Ketoreductases in the synthesis of valuable chiral intermediates: application in the synthesis of α-hydroxy β-amino and β-hydroxy γ-amino acids

A general method for the synthesis of β-alkyl α-hydroxy β-amino and α- and γ-alkyl substituted β-hydroxy-γ-amino acids is described. The synthesis of all three classes of amino acids proceeds through a common chiral alcohol intermediate that is generated from a pro-chiral ketone diester via the action of a nicotinamide-dependent ketoreductase. Regioselective chemical or enzymatic hydrolysis followed by rearrangement under Hofmann or Curtius conditions gives the final amino acid products. High yields of single diastereomers of the final amino acids are obtained. Amino acids with both natural and unnatural alkyl substituents can be accessed using this methodology.