Preparation of Chiral 2-chloromandelamide: Stereoselective Reduction of an Aromatic α-keto Amide with Actinomycete Strains

The stereoselective reduction of an aromatic α-keto amide with actinomycete strains was investigated. It was found that 2-chlorobenzoylformamide was reduced to the corresponding 2-chloromandelamide by mesophilic and thermophilic strains of actinomycetes. Among the strains tested, the reduction of 2-chlorobenzoylformamide by Streptomyces thermocyaneoviolaceus (one of thermophilic strains) in the presence of glycerol as an additive produced only (S)-2-chloromandelamide in >99% conversion with 99% enantiomeric excess (e.e.). On the other hand, the reduction by Streptomyces thermocarboxydovorans NBRC16324 at 45 °C or Thermoactinomyces vulgaris NBRC15851 cultivated in a soluble starch-based medium gave the corresponding (R)-hydroxy amide (conversion, 99%; >99% e.e.). Mesophilic and other thermophilic actinomycete strains also catalyzed the reduction to the corresponding (R)-hydroxy amide with 85%–>99% e.e. Thus, the syntheses of both enantiomers of 2-chloromandelamide was achieved though the reduction of 2-chlorobenzoylformamide with different actinomycete strains.