The Collaborative International Dictionary of English v.0.48:

diiodotyrosine \di*i`o*do*tyr"o*sine\, di-iodotyrosine
\di-iodotyrosine\n. (Chem., Med.)
   a chemical substance consisting of tyrosine with two hydrogen
   atoms on the benzene ring replaced by iodine atoms.

   Note: The isomer 3,5-diiodotyrosine is an inhibitor of
         thyroid function.
         [WordNet 1.5]

WordNet (r) 3.0 (2006):

di-iodotyrosine
    n 1: tyrosine with two iodine atoms added