impact of substrate inhibition, an AEH engineered to improve substrate inhibition was simulated and Pareto optimal fronts for a CSTR catalyzed with the current AEH were compared to Pareto fronts for the improved AEH. Overall, reduced substrate inhibition would allow for high substrate conversion, fractional yield, and productivity with only a single CSTR.

Enhanced Dissolution of 7-ADCA in the Presence of PGME for Enzymatic Synthesis of Cephalexin

Enzymatic catalysis has been recognized as a green alternative to classical chemical route for synthesis of cephalexin (CEX). However, its industrial practice has been severely limited by the low productivity due to the low solubility of 7-amino-3-deacetoxycephalosporanic acid (7-ADCA) and high hydrolysis of D-phenylglycine methyl ester (PGME). In this work, the enhanced dissolution of 7-ADCA in the presence of PGME for efficient enzymatic synthesis of CEX was investigated. Results showed that the solubility of 7-ADCA in water could be improved by PGME. Moreover, supersaturated solution of 7-ADCA could be created in the presence of PGME by a pH shift strategy. The supersaturated solution of 7-ADCA possess good stability, which could be explained in terms of the inhibition of 7-ADCA precipitation due to the presence of PGME. The interaction between 7-ADCA and PGME is explored by spectroscopic determination and DFT analysis and the mechanism of enhanced dissolution of 7-ADCA in the presence of PGME is discussed and proposed. The feasibility of supersaturated solution of 7-ADCA for the enzymatic synthesis of CEX is evaluated. It was demonstrated that high conversion ratio (> 95.0%) and productivity (> 240.0 mmol/L/h) was obtained under a wide range of reaction conditions, indicating that the supersaturated solution system was highly superior to conventional homogeneous solution system. The information obtained in this work will be helpful to industrial production of CEX via enzymatic route.

Immobilization of Aspergillus oryzae β-galactosidase in cation functionalized agarose matrix and its application in the synthesis of lactulose

Aspergillus oryzae β-galactosidase was immobilized in in-house quaternary ammonium agarose (QAA) and used for the first time in the synthesis of lactulose. A biocatalyst was obtained with a specific activity of 24,690 IU_H∙g^-1; protein immobilization yield of 97% and enzyme immobilization yield of 76% were obtained at 30 °C in 10 mM phosphate buffer pH 7 for standard size agarose at 100 mg_protein∙g_support^-1 which the maximum protein load of QAA. Highest yield and specific productivity of lactulose were 0.24 g∙g^-1 and 9.78 g∙g^-1 h^-1 respectively, obtained at pH 6, 100 IU_H∙g lactose^-1 enzyme/lactose ratio and 12 lactose/fructose molar ratio. In repeated-batch operation with the immobilized enzyme, the cumulative mass of lactulose per unit mass of contacted protein and cumulative specific productivity were higher than obtained with the soluble enzyme since the first batch. After enzyme activity exhaustion, the enzyme was desorbed and QAA support was reused without alteration in its maximum enzyme load capacity and without detriment in yield, productivity and selectivity in the batch synthesis of lactulose with the resulting biocatalyst. This significantly decreases the economic impact of the support, presenting itself as a distinctive advantage of immobilization by ionic interaction.

Theoretical study on enzyme synthesis of cephalexin in a parallel-flow microreactor combined with electrically driven ATPS microextraction

A mathematical model of a microfluidic device with two aqueous phases for the simultaneous cephalexin production and its separation from a reaction mixture was developed. The model anticipates the continuous cephalexin synthesis and enzyme recyclation.

Model development for enzymatic reactive crystallization of β-lactam antibiotics: a reaction–diffusion-crystallization approach

A mathematical model for production of β-lactam antibiotics via enzymatic reactive crystallization is developed, and its application for catalyst and process design is discussed.

Hairy Particles with Immobilized Enzymes: Impact of Particle Topology on the Catalytic Activity

Enzymes are described as ideal green biocatalysts because they are highly specific and selective. However, their practical application is hampered because of the low stability and missing reusability of free enzymes. One method to overcome these problems is the immobilization of enzymes onto carriers. Although numerous publications discuss different immobilization strategies, optimization of these carriers for the highest enzyme activity and loading capacity, enzyme selectivity, reusability, and reactor system configuration still remains a challenging task. In this contribution, we aim to address the role of the core-shell particle design with respect to their geometry as well as the polymer shell thickness on the immobilization of biomolecules. We discovered that spherical particles with a core diameter of 200 nm and intermediate shell thickness as well as platelet-like particles exhibited excellent results with a maximum immobilization yield of laccase from Trametes versicolor of up to 92% and an activity on the carrier material of 5.722 U/(g particle). Especially, the platelet-like particles offered a scalable and convenient alternative for the immobilization of laccase. Circular dichroism measurements proved that the secondary structure of the enzyme is not impaired by immobilization onto all kinds of carrier particles. Moreover, the immobilized laccase was successfully used for the decolorization of Cibacron blue P-3R in up to 18 cycles. Finally, particle separation was achieved via citrate-induced flocculation within 10 min. This detailed study contributes to the understanding of rational design of catalytically active hybrid materials and their effective performance at interfaces for applications in textile industry and environmental technologies.