The reaction of N-(2-oxo-2-phenylethyl)acetamide (I) with glyoxylic acid (II) by means of NaHCO3 in water gives threo-(2RS)-3-acetylamino-2-hydroxy-4-oxo-4-phenylbutanoic acid (III), which is reduced with H2 over Pd/C in acetic acid yielding threo-(2RS)-3-acetylamino-2-hydroxy-4-phenylbutanoic acid (IV). The treatment of (IV) with (S)-1-phenylethylamine followed by a fractionated crystallization affords (2S,3R)-3-acetyl-amino-2-hydroxy-4-phenylbutanoic acid (IV), which is hydrolyzed with HCl in refluxing water to afford (2R,3S)-3-amino-2-hydroxy-4-phenylbutanoic acid (V). The protection of (V) with benzyl S-4,6-dimethylpyrimidin-2-ylthiolcarbonate (VI) by means of triethylamine in dioxane - water gives (2S,3R)-3-benzyloxycarbonylamino-2-hydroxy-4-phenylbutanoic acid (VII), which is condensed whh benzyl (S)-leucinate (VIII) by means of di-cyclohexylcarbodiimide and p-toluenesulfonic acid yielding benzyl (2S,3R)-3-benzyloxycarbonylamino-2-hydroxy-4-phenylbutanoyl-(S)-leucinate (IX). Finally, this compound is deprotected by hydrogenation with H2 over Pd/C in acetic acid.