Simulated moving bed enantioseparation of amino acids employing memory effect-constrained chromatography columns

Characterization of an Immobilized Amino Acid Racemase for Potential Application in Enantioselective Chromatographic Resolution Processes

Enantioselective resolution processes can be improved by integration of racemization. Applying environmentally friendly enzymatic racemization under mild conditions is in particular attractive. Owing to the variety of enzymes and the progress in enzyme engineering, suitable racemases can be found for many chiral systems. An amino acid racemase (AAR) from P. putida KT2440 is capable of processing a broad spectrum of amino acids at fast conversion rates. The focus of this study is the evaluation of the potential of integrating AAR immobilized on Purolite ECR 8309 to racemize L- or D-methionine (Met) within an enantioselective chromatographic resolution process. Racemization rates were studied for different temperatures, pH values, and fractions of organic co-solvents. The long-term stability of the immobilized enzyme at operating and storage conditions was found to be excellent and recyclability using water with up to 5 vol% ethanol at 20 °C could be demonstrated. Packed as an enzymatic fixed bed reactor, the immobilized AAR can be coupled with different resolution processes; for instance, with chromatography or with preferential crystallization. The performance of coupling it with enantioselective chromatography is estimated quantitatively, exploiting parametrized sub-models. To indicate the large potential of the AAR, racemization rates are finally given for lysine, arginine, serine, glutamine, and asparagine.

High-Performance Liquid Chromatography Enantioseparations Using Macrocyclic Glycopeptide-Based Chiral Stationary Phases: An Overview

Since their introduction by Daniel W. Armstrong in 1994, antibiotic-based chiral stationary phases have proven their applicability for the chiral resolution of various types of racemates. The unique structure of macrocyclic glycopeptides and their large variety of interactive sites (e.g., hydrophobic pockets, hydroxy, amino and carboxyl groups, halogen atoms, aromatic moieties) are the reasons for their wide-ranging selectivity. The commercially available Chirobiotic™ phases, which display complementary characteristics, are capable of separating a broad variety of enantiomeric compounds with good efficiency, good column loadability, high reproducibility, and long-term stability. These are the major reasons for the frequent use of macrocyclic antibiotic-based stationary phases in HPLC enantioseparations.This overview chapter provides a brief summary of general aspects of antibiotic-based chiral stationary phases including their preparation and their application to direct enantioseparations of various racemates focusing on the literature published since 2004.

Multi-objective optimization for the economic production of d-psicose using simulated moving bed chromatography

The biocatalytic production of rare carbohydrates from available sugar sources rapidly gains interest as a route to acquire industrial amounts of rare sugars for food and fine chemical applications. Here we present a multi-objective optimization procedure for a simulated moving bed (SMB) process for the production of the rare sugar d-psicose from enzymatically produced mixtures with its epimer d-fructose. First, model parameters were determined using the inverse method and experimentally validated on a 2-2-2-2 lab-scale SMB plant. The obtained experimental purities (PUs) were in excellent agreement with the simulated data derived from a transport-dispersive true-moving bed model demonstrating the feasibility of the proposed design. In the second part the performance of the separation was investigated in a multi-objective optimization study addressing the cost-contributing performance parameters productivity (PR) and desorbent requirement (DR) as a function of temperature. While rare sugar SMB operation under conditions of low desorbent consumption was found to be widely unaffected by temperature, SMB operation focusing on increased PR significantly benefited from high temperatures, with possible productivities increasing from 3.4kg(Lday)(-1) at 20°C to 5kg(Lday)(-1) at 70°C, indicating that decreased selectivity at higher temperatures could be fully compensated for by the higher mass transfer rates, as they translate into reduced switch times and hence higher PR. A DR/PR Pareto optimization suggested a similar but even more pronounced trend also under relaxed PU requirements, with the PR increasing from 4.3kg(Lday)(-1) to a maximum of 7.8kg(Lday)(-1) for SMB operation at 50°C when the PU of the non-product stream was reduced from 99.5% to 90%. Based on the in silico optimization results experimental SMB runs were performed yielding considerable PRs of 1.9 (30°C), 2.4 (50°C) and 2.6kg(Lday)(-1) (70°C) with rather low DR (27L per kg of rare sugar produced) on a lab-scale SMB installation.