A process is disclosed for preparing an (S)-2-amino-&ohgr;-oxoalkanoic acid derivative in which the corresponding aldehyde is converted into the corresponding acetal-protected aldehyde, the acetal-protected aldehyde is converted into the corresponding aminonitrile, the aminonitrile is converted into the corresponding amino acid amide, the amino acid amide is subjected to an enzymatic, enantioselective hydrolysis in which the (R)-enantiomer of the amino acid amide remains and the (S)-enantiomer is converted into the (S)-amino acid, and the (S)-amino acid is isolated. Preferably,the reaction mixture obtained after the conversion of the aminonitrile into the amino acid amide is treated with a benzaldehyde to form the Schiff base of the amino acid amide. The Schiff base is separated out and is converted into the free amino acid amide.