This invention to provide a process for producing an optically active threo-phenylnorstatin derivative which does not require a toxic cyanating agent or a costly reagent, or a complicated procedure, and can be practiced on a commercial scale.
This invention is directed to a process for producing a &bgr;-amino-&agr;-hydroxy acid derivative which comprises treating either a &ggr;-amino-&bgr;-keto sulfoxide derivative with a halogenating agent to produce a &ggr;-amino-&agr;-halo-&bgr;-keto sulfoxide derivative, treating the same with an acid and an alcohol to produce a &bgr;-amino-&agr;-keto ester derivative or &bgr;-amino-&agr;-keto acid derivative, and followed by reducing.