Synthesis of 2(S)-benzyl-3-[hydroxy(1 '(R)-amino ethyl)phosphinyl]propanoyl-L-3-[I-125]-iodotyrosine: A radiolabelled inhibitor of aminopeptidase N

2(S)-benzyl-3-[hydroxy(1'(R)-aminoethyl)phosphinyl]propanoyl-L-3-[I-125]-io do tyrosine was prepared from 1(R)-(N-benzyloxycarbonylamino)ethylphosphini c acid in a six step synthesis. This new iodinated compound, which is a hig hly efficient aminopeptidase N inhibitor (Ki = 0.95 nM), can be used for co mplete characterization of the biochemical and pharmacological properties o f aminopeptidase N and its in vivo inhibition. A high radiochemical purity was obtained with a specific activity of 2.17 Ci/mmol at the end of the syn thesis.