(412f) Improving Enantioselective Continuous Chromatography By Integration of Enzymatic Racemization

Stereoselective production processes are of large importance for the life science industry. An attractive approach is to perform non-selective synthesis and subsequent resolution of the racemic mixtures by chiral simulated moving bed (SMB) chromatography. The resulting 50 % yield constraint can be tackled by exploiting the unwanted enantiomer by racemization [1]. It can be then recycled into the resolution process by coupling the two units under suitable conditions. This process integration can provide an improved overall process performance [2] while the increase process complexity can be managed with model-based optimization [3]. An environmentally friendly method for racemization is the enzymatic approach, even though the number of available racemases is still limited. In principle a suitable racemase can be provided for most chiral systems and the ability to immobilize the enzymes support their application and makes them very attractive.

In this contribution enantioselective chromatography and enzymatic racemization are coupled in a continuous way with simulated moving bed (SMB) chromatography and an enzymatic fixed bed reactor. This approach is used for the provision of two chiral model systems: a) L- or D-methionine with an immobilized amino acid racemase [4] and b) S- or R-mandelic acid enantiomers with an immobilized mandelate racemase [5].

In preliminary experimental steps a compatible eluent was identified for both process units. For both model systems an aqueous solvent with ethanol or methanol could be used in combination with the stationary phase Chirobiotic T. Subsequently, the thermodynamic and kinetic parameters for the chromatographic separations were determined analyzing elution profiles and the reaction rates of the immobilized racemases were determined analyzing fixed bed reactor runs. Exploiting these parameters, the systems were modeled and efficient coupling conditions were found for increasing the yield. Main reason for this improvement is that, due to the recycling of the by-product stream of the SMB unit, purity constraints can be relaxed and product losses are minimized. This allows operating the unit as an 3Z-open-loop-SMB, increasing its efficiency by up to 33 % [6]. Also, the racemization unit profits from this type of coupling as complete racemization is no longer required for yield maximization. This results in productivities of around 3-4 g/h/mg_carrier. Thus, both units can be operated at higher efficiency and productivity than in decoupled setups.

Reference:

[1] Jacques J, Collet A, Wilen SH (1981) Enantiomers, racemates, and resolutions. Wiley

[2] Palacios JG, Kaspereit M, Kienle A (2011) Chemical Engineering & Technology 34:688–698

[3] Kawajiri Y (2021) Adsorption 27:1–26

[4] Carneiro T, Wrzosek K, Bettenbrock K, Lorenz H, Seidel-Morgenstern A (2020) Engineering in Life Sciences 20:550–561

[5] Wrzosek K, Harriehausen I, Seidel-Morgenstern A (2018) Organic Process Research & Development 22:1761–1771

[6] Harriehausen I, Wrzosek K, Lorenz H, Seidel-Morgenstern A (2020) Adsorption 26:1199–1213