-3-Amino-2-hydroxy-4-phenylbutanoic acid, a novel amino-acid contained in bestatin, an inhibitor of aminopeptidase B and leucine aminopeptidase, and-3-amino-2-hydroxy-5- methylhexanoic acid, a novel amino-acid contained in amastatin, an inhibitor of aminopeptidase A and leucine aminopeptidase, have been synthesized