(139e) Magnetophoretic Solid-Solid Separation of ?-Lactam Antibiotics from Biocatalyst on a Pilot Plant Scale

Enzymatic reactive crystallization is a promising green synthesis route for the production of semi-synthetic β-lactam antibiotics. Enzymatic ß-lactam antibiotic synthesis is also a focus for continuous pharmaceutical manufacturing as a study to improve pharmaceutical production quality through continuous processing. In addition, simulations have shown that use of continuous reactive crystallization for β-lactam antibiotic synthesis can be optimized to increase productivity and conversion compared to batch synthesis [1]. One major limitation is in the use of a solid catalyst (immobilized enzyme) in the presence of crystallizing product and the resulting solid-solid separation that is required to purify the API and recycle the catalyst.

Solid-solid-liquid separations are uncommon design problems rarely used in the pharmaceutical industry. Magnetic separation is one possible method to separate enzyme immobilized to paramagnetic material from the nonmagnetic crystalline product. While magnetic separation has been implemented in prior systems, including with the enzyme penicillin G acylase (PGA) [2-4], the application detailed herein is unique due to its continuous nature and its use at the pharmaceutical pilot plant scale. In this work, a continuous magnetic separator designed for separation of synthesized β-lactam antibiotics from penicillin G acylase (PGA) immobilized to magnetic particles is demonstrated on a pilot plant scale. The separators operate through use of neodymium magnets to generate a stable magnetic field gradient for magnetophoresis, allowing for isolation of crystallizing product from magnetic particles in separate channels. The separators are modular and can be incorporated in series to improve separation efficiency or in parallel to increase throughput.

Separators in series were first demonstrated through separation of paramagnetic particles from amoxicillin crystals generated through a pH-shift crystallization. The magnetic particles enter two separators in series before being recycled back to the crystallizer. The amoxicillin crystals are removed from the system and pass through a magnetic trap to capture any remaining magnetic particles before being collected and analyzed for purity. PGA was then immobilized to functionalized magnetic particles for demonstration of the reactive crystallization of amoxicillin and subsequent separation of amoxicillin trihydrate from magnetic catalyst. Amoxicillin is synthesized through coupling of a β-lactam ring donor, 6-aminopenicillanic acid (6-APA) with an activated acyl donor, hydroxyphenylglycine methyl ester (HPGME) catalyzed by the immobilized penicillin G acylase. In this system, amoxicillin is simultaneously crystallized out of solution. The slurry of immobilized PGA and amoxicillin are then fed to a series of separators where pure amoxicillin crystals are isolated for washing and drying and the magnetic catalyst particles are recycled back to the reactor for reuse as demonstrated in the pH shift crystallization.

Amoxicillin trihydrate was generated and isolated continuously in a mixed suspension–mixed product removal (MSMPR) at the pilot plant scale for 10 hours. The separators were found to be capable of processing >700 mL/hour of amoxicillin and catalyst slurry with a separation efficiency of >99.9% upon incorporation of a magnetic trap in both the pH-shift crystallization and reactive crystallization. Final amoxicillin trihydrate was analyzed for iron oxide content to determine purity. While the system was demonstrated for amoxicillin trihydrate, magnetic separation could be incorporated for synthesis of other β-lactam antibiotics by PGA and likely be tuned for other continuous or batch systems where multiple solid phases are present. Scaling the separation is also possible through use of separators in parallel and will be a focus in future studies.

1. McDonald, M.A., et al., Continuous reactive crystallization of β-lactam antibiotics catalyzed by penicillin G acylase. Part I: Model development. Computers & Chemical Engineering, 2019. 123: p. 331-343.
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