Diastereoselective synthesis of optically active (2R,5R)-hexanediol

Diastereoselective reduction of diketones with Lactobacillus kefir DSM 20587 was examined. The reduction of both oxo-functions proceeded highly diastereoselectively. (2R,5R)-Hexanediol 3 was produced starting from (2,5)-hexanedione I in quantitative yields with enantiomeric excess >99% and diastereomeric excess >99%. The reaction conditions were optimized: maximum yield of (2R,5R)-hexanediol was reached at pH 6, 30degreesC and with equal amounts of substrate and cosubstrate. The applicability of the system in fed-batch experiments was demonstrated. The feed specific biomass concentration required to reach maximal yield and selectivity in fed-batch mode was determined.