Preparative Asymmetric Reduction of 3‐Ketobutyrate and ‐valerate by Suspended Cells of Thermophilic Bacteria ( Thermoanaerobium brockii ) in Ordinary Laboratory Equipment

The thermophilic and anaerobic bacteria specified in the title are isolated on a 0.8 kg scale by tangential flow filtration and centrifugation from a 300‐1 bioreactor. The microorganisms are stored in a freezer (−20°) and used, analogously to baker's yeast, for asymmetric reductions. Thus, ethyl 3‐ketovalerate (4.3) g/1 (H 2 O) is converted in 40% yield to ( S )‐3‐hydroxyvalerate ( 6 ), with an enantiomeric excess of 93% (24 h at 72°).