Highly Efficient Production of Optically Active (R)-Tetrahydrothiophene-3-ol in Batch and Continuous Flow by Using Immobilized Ketoreductase

In this work, an engineered ketoreductase, apKRED-9, derived from Acetobacter pasteurianus 386B was successfully immobilized on two platforms, namely, glutaraldehyde-activated amino polymer beads, LX1000 HA, and cofactor enriched poly(ethylenimine) (CEP) mediated coaggregation followed by glutaraldehyde cross-linking, respectively. The enzyme apKRED-9 immobilized on LX1000HA was evaluated in a packed bed reactor (PBR) for continuous-flow synthesis of (R)-tetrahydrothiophene-3-ol from 3-keto tetrahydrothiophene in an aqueous-isopropanol mixture, while the enzyme apKRED-9 immobilized on CEP was tested in batch mode until pilot scale for the same reaction. The long-term operational stability of the enzyme in both continuous-flow and batch modes was demonstrated, with high conversion of >99.0% and ee > 99.5% in both the cases. From the pilot-scale application of apKRED-9-CEP, (R)-tetrahydrothiophene-3-ol was obtained (118.0 g, GC purity 99.9%, chiral purity ee 99.9% and yield 76.3%). In the PBR flow reactor, the productivity in terms of space time yield (STY) 729 g L–1 d–1 was achieved with 64 h of continuous usage. Based on performance metrics, both platforms are scalable and reproducible, while CEP offers additional advantages on effective cost and adaptability to other enzymes.